Help me diagnose a stumble on a 3.8

[Rick99]

My wife's '01 T&C with the 3.8l v-6 has an occasional "stumble" or what seems like a miss during idle. It doesn't happen rythmically, but if you let it sit and idle long enough it will occasionally stumble hard enough to shake the van-- not back and forth, but just one thump, then it just continues idling smoothly until the next time. This seems to happen whether the engine is cool or warm-- at home after starting it in the morning or at a stop light after driving for a while. Sometimes, but not always, it will happen when accelerating from a stoplight.

Oh, I should add that once in a blue moon-- not often enough to even be annoying, the van will be very hard to start-- it will crank, but not start for several attempts. Don't know if that's related, but I thought I'd throw it out there.

The plugs and ignition wires were old enough that I just replaced them rather than test them and the problem did not go away. The PCV valve is fine too. Also, there are no PCM codes-- none stored, none pending.

So any ideas on what I should check next?

[Merit]

Throttle body/Throttle positioning sensor? Ever notice any RPM jumps while in cruise? I had something similar happen to another Chrysler product. Cleaned the throttle body and replaced the TPS. Worked like a dream.

[sgillett]

Is it possibly the air conditioning clutch cycling?
My $.02
Scott

[Rick99]

Thanks for the thoughts. It's definately not the A/C clutch cycling. The TPS is a thought-- could that cause a miss/stumble at idle though? This is happening only when you aren't pushing the throttle at all.

[XDGT03]

I think it could cause it. Does it idle perfectly smoothly otherwise. Does it hunt around at all?

How about the map or maf (I don't know which it has). Possibly need cleaning/replacement? Crank position sensor? If the crank is walking at all it could cause it to stumble.

[Rick99]

I hadn't really noticed if it was hunting, so I went outside to give it a test. I used the scan tool to watch RPM rather than just watching the tach. The van was cooperating with me a bit as it was missing constantly as I was testing it and the RPM was fluctuating from about 800 to 680. That was after letting it run a couple minutes to stabilize.

I also checked out the TPS voltage readings and with the engine off, it seems to move smoothly from .78 volts to about 3.88 volts. I think that's in spec as far as the voltage ranges, but the strange thing is that the scan tool is reporting TPS % at only 85% with full throttle. I checked it by pushing the throttle lever under the hood with the same result, so no linkage problem.

The TPS seems to fluctuate about .02 volts with the stumble and the MAP about .10 volts. Not sure if that's significant.

So does anyone know how I can test some of this stuff out without just replacing parts?

[donald7150]

my '98 has the same problem and it happens under just about all driving conditions. cold, warm, idling, highway speeds. it happens when the a/c cuts in and its like a hard bump when it does

there is a TSB on this issue that reprograms the PCM to dump a bit more fuel into the engine to allow the engine to absorb some of the bump when the compressor cuts in

but take note that the A/C WILL cycle in the defrost or defrost/floor setting no matter if the snowflake button is on or off

[XDGT03]

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the powertrain control module) represents throttle blade position. The TPS output voltage to the PCM varies from approximately 0.6 volt at minimum throttle opening (idle) to a maximum of 4.5 volts at wide open throttle.

Along with inputs from other sensors, the PCM uses the TPS input to determine current engine operating conditions. The PCM also adjusts fuel injector pulse width and ignition timing based on these inputs.

Also like the cam and crank sensors, a 5 volt reference is supplied from the PCM and returns a voltage signal to the PCM that reflects manifold pressure. The zero pressure reading is 0.5V and full scale is 4.5V . For a pressure swing of 0 - 15 psi the voltage changes 4.0V . The sensor is supplied a regulated 4.8 to 5.1 volts to operate the sensor. Like the cam and crank sensors ground is provided through the sensor return circuit.

[Rick99]

Donald-- Good thought-- I just flashed the PCM and the TCM up to the latest software two weeks ago and unfortunately, it didn't fix the problem.

