Chrysler Repair: 94 Jeep G.C. 4.0, throttle position sensor, jeep manuals

Question
QUESTION: Roland,
I have a 94 JGC 4.0 with a sputter and die out problem. Fuel pump pressure was 30 psi, I replaced that, still had problems. I replaced everything I could think of, ie.. Filter, crank and cam sensor, iac, tps, injectors, pressre regulator, plugs and the ecm. still having problems. it will run for a lil bit and then sputter, backfire and die. Any suggestions?

Robert
California

ANSWER: Hi Robert,
Try for fault codes using the ignition key: "on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the check engine light which remains on to see it begin to flash, pause, flash, etc. Count the number of flashes before each pause, then repeat the process to be sure that your set of flash counts is accurate. Tell me what you saw, in order of appearance, as flash counts and we'll go from there. I assume the Jeep line is like the Chrysler as far as self-readout of fault codes is concerned but I can't be sure of that because I don't have Jeep manuals. But give it a try.
Roland

---------- FOLLOW-UP ----------

QUESTION: Sorry Roland,

I forgot to add those. I now get a 12, 62, 24, and then the 55 which we all know s the end. 12 is battery disconnected, 62 is something about the miles cannot be stored and the 24 is tps sensor voltage high. I just got these codes today. The problem has been going on for awhile.

Robert

ANSWER: Hi Robert,
The 24 code is probably the relevant one but this time I would be inclined to check out the wiring/voltage of the throttle position sensor because you already replaced the sensor. One wire should have 5V on it, one is a sensor ground, and one is the tps variable voltage position sensor. You could check the voltage reading between the two wires that don't have 5V on them ( find which that is just by looking at the pins of the plug, with the ignition on, to figure which is the 5V wire putting the other lead of the meter on chassis ground).
When the plug is attached to the sensor, then vary the throttle position to see if the reading changes between those two wires. If not, then one of the wires is 'open' between the plug and pcm, or one of them is shorted to the 5V wire or to ground, but in any case look for that and also look at the condition of the harness wires as far back from the plug as you can to try and locate some damaged insulation. The 24 code could be either as it means the voltage is eiher too high (shorted to a 5v or higher wire) or to low (shorted to ground). Unfortunately I don't have the wiring diagram to tell you which pins at the pcm there 3 wires are attached to, and that would be the better place to do these measurement should one of the wires be open somewhere between the pcm and the tps.
Roland



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QUESTION: Hey Roland,
I checked the wires on the tps, 1 has 4.97, the 2nd has 4.4 and the 3rd has 0.00. That is unplugged and grounded. When I hook it back up and start it, the 1st is 4.95, the second drops to .88 and the third is still zero. Does this mean the wiring is shorted and that is my problem? I really appreciate your help.

Robert
California

Answer
Hi Robert,
I am not sure what you mean by "...and grounded." But in any case, I think the .88 when it is plugged in is acceptable, but just in case try looking at the voltage when hooked up and the ignition is 'on' (no need to start the engine), then open the throttle. If it ranges up to the 4+ V level, smoothly, as you open the throttle then I think there is no problem with the wiring. It would be desireable to check the pin on the pcm for that 2nd wire to be sure it too shows .88 (with the pcm plug removed) but I don't have the wiring diagram to tell you which pin that is.
Roland