QuestionHello Mr. Finston,
I am writing to you on behalf of my brother, who is currently pulling his hair out over this. He has been an auto mechanic his entire life and is rarely stumped, but now he is. He is working on a 1997 Voyager with a 3.3 liter engine. The vehicle starts and runs fine, then without warning it will sound as if it is about to stall, sometimnes it does, other times it doesn't. No matter what, no error codes are showing up on the monitor. The only thing that does show up is "open loop fault" for the fuel system. I know he hooked up some sort of idependent fuel delivery system to bypass the vehicles system and still has the same problem. He tried changing the computer, no help. I know he also changed the alternator, ( he said there was some rare problem that that sometimes corrects, this time it didn't). He has consulted with other mechanics in the area nad no one has heard of this problem. He checked his recall list and I know he gets CD's for troubleshooting and he could'nt find the problem listed there either. If you can offer any help he would greatly appreciate it. Thank you for your time!
AnswerHi William,
It would be useful to separate spark issue from mixture issues in this intermittant stalling situation. If he had a scope or access to one it would be useful to be sure that it isn't something to do with the spark generating circuitry, and that would be revealed by a scope.
If I think about items that might affect the mixture my first ideas always bring me to the egr valve which if it is marginally clogging up or the valve stem is sticky it can spontaneously go ajar slightly at idle or at start up which makes for a stall or no start condition. So if he hasn't checked for the free play of the valve stem of that valve and going further removed the valve and checked its channel for build up, and cleaned that out, then I would recommend doing that. Another possibility is that the MAP sensor, coolant sensor, tps or throttle body temp sensor, or other such mixture-related item is flakey, has a cracked vacuum line or fitting, has a loose electrical connection,etc. so that when it spontaneously shifts voltage reading that throws the mixture off of what it needs to be, but without setting a fault code because it isn't so great as to rise about the threshold for a code to be set. That you could check with a diagnostic readout box that displays all the voltage values of the sensor "live" and then he could watch for one the jumps at the time of the onset of the stall. Also recall that the management of the engine is open loop until it warms up at which point alot of the sensors and the vapor recovery system come into play for the first time. So the onset of the stumble might be associated with going into closed loop condition (that would be revealed by the diagnostic box) and then you have the possibilitiy that an O2 sensor is marginal or the vapor recovery system has a vacuum leak which won't appear until that changeover to closed loop operation.
He might also want to clean the throttle body butterfly and the idle air intake passageway, and then remove the AIC motor and check that it is free to move in its channel as well.
Those are my only thoughts at this point. I would be most appreciative if/when he figures it out he would let me know.
Roland
