2 cylinders not firing, checked EVERYTHING

[aidanair]

so i have checked the plugs, coil pack, air obv, i pulled the plenum and injectors are fine, swapped ptu's and cas's and theyre fine. cant figure this out! cylinders 4 and 5 wont fire... maybe a compression test is next? i know my rings are bad but can they be so bad 2 cylinders stop firing out of the clear blue (at the same time i might add)

[marty1mc]

All depends, if you know your rings are bad, then you have compression loss. I would do a quick compression test.

Have you pulled codes? I would do that first in any case.

After that, try to narrow it down to fuel/spark.

[aidanair]

code 55, all clear on ecu. should be getting fuel and spark.. checked all possible culprits..

[marty1mc]

should be or are getting fuel and spark? Are the plugs wet when you pull them? is the coil pack sparking? You can test the coil pack by pulling it out , grounding the spark plug body to the plenum and see if the plug sparks.

[aidanair]

good point, i havent checked spark like that yet, plugs are dry when i pulled them though, not fouled or anything either. ill do the spark test tmrw and let you know, but my guess is it will be fine, we shall see... thanks

[aidanair]

threw codes again, still code 34. well i checked and both plugs do not spark when plugs are grounded to the plenum, so it must be electrical. maybe PTU? weird thing is my PTU is only about a year old =// my buddy is hellbent on convincing me its the EFI, but im hoping not.. any thoughts?

[robomatic12]

EFI doesn't mean anything... "electronic fuel injection"... I'm guessing he means your ecu?

If you have the series 2 ptu, you will have a subharness which is a common point of corrosion. Remove all the connectors on the ptu/going to the ptu and clean them well! I had a cylinder that would die anytime I hit a speed bump too hard, it was the PTU subharness jiggling around. I ended up soldering the harness together instead of the crappy connectors that are prone to moisture damage.

Swap the coil packs around and see if the no-spark follows the coilpacks.

[aidanair]

thanks for the tip ill check, i already swapped coil packs and found it didnt move cylinders to bring you up to speed i already threw ecu codes and got a 34 (det sensor) and EFI i meant is the EFI harness aka the main engine harness

[aidanair]

so i checked the spark by grounding the plug, no spark. i replaced the PTU and subharness, no change. this is starting to get overwhelming and im thinking about giving up and taking it to a shop, i feel i have done everything short of tracing the wires all the way from the coil pack to the ecu to see where the signal is stopping. any other ideas?

[aidanair]

So two years later, for anyone counting, and after a shop told me it was my compression (which i checked myself, and it was not)... I replaced the main engine harness. Well, at this point, my car was running on 3 cylinders. After replacing the harness, it was on 4. Swapped ECU's, and voila. 6. SO, what happened was the harness shorted out, and fried two injecotr drivers on the ECU as well as a transistor on the back of the ECU motherboard. ALso, the two wires from the harness that run injector pulses were shot. Now, car is on 6 cylinders, and very very fast. So anyone having similar issues, replace your main engine harness. Chances are after 100k miles, its on its way out.

[t.mcginley.jr]

So two years later, for anyone counting, and after a shop told me it was my compression (which i checked myself, and it was not)... I replaced the main engine harness. Well, at this point, my car was running on 3 cylinders. After replacing the harness, it was on 4. Swapped ECU's, and voila. 6. SO, what happened was the harness shorted out, and fried two injecotr drivers on the ECU as well as a transistor on the back of the ECU motherboard. ALso, the two wires from the harness that run injector pulses were shot. Now, car is on 6 cylinders, and very very fast. So anyone having similar issues, replace your main engine harness. Chances are after 100k miles, its on its way out.

^ Good to know!

[BarzOnTheWindow]

How invasive, or laborious was replacing the Main Harness? Seems I have the same problem...

[NolimitZ32]

Its a BIG OLE HONKIN BISHHHH, test everything before you do so, check continuity at the ECU terminal too.