XDGT03-- Thanks for the info on the TPS and MAP sensor. I think I read some factory materials that showed 0.78 volts at closed and 3.88 volts at WOT was within spec, but the fact that it should be as high as 4.5volts and that the PCM is reading it as only 85% makes me think that spec is off and something is wrong with the TPS in any case. I may replace that, since it seems to be messed up whether it is causing this problem or not. When I'm in there, I'll see if the throttle body and IAC are dirty.

Does anyone know what the MAP should be reading at idle? Maybe that's a way to test it.

[XDGT03]

Well, I think you would actually want to monitor it at the stumble to see if its reading varies prior to or after it. My guess would be something around 1.5 v at idle.

[vipergg]

Could be a flakey or partially gummed up egr valve even if it doesn't throw a code .

[Rick99]

Could be a flakey or partially gummed up egr valve even if it doesn't throw a code .


I'm going to have to take back some of the information I provided above. Last night I took off the EGR valve and it did have plenty of carbon in it but seemed to be opening and closing smoothly with a vacuum pump. I cleaned it up a bit anyway and put it back on. When I started the engine and let it idle it was smooth as silk-- great right?

Well, I realized the A/C was off and tried turning it on. With the A/C on, the stumble came back. The strange thing is that the stumble does not happen at the time that the A/C compressor engages or disengages (I can hear the click and watch it on my scan tool), which is why I said this wasn't related, but it definately happens while the A/C compressor is already engaged and it does not appear to happen when the A/C is off. I may run it a little more to verify this, but it seems to be what's going on.

[donald7150]

IAC motor maybe? the PCM will open it up some at the same time as the A/C compressor to take up the extra load that the compressor puts on the engine

[STEAMFITTER]

Im having the same problem with my 99 3.8 caravan. This thread was helpful. Thanks

[Rick99]

Im having the same problem with my 99 3.8 caravan. This thread was helpful. Thanks


Yes, it's been helpful for me too-- just to think through what may be causing this-- so thanks to all that are responding. My next step is to clean up the TB and IAC and I'll report back with results.

[XDGT03]

I found this TSB

NUMBER: 18-008-02

GROUP: Vehicle Performance

DATE: Feb. 11, 2002

THIS BULLETIN SUPERSEDES TECHNICAL SERVICE BULLETIN 18-008-01, DATED MARCH 16, 2001, WHICH SHOULD BE REMOVED FROM YOUR FILES. ALL REVISIONS ARE HIGHLIGHTED WITH **ASTERISKS** AND INCLUDE ADDITIONAL MODELS.
SUBJECT:
Engine Sag/Hesitation And/Or Closed Throttle Start Stall

OVERVIEW:
This bulletin involves replacing the Throttle Position Sensor (TPS).

MODELS:

2001 - **2002** (RS) Caravan/Voyager/Town & Country

2001 - **2002** (RG) Chrysler Voyager (International Market)
NOTE :**THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 3.3L OR 3.8L ENGINE AND BUILT BEFORE OCTOBER 01, 2001 (MDH 1001XX).**

SYMPTOM/CONDITION:

Engine hesitation/sag, closed throttle start/stall, and/or Diagnostic Trouble Code (DTC) P0123 - "Throttle Position Sensor Voltage High". May be more prevalent in cold temperatures below 0°C. (32°F).

DIAGNOSIS:

If no DTC's are present or DTC P0123 is present, perform the Repair Procedure.

If other DTC's are present further diagnosis is required.



PARTS REQUIRED:

REPAIR PROCEDURE:
1. Disconnect the negative battery cable.

2. Remove the electrical connector from the Inlet Air Temperature Sensor.

3. Remove the air cleaner box lid. Remove hose from throttle body.

4. Disconnect the electrical connector at the TPS.

5. Disconnect the electrical connector at the Idle Air Control (IAC).

6. Remove the three (3) TPS mounting bolts and TPS.

7. Reverse the previous steps to install new TPS, p/n 04686360.

POLICY:
Reimbursable within the provisions of the warranty.

