So I've had a miss on my 97 LT1 Z28 and can't fix it. I've tried everything
Last though I had is that the lobe on the cam is maybe worn out cause the miss. I talked to my instructor though and he says that the cam in my car is a "roller" cam? And if it was worn out it would be very noticeable by how loud it would be. What are yalls thoughts? And how does it work?

 

Tell us the "everything" you have tried. Have you put an ignition scope on it as I asked about in your last thread on this issue? Is it missing all the time? Under heavy or light load?

 

x2. What have you tried? And yes, a 97 LT1 would certainly employ a roller cam, which would rarely "eat a lobe" as the flat tappet cams of yesteryear were prone to. Have you checked (or have you had checked) for any trouble codes? Not all codes that could cause a miss will necessarily throw an SES light. More detail on what you have tried please

 

Compression, leak down, plugs, wires, opti, injectors (yes we checked with the scope), sprayed around for vaccum leaks, cleaned air sensors, and am in the process of changing the o2. It misses at idle that's it really. When I drive around its just fine. We checked fuel trim and bank 2 runs at +25 long term and +3 short & long term bank 1 runs +3

 

Is it a consistent miss at idle? If so, maybe you could pull an injector plug at a time, just to isolate to a particular cylinder? Just tossing this out there

 

Thanks for any feed back!

 

I've done it :/ and yes its incredibly condisistsnt

 

I've done it :/ and yes its incredibly condisistsnt

 

The ICM is really all that's left. How do I check that? Or whatever it is I should do.

 

25% on bank two is suspect. Which is same side as #2. It may be adding fuel due to the unburned O2 from #2.

So you still have not put an ignition scope on it?

Have you put a new injector on #2? If it doesn't miss at say 1500rpm, then it almost sounds like a lazy injector...maybe even a damaged PCM driver. A low amperage amp clamp(comparing #2 with #1..as you know Bank 1 has no issues) on a scope may show this issue.

Are the lifters on #2 in good working order?

The ICM provides spark to all cylinders and the opti distributes it. If the other cylinders are not missing, I would not think that the ICM is the problem. However you could put a new one on it for piece of mind....if you do that, replace the ignition coil as well. I recently replaced, wires, ICM, and ignition coil. I developed a miss during light cruise and could see high voltage leaking out of the coil at night. 16-17 year ignition components could stand to be replaced as age breaks them down. However, I don't think the ICM and coil are your problems here.....

 

I see scan data, but I don't see "scanned it for codes" in your list. If you use a scanner with GM enhanced parameters, you can pull the misfire count by individual cylinders.

 

Yes I've done ignition scopes. Weve switched injectors 2 and 4 to make sure.miss fire stays on #2. Lifters are fine. And yes we saw how many were missing. #2 had about 80% of the misses. The other misses where still in bank too.

 

I assume you mean bank two.

As I think was mentioned above, a misfire on on cylinder in the bank causes a false lean condition when the O2 sensore reads the unused oxygen from the misfiring cylinder. Then it richens up the entire bank, and now you have one cylinder misfiring, and the other three running too rich.

I think your instructor was indicating the if a roller LIFTER had failed, it would be making noise. How did you determine "lifters are fine"?

Put a dial indicator on the rockers, comparing #2 to a healthy cylinder. That will tell you if there is a cam lobe problem.

 

Ohhh I'm sorry when you said lifter for some reason I thought of the head lol.

 

The only thing that would make me nervous about the above is you the swapped components on the bank that has the problem(2 and 4).

Good troubleshooting involves swapping known good components for the suspect ones. Since the problem is on bank 2. Any components swapped should be from bank 2 to bank 1.....since you know bank 1 has no issue.

BTW, if your PCM has a injector driver problem on #2, then it will not move. Have you scoped the current waveform(not the voltage) on injector #2 compared to #1?

If you did ignition scope it, why are you questioning the ICM? Did it not show you that it was working? Not trying to be argumentative, just asking.....

Does the oil smell like fuel? If #2 is truly missing that badly and the injector fully working, I would expect the wash down on that cylinder to be terrible(maybe even dangerous from a cylinder wear prospective).

From my point of view, you are telling us the fuel is fine, the spark is fine, the air is fine, and there no mechanical issues.....however it is still misfiring. You've got to be missing something in the diagnosis somewhere.

Watch this...there are some EXCELLENT principals that are taught in this case study in regards to ignition troubleshooting. The LT1 is different in how it operates(does not rely on crank signal to fire coil....opti signals do that), but it shows you how to use the troubleshooting tools properly.
http://www.youtube.com/watch?v=ws59z...oy4alB2WXJCIqA