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Discussion Starter · #1 ·
Hey Guys. I had posted my issue last year and I'm still trying to figure it out. 1991, D150 360 MPI, automatic. On cold start and running for 5-10 minutes or so, it runs great. After it has warmed up and the longer it runs, if I get into the pedal, it simply bogs down. Like it's leaning out. The longer I drive, the worse it gets. Just can't give it gas under load. However, when I shut it down and immediately start it back up again, it will run fine for a bit, but eventually the problem returns. I checked for codes onboard, as well as with an OTC scanner and none show up. Just 12 and 55, which is normal. Any ideas, guys?? I'm lost. Oh, as a side note, on first start up after sitting in my garage all winter, it actually ran perfectly for 2 weeks straight. I was thrilled, but one day, the problem simply reappeared and has not gone away.
 

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Might be "Canister Purge Solenoid" and "Evaporitive Canister" related, the sol is energized on the "good during warm up, and after hot starts for a time" periods you describe. Might be stuck sol, bad hose/s, or bad canister(was ok for 2 wks after sitting all winter). Just guessing.
 

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Discussion Starter · #3 ·
Thanks Key, I'll check the solenoid, canister and hoses to see what I find. At this point, I have nothing to lose!!
 

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4 Wheel Power Disc Brakes
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A '91 360 should be TBI. (12 is start codes, 55 is end so there are no codes stored.)
It could have a bad coolant temp sensor which would cause it to continue to run rich even though the coolant (engine) is warm.
This won't set a code and happens when the thermister inside the the sensor becomes loose inside on longer making contact with the metal part of the sensor.
 

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Discussion Starter · #5 ·
B300, My apologies, I meant to say TBI, not MPI. Thanks for catching that. As far as the temp sensor is concerned, I've heard that they go bad quite often, however, rather than a rich condition, I'm getting a lean or starving condition once at operating temperature. I'll take it out and bench test it to be sure it is working properly, though. Thanks for your help.
 

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B-300 has a far better suggestion, I only gave you a excess vapor issue.
Im also guessing rich is the problem, if lean would prolly stumble/stutter/jerk/miss.
 

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Discussion Starter · #7 ·
Well, as a precautionary measure, I replaced the coolant temp sensor. Took the truck out for a 20 minute ride. All was good, but sure enough, near the end of my ride, under moderate/heavy acceleration, it started to starve. I could give it half throttle, it would starve, then I would back off and it would slowly catch up. However, for those first 20 minutes, it was great, even on the highway. When I got home, I checked for codes and pulled a 23: Throttle Body Temp voltage too high. Could a bad TB temp sensor cause this much havoc?? Again, it seems to occur after the truck has been running for awhile. What do you think??
 

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Sediment/rust in the fuel tank blocking the sock filter as it draws fuel from the tank. Shut it off and it releases the vacuum and all the debris falls off the sock filter.. restart it and starts picking it back up. It really settled over the winter till you started pumping fuel into the tank again??? Just a guess??? or maybe a weak fuel pump as it gets warmer the pressure drops?
 

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Scooby67; said:
When I got home, I checked for codes and pulled a 23: Throttle Body Temp voltage too high. Could a bad TB temp sensor cause this much havoc?? Again, it seems to occur after the truck has been running for awhile. What do you think??
IDK squat about sensor, but a sensor wire "shorted to voltage" could cause your "#23 voltage too high" code. Sensor provides TB/fuel temps to controller to enrichen mixture for hot restarts. ... DK if this helps but; 92 FSM says "throttle body temps"(and 7 other inputs) are used by engine controller to adjust timing(IDK if open loop, or closed loop, or??).
 

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It sounds like lack of fuel supply is the problem now (pump and/or filter assembly) are most likely. Check the wiring to the TB temp sensor, as mentioned it's value is primarly used a restart before the coolant gets warm enough to go into closed-loop mode were the computer fine tunes the fuel trim with help from the 02 sensor.
Also when it's warm and does this check the spark to be sure it's strong with a friend or remote starter switch. A weak coil will cause a consistantly weak spark when hot.
 