[Rick99]

Hey, nice find! I guess I will replace the TPS as well as cleaning the IAC then.

[STEAMFITTER]

Post #16
I found this TSB

NUMBER: 18-008-02

GROUP: Vehicle Performance

DATE: Feb. 11, 2002

THIS BULLETIN SUPERSEDES TECHNICAL SERVICE BULLETIN 18-008-01, DATED MARCH 16, 2001, WHICH SHOULD BE REMOVED FROM YOUR FILES. ALL REVISIONS ARE HIGHLIGHTED WITH **ASTERISKS** AND INCLUDE ADDITIONAL MODELS.
SUBJECT:
Engine Sag/Hesitation And/Or Closed Throttle Start Stall

OVERVIEW:
This bulletin involves replacing the Throttle Position Sensor (TPS).

MODELS:

2001 - **2002** (RS) Caravan/Voyager/Town & Country

2001 - **2002** (RG) Chrysler Voyager (International Market)
NOTE :**THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 3.3L OR 3.8L ENGINE AND BUILT BEFORE OCTOBER 01, 2001 (MDH 1001XX).**

SYMPTOM/CONDITION:

Engine hesitation/sag, closed throttle start/stall, and/or Diagnostic Trouble Code (DTC) P0123 - "Throttle Position Sensor Voltage High". May be more prevalent in cold temperatures below 0°C. (32°F).

DIAGNOSIS:

If no DTC's are present or DTC P0123 is present, perform the Repair Procedure.

If other DTC's are present further diagnosis is required.



PARTS REQUIRED:

REPAIR PROCEDURE:
1. Disconnect the negative battery cable.

2. Remove the electrical connector from the Inlet Air Temperature Sensor.

3. Remove the air cleaner box lid. Remove hose from throttle body.

4. Disconnect the electrical connector at the TPS.

5. Disconnect the electrical connector at the Idle Air Control (IAC).

6. Remove the three (3) TPS mounting bolts and TPS.

7. Reverse the previous steps to install new TPS, p/n 04686360.

POLICY:
Reimbursable within the provisions of the warranty.

[STEAMFITTER]

Thanks to the person who sent this to me. Much appreciated.

[STEAMFITTER]

this did not work for me. ill try a reset

[77Utiline]

Clean off your camshaft and crankshaft position sensors also check your emission system there is an alternate emission system on these 3.8's (whatever that means) and it will cause issues.

[fatguy]

this may sound stupid but check you fuel filter or pump

[77Utiline]

this may sound stupid but check you fuel filter or pump

Not stupid just difficult the filter and pump are both in the tank

[Rick99]

I finally got around to this and bought the new TPS. I'm installing it now to see if it makes a difference, then I'll move on to other things if need be.

[XDGT03]

I think it is funny that what we are doing here is exactly what the stealerships do (replace parts), only it costs us about 50% less for the parts and no labor but probably a higher cost in beer. LOL

[Rick99]

I think it is funny that what we are doing here is exactly what the stealerships do (replace parts), only it costs us about 50% less for the parts and no labor but probably a higher cost in beer. LOL


So true. Not to mention that I pulled my wife's van into the garage and popped the new TPS on there in about 10 minutes on Saturday vs the logistics involved when our family with three kids has to drop off and live without the minivan for a day.

BTW-- it seems to be idling much better now, though I haven't had the chance to take it for a good long drive yet.

[Rick99]

Since my last post in this thread, I've driven the van and it still has the stumble. So the TPS didn't help. I checked the fuel pressure and with the engine off, it jumps right to 58 psi (58psi +/-5 is spec) when the key is turned on. Two strange things though:

1) When I shut off the key, the pressure will gradually (over about an hour) bleed down to about 28 psi-- I didn't leave it longer.

