Random Misfire

[jstory352]

So my first post on here, I'm not knew to engines just dsm's. I've had my car for a couple years now and seem to have a pretty good grasp on how these cars seem to work. My car overheated so I pull the head get it decked and valves checked for sealing. Bought the new gasket sets, T-belt has less than 5k miles on it and the teeth are all still intact with no cracks. Since I put everything back together it has a misfire. Pulling each injector didn't seem to make much difference, so I pull and inspect plugs. Plus 1-3 all looked good, but plug 4 looked new still with fuel on the electrode. Double check the gap, .028 ngk bpr7es. Put it back in, nothing changes. Swap cylinders 1&4 and check the plug. Plug has slight carbon buildup which tells me the plug works. Pulled the number 4 wire off, still running like hell but notice an arc through the boot, so I run around town and find a set of wires, auto zone specials just to see if that will fix it before I can order some better quality wires. New wires installed and still no change. Pulled my timing covers back off thinking it can't be it but to double/triple check my work. I have checked the coil packs and the power transistor. I am at a loss right now. I don't have a compression tester but will be buying one this week to make sure that compression isn't my issue. In the meantime I am open to any suggestions.

 

[boostdawd]

Is the ecu not picking up the misfire? No obd codes?

 

[jstory352]

It would throw a cel but I really didn't want to drive the car to the auto parts store to get it read. Afraid of doing more harm than good.

 

[boostdawd]

With your car idling pull each cable from the spark plug and see if u can get it to stumble. Sorta like u did with your injectors.

 

[jstory352]

That was done along with the injector connectors and what drove me to replace the wires when I saw the arc through the plug boot.

 

[cheapracer]

You can use a spark tester to see the quality of spark at each wire. You'll probably see spark at number 4 is weak or non existent.
I suspect the coil is bad

 

[jstory352]

That's what I'm leaning towards. I want to run a compression test just to be sure but I know it should turn out fine considering the car was running great before. But I am looking at getting a couple coils just to have on hand.

 

[cheapracer]

Ya if you can get a known good coil pack to throw on there, be a good place to start.

 

[jstory352]

Yeah, contacted a few people on here to try and get a hold of a coil quick.

 

[jstory352]

Well I replaced both coils, still no change. Finished putting the car back together and drove it to the mechanic to put a code reader on it. Only codes were the emissions and the boost solenoid which I expected both of those. No random misfire even though he was sitting right there and could hear it also. So he continued checking all my sensors with the snap on tool. While asking me to Rev and pause for a second and then let off to read the maf and then cut the car off a second later just to crank it back up low and behold misfire is gone completely. I'm going to go out on a limb here and say that maybe the valve just wasn't wanting to seal for whatever reason but car has ran good all day. Just wanted to say thank you for everyone's input in trying to assist me in fixing this problem. Now it will be time to move on to the next list of upgrades and I hope to be able to become a productive member of this forum.

 

[Murdertalon]

Hey if you haven't already done so I would change the fuel filter and take your fuel injectors in for a cleaning. It's good to get a flow test done to them to make sure they are all the same spec.

 

[jstory352]

I change the fuel filter not long ago and have looked into getting the injectors cleaned but there is no place local so I will just replace them when I decide to go bigger here soon.

 

[Murdertalon]

Sounds like a solid plan. I think when I got mine cleaned I found a local guy in Idaho Mr injector or something like that.. I plan on eventually getting larger injectors but I plan on running stock for a grip till then so figured it was insurance. One was flowing about 10% under spec so probably good thing I did. I was actually thinking that could cause misfire too so just looking out.