Whats up guys? Alright, just rebuilt my motor and after getting it to run im having some troubles with backfiring. I also pulled a code 42, est shorted to ground. Ive tried a different opti, ignition module and ecm. Really, Im just looking for more possibilities and maybe a flow chart for the code if anyone has one. Help would be greatly appreciated.

As far as mods go, I have a mild cam and hooker headers.

 

Not sure why you messed with the opti but don't forget the PCM will think that a lack of voltage is the same as being grounded.

First, does the 42 return consistently? I assume yes.

Disconnect the ICM and probe the white wire at the ICM connector while someone cranks it over. Should be 1 - 4 volts AC not DC, present. If so, the problem could be the number 11 U/H fuse, its contacts at the fuse or it's wiring (pink wire) to the coil or the wiring to the ICM (pink/black and white/black wire).

 

I changed the opti for the backfire, not sure wether or not the 2 problems are related. And yes, the code is consistent.

 

I had 3 volts at the white wire while cranking. The fuse is good and the wires from the fuse ohm out good and arent shorted to ground. I also was checking that white wire to ground, with the key off and the pcm and coil plugged in, I am directly grounded, but when I unplug the black connector on the pcm, my direct short goes away. Is it normal for this wire to be grounded by the pcm?

 

No one has any more ideas?

 

You should never put an ohm meter on PCM pins. An ohm meter uses voltage output to measure resistance and it can damage circuitry.

First if you measure something unplugged and it changes when it is plugged in, then read the pin you are plugging into with the wire off to see if it always reads that way. But not in this case, just an example of what to look for. In the case of the PCM you have eliminate all other possibilities.

Second, never ohm a wire with voltage on it. Remove the source before measuring. However that brings the third ohm rule and that is never ohm a wire connected to circuitry. You can ohm from one end to the other when one end is removed from the circuit. The reason is you will measure the wrong resistance since, as you found out, you will be ohming not only the wire but the circuitry inside the PCM for example.

We have to assume since you read ground at the pin with the harness connected that it is normal(see rule 3 above). Because you did observe 3 volts AC (I hope you were on the AC scale) during cranking. If the pin was truly grounded, it would not have showed the 3 volts. Capish?

Now back to the 42 problem. It's a bit puzzling since a 42 will disable the injectors. So if your code is active, the engine should not run. So let's assume for the time being that it is a consistent code and the engine runs. This would indicate an intermittent problem. Such as a wire periodically breaking contact. Therefore the place to look is the ground wire to the ICM which is connected on the head near the ICM. I would disconnect the plug at the ICM and ohm the black wire to ground while wiggling the wire and look for changes in the resistance.

That same black wire also goes through a splice located where the engine harness splits from the driver side to go to the passenger side over the intake. That splice may be bad so be sure to check it.

If grounds are not your problem, do the same for the other wires from the coil to the ICM.

 

I do appreciate the help Speedy. I want you to know a bit of my backround so that you dont think im incredibly stupid. I work at a Chrysler dealer as a mechanic and Ive been at it for a few years. This problem is just frying my brain. I failed to mention this before, but I actually bought the car pretty recently with a blown motor, and after I rebuilt it the first time, it ran great. I started over because of my own stupidity, nothing to do with electrical... After the second build, from the first time I started it ive been having these problems. From my understanding, the code 42 will kill injectors, but I didnt think it would kill ALL injectors. My car runs, but it has no power at all. It feels as if im running on maybe 4 cylinders.

 

OK well how about this. When the engine is dead cold, have an IR thermometer in hand and start the engine and immediately measure the temps on each exhaust outlet tube to see if any are drastically colder than the others????? This makes it much easier to find dead cylinders than unplugging spark plugs but then you could pull injector clips to find the cylinders that have no effect when unplugged.

 

Reviving an old one here....

Was this ever reslved? I have a 93 z with #5, #7, #6 and #8 cylinders down. I pull the injuector plugs and nothing changes. So these cyliders are down. I also has code 42. I have traced both the ground and the white wire with no obvious breaks. Where should i go now?

I will have my buddies meter here tomorrow so I can ohms the wires. I have a old meter that shows 2 volt on the white wire while cranking....

Could it be as easy as a bad ICM?

I just picked up the car for cheap cause of the cylinders down...so hoping for cheap easy fix...if that is possible...

 

Have you checked to see if you have spark on theses cylinders? Take the boot off the plug, hold wire next to block(with insulated pliers) and have someone crank the engine.

Have you pulled the plugs on the dead cylinders? Maybe fouled?

Mike

 

The 93 has a batch fire injection system with 4 injectors supplied from a single fuse. Check the fuses - #9 and #10 in the under hood box. Key on - Check for 12V on the pink wire in each harness connector.

 

I have spark on these cylinders. I pulled the plugs and checked.

 

Injuneer,

Thanks for info. I have checked the fuses them selves multiple times but will double check again. I metered one of the injectors plugs last night and it had 12v KOEO. Not sure which wire it was though as I read they both will have 12 volts. I will go thru and check each pink wire on the injector plugs tonight.

How does code 42- ignition control direct short- play in with this batch of injectors being dead? Does the ICM itself contol this or is that a function of the PCM (my guess)?

Thanks for the feedback, big help.

Steve

 

Check the voltage on the pink wire in the harness connector, with the harness connestor off the injector. Make sure the injector you check is one of the ones that does not cause the engine to change rpm when you pull the injector harness off.

You appear to be indicating the front four cylinders on the engine are running fine, and the rear four cylinders are not working at all. There is no reason a faulty ICM would only affect four of the 8 cylinders. It has to be something related to those four cylinders.

But looking at the 93 wiring diagram, the injector harness connects #1/#3/#5/#7 to fuse 10 and #2/#4/#6/#8 to fuse 9, so it isn't likely to be an injector wiring problem.

 

Well I metered everything out and it is all checking out. Coil, icm wiring, signal to optispark, injector plugs, fuses and grounds.

I even pulled the fuel rails up and all the injectors are squirting, even the four I thought were dead.

I am going to check the optispark harness and if that checks out fine I guess its down to optispark itself.

I took a better look at the spark on those back 4 cylinders and the spark is intermittent. I pulled a wire an used an extra plug to look while it was running. It misses ever 4 or 5 one. I was reading the Haynes manual and they say that's the same as no spark at all.

My guess is the spark timing events for those cylinders is off because of a bad optispark.

Any other thoughts?

Thanks again for feedback.

Sent from my DROID3 using Tapatalk 2