2) When I start the engine, the pressure at idle jumps to about 70psi.

Both of these things seem like they shouldn't be happening, but what do I know? Is there anyone that can tell me if this means I have a problem? (I'm thinking with the pressure regulator perhaps?)

[peter_x]

I know that e30 BMWs are designed to retain some fuel pressure after shut-off to avoid fuel vaporization. There is a check valve in the regulator and the fuel pump outlet. The regulator is often a problem in these cars.

[peter_x]

Any updates Rick?

[Rick99]

Any updates Rick?

Well, I checked the fuel trims with my scan tool and the long term trims are running about -10%, meaning that the computer is compensating for too much fuel going through the injectors. I can't think in theory why that would cause my problem though because -10% is well within the range that the computer can make adjustments, so although the engine would be running rich with high fuel pressure, the computer is compensating by appropriately reducing injector bandwidth.

Anyway, before I drop the fuel tank to replace the fuel pressure regulator, I thought I'd check some of the other stuff. I decided I'd rather not throw new sensors at this and RickMN kindly provided some guidance as to how to properly test everything.

I used a lab scope to check the TPS (even though it's new), the crankshaft position sensor and the camshaft position sensor. As far as I can tell, all of them are giving me exactly the pattern that they should be.

I'm having trouble figuring out how to resize pictures with Windows Vista on my new PC, or I'd post pics of the scope patterns.

The camshaft pattern is 1..2..3....1..2.....1..2..3 and the crankshaft pattern is 4...4...4...4 (with the numbers representing the number of pulses in the square wave).

I have not checked the O2 sensor yet and the other possibility is an intake gasket leak (which I will check by spraying carb cleaner on the intake gasket while watching the O2 sensor and fuel trims.

[peter_x]

Whoa... the regulator is not located at the end of the fuel rail?

[Rick99]

Whoa... the regulator is not located at the end of the fuel rail?

No, it's part of the fuel pump assembly in the fuel tank.

[ml2f]

I was having this problem 97 caravan 3.3L 152000 miles, rebuild tranny 2 weeks ago, I replaced the camshaft sensor, the van ran smooth as silk till today, so I would try that sensor, now I need a figure out my new problem, the van bogged when I gave it gas thank god I was almost home, now it won't start, it turns over but won't start where should I begin to look for this new problem. Thanks!

[Rick99]

I was having this problem 97 caravan 3.3L 152000 miles, rebuild tranny 2 weeks ago, I replaced the camshaft sensor, the van ran smooth as silk till today, so I would try that sensor, now I need a figure out my new problem, the van bogged when I gave it gas thank god I was almost home, now it won't start, it turns over but won't start where should I begin to look for this new problem. Thanks!

Yeah, of course when I hooked the scope up to the sensor, the engine was running smoothly. Maybe I should run it some more and see if I can record the signal during the miss. I guess for $100 I could just replace all the possible sensors, but at least for now I'd like to see if I can actually figure out what's wrong first.

[GEORGEBOOTH]

Mine turned out to be the MAP sensor. apparently it would giltch
and tell the computer to cut off the fuel to the engine resulting
it a stall, hesitation and no starts. you have to have a recording
scope hooked to the sensor at time of the stall and then play it back.
here's what mine looked like.
recomend everyone replace map sensor at 50k because it looks
like its been blasted by egr gasses.
hope this helps

[ml2f]

Mine turned out to be the MAP sensor. apparently it would giltch
and tell the computer to cut off the fuel to the engine resulting
it a stall, hesitation and no starts. you have to have a recording
scope hooked to the sensor at time of the stall and then play it back.
here's what mine looked like.
recomend everyone replace map sensor at 50k because it looks
like its been blasted by egr gasses.
hope this helps

Do I have to have the scope to replace the sensor and where would that be located on a 97 3.3L? Thanks

