I am working on a 97 LT1 camaro. It has a bad misfire under WOT at between 5-6K rpm. I used an o-scope to record the pulses from the low resolution signal out of the opti. Attached is the link to the pics from the scope. Can anyone tell me if this looks normal? To me it appears that the signal is scattered instead of being a nice squared off pulse.
Just looking to compare this info to what a known good opti output looks like.
Thanks,
Chris
http://s819.photobucket.com/albums/zz117/wilsoncd2/

 

It might be hard to find anyone that has ever seen a trace from an opti. Your pics were my first.

 

Use the scope on another car that has no missfires and see if there is a differnece.

 

Thanks for the replies, I was hoping that someone else had actually done the same thing before. Right now I don't have another LT1 car that I can scope, mine has the LS1 PCM conversion (for these exact reasons).

Just looking at the graphs, you can see that some of the signals look good (nice and square) like you would expect from the optical sensor looking thru the slot (basically on vs off). On other parts of the graphs it looks like the signal is intermittent, as in it dips or is scattered in the middle of that wave. My understanding is that the PCM looks for the different length pulses (by different size slots in the opti) to determine cam position. If the signal isn't clear, the opti wouldn't be able to determine which cylinder the slot is correlating with.

I also logged the signal from the PCM to the ICM. It also looked like it broke up in certain places. For the most part the square waves were very clear, but in some places the voltage would drop by over 50% or more in the middle of the square wave. This is what led me to test the signal from the opti.

The car isn't throwing any codes for the opti, just a P0300 random misfire. I can see multiple misfires on all cylinders thru out the RPMs. Plugs, wires, coil, and ICM have all been changed. I was told by the owner that the opti was recently replaced and it didn't fix the misfire at high RPMs. I am trying to determine if it has really been replaced or if it still needs to be replaced.

Any other opinions?

Thanks,
Chris

 

93 Formula, M6, hot cam, 1.6 rockers, LS1 PCM
I am working on a 97 LT1 camaro.
mine has the LS1 PCM??????????

Just the fact that you don't have a DTC16 indicates that is not the problem. Second notice that every other wave is a delta spike while the others are more square. Another indication of no problem. Third, I believe the trigger is not the level itself but rather the transition from one level to the other. Another reason there is no code.

Before the opti feedback signal could be the cