Right now my car sounds like a subaru with exhaust. It has a slight misfire that 2 shops haven't been able to pin point. Their recommendation is to replace the wiring harness. I want to see if I can find the exact issue before replacing the whole harness and maybe not even resolve the issue.

I just replaced the ECU and it is throwing codes U1000 and P0138 and P0158 which is high voltage to the rear o2 sensors. The shop replaced cam sensor, crank sensor, spark plugs, smoke tested, checked all coil packs and injectors, cleaned MAF, checked the maf voltage via uprev, tuned it on dyno and street.

I just checked all the grounds in the engine bay, removed them, cleaned them up and put them back but still sounds like a subaru.

Should I check the grounds in the cabin? Any recommendations or ideas what to try next? Thanks

 

I am continuing to mess with the car and it looks like cylinder 6 is not firing. Using Uprev I did the cylinder power test and when turning off 6 I don't have any drop or RPMs or rougher idle.

I swapped the spark plug and coil from cylinder 2 and 6 still is not working. The spark plug was black and still wet with fuel so doesn't seem like it is sparking yet all spark components are good.

 

How long ago did you replace the spark plugs before cyc 6 turned "all black"

Could it be the valve cover gasket is not sealing off causing oil to drench the spark plug?

Do you have a CEL?

How many miles? Mods? Will the shop offer any kind of money back if it turns out not to be the wiring harness?

My first guess going into this issue would be to try a new coil pack, but it sounds like they;ve already tried that...

Keep us updated!

 

I have a built IPP block on my stock heads...the block has roughly 5k miles on it and the head/rest of the car has 57k miles. I am running a vortech kit with 660cc injectors, pmas MAF, walboro 255lph pump, uprev for tuning, etc.

I swapped coils and plugs out of cylinder 6 and swapped them with the perfectly fine ones from cylinder 2. The bad cylinder did not change...cylinder 6 is still the issue. I am thinking I have a short or something somewhere that isn't sending power to the coil on 6.

I checked the ground (removed, cleaned, and reinstalled) in the engine bay and the ground behind the stock navigation system. There is one behind the gauge cluster but I am not sure how to check that one and if that will even make a difference.

 

What I would do: Since the shop is suggesting it could be the wiring harness ($$) I would ask,

"I understand diagnosing issues can be challenging & time consuming, though I'm not sure how much more my pocketbook can handle without a 100% clear diagnosis. I would like to get this issue sorted out in the most cost effective way possible. I hope you can understand where I'm coming from."

see what they have to say

"If changing the wiring harness doesn't fix the issue, I've just spent $XXXX on multiple incorrect diagnoses. Can you (shop owner/manager) offer me any sort of re-compensation, discounted labor rates, wholesale pricing for my peace of mind?"

see what they say, and I would ask them what the next step they would take if it's not the wiring harness.

Just my $ 0.02

 

I'm still curious if it's a "gas" liquid on the spark plug.. vs. a valve cover gasket not sealed/fitting correctly is my only other diagnosis that it *might be*

 

Have you done a compression test on #6 yet? And it could be the coil harness itself it's not uncommon for them to go bad and if you swapped #6 coil into the #2 spot and the #6 coil still works as you said then it is definatly low compression or harness

 

Compression is fine...the motor only has 5k miles on it and the shop compression tested it right off the bat to make sure that wasn't it.

How to go about replacing the coil harness? I was thinking of running temporary wires from the ECU directly to the coil to see if it gets power but I am unsure where to tap and where those 3 wires from the plug actually go.

 

Or are you talking just cutting off the connector and replacing just the connection to the coil?

 

No sometimes the wires get brittle and ground out you can buy the harness I believe it is broken upso you can buy different sections

 

I cant seem to find a sub harness for the coil packs but you can try the dealer, I would peel the wrap back on the wires and see what they look like

 

That is the problem I don't think there is a sub harness, I would need a whole new wiring harness which is expensive, very time consuming, and doesn't even guarantee a fix.

Do you or anyone know how I can temporarily run new wires from the ecu to the coil to test to see if replacing the wiring harness will resolve the issue?

 

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That is the plug that I pulled out of Cylinder 6...running rich from the coil not firing or oil in the cylinder?

 

Checked it again tonight...new spark plug I put in 6 is soaked in gas so again obviously cylinder 6 is not firing. I also hooked up the coil and spark plug outside the cylinder and cranked but no spark from spark plug.

Checked the ground on the connector for continuity and it checked out.

I just need to figure out how to run new power wires to the connector. Anyone ever do this?