[GEORGEBOOTH]

no they sell diagnostic scopes for hundreds. I'd just replace sensor
and save the scope cost

[Rick99]

no they sell diagnostic scopes for hundreds. I'd just replace sensor
and save the scope cost


Right, and thanks for the scope patterns too. Just so anyone knows, it would be possible to just replace all these sensors within about 1 1/2 hours or less for about $100 or so. I'm just taking the long route and using this as a chance to learn about engine management and diagnostics. I just got tired of throwing parts at problems, even if that's often a more efficient approach for a DIYer. In the end, I'll hopefully even get my wife's van fixed :D

[ml2f]

Right, and thanks for the scope patterns too. Just so anyone knows, it would be possible to just replace all these sensors within about 1 1/2 hours or less for about $100 or so. I'm just taking the long route and using this as a chance to learn about engine management and diagnostics. I just got tired of throwing parts at problems, even if that's often a more efficient approach for a DIYer. In the end, I'll hopefully even get my wife's van fixed :D

Well Rick99, keep us updated on your progress, because my van is still sitting in the driveway, its dark and cold right now so I'll take a look at the MAP sensor and the fuel rail tomorrow, my eye's hurt from scanning ton's of website for help with this, I don't have a whole lot of engine management skills, I'm just a lady with some knowledge, the wiliness to try, limited income and grateful for this site... :cheerl:

[Rick99]

Well Rick99, keep us updated on your progress, because my van is still sitting in the driveway, its dark and cold right now so I'll take a look at the MAP sensor and the fuel rail tomorrow, my eye's hurt from scanning ton's of website for help with this, I don't have a whole lot of engine management skills, I'm just a lady with some knowledge, the wiliness to try, limited income and grateful for this site... :cheerl:

Let us know the exact problem you're having then and we'll see if we can give you some more specific help.

[ml2f]

I'm having the same issues you are, well it started with it dying out while driving down the road, throw it into neutral and it would restart after a couple turns of the key, took it to autozone code came up for camshaft sensor replaced that drove around without a problem for over a week, ran nice no dying no hesitation nothing, wiper motor went out the other day, the gear inside was stripped, all plastic on the inside, went and pulled one from the junk yard on my way home it bogged down like it was running outta fuel, gave it gas it caught was able to get home, parked in driveway to fix the wiper motor now it won't start, cranks trys to turn over just won't. Only codes I get now from doing the 3 turns of the key are 12 and 55, 12 for battery draining, and 55 for test complete..:(

[Rick99]

OK, so I guess the first issue is that it's not starting. I would consider simple things first. Your engine needs more than just enough battery power to turn it over. It needs enough to turn it over and at the same time keep the computer and fuel pump and other accessories powered up. The first place I'd start is by making sure that you have plenty of battery power. You could try giving it a long slow charge with a charger or you could try jumpstarting it and see if that helps. (Unless you just want to put a new battery in, which it sounds like you don't want to spend the money on unless you know that's the problem.) You can also take the battery in to a parts place like autozone to get it tested.

Try this and see if you can get it to start and post back.

[ml2f]

New battery, the only reason I got that code is because I wore it down trying to start it, It has a new battery, new alternator, new camshaft sensor, new rebuilt tranny (2 weeks ago), check all the relays, like the fuel pump, actually switched them back and forth to see if that made a difference, its got gas in the tank, put it on a trickle charger to recharge the battery still won't start, so its definitly not the battery that wasn't the issue before it died. I went out again today disconnected the map sensor, still wouldn't start checked to see if the camshaft sensor shifted it hasn't, still just cranking. Did you ever find out what was wrong with yours?

[Rick99]

I haven't gotten around to it yet, but I just have a bit of a stumble-- annoying, but not a major issue-- not even a check engine light or code. A failure of the MAP sensor shouldn't stop the engine from running though. However if either the Camshaft position sensor or the Crankshaft position sensor fail, the engine won't run because the computer won't be able to time the spark and fuel.

