Hey Everyone,

I have a 1991 318 TBI and it runs great 95% of the time. The only exception is that when it's not fully warmed up & you put the pedal down, it starts to rev up & then entirely cuts out until you let off the gas. In all truth it acts like a choke problem, but the TBI isn't choked.

Any ideas what could be causing this? Faulty temp sensor somewhere?

Thanks!

 

Have you pulled the engine codes from the onboard diagnostics? If so what are they? If not why not?

 

Didn't know I could pull codes on a '91. What's the procedure?

(No check engine light, but I assume it can store codes w/o one showing...)

 

That is a very good reason for not pulling your codes. The system can store codes and rarely turns on the check engine light. Here is how you do it.

ON-BOARD DIAGNOSTICS Dodge OBD1 Pre 96

1. Cycle the ignition key ON-OFF-ON-OFF-ON within 5 seconds. To cycle the ignition key ON means to turn it only as far as it takes to get the radio to come on. It does not mean to turn the engine on.

2. Count the number of times the "check engine" lamp on the instrument panel flashes on and off. The number of flashes represents the code. There is a slight pause between the flashes representing the first and second digits of the code. Longer pauses separate individual codes. For example, flash-flash-flash [pause] flash-flash represents the code 32.

A code of "55" represents end of error codes. If this is all you get then no error codes are stored in the computer. This is the normal condition

 

Thanks!

Codes stored are:

12 Direct battery input to PCM was disconnected within the last 50 key-on cycles (normal)
37 Torque converter clutch solenoid CKT or park/neutral switch failure

Hmm... Neither of those look like part of my problem... The TC Clutch code is worrisome, if not part of this problem.

Anyone interpret these any different??

Edit: And what does CKT mean?

 

Additional info on the condition:

When the engine is not entirely warmed up and you're accelerating from a stop the engine will cut out entirely until you lift your foot off the accelerator, at which point it will start idling normally. The only ways out of it at that point are to pull off the pedal & feather it back in, coaxing it along. The only other thing to do is manually drop the auto trans into 1st and it will rev right up and take off like a banshee.

This only happens from a stop, not when you stuff the pedal at speed.

Do that help diagnosis at all? Or connect the problem to the code 37 somehow...

 

CKT is short for circuit. I have had a code 37 since the day my truck rolled off the dealers lot in 1989 so if you find out what causes that let me know. I would check the temp sensor, the TPS (throttle position sensor), and the hall effect switch with their associated wiring. Something is breaking down when cold and so all trouble shooting will have to be done before the engine warms up.

 

I have a code 37 also and I think it is because I do not have a locking torque convertor in my truck. The torque convertor clutch solenoid only comes with some transmissions that have a locking torque convertor. May be that the computer is looking for the solenoid but it is not there so it thinks there is a problem. Should not cause any problems. I replaced my truck transmission with a Ram Charger trans which has a locking convertor which I just left disconnected. Your hesitation problem sounds like mine. I have MPFI in my 1992 though. I cleaned the injectors but didn't help.

 

I tested most fuel-related components under the hood. Both the Throttle Position Sensor & the TBI Temp Sensor tested out of spec.

The Idle Air Controller is unlike anything I'm used to on my germans & after reading up on it's functionality I'm convinced that it's the manifestation of the problem. It tests OK, but even if it's not the root problem, whatever is the root problem it has to go through the IAC to manifest.

 

Sounds like you found the problem. A TPS is nothing but a variable resistor that changes resistance as the the throttle changes its opening. The computer reads this resistance change and varies the fuel mixture to maintain the proper air/fuel ratio. If the TPS gives an improper resistance value to the computer, the computer will give an improper fuel ratio and cause your problem. (garbage in garbage out) The TBI temp sensor can also exacerbate the problem because it tells the computer how much to modify the air/fuel mixture to account for the changes in the density of both the air and the fuel as the temperature changes.

The IAC simply does what the computer tells it to do so I doubt it is the problem.

Do either the TPS or the Temp Sensor come back into spec once the engine warms up? If one does I would replace it first since the problem seams to be temperature related.