SR20 240sx s13 Running Rough

[Louprint]

Hey everyone,
I have an 89 240sx hatch with an sr20det red top that has a horrible misfire/running very rough for a while now.

I thought it was wiring related so I purchased a whole new wiring specialties harness and no change. It has good compression across the board (~145psi)

Changed spark plugs, made sure the CAS and the timing was perfect. It was perfect, no vacuum leaks, thought it was a bad coil pack or injector, so I replaced all injectors and tested coilpack with my buddies, but no change. Tried his ECU as well, no change.

The rough running started and progressively got worse. It is undrivable and the motor shakes it misfires so bad. Minimal exhaust smoke but does pop ALOT

Could it be the head gasket failed and the cylinders are leaking into each other? Really at a loss here thanks

[centralcoaster33]

Hey, welcome to NICO Club! I don't have an SR, but many do. Please check out these threads:

sr20-common-problems-general-maintenanc ... 45721.html

rwd-sr-faq-version-2-0-t306956.html

[centralcoaster33]

Do you have exhaust leaks at or before your sensors? How about fuel pressure?

Classic method is pull a plug and check the color...

[Louprint]

Thanks for those pages.

No exhaust leaks, I have an aftermarket AFPR and a walbro 255lph, so fuel is good. The first two cylinders get fuel and spark, but the spark plug color looks a little wet and black. Cylinders 3 and 4 are white.

I may pull the head to check if my headgasket failed between cylinders 1 and 2 because I can disconnect both injectors and coils on 1 and 2 with no BIG change.

I got progressively worse and seems to barely run on cylinders 1 and 2, but 3 and 4 are pretty good

[centralcoaster33]

Hmm, check the OHM resistance of your injectors, maybe they're stuck. Stuck open or not closing all the way I'd guess. Wet and black is a rich condition I think, or the plug isn't firing, or oil getting in there. I guess a compression check would be appropriate on each cylinder. Also, have you measured your fuel pressure after the AFPR? I mean, is it dialed in? I'm pretty sure you'll want to replace your current spark plugs at a minimum. "Run" the engine a bit on the starter with the fuel pump fuse pulled out and that will clear out any extra gas in the engine.

[nisileighty]

Hey,
I had a similar issue when I did my first SR swap. The motor would crank and start but run really rough and shake violently until it died. I spent days and days looking for the issue, tried timing, plugs, injectors, coil packs, everything. I looked under the kickpanel to the ECU and on the brown plug/connector that goes under the dash to the cluster and whatnot there's an orange wire that tells the ECU that it's a cold start. The wire was disconnected for me and after resoldering it and playing with CAS timing it started and ran like a dream. This might be your issue.
Hope all works out!

[Louprint]

So I ended up pulling the head and found that cylinders 3 and 4 exhaust valves are super white and cylinders 1 and 2 are all black valves.

Pistons are in perfect shape and head gasket is fine