The next thing I'd do if I were you is look carefully at the camshaft sensor connector and wiring. You could visually inspect the harness for damage and/or disconnect the connector at the PCM and at the sensor and check each wire for continuity with an ohm meter as well as shorts to eachother or shorts to ground. If the harness is damaged, it could have caused your original code and then finally failed completely after you messed around with it while changing out the sensor.

A bad new sensor is a possibility as well (N.E.W.= Never, Ever Worked), but a good mechanic would have checked the wiring before condemning the sensor in the first place.

Before you unplug the connector at the computer, disconnect the negative terminal of the battery and wait a few minutes. (There's a TSB that warns to do this or risk destroying the computer.)

Another test that should be done on the wiring (with the computer and battery connected and the ignition in the "run" position) is to check for 5V reference voltage at the sensor connector with a volt meter.

[TomQuick]

Generally, when something goes wrong with one of my cars, the first place I look is at the last thing that I (or a mechanic) messed with, as that is often where the problem lies. Since the camshaft sensor was recently replace, I would look at the wiring, and the sensor before messing too much with anything else.

One of the simplest tests to perform is the good old fashioned spark test. Grab an old spark plug (or buy a new one if you need to, the cheapest one the store has will do fine), ground the body of it, and attach one of your spark plug wires to the terminal. Have someone crank the engine for you while you watch the business end of the plug. If you don't get a good spark, then look at the ignition system. If you don't get any spark, then I would be very suspicious of that new sensor and it's wiring. If you get a good regular spark, then you might need to look at the fuel system.

[ml2f]

ok heres where Im at, changed out camshaft sensor, still no start, checked for spark got good spark, heading out to check the fuel rail

[ml2f]

I think I found the nipple to the gas line, its inside the engine compartment right, so if I put something in to open the valve shouldn't I get a gas spray? and what happens if I don't does this mean I have no fuel pressure and how to I fix that?

[Rick99]

My fuel service port has a little plastic cover on it that you unscrew and underneath is a shraeder valve. With the key on there should be about 58 psi there, so yes it should spray out if you push the schraeder, but be careful doing that of course!

If there is no pressure then you need to check if your fuel pump is coming on. When you first turn the key on, you should hear the pump hum for a second. Does that happen?

[ml2f]

Ok I found the fuel service port, I used a screw driver no fuel came out and now no air, the fuel pump is kicking on when I turn the key I can hear it.

[Rick99]

Can you have someone turn on the ignition while you hold the screwdriver at the service port? Again, be careful about spraying fuel-- have a rag over it and see if anything comes out when the pump is running for a second when the key is turned on. I'm wondering if your pressure regulator is bad.

[ml2f]

unfortunately no one here but me atm, I did buy a new fuel filter and will replace that tomorrow getting damn cold outside in the garage. I did go out and turn the ignition on and checked the service port again, had some air come out no fuel though. To update on what I've done to this point:

I changed out the new camshaft sensor, made no difference.
Replaced battery cables
Replaced Relays, fuel pump and ASD
Checked all other fuses
Checked for spark...got spark.

[Rick99]

Air? I'm not sure how you'd get air in the fuel line. What engine do you have?

[ml2f]

the fuel rail port has air coming out when I press the valve, shouldn't gas be coming out as well?

[Rick99]

the fuel rail port has air coming out when I press the valve, shouldn't gas be coming out as well?

There should not be air in the fuel lines assuming that your fuel tank has gas in it. You haven't had any trouble with your fuel gauge have you?-- You could try adding a couple gallons just to be sure.

I'd also like to be absolutely sure your not mistakenly checking the EVAP service port (which has a green cap) or one of the A/C service ports-- which have black caps and quick-connect style fittings (as opposed to threaded fittings) with a schraeder in them. It would be a big help if you could post up a picture.

What size engine does this van have?

