hey guys, I need some help troubleshooting here.

When I get to around 6kRPM my check engine light flashes, and I get codes for random cylinder misfire, along with codes for 3 other cylinders. I don't remember which ones they are right now though.
I can't feel any surging or anything to indicate a misfire, but the car has had this issue since I've owned it, so maybe im missing out on some power up top.

I checked the coils and spark plugs for obvious signs of wear, everything looks fine. The plugs however are not OEM. but they are a "suitable replacement"

I can clear my codes and If I don't rev past 6k the check engine light will not come back on, so it is only an issue at higher RPM, which eliminates a compression issue causing the misfire. that leaves me with fueling, which seems really unlikely, and spark.

Any suggestions on how to troubleshoot this?

 

You should use the recommended ngk plugs as per owners manual to eliminate a possible causes.

Are you 100 percend sure no cylinder is misfiring?

If sure then check fuel pressure.

If fuel pressure is ok then check valve clearances.

If everything checks ok then replace with ngk plugs if you haven't done so.

 

I'm relatively sure it's not the valves,

The first time I revved out past 5k or so was after I did my timing belt, due to unsure maintenance history, and that is when I got the CEL. I then did my valves, since there was quite a bit of valve train rattle and again due to unsure maintenance history. It made no difference in the CEL but it runs much smoother. I'm quite certain my valve tolerances are on point, so for now I will remove valves from possible causes. I can re-visit later if necessary.

I don't really know that no cylinder is misfiring, honestly I wouldn't even know what that would feel like at high RPM, but the is no plateau in power or surging, nor are there any strange noises.

I guess its time to go drop some dough on those spark plugs and go from there.

 

an over-rev condition is usually the opposite....funny misses at idle and smooth sailing at speed.

automatic or manual?

 

When changing the plugs if you find one fouled or abnormal change that coil pack too.

 

Manual trans. and I checked all the plugs recently, they were all on the whiter side, but very consistent between them all.

 

Just had a though. when I had my intake manifold and everything off I went through and did a quick cleaning. I didn't really have a good place to really go at it with brake clean or anything, is it possible I could have loosened a piece of carbon or something and it is stuck in a sensor? more specifically. could that cause a missfire?

 

Is it possible that you installed the plenum gasket on backwards and blocking some passages?

Are all your coil packs oem? If not it could be the problem.

 

As far as I can tell they are factory coil packs. Anyone know a test procedure I can preform on them? Plenum gasket is installed correctly. I pulled it all appart last weekend to look for issues.

 

well... I pulled the codes. I have P300-306 and P1399,

Ive gone through the top of the motor for the third time... nothing seems wrong. looks like all thats left is fuel or spark...

The fact that EVERY cylinder is misfiring leads me to believe it is not spark unless its an ECU issue. the chance of 6 coil packs failing all at once seems pretty unlikely

I've read a thread on here where the issue was caused by gunk in the injectors... i guess i'll check that out.

Ive also read that a bad cat could cause the issue, but im skeptical since it passed smog with this issue going on (i just cleared the codes and didnt rev past 5k till it was done)

Any other ideas guys?

 

Also, how abnormal is it for a little moisture to be inside the intake manifold? a bunch of tiny droplets were underneath intake manifold cover's gasket.

 

Unless you have all oem ignition parts you might be chasing the misfire around the six cylinders.

 

 

I don't like how many of the trouble shooting steps end with replacing the ecm. haha.

Thanks a lot for the awesome post. where did you find this?

 

I take the Fifth.

 

Have you put proper NGK plugs in yet? Don't come back until you do.

 

proper plugs have been installed, and i just tested all the injectors, 13.5 to 13.5 ohms of resistance on every single one, i see that it is outside the operational range, but the consistency between them leads me to believe it is my multi-meter that may need to be calibrated.

i also went in and quadroople checked my valve clearance. found a few that tightened up a tiny bit, must not have torqued the lock nuts enough... we will see how she does tomorrow when i get it all back together.

 

I got it all back together last night... after letting it warm up for a bit I did several 2nd gear pulls from 2k to 6.5k rpm. The first two pulls were fine, after that it got worse and worse to now I have surging even at lower rpms under full throttle... Very strange that it got worse... By a lot. I could also smell the cats a bit by the end of it... Wonder if they are fouled and causing fueling problems?

 

I could be wrong but... quite possibly your timing is off nothing seems to be firing properly and after you put the proper plugs in, and your injectors seems to be fine. I would look into that

 

Do you think the car would have ran fine (except past 6k rpm) and passed smog if I was off a tooth on one can gear?

 

I'm not a mechanic this is just my opinion but, yeah it would run ok until you get into the higher rpms, if the timing is off just that one tooth, the computer is adding more fuel to the cylinder to make up for the misfire. I wouldn't say it would pass smog,you have a bunch of un burned fuel going threw you exhaust system, and it probably ruining your cat and o2 sensors

 

the timing controls how the engine runs including your spark, so no spark at high rpm with fuel not being burned could cause lots of problem, that would be the next route to go man let us know what happens!

 

On most any typical old car, I would expect a nasty carbon buildup inside the combustion chambers, and that might explain the rough running...
Do you have a way to inspect inside the CC? Boroscope?

 

I checked out the combustion chambers a bit when I had the plugs out and the valve covers off and the fuel injectors out. I could see little parts of the top of the piston, no excessive carbon buildup. Although it was by no means a complete picture I don't believe that is the cause

 

Did a compression test finally... All is well with pressures between 190 and 205 psi across all cylinders. I am so at a loss right now

 

Check your timing marks. There are plugs on the timing belt cove that can be removed for this purpose.

 

Did you test the fuel injectors for good spray pattern, etc?

 

timing, timing, timing!

 

How can I check timing without taking the timing belt cover off?

 

 

 

hmm, i've done it that way, i'm wondering if there is maybe a more accurate way? (story time)
While changing my timing belt I ran into some issues i didn't have on the last 2 J series i've done. None of the cam gears moved while taking it apart, but when I went to assemble everything the rear cam gear did not line up with the teeth on the new belt (goodyear, supposedly high quality belt) There was no slack between the crank and the front timing gear, the belt was not on the lip on the water pump pulley and there was no slack there either, but the teeth still did not line up. I could rotate the cam gear forward slightly and it would work, or back slightly and it would work. (the crank and forward cam gear were both lined up with their respective timing marks.) It looked to me like rotating it forward left it closer to the timing mark so I went with that, and cranked the motor over 4 times by hand to make sure there was no interference, re assembled and crossed my fingers when I started it.

No stumbling on idle or weird noises so I assumed everything was good. until I hit redline a few times... then the check engine light started. I think i mentioned earlier that I didn't take the engine up to high RPM before I did the timing belt so I have NO idea if the problem existed before hand.

I'm getting to the point that I want to take this car to a shop and let them sort it out. and I have never taken a car to a shop (except for tires) in my life.