I've been trying to chase down a miss for a couple of weeks now. at the bottom are a coupe of videos from inside the cockpit for audio puposes, the vid doesn't tell much.

Mods: P1SC, blower cam, LS6 intake, 60lb inj, KB BAP, ported 243 heads with pgraded springs, LP fuel pump, Kooks headers w/ X-pipe adn HF cats.

Here's what I know:

I had P0300 on DIC then checked with scantool. It showed a P0305. After checking things out thisafternoon, I have only gotten p0300 so far. I'll be making a long drive tonight, I'll double check the codes after that.

It seems to run OK at part throttle most of the time, although it has always had a strange miss at low RPM since I modded. It seems to be more throttle position related than RPM related.

The new miss seemed to start right after a plug change.

Thought it might be spark blow out, but I am only running 6lbs of boost. I regapped the plugs, no change.

Replaced wires, no change

If I ease into it all the way to full throttle it seems to run OK almost always, but not always.

Happens always when going full throttle quickly.

Wideband reads around 12 at the time.

DIC was showing p0300H along with p1571H and c2120HC-TPS issue, not related.

I put an ingnition tester on the #5 plug wire and seem to be getting good spark,at least at idle. I can't put the car under a load with the checker.

I pulled the valve cover and see no signs of valve train failure.

No runner on the intake seems to be any hotter than the rest.

O2 sensors have been replaced not long ago, I havent visually verifued they are in correctly, but I am 98.9% sure they are.

I did a leak down test and found a busted coupler, replaced it, no change.

Vids:

 

I just took a trip about 45 minutes each way, plus a few miles of around town driving. No codes were set so that tells me there is something throttle/RPM/load related

 

Since you ruled out the spark plugs, plug wires and 02 sensors - you might want to check your ground wires and verify your fuel pressure since you're FI and using a Kenne BAP. Did you account for the larger 60psi fuel injectors when you did you updated your tune? These issues might could account the the mis-fires at the higher RPMs and increased load. I'm no expert, but I did sleep at a Holiday Inn last night.

 

I think the FP is ok. The BAP is set on the lowest setting so i'm not sure it is doing anything anyway. The car was running great up until the plugs we're changed. That is the only thing I can think of that changed

 

Did you replace all the spark plugs and ensure a positive connection for all the wires? No change of a damaged plug or a plug wire not "clicking" to ensure its properly seated? Did you verify a good spark on the #7 cylinder - seems to be harder to reach for plugs/wires then the other cylinders. No other codes besides the P0300? What type of spark plug are you now using?

 

It could be a bad plug. Just because you put in a new "anything" does not mean that is wasn't defective when you bought it. I always start simple when I change anything that was working good in the first place. Fuel, air and spark. Start with the basics. Also, if there was a problem from the start, and what you did offered no improvement, did you address the right area in the beginning? If you take a normal running engine and add or change something, only to have it not run right, you have to start with what you did or the parts you replaced.

 

Many random misfires that don't go away after plug/wires are injector related (clogged or leaky). Move the injector on cylinder 5 to another cylinder and see if it follows where you moved it to.

 

Yep, I have changed all the spark plugs and replaced all the wires. I have pulled them and put them back ona few times actually, making sure I get the double click on the coil and the click on the plug. I replaced the #5 plug after I got the p0305 and it didn't help. I have not verified #7, but every time I have put the wire and plugs, I made a conscious effort to be sure all plugs and wires seated correctly. I am 95% sure they are connected OK.

As for other codes, I did also have a P1571, which is a traction control deal and apparently common on 97s. I have had that code previously and it wasn't missing the way it is now and I don't get a reduced power message on the DIC.

The other is a C2120, TPM sensors. I don't have sensors, so I ruled that out as well

I replaced the plugs, had the issue. Pulled them and re-checked the gap thinking I was getting spark blow out and it the problem continued. replaced the plugs again and still had a problem. Bought new wires and installed them and still had the issue. I have another set of plugs, maybe i will put them in one more time and see what happens. It probably won't be until tomorrow though.

That I might try as well. I reset all my codes after I got the p0305 in hopes of verifying a problem in that cylinder and have only gotten p0300. I haven't been driving it hard though, so maybe I'll have to go romp on it a bit.

 

Well, my tuner suggested I open the gap up a bit. I pulled the plugs and 2 plugs on the driver bank looked white and the other 2 were kind of brownish. The 4 on the pass side bank looked the same as the 2 white ones from the driver side.(see pic below)

I just happen to have an extra set of plugs, so I gapped them at .040 and put it all back together. Car runs like a champ.

 

I almost made a mistake like that. I bought new Iridium plugs and gapped them at what the book said (which was incorrect for those plugs). I had them all installed and was poking around and discovered my mistake before I fired it up. Got pretty good at #7 by then. The gap was .040" which was what they wre aout of the box.

 

On the FI section, it is recommended to gap at .036. I am only running 6 lbs of boost, so I guess I needed to go a bit wider.

I did end up with 2 codes though:

P0335 - Crank sensor malfunction
P0300 - random misfire - This is from a code reader, not the DIC.

 

So you didn't really solve the problem??? The crank sensor could be the real problem.

 

That is how it appears. I'm going to reset it and drive around again and see what happens. It is definitely running like it used to before the problem though, so at least I did fix something.

What's weird is I have been fighting this thing for a while now. THis is the first time this crank sensor code has come up.

 

The GM cars I've had in the past, the crank sensor gets flaky at first then slowly gets worse.

 

hmmmmm...guess I'll start pricing a new one then

 

Ok, The car is running pretty good at WOT, but I am still having a miss when cruising at a constant speed, mostly noticeable in the lower gears.

I have gotten a P0305 a few times now which tells me that I have a problem with cyl #5.
I also know that the wideband is constanly bouncing lean which makes me think I have a bad injector or the injector is not getting a signal to pulse.

Tomorrow I plan to do one of two things, whichever you guys think would be best. I can either switch 2 injectors and see if the problems moves to a different cylinder. The only problem I have with that is that sometimes it takes a while to throw a CEL.

My other option is to install one of my stock injectors and see if the miss disappears. I would know instantly that the miss was gone. I just need to be sure that driving on a stock injector for a short time at low speeds isn't going to hurt the engine at all.

 

Have you checked the injector ground connections? Just a thought.

 

Switch injectors and see if the problems follows the injector. Sounds like one is sticking or clogged.

 

I'll try to switch them out today. If that doesn't show any progress, I'
ll track down the grounds and see where we are.

 

What plugs are you using?

NGK TR6 plugs gapped at .035 worked best for me when I had a supercharger.