[ml2f]

Ok rick I managed to change the fuel filter and still not starting heres a pic of the port I was talking about. Its 1997 GC SE with a 3.3L.

http://i33.photobucket.com/albums/d87/mylove2five/My%20Pictures/000_0066.jpg

http://i33.photobucket.com/albums/d87/mylove2five/My%20Pictures/000_0065.jpg

[Rick99]

Yup, that's the fuel test port. You say you're getting good spark-- I'm pretty sure that the PCM will not/can not command sparks without a camshaft and crankshaft signal. You also say that you're only getting "air" out of the fuel test port. The way you described the stalling, I think it's pretty clear you have a fuel delivery problem. Since you can hear the fuel pump running here's my list of things that could be wrong:

1) Fuel line leaking, damaged inside tank, pinched or restricted
2) Fuel pressure regulator stuck completely open preventing pressure from building
3) Bad fuel pump that runs, but can not deliver fuel.

I would carefully inspect the fuel line for any kinks or leaks (though I suppose you'd smell gas if there was a good enough leak to cause this--check for any kinks though.) Failing that, I'd remove the fuel pump/sending unit from the fuel tank and either replace it entirely or replace the pump and pressure regulator. I don't know if you'll be able to do those things yourself though because you'd have to drop the fuel tank.

[ml2f]

I did drop the fuel tank had to, to get to the fuel line there just wasn't enough room under there to loosen the filter, so I released 2 straps on one side, I left it hanging just in case your next response was to check the fuel pump, didn't want to have to start from scratch, not a fun job to do..:( thanks for sticking with me on this going to remove the fuel pump tomorrow.

Oh let me add this and see what you think, the starters going out, the mechanic who rebuilt the tranny said it was the starter bendix, you have to turn the key on and off several times before it catchs, will this be the reason it won't fire up and just crank? Its been doing this for awhile now though.

[Rick99]

I did drop the fuel tank had to, to get to the fuel line there just wasn't enough room under there to loosen the filter, so I released 2 straps on one side, I left it hanging just in case your next response was to check the fuel pump, didn't want to have to start from scratch, not a fun job to do..:( thanks for sticking with me on this going to remove the fuel pump tomorrow.

Oh let me add this and see what you think, the starters going out, the mechanic who rebuilt the tranny said it was the starter bendix, you have to turn the key on and off several times before it catchs, will this be the reason it won't fire up and just crank? Its been doing this for awhile now though.

If you can disconnect and blow the fuel lines out (from front to back) while you're at it, it might be a good idea-- that will help if for whatever reason this is being caused by a clogged line. Be very careful around all that fuel-- best to wear rubber gloves and use a siphon pump and remove as much fuel as possible from the tank before dropping it.

Although strange things can happen with computer controlled vehicles (ie caused by electrical "noise" in the system), I don't think the starter going out should cause any trouble. All the starter does is turn the engine over. If it's doing that and at a normal speed, you should be good. It's very clear that air should not be coming out of your fuel pressure test port though.

[TomQuick]

Air pressure at the fuel rail has to be a problem, and that has to be addressed first, as there is no way the engine can run without fuel.

[GEORGEBOOTH]

The Map Sensor Will Shut Down The Fuel System Faster Than You Can
Say Map Sensor. It Did On Mine. No Start, Start Run Die, Stall,
And Hickup. The Throttle Posision Sensor Data Is Not A Priority.
If It Was Then While My Foot Was Down On The Hammer It Wouldn't
Be Shutting The Fuel Off And Causeing The "hickup".

[Rick99]

The Map Sensor Will Shut Down The Fuel System Faster Than You Can
Say Map Sensor. It Did On Mine. No Start, Start Run Die, Stall,
And Hickup.

I don't think this is right (unless the MAP sensor shorts out or something so proper reference voltage doesn't go to the other sensors). Unplug your MAP sensor and you will find that the engine runs and idles fine without it. You'll get a check engine light and the engine may run rough under certain conditions, but it will not shut the fuel down-- I've done this "just for fun".

