98 Cobra: Random Misfire code. Any suggestions?

[Big Top GT]

It's been a few weeks of pain, to say the least.

I FINALLY thought the car was ready to strap down for a tune, only to have the fan die on the way to the dyno. Long story short, the car overheated and I ended up at the doctor's office with second degree burns on my right arm.

It's amazing what pressurized coolant and a radiator cap that blows off in your hand will do for your day. :shrug:

Anyway, I got the car back and straightened out again (thanks to Jake and the crew at Power by the Hour in Delray Beach,Fl, as well as Nitrostang Racing in Margate) for helping me diagnose and repair this evil machine.

Seriously, it tried to kill me this time. :lol:

Now, the car seems to be running a little rough at idle and when we scanned it, it's showing a random misfire code, as well as a rear 02 sensor error.

The rear 02 sensors are turned off in the tune, so I'm not sure if this is a related issue.

As some of you know, it's a 98 Cobra with a Moduar Powerhouse built short block, Sean Hyland heads that were straightened out by Al Pappito @ Boss330 Racing (valves were 1mm undersized from SHM with 0 miles on them), and stock 98 Cobra cams.

It's also being force fed by a pair of 60MM master power turbos.

So, in an effort to not blow the car up, can anyone give me some ideas as to where I should be looking to figure out the random misfire codes? It felt like it was running fine before, maybe a little rough, but the CEL was on before the cooling fan melt down. (Literally. The connector melted.)

I don't want to blow it up; especially given that the motor's only got like 3000 or 4000 miles on it, all with ZERO boost. The car's only tuned for a break in drive on the street. (new clutch, too)

It's got brand new NGK TR6's gapped at .28, brand new plug wires and brand new OEM Ford coil packs, along with High Impedance 83# injectors.

Thanks in advance guys. I really appreciate the input.

Alan

 

[coolguy10786]

Does it seem to be running rich or lean? I would be leaning towards a vacuum leak. Does it seem to miss all the time, just light throttle, idle, or heavy acceleration? Some scanners allow you to look at which cylinders are misfiring and how often, if you have access to one.

 

[Big Top GT]

Thanks man.

I went out to look at the car and the passenger side valve cover is open. No breather, no tube to the intake.. NOTHING.

I'm sure it was there, so I'm wondering if maybe it fell off.

I'd like to get it plumbed back into the intake ASAP.

 

[mwolson]

Let us know if this fixes it. These codes can be a b**ch to diagnose.

I had this problem for weeks a couple of years ago, and I could not find the problem. It started after I flashed a tweak of my tune into it. I tried going back to the previous version of the tune, but the misfire stayed there. I finally solved the problem by starting over with a new base tune and building it back up from scratch. Go figure.

 

[Big Top GT]

The funny thing is the car never misses when you drive it. (or at idle)

It seems to be idling a little rough, but it could be my imagination.

 

[mwolson]

Mine never missed either. I am pretty sure the PCM can detect misfires that are too small for us to notice. Good luck. These can be really frustrating. And here in California, you can't pass the smog test with any DTCs, so I was afraid I was going to be hosed. But a new tune fixed me up and no misfire DTCs for a couple of years now.

 

[Big Top GT]

I'm kind of stuck with a catch 22. I don't want to get the car tuned because of the random misfire code, but there's a chance that a new tune will fix the random misfire code.



I can't win.