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Discussion Starter · #12 ·
Street Hemi and B-300 bring up a good point with the fuel pump as a possible cause. It does seem to be a lack of fuel, but it literally takes 15 minutes of driving to occur. The sock on the pump could very well be a mess. I was getting 12.5 psi at the TB when I checked it a few months ago. Of course, that was at idle, not under any load. Sitting all winter could have allowed the debris to settle, which is why it ran well for 2 weeks thereafter, then ran poorly. I did replace the fuel filter last year before I put the truck away. I REALLY don't feel like dropping the tank for the pump, but I just may have to bite the bullet. I'd like to check the pressure while I'm driving and it acts up to see what pressure I'm getting at that point. Thanks guys!!
 

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AirFuelEddie
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It's NOT the pressure that 'gets' you it's the fuel volume. Find someone who has a fuel pressure/volume tool. OTC, Snap-On ectt
 

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its the pu,p u said u had 12 psi at idle u should have 15 and dont drop the tank lit the bead off the truck with a buddy it so much easier
 

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Discussion Starter · #15 ·
I ran a few tests today to check the fuel pump. I'm getting 11.5 to 12psi at idle. When I remove the vacuum hose from the regulator, although the pressure should increase, nothing happens. In fact, I'm getting no vacuum reading from that port at all. Line and port are clear, so I have no idea what's going on there. When I apply 5 inches of vacuum to the reg. with a Mighty Vac, the truck nearly stalls. I also pinched the return line to check for a fuel pressure increase. It does, but to around 38-40psi. Any idea what the pump is supposed to put out prior to the regulator?? I just want to confirm it's the pump so I don't perform the unnecessary task of replacing it for no reason. Thanks guys for any input.
 

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14.5 is the correct pressure at idle with an accurate gage. The vacumm port is a ported type if I recall correctly so vacumm will be low at idle and increase when the throttle blades are opened.
As vacumm increases fuel pressure will also causing the stall you report.
Fuel pressure will increase if you pinch the return line. 40 psi seems reasonable if this is done.
I have seen fuel strainers for the fuel pump online also seperately from the pump. A clogged strainer will restrict flow when under load and more fuel is needed than at idle.
The problem could be debris (rust particles) from the reluctor in the distributor getting into the sensor and causing a lack of spark and fuel being injected however it would be more erratic than a fuel retriction caused by a clogged strainer.
 

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Discussion Starter · #17 ·
Sooo, here's what I've found. I attached a gauge to the TB with an extended hose and taped it to the windshield. After a 20 or so minute drive, she started to starve for fuel and the pressure began to drop the more pedal I gave it. Got progressively worse. Down to 3 pounds under load. Pulled over and removed the gas cap. Drove like this for a short distance. Still dropping fuel pressure. Stopped and pinched the return line at the TB. Fuel pressure very, very slowly raised. Not an immediate jump, like it should be. Therefore, either the pump's motor is beat or the impellor OR after the long drive, the sock is getting clogged. Fuel pump time!! Since the tank may be contaminated (I think Hoffa is in there!!), I feel I need to drop the tank and clean it. Otherwise, I would remove the bed and save myself the headache. What do you guys recommend?? It's a short bed, so I imagine myself and my friend could lift it off.
 

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Discussion Starter · #18 ·
Fuel pump is in after a day of laying on my back. Not fun!! While I was there, I replaced all the rubber lines with the proper FI hose. I split the factory line-to-rubber metal connections with a small cut off wheel on my Dremel and used FI clamps. Took it out for an hour drive and it runs properly now. No issues. No flopping out when I romp on it!! The old pump's strainer was not terribly dirty, but there was sand and sediment in there. I emptied and cleaned the tank, as well. The old pump was a Carter, but the product number was old. I looked it up. Who knows, it may have been original. Not sure who Dodge used as a supplier when it was built.
 

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Sounds like it runs as good as it looks!! Thanks for the result Scooby67.
 

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overandover1
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same thang

dude, im having the same problem, do u have the part number for the intank pump, i checked mine today and someone has installed a ford pump at the bottom of my sending unit, sick!!
 
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