'90 RamCharger missing at part-throttle

[M.L.S.C.]

My friend just bought a 1990 Ramcharger 4x4 with the 360 TBI setup, and it's having some issues I'm trying to resolve for him (he don't know much about cars and trucks):

a) idle - it don't wanna idle smooth, it revvs up and down a bit all the time, I can see the ISC moving a bit so it's obviously trying to compensate for the fluctuating engine speed, but it don't seem to succeed much. Also, when releasing the throttle completely and let it come to idle (for instance when getting on the brakes) it sometimes stalls, both while in park (free-revving it) and while driving (there's some load on the engine)

b) part-throttle - misses, big time! When I accelerate from stop it starts bucking and shaking all the way till maybe half throttle, once I put the gas pedal down more it wakes up and takes off pretty good.

So far I have done:

- disassemble ISC, clean the old gunk and put new dielectric grease - it's quieter now, but that's about it.
- vacuum hoses - the air pump and the purge canister have been removed, I found the correct vacuum diagram from a post by NoPavemntNoProb and capped off all the ports leading to these components (that's a port on the Purge and ASSV solenoids, along with two ports on the front of the TBI unit). I also notice this truck has no heated air diaphragm, so I capped that port as well. Heck, at one point I had all vacuum ports but the MAP one capped off, and it still made no difference, so I'm thinking it ain't no vacuum leak...
- Pulled EGR, made sure it ain't stuck open, cleaned it and reinstalled it.
- replaced fuel filter and some fuel hoses that were old and cracking.
- checked the coolant temperature sensor next to the thermostat, it has resistance of 40Kohms when cold and drops down to 90 ohms or so when engine is all warmed up, so I assume it works properly.
- there was an MSD box installed, I tried running with and without it, made absolutely no difference.
- tried measuring the timing, it's all over the place - now, I'm used to Ford trucks, and they have a plug you can disconnect to disengage the ECM control over distributor advance so you can actually measure up the base/initial timing - is there such a thing with Dodge distributors? I didn't see no vacuum pod on the distributor, so I assume the advance is computer-controlled?

Overall there has been no effect on how the truck idles and runs at part throttle, and I have no idea what's up with it...

One more thing - there's a very looong harness with two green and two black wires and a square 4-pin plug with yellow rubber seal on it at the end of this, it's all just hanging in there, it comes from the main harness in front of the TBI unit - I'd assume this is for the air pump and diverter valves that are no longer present?

So - inputs, comments, suggestions please? Thanks!

[threetwos]

To place the engine in base timing, disconnect the ECT sensor,(Engine Coolant temp sensor), also are you getting any codes? I bet with all the emissions controlled stuff disconnected and plugged it will set off many codes. Have you tried to see if the timing chain has a lot of slack in it? Pop the dizzy cap, bring the damper up to the TDC mark then manually turn the engine over while observing the timing mark, the rotor should turn the same amount or near it. You can measure the amount of degrees using the timing mark. Turn the engine by hand up to the TDC mark, then reverse the direction, this takes up any slack in the chain. Are you sure the 4 pin harness isnt for the Idle Speed Controller, located at the the throttle body.

[M.L.S.C.]

I dunno about the emissions codes, the solenoids for them are still plugged in the harness so when the ECM commands them to open they will, there just won't be any vacuum flowing through them but the ECM has no way of knowing that as neither the EGR nor the EVAP canister have position sensors on them.

The 4-pin harness is not for the ISC, that's already plugged in - this plug we have just hanging there is square, not a flat one like the ISC takes.

Timing and chain slack - I'll check on that, how much degrees should I set the base timing at when playing with it?

[threetwos]

The base timing can only be changed through the use of a scan tool. Moving the dizzy is pointless and only serves to sync the #1 cylinder for the fuel injection. The timing chain slack can be measured 2 ways. The method I described or with a dial indicator on the valvespring retainer. The timing tab method is quick & easy but not as accurate. Anything over 10 degrees will affect low speed driveability. If it's over 15 degrees the engine should be repaired and NOT driven. The valves WILL contact the pistons in case of breakage,(doubtful it will break), but can cause many problems.

[M.L.S.C.]

Well, if moving the dizzy has no effect on timing, why does it change the way the engine runs? Turning it clockwise caused lower idle speed and also rougher running as well...

Also, if I'm looking at the timing tab, wouldn't I see half of those degrees at the dizzy? You know, since camshaft always turns at half the speed of the crank, and the dizzy runs off the camshaft, if I turn the crank 30 degrees the cam will only turn 15 degrees, and so should the dizzy rotor, correct?

[threetwos]

Well, if moving the dizzy has no effect on timing, why does it change the way the engine runs? Turning it clockwise caused lower idle speed and also rougher running as well...

Also, if I'm looking at the timing tab, wouldn't I see half of those degrees at the dizzy? You know, since camshaft always turns at half the speed of the crank, and the dizzy runs off the camshaft, if I turn the crank 30 degrees the cam will only turn 15 degrees, and so should the dizzy rotor, correct?No the dizzy on all Chrysler Throttle body fuel Injection systems is just to distribute the spark, and synchronize the #1 Cylinder for the PCM to initiate it's fuel injection sequence. Moving the dizzy is affecting this synchronization thus affecting the way the engine runs. IT DOES NOT AFFECT THE TIMING!! You are correct about the 1/2 crank speed, but it's the movement of the crank in relationship to the movement of the rotor that you are observing, the timing tab can be used as a 'reference' for this movemet and YES you are smart to deduce that this occurs at 1/2 the crank speed, thus the actual movement in degrees can be observed. Of course with only a 10 degree tab you can 'estimate this stretch/wear fairly accurately. anything over 10 degrees is cause for concern and replacement. A stretched timing chain causes the engine to have a loss of bottom end power and response, as the vehicle comes up to cruising speed it runs normally.