As for the TPS, I've never tried to run an engine without one, so I can't say if it would run OK (maybe I'll try). The usual problem is that the TPS has a bad spot where it drops out and that causes the engine to stumble when you hit that bad spot, but won't stop the engine from running/idling.

In the specific case we're dealing with (not to confuse this with the problem my van is having) it appears that the fuel pump is running (meaning that the PCM is telling it to run), but only air is coming out of the fuel test port. Sounds like a bad pump, a bad pressure regulator or a blocked/pinched/leaking fuel line. I don't think sensors are the issue at this point.

[TomQuick]

The MAP sensor supplies input to the ECU, which in turn adjusts the pulse width of the injectors. There is no way that the ECU, or any sensor should cause the fuel pump to be pumping air instead of fuel. There should be fuel pressure at the test port. If there is air pressure there, then there is something wrong with the fuel delivery system. That problem will need to be addressed before anything else can be dealt with. Once fuel is getting to the fuel rail, if the engine still won't start, then other things can be looked at, but it does no good to speculate beyond this problem, as this alone is enough to keep the engine from running.

[GEORGEBOOTH]

First off, pull your map sensor and look at it, does it look
like it's been sitting inside your valve cover because the egr
gasses blow over it?
As for pulling the wires on the sensor I'm not sure what happens
but if the sensor has a direct short to ground or shorts the wires
together internally you won't duplicate it by disconnecting it.
Remember my Map sensor never threw a code. Probably what happens
is like the bad solder joints on the back of the instrument cluster.
The bad connections at the back cause a "spike" in the electrical
system because they all communicate now, the ecm, bcm,tcm and
the glitch of a bad connection "freaks" out the computer and it does wierd
things to the engine. Look at my previous post pics of the spike,
it was my problem and I'm sure others as well.

[Rick99]

ml2f--

Let us know how it's going.

[Rick99]

OK, time to bring this thread to life again (this has turned into a long-term project). I finally figured out it might be good to use my scan tool to watch the OBDII misfire monitor. The PCM uses the cam/crank sensors to "sense" a change in speed and reports what cylinder that is associated with. In other words, as the engine thumps away at idle, it counts the misfires at each cylinder and the scan tool gives you the count on the screen.

Although there are no codes, during the misfire at idle, I am seeing misfires on cylinders 2 and 5 only. Mostly on 2, but often on 5 as well. The thing that peaks my interest is that both of these cylinders share the same coil on the coil pack.

So I pulled the coil pack to check resistance and I get the following:

Primary: All coils about .19 Ohms

Secondary:

Cylinder 3 and 6: 13,360 Ohms
Cylinder 4 and 1: 13,070 Ohms
Cylinder 2 and 5: 12,210 Ohms

So the Cylinder 2 and 5 coil is reading about 1,000 Ohms less than the other coils. The trouble is that I'm not able to find any specs for this-- Haynes only shows specs through MY 2000.

So before I buy an expensive coil pack, does anyone have stats for an 01 3.8 engine coil, or does anyone have any other thoughts on testing this?

[XDGT03]

Seems like the ohm difference is significant and consistant with what you are experiencing. I checked alldata and I could not find anything. Should be able to get a new one for about $60 and probably a lot less from a junk yard. It is the same as the 3.3l one.

[dlm4ut]

On alldata it says resistance on the primary side of each coil should be 0.45-0.65 ohms at 70-80 degrees F.

For secondary it says that it should be between 7000 - 15800 ohms.

This is for a 96 3.3 Dodge Caravan.

dlm4ut

[Rick99]

Just wanted to let everyone know that I installed a new coil and it fixed the problem. All of the secondary coils on the new pack measured at about 12,400 Ohms-- strange compared to my results above with the old coil. But the problem is fixed and that speaks for itself.

Thanks everyone for your ideas.