[Bob Lincoln]

I don't have much info, this is what I've got:

A friend has a 2003 Caravan with 3.3L V-6 and automatic. Van had been bucking and loss of power whether hot or cold, intermittently. He had a fault code for a misfire. Mechanic changed plugs, wires, dist cap and ignition coil(s). Also reported was that the gauges were slamming around while the problem was occurring. Mechanic them replaced ECM, which cured the gauges problem. Now it reportedly has a fuel injector code, and still bucks. He says that feathering the throttle carefully will help get past the problem some. Thoughts?

I gave him the code list and instructions, and asked him to check current codes. The van is in a mechanic's hands now, and my friend is $1,500 deep into it and turned off to Chrysler. He says the mechanic is not charging him for any diagnostic efforts, to minimize the impact.

 

[chuzz]

Bob, I don't think there's a distributor in the 03 3.3 liter engine. At least, there's not one in my 99 GC with the same engine. Your friend needs to look over the repair list very closely. Maybe he's also go the infamous instrument cluster failure.

 

[John Wood]

It would be helpful to know if the misfire code is the "random" misfire, or specific to one cylinder. The P code would identify that.

My initial though is just a bad connection or loose connector on the PCM. Replacing the PCM may have just improved the connection for the data buss (for the BCM or instrument console), but perhaps not to one of the injectors (assuming the code is injector specific). I would inspect the mating plug to the PCM for any darkening of the connector pins for the affected injector and do a simple continuity test to the injector connector.

The setup on this vehicle has the battery real close to the PDC and to the computer, so if any electrolyte that might have got on the top of the battery was washed on to a connector, corrosion could occur. A visual inspection of the battery, cables, and adjoining components might provide a clue.

Note: I'm trying to tie the instrument cluster problem with an injector misfire, but they could be totally unrelated.

Bad solder joints on the cluster could certainly be the problem if the P300 (random misfire) is the code that comes up.

I think it is important to get the specific codes here.

 

[Bob Lincoln]

That's what I told him. He wasn't given them, and the van is at a mechanic's shop now. He has the procedure to get the codes if he can and wants to get to his vehicle to run them.

 

[Doug D]

Bob, I don't think there's a distributor in the 03 3.3 liter engine. At least, there's not one in my 99 GC with the same engine. Your friend needs to look over the repair list very closely. Maybe he's also go the infamous instrument cluster failure.

Correct Chuzz. No distributor - it has an integrated electronic ignition system. Without knowing the fault codes it will be difficult to diagnose.

Aside from possible a bad instrument cluster, I'm puzzled. Possibly a fuel issue?

Bob - what repair expenses have totalled $1500? Seems like an awful high price for what has been replaced.

 

[ImperialCrown]

Does he have the past misfire and present f/inj. 'P' codes? If they are at the same cylinder, this might help speed diagnosis.
The f/inj. code is electrical to make sure that the internal inj. solenoid has the correct continuity (the PCM actually looks for the inductive 'kick' after firing it to make sure that the inj. internal solenoid coil is still a coil) .
Unplugging one while running or with the ign on can set this injector code.
The code won't check for a fuel-restricted or mechanically faulty injector.
I agree that bucking is usually a symptom of a cylinder not firing. Whether ignition, fuel or mechanical.
The sag can be caused by the raw fuel from the misfire being read by the O2 sensor as a high-oxygen (low fuel) condition and the PCM may then try to command the injectors rich.
This can be a real Pandora's box and carbon-foul spark plugs and damage cats.

 

[Bob Lincoln]

What you see is all the info he told me. It takes some prying to get all of the info and accurate info from him, and that's as far as I've gone with him.

The $1,500 may be for other recent repairs, or it may be that he took it to the dealer who pillaged his wallet, so that he went to a different shop.

 

[Bob Lincoln]

Does anyone have the pinout for the PCM for the 2003 Caravan? It would be helpful in looking at which wires could generate which codes.

 

[Bob Lincoln]

Anyone?

EDIT: Nevermind. Just found a diagram online.

 

[Bob Lincoln]

My friend diagnosed it himself and found:

Wiring harness to the injectors *disintegrated*. The wiring insulation actually crumbled into powder when he handled it, and there was a short between two injectors. Apparently the exhaust heat cooked the insulation. This effectively reduced the injector resistance to 1.5 ohms, dumping 100 watts into the internal MOSFETs firing the injectors, which damaged his PCM. There apparently is no other protection against shorts other than the fuse to the PCM. He fixed the wires, is shopping for a PCM. Dealer wants $700. Others want to repair the one he has, saying that reman is not available.

He is fighting the dealer to get the cost back on the mis-diagnosis and unnecessary parts. He says if they don't pony up, he is done with Chrysler forever.

 

[ImperialCrown]

Is he sure that the PCM is damaged? The PCM fuel injector driver MOSFETs are switching the injector on the ground-side which shouldn't hurt them. If the ground side of the injector is grounded, the injector would be on all the time. It may overheat the injector, but should leave the PCM alone. Fuel injectors are only rated 'intermittent-duty', they aren't rated to stay on.
The current has to go through the injector resistance-drop to get to the PCM anyways. 12 volt (+) power comes in from the ASD relay.

 

[Bob Lincoln]

It's correct that the ground side of the injector is grounded by switching the MOSFET on. It's also true that with the harness shorted, and 1.5 ohms presented to the MOSFET instead of 14, it's trying to pull 100 amps instead of 10 through the MOSFET (whose on-resistance is probably less than an ohm). Thus, the MOSFET overheats and fries. The injector also stays on when the bare wiring intermittently finds a ground underhood.

He's had several other wiring shorts with this vehicle, one of which killed his headlights at night while driving, and one that disabled the sliding door. To be fair, he bought it used in 2006 from a dealer.