[M.L.S.C.]

Ah, okay, it all makes sense now - well, the truck is coming in later tonight, so I'm gonna check the timing chain slack and see what codes it's throwing, and I'll report back.

[M.L.S.C.]

Got the codes: 12, 21, 37, 22, 14, and 55. 12 and 55 I ain't worried about, but the others bug me, especially the 37 one... One thing tho - does the engine need to be all warmed up when reading the codes? Cause it's been sitting for like two hours, so it probably is pretty cool by now.

[M.L.S.C.]

Well, dug some more in the engine - there seems to be no timing chain slack, or if there is then it is very minimal - the dizzy rotor responds promptly to even the smallest rotations of the crank. Then I checked the #1 cylinder synchronization for the ECM - sure enough, the dizzy was advanced so much it was like a cylinder ahead in the firing order! Brought it back to where it the rotor sits right under the #1 tower in the dizzy cap, that should help. And here's the interesting part - one of the DTCs was for the O2 sensor, well no wonder - this truck is missing its O2 sensor, when the long-tube headers were installed apparently no one bothered to weld in a bung for the O2 sensor, instead they just unplugged it and coiled the harness up on top of the engine! So now it has to visit an exhaust shop so we can put in a new O2 sensor and be done with it. Here's the interesting part tho - it don't seem to run rich at all without the O2, actually the plugs looked about perfect as far as combustion quality goes, and most weird of all the Check Engine light on the dash ain't glowing!

[M.L.S.C.]

New CTS and MAP sensor today, also new 195F thermostat (old was 180F), so $75 and she's much much better now. No more stalling while in gear (I did turn the manual idle screw to help it out tho), and lots of power even at part throttle. Now just to get the exhaust work done for the O2 sensor, and it should be good.

One more question tho - why does the OD only come on at 65 mph or more?

[threetwos]

The O2 Sensor is only needed to 'fine tune' the engine during closed loop. The engine will run without it. 5-10% loss of fuel economy without it.

[M.L.S.C.]

You know, that's just what I thought too, but here comes a weird one - truck ran just fine on Friday, then sat on Saturday, then today we went to drive it and it's back to its previous self, bucking and no part-throttle power. Scan the codes, and this is what I get, in that very order - 12, 21, 37, 21, 55 - yes, that's twice on the 21. What gives?

[threetwos]

21 is NO Oxygen Sensor Signal. 37 is a Torque Convertor Clutch circuit@part throttle,, if you have the a-500 or A-999 only. I would get the Oxygen sensor replaced and in operation as soon as possible. If are running the engine without it and you have a catalytic convertor, it will cause the convertor to 'meltdown and become plugged, it has to be at stoiometrich to operate within a close parameter and this causes the release of oxygen at a slow rate at a certain temperature. YOU are NOT at this temperature! The fuel injection is dumping fuel, then going lean, then dump ectt as far as concerning fuel economy at a 5% give or take a few percentage rate, I meant fine tuning, you must have the sensor operating. It's part of a "team", omit one component, it snowballs downhill quickly, the exhaust becomes plugged which raises the temp, causing the ECT to give a false signal to the SBEC which may cause it to dump more fuel thinking the engine is overheating and richer mixture will cool the cylinders down some,,, see where this is going??

[B-300]

The 02 sensor works at part throttle only when warm. When cold or at full throttle the PCM has a pre-programmed amount of fuel to use known as open-loop.... That 4 pin square connector is for a heated 02 sensor, 2 for the sensor, 2 for the heater.
TBI uses the distributor pickup for ignition and fuel timing as there is no crank sensor like the MPI injection on the magnum engine.

[threetwos]

All true 'B' but he doesnt even have the sensor in place! Without that, how is the SBEC supposed to advance to closed loop strategy? It never recieves the signal, so it has to default to another fuel map to compensate. The only problem with that is the fact that the SBEC uses a speed density fuel mapping strategy with very little room for 'AI' as the more modern MPI DI systems use, which can 'learn' to compensate for this very problem, no sensor signal. He needs to have a working O2 period!

[B-300]

Working 02 is a must. Do to oxygenated fuel, what was considered rich is closer to stiochromatic. (chemically correct air/ fuel ratio) since the PCM was programmed in the 80's.
The magnum engine is also speed density.... No mass air flow meter.

[threetwos]

Working 02 is a must. Do to oxygenated fuel, what was considered rich is closer to stiochromatic. (chemically correct air/ fuel ratio) since the PCM was programmed in the 80's.
The magnum engine is also speed density.... No mass air flow meter.Yes it's speed density also, but has a capability to 'Block Learn' or enrichen/Lean the mix up to approx:+ or - 10% the older TBI couldnt do that. The Magnum engines also used a dual bed cat with dual O2 sensors. As all OBD-II engines. But yes, he needs it.

[M.L.S.C.]

Threetwos, the exhaust of this truck consists of long-tube headers, straight midpipes, Flowmasters, and tails - no cats nowhere, so plugging up exhaust is not a concern. Exhaust also runs pretty cool, compared to my MPFI Lincoln and carbed Chevy, both of which ran perfect.

But I think I found the problem, other than the O2 sensor - there was a JET power control module plugged in between the harness and the factory PCM, I pulled it out and the second #21 code went out immediately, now it accelerates just fine. There's still some hesitation at part-throttle, but I guess that could be explained with the rich-lean-rich-lean cycle the PCM does without the O2...