P304 cylinder 4 misfire

[SilverXJ]

Stock fuel pressure for 05-06 is 58 psi.

Everything is pointing towards too large of an injector. For test purposes put the stock injectors back in and reset the PCM to see if that fixes issues at idle. Of course avoid WOT during this time.

[Jpross]

I have a custom Diablo tune that addressed the injectors when I first installed them. The engine has run fine for some time on these same injectors so why would it now be an issue? Plus wouldn't it be running rich if the injectors were too large? I'll admit I don't have as much experience as many of you on here so please correct me when I think things the wrong way.

[jsawduste]

The trims are bothering me.

at idle
stft bank1: -3.9%, bank2: -2.3%
ltft bank1: -11.7%, bank2: 0.0%

Even the variance from the st trim 1.6% and the big difference from the lt trim of 11.7%.

I will not claim to be a tuning wizard or having a good understanding of the trims but the logical read on your numbers is suggesting a Bank 2 problem.

Again my comments may be totally off base but what would happen if you swapped the bank 1 and bank 2 injectors and reread the trims ?

After 10 years I had an issue with cylinder 4 injector. Stuck open, replaced with new and then shortly there after stuck closed. Replaced again under warranty and thus far no more problems. This is with SBEC.

Could you have bank 2 12 volt feed problem ? A noid tester might be your friend here.

Could you have a leaky injector that is causing the ECM to pull fuel at idle thus causing the leanness ?

Again, I admit to reaching out into unfamiliar territory so my comments may not pertain.

[SilverXJ]

The trims are bothering me.

at idle
stft bank1: -3.9%, bank2: -2.3%
ltft bank1: -11.7%, bank2: 0.0%

Even the variance from the st trim 1.6% and the big difference from the lt trim of 11.7%.

I'm glad you pointed this out. I saw the -11.7% but some how missed that the rear bank is at 0%.

You will see a bit of variance between the banks, but not to that severity.

I will not claim to be a tuning wizard or having a good understanding of the trims but the logical read on your numbers is suggesting a Bank 2 problem.

Could be a bank 1 or bank 2 problem. If there was an intake leak on bank 1, which would cause the PCM to add fuel to enrichen the mixture. It could also be an stuck open injector on bank 2, causing the PCM to pull fuel. And it could be the inverse.

I would first start by swapping the front 3 injectors with the rear 3 injectors, reset the PCM and see what happens. If the fuel trims switch positions you have narrowed it down to the injectors. If the trims don't change I would consider a vacuum leak. I would look at the intake manifold to head seal first. Keep in mind that some exhaust headers can interfere with the intake manifold and create sealing problems.

[Jpross]

The trims are bothering me.

at idle
stft bank1: -3.9%, bank2: -2.3%
ltft bank1: -11.7%, bank2: 0.0%
...

...

At your suggestion, I swapped the old injectors back in. I also reverted to the factory tune.

What I saw was that the two long term trims above shifted up by about 20.

new values at idle
stft bank1: -3.1%, bank2: -2.3%
ltft bank1: 7.8%, bank2: 17.2%


Next step is to get a smoke test.

[Jpross]

What I saw was that the two long term trims above shifted up by about 20.

this tells me that the the difference in bank 1 and bank 2 ltft is not caused by the injectors. We are seeing simply a shift in the "base" percent the computer accommodates the different size injectors. The difference between bank 1 and bank 2 did not change when changing injectors.

[Jpross]

Took it to the dealer to have them take a look. They checked the distributor gear first and realigned the spark after that they replaced all the plugs and they say they are only getting cylinder 4 misfire now. Next they want to tear into the engine, they suspect valve rockers lifters or cam lobe. I'm planning on getting it to the engine builder at this point.

[Jpross]

As an update, I brought it to the builder and he pulled the valve cover and everything checked out. We measured the lift and it was spot on. I had my tuner tune out the misfire as it has been running fine except for a cam synch issue the pops up intermittently. I'm sucks because some days I start it and there will be no check engine light and it will run strong all the way to redline... But most days I now get a cam sensor code intermittent and it goes into limp mode and I have to shift before 2.3k or else the computer will cut the fuel and spark.
Right now I am going tomorrow to pickup a new car from car max and will work towards selling the jeep... Of course I will tell any potential buyers the history. For the cam I tried redoing all the grounds and switching the sensor but still the issue. Oh well it is probably something simple i think it is time to move on.