Weird misfiring problem

[41085\\]

ok I was driving one night and my check engine light came on and the car started to shake, so I was like shit that can't be good so I took it home plug a scanner to it and
p0304 code came up misfire on 4th cylinder. I replace the plugs and wires I even bought a new coil pack put a new fuel filter in it but none of them solve the problem. I'm starting to run out of ideas so I need some help from you intelligent dsm fellas. thanks

 

[larsrya8]

How's the #4 injector doing? Is it firing? Is it clogged? Is it plugged in?

I don't know if it matters, but what's the compression in that cylinder compared to the others?

 

[41085\\]

I checked the compression on that cylinder and I saw 150 didn't checked the rest of them though. The only thing I checked on the injectors is the harness plugged in or not I don't really know how to check injectors . Anyways it only happens on WOT on higher rpms. It will stutter really bad then if I shut it off or let it idle(idling really shitty too btw) for a while it will go back to normal.

 

[staticbrainwash]

What injectors are you running? Have they been cleaned recently? And how old are they?

A lot of the miss problems i've had have been due to bad or improperly firing injectors. So i'd check those.

 

[41085\\]

I'm running stock injectors with 140,000 miles on it. As far as cleaning goes I put some Lucas fuel injector cleaner in my gas tank last night with a quarter of a tank left. I know this sounds like a stupid question but how can u check if the injectors are firing or not

 

[staticbrainwash]

I don't really know honestly. But what i did was just pick up a set of 450's and send them out to get cleaned. The ones I got had already been sent to RC engineering for cleaning (80 bucks for 4 450's, which IMO isn't a bad deal for pro cleaned injectors).

I got cleaned 450's and I was set. Maybe someone else knows a way to test aside from shutting them down one by one through a logger or dsmlink, which wouldn't help you anyway because you're already missing on that cyl.

If you have a couple days you can leave the car down, i'd just pull the injectors and send them to a good machine chop or mechanic and have them cleaned and tested. That will be you best bet, Or just pick up some used 450's and send them out or take them somewhere.

 

[HRCEngineering]

i will tell you how to test them for mechanical and fuel delivering operation. in order to make sure the computer is controlling the pulse width on the ground side of the circuit, take a noid light and check to see it is flashing on the ground side of the circuit. this tells you the pcm is pwm'ing the injector.
next, take a stethascope and listen that the injector is operating mechanically. also, check cyl injectors 1,2,3 to compare the number four to. this further verifies the pcm is modulating the injector.
next, take a snap on or similar injector tester tool, thats what its called. hook it up to b+ source voltage and chassis ground. plug the test connector into the connector on your injector. the tool is set up. now, hook up a fuel pressure gauge to the rail. with KOEO (key on engine off) you will see your residual fuel pressure reading. recrd this reading. now actuate the injector with the tool. record what your pressure drop is. compare this oem specification.
now that the diagnosis test is done, inspect and replace the filter screen on the top of the injector.
you can also get REAL injector cleaner. you need compressed shop air, the pressure canister, and the adapter to tee into your fuel in side. this is what any major dealer does when they perform an injector flush.

I hope this helps. any questions, find me on aim. Rayjneal.

-Ray

 

[staticbrainwash]

^^ Thank you for being more in depth about the injectors than i was. Hopefully this is his problem. For it's a cheap and easy fix.

 

[41085\\]

thanks for the help guys I'll try to test them out.

 

[41085\\]

I haven't checked the injectors yet but I'm just curious b/c I just changed the spark plug again yesterday and it ran alot better it would only misfire under boost instead of misfiring all the time. I don't think my problem is fuel related but ignition.

 

[DiamondStarM]

Im am having a similar problem in cylinder 2. I replaced the plugs and wires with no results. I switched the coil packs to see if the problem would change cylinders, but it stayed on cly. 2. I then switched injector 2 with injector 1 hoping to see the problem move to cly. 1. No luck there. The problem comes and goes as it likes, usually happens with a female in the car for some reason, haha. My injector clips are on tight and the only things left I can think of are the computer itself is not switching injector 2 on or the wiring from the computer to the clip is bad somewhere. Hopefully that will help you a little more with your troubleshooting and if someone can chime in if I am overlooking anything else because I still have the same problem and its so random that by the time I get home to try to find the problem, the problem is gone.

