Random misfire....

[Jhafert]

So, here goes. I have a 97 GSX with a fresh motor, fully built blah blah blah, but I now have this wonderful misfire issue. The car can be driven all day as long as speeds do not increase past 40 MPH, once the car goes above 40 and sustains a RPM higher than the usual 40MPH for about 5 minutes or so, it starts misfiring, now before you go ahead and say replace the power transistor and what not, I believe its only 1 cylinder thats misfiring, I've replaced both coils, I've tried 3 brand new sets of plug wire, 2 different but brand new power transistors, and 3 sets of new plugs, so with that being said, I'm still having the same issue, so now for the juicy part. I have a head gasket issue. I had a few buddies of mine when I was in Afghanistan assemble my motor. Now it burns coolant under boost, and all my parts are BRAND new. So what I've come to think is that the block, or the head were not decked correctly (nightmare) or my head was not tourqued correctly. Being in the military its hard to pull my head let alone find somewhere to do, the MP's on post seem to have issues with people working on their cars. So with that being said, I've come to some conclusions and I want to hear what you guys have to say. Either 1. I have some kind of short in my engine harness going to my ignition system, or 2. once the RPM's get higher more coolant is let into that one cylinder and its causing the spark plug to no longer ignite. Keep in mind, after it starts misfiring, all I need to do is shut the car down, unplug my power transistor, plug it back in, and give a snugging push on all my plug wires and she runs like a champ. Let me know what you guys think.

 

[Afizzle]

You are probably pushing coolant into the cylinder. If I were you I would take it all apart and do it myself so you know its done right. The block will not need to be decked, only the head, since it is aluminum. Its about 80$ to deck the head and 100$ in head studs.

Its kind of hard to address your problem when you have other known problems.

 

[heller34]

Could be your cam position sensor. My timing plate was hitting the sensor and had similar issues. Doesn't explain why it only does it after 40mph though. I would get your coolant problem fixed first.

Also, thanks for your service to you and all of our armed forces so the rest of us can enjoy the freedom of fast cars! We all greatly appreciate it!

 

[PieEyedPiper]

Are you getting a DTC?

 

[Talonman86096]

Is it a 6 bolt swap?

 

[Jhafert]

Are you getting a DTC?

Random misfire.

 

[Jhafert]

Is it a 6 bolt swap?

No, it's a seven bolt, but I'm running a 1g CAS.

You are probably pushing coolant into the cylinder. If I were you I would take it all apart and do it myself so you know its done right. The block will not need to be decked, only the head, since it is aluminum. Its about 80$ to deck the head and 100$ in head studs.

Its kind of hard to address your problem when you have other known problems.

No need for a new head gasket?

 

[BlackKnight2013]

its recommended to install a new head gasket every time you take the cylinder head off to do any work. reason being is the gasket is now "crushed" from tightening the head bolts to get the gasket to seal between the cylinder head and the block. Re-using head gaskets can cause further problems. its best to avoid further issues by using a fresh new head gasket.

 

[Jhafert]

yeah I was going to get a new head gasket and new studs.

 

[c2ypt1c]

No, it's a seven bolt, but I'm running a 1g CAS.

Running a 1g cas will cause a random misfire DTC. A 1g cas can't accurately detect misfires so you'll have to disable it in ecmlink...

 

[HaveBlue83]

^^^yup. Gotra disable rmf in link too. Might need to inveet cas signal

 

[boost97gst]

Thread jack for a sec: So you can throw(wire in) a 1g cas in a 2gb 7 bolt and basically delete the crank pos sensor? Thats Fing awesome.