May sound crazy to you, but we have cured this same type of situation with running high octane gas. Lots of crap sold as gas nowadays

 

This is something new I could try. It’s the same gas from almost a year ago. It’s probably worth putting new in anyways. Thanks for the idea!!!!

 

You mentioned replacing a crap load of parts, but I didn't see ignition wires listed. Spark plug wires age and degrade. You may have arcing through the insulation causing the misfire. The fouled plugs would substantiate this. Ignition wires are typically rated for about 1000 ohms per foot. (This would be about 3030 ohms per meter). It might be time for new wires.

 

You’re right. I also replaced the wires 3k miles ago. I forgot to mention that 😅

 



Leak down test at 70psi, 17% loss at TDC (cold) cylinder 1. Sounds like it’s coming from the head/ oil fill tube. I feel like it should fire?

3 looks better

 

New gas didn’t make a difference. Said screw it and pulled the intake to check the valve train, and also make sure I didn’t leave a rag in the runner 😅

everything looks good to me. Rods are straight, lobes aren’t worn down, I can’t take the lifters all the way out with the head on, but the rollers spin free and they move in the bore just fine.
I’ve quadruple checked the plug wires and none are crossed. They’re run properly with no overlap besides 90 degrees if needed.
I don’t think I’m missing anything. At this point it has to be the ECM pushing too much fuel into those cylinders right? I’m just at a loss as to why it’s only these 2…

 

Another question, does this engine loose coolant over time?

 

To be honest, I don’t remember. I haven’t been able to drive it for about a year. I have the intake off. Since I’m this far already maybe I’ll pull the head to investigate.

 

I would suggest swapping plugs and injectors from suspect cylinders to other cylinders to see if the problem follows the swapped parts. Point: You say you have a '94, yet you claim to have diagnosed misfires on cylinders 1 and 3. OBDI doesn't have the ability to isolate individual cylinders on misfire codes (which I don't think your '94 even has misfire codes); so, how did you determine your misfires were on cylinders 1 and 3?????

 

I’m using a temperature gun on the exhaust manifold. Also, I can pull the injector plugs/spark plug wires on these cylinders with no effect on the idle

 

You might pick up an old Snap On MT2500 red brick scanner; it can talk to pre-OBD-II vehicles. Or find someone with Chrysler's DRB-II scan tool.

Question from your initial post confusion - is your 1994 ZJ Check Engine Light not ON, or the instrument cluster has no CEL? I have a 1994 Chrysler LHS 3.5L and it has a CEL (a proprietary diagnostic port instead of an OBD-II). Your 1994 may have a similar arrangement. There is a DRB-II connector under the dash, another for the engine under the hood, and another for the anti-lock brakes under the hood. They are not networked together like 1996 and later.

 

The CEL is not on. It works. When I disconnect any injector or the MAP/TPS it turns on, but goes away when I shut it off and back on.
I have a lead on somebody I might be able to borrow a scan tool from. If I was gonna pay DRB-II money I’d probably rather get a microsquirt to just be done with all the obd1 malarkey lol.

 

Oh and yes. There’s a 6 pin data link connector beside the ecm.

 

I'm using the rusEFI as a Daughter Board; where the stock ECU still controls transmission, cruise control, gauge cluster... I've been ruling over ignition timing (with 6 GM LS Coil-Near-Plug). Just getting started controlng the injectors. It's my way of easing into it where I don't have to write every single table all at once. Here is my build thread, with rusEFI entering the script around Page 8.

 

Awesome. Thank you! I’ll have a look through it.

 

You wrote the injectors were cleaned and tested, by who and how? Are these the original injectors or some after market replacements? The heads are known for cracking and can cause this issue, pull the heads and inspect.

 

By me. They’re the factory injectors. I bought a tester that you can put the injectors into and pressurize them with a can of cleaner, then actuate the solenoid with a pulse. They all pulsed perfectly with none were stuck open, and all had consistent streams.

Yes I think pulling the head is what I’ll do next. What I don’t understand though is how through both compression and leak down tests I haven’t see any sign of this being the problem.

 

I have had stuff like that happen on AC systems. I can't explain it either