 

[staticbrainwash]

It still may be an injector. That same thing happened to me in my 92. I switched them around, nothing happened, changed it back, happened again. But it was dependant on engine temp, and a bunch of weird stuff. But if i were you, i'd change around 2 and 1 and drive it like that for a while to see if it transfers to #1. Unless you DID try that, and it still had an issue on 2. Then it has to be spark or fuel on that cyl.

Just out of curiosity, whats your compression?

 

[41085\\]

I did a compression test again and saw 155 on 4th and 160 on the rest of them. Another thing, if I boost it the car will start misfiring and it won't stop until I turn the car off and turn it back on again. It misfires all the time before until I changed the plugs and wires. I also switch all the injectors from my friends gsx hoping to see a difference but no luck

 

[ekanddsm]

So you know where your misfire is, Do you know if it is a lean or rich misfire?
I would watch your O2 signal while it's misfire to see if its to much fuel or not enough.
And dont rule out engine! just because compression is good does not mean engine is all ok. I have seen Broken valve springs that would work great until 3000+rpms then valve would float.

 

[gridlyne]

i will tell you how to test them for mechanical and fuel delivering operation. in order to make sure the computer is controlling the pulse width on the ground side of the circuit, take a noid light and check to see it is flashing on the ground side of the circuit. this tells you the pcm is pwm'ing the injector.
next, take a stethascope and listen that the injector is operating mechanically. also, check cyl injectors 1,2,3 to compare the number four to. this further verifies the pcm is modulating the injector.
next, take a snap on or similar injector tester tool, thats what its called. hook it up to b+ source voltage and chassis ground. plug the test connector into the connector on your injector. the tool is set up. now, hook up a fuel pressure gauge to the rail. with KOEO (key on engine off) you will see your residual fuel pressure reading. recrd this reading. now actuate the injector with the tool. record what your pressure drop is. compare this oem specification.
now that the diagnosis test is done, inspect and replace the filter screen on the top of the injector.
you can also get REAL injector cleaner. you need compressed shop air, the pressure canister, and the adapter to tee into your fuel in side. this is what any major dealer does when they perform an injector flush.

I hope this helps. any questions, find me on aim. Rayjneal.

-Ray

Wow, if that works then thats an amazing walkthrough. I think it should be in the tech library if it already isn't. Rep for u

 

[DSM007]

I'm running stock injectors with 140,000 miles on it. As far as cleaning goes I put some Lucas fuel injector cleaner in my gas tank last night with a quarter of a tank left. I know this sounds like a stupid question but how can u check if the injectors are firing or not

They are called noid lights....you unplug the harness from an injector and plug the light right into the harness while its running and compare with the rest of the harness plugs to make sure they are lighting up the same......you can get them at advance auto parts in a little package for like $25.

 

[DiamondStarM]

So once I determine that the problem is from the wiring back that means it can either be the wiring in the harness *somewhere*, the ecu, or the injector resistor pack? I just want to make sure Im on the right track. My problem is the misfire is so random that Ill pull over to try to test it and it and the car will be back to normal again. If anyone has any other ideas that would be great.

 

[41085\\]

So you know where your misfire is, Do you know if it is a lean or rich misfire?
I would watch your O2 signal while it's misfire to see if its to much fuel or not enough.
And dont rule out engine! just because compression is good does not mean engine is all ok. I have seen Broken valve springs that would work great until 3000+rpms then valve would float.

if I pull over and turn the car off when its misfiring and turn it back on again it runs good again as long as I don't boost it its fine. Will valve springs cause that too.

 

[arash15]

sounds kinda obvious but double checc to see if your maf plug is snug on the mass air flow sensor.

 

[41085\\]

I check that too. I'm kinda thinking that its probably my CAS after reading this thread
http://www.dsmtuners.com/forums/showthread.php?t=206019&highlight=cas
wut do you guys think?

 

[arash15]

it can possibly be it. when i had my gs-t the cas messed up and caused symptoms that you are having. id replace it. its like 60 buccs when i got it for my old 97.

 

[DiamondStarM]

any update, my problem just kinda went away for about a week so far, but i know it will resurface at a bad time

 

[41085\\]

Replacing the CAS didn't fixed it. I even swapped out my injectors from my friends GSX. I'm probably not gonna work on it for a while because I don't have any money. As soon as I fix it I'll let u know.