I recently have been experiencing a misfire(s) and spent countless hours troubleshooting with no end in site. I have a 04 nonZ with 78k 6spd. I have the following mods, blackwing with big air bridge, headers, 3 in xpipe straight pipe, tuned, brand new ngk plugs msd wires (changed 3 days ago)and a catch can. It started a few weeks ago when i changed my front bumper to a tigershark. After it was changed sat for about 4 days then when I started driving I felt the miss. I new I had a lazy O2 so I changed the upstream. Later that night when driving car went lean code crazy and reduced engine power stalled. opened hood to find my air filter and MAF was disconnected. Went to parts store and replaced MAF because previous owner cut the honeycomb. Next day still misfiring so started getting hands dirty. Iwent to a shop because I was baffled the hooked up a genysis scan tool and showed one O2 was not registering. went home and hooked up snapon modis scan tool saw all 4 and saw that I had an O2 dropping out and misfiring on random cyl. 125 then 764 no pattern or consistency. so tested wiring on the O2 to PCM and ground everything checked out. I have probed coilpacks all fine. changed spark plugs and wires. i have checked for vacuum leaks and non apparent vacuum is 30HG. voltage on MAF, tps ect are good. Fuel pressure is 60psi fuel trims are good LT and ST. I did a spray test with injectors all good. I thought it may have been bad fuel so I ran a few bottles of tchron 2 tanks and 1 tank with seafoam. I had a tuner look at my tune to see if anything looked out of the ordinary and he said nothing looked bad. I seem to notice the miss when decelerating the most but still present when cruising. I have also noticed my RPM will drop into the 200-300 range when I press the clutch in then take a sec to settle and at a stop in neutral sometimes the RPMs fluctuate up and down from 600-1300 for a few sec then settles at 800. I keep wanting to lean toward my tune but trying to rule out anything mechanical before i spend 300+ on a new tune. The worst part of all of this is NO CODES!!!!! not one misfire code and no codes once the MAF was replaced. if anyone can give me any place to troubleshoot next that would be a huge help i am at this point and running circles day and night.

 

Not to take issue, but 30HG? Your gauge might be having fits there... I've never seen an engine come close to that.

The rest I quoted generally points toward your tune. The misfire parts and the intermittent nature of it make me think wiring too close to exhaust or something of that nature.

If you or someone you know can datalog it, that'd be the next step (imo).

 

I have HP tuners and was data logging the other night for an hour or so I am going to continue this because its free. Can you go into more detail about wiring too close to the exhaust?

 

If your wires r not burn Idont see it being this. More than not it is in the tune with the weather chging here to colder weather. And your tune befor was ok when it was tune but it being to a point if the weather chg it is doing this in your VE table. Get a copy of your tune and on the ve table should be a really smooth going up in rpm. Not curves r edges going up it. If that makes sence... Robert

 

This would make sense if the weather was changing but I live in FL the weather doesnt change....its 90 now and it was 90 then... I have HP tuners and able to see these tables and have done hours of logging to get my curve very smooth. I know my O2 wires are fine so I will add checking the starter wires to my checklist.

 

Wonder if you have a broken valve spring?

 

what is your indication that this may be the problem? I did compression test and all were 180's. would I have these symptoms if I have a broken spring but the valve did not drop? also would there only be a mis in one cyl ?

 

I will PM you my phone number... Too many things to type...

PM SENT

Bill

 

The reed vapor pressure of the fuel is adjusted periodically throughout the year, not based on what the thermometer says today, but based on historic temperature trends. This would tend to manifest itself as a starting issue though, so you are right, but for the wrong reason.

Thanks to the Imperial Federal Government, many other changes may have been made to your local fuel blend, due to the change of season.

It does take a finite amount of time for the PCM to adjust to these seasonal fuel variations. It will also take a finite amount of time for the PCM to adjust to all of the new parts that have been installed. Have you tried clearing the adaptions and starting fresh?

 

What are you referring to when you say adaptions? If you are reffering to my tune i have wiped clean went to stock, ran like poo then re mapped still missing.

 

No, not the tune, but the fuel map offset, based on feedback from the lambda sensors. If you blew a new tune into the PCM, I suspect that this cleared the adaptions.

I would expect a surge, at cruise with the OEM tune, because the intake and headers will cause a lean condition.

Do you have the idle instability with the OEM tune, or only the custom tune?

A miss and popping in the exhaust is pretty common for an engine equipped with headers. Is this what you are describing, or something else?

 

I had general misfiring with a P0300 code - I could not isolate it to one cylinder. I checked everything else - fuel pressure, manifold vacuum, MAF, replaced plugs and wires, reworked all the grounds, charged the battery.

Finally I took someones suggestion to pull the valve cover and look at the valve springs. That was the problem.





It might be your problem, but it is worth a look.

 

I took a look into a few things last night not too in depth but ended up putting stock tune back in and all I did to it was richen it up. The ghost miss is still present. I am going to do a few htings electricly that bill suggested and pull my valve covers this weekend but what are some indications my PCM may be bad? from what I have read I would have alot of codes but is it possible this is the issue?

 

Last night I pulled my intake and valve covers.... Springs were beautiful, no cracks in the intake, I did have a pretty corroded knock sensor that I am replacing. Other than the KS I did not see anything out of the ordinary. I originally went in to check out the PCV system and was pretty anticlimactic. If anyone has a link on how the 04 PCV system works that would be helpful. I thought there would be a valve in there but its just a breather box... so I want to know if there is anything in this "PCV" system that can fail? In the mean time changing all the gaskets and cleaning things I found a small crack on the plastic under the o-ring on the fuel injector and wondering if this can cause a problem?

 

Don't think that crack would do much, how many are that way? I would suspect something in common with all the cylinders (wiring to the injectors, fuel pressure going low, etc).

 

That injector almost looks like it was molded that way. That is a sealing surface, but it's not _as_ important as the one at the top. If it were there, that could potentially leak fuel, and it would be at 60psi, so you'd know soon enough. If that is a crack and it wasn't molded that way, it does then indicate age, and it would be worth looking at all the others, especially the tops of them.

 

I read through this twice, and must say, I'm confused. You saw an O2 sensor dropping out, and did what? Checked the wiring, and called it a day....and proceded to disassemble the motor? Now that you have everything put back together, does the issue with the O2 sensor remain?

 

i would reinstall the original maf (was it a GM unit or aftermarket?), or try a different maf... where did you buy maf#2 at? are you sure that you don't have any air leaks between the maf and the throttle body?

just my opinion after reading your thread.... and since it started after changing the front bumper....

 

To lucky: haha yes the 02 sensor is good now and functioning properly.

To Tommie: I had a Delphi and replaced with a Delphi. I have checked over and over for leaks and none present.

To spaz: there were two injectors that looked like this others were with out the "crack"

After everything was put together I went on a test run. Unfortunately I may have pinched a knock wire because I am getting p0332. So I am going to disassemble again. However the car is running smoother still a little hesitation. Wile I was at the auto parts store I thought I would replace my MAF again because I read you can have bad ones. It was under warrenty so why not. Now I am getting a p0101 first time this showed. However the misfire is not there on decel but still dying on me. So I'm going to fix the knock wire and look into the MAF code more.

 

http://www.obd-codes.com/p0101

This suggests the p0101 could be map sensor related. I get the principle on why that is possible so do you have to test on the car or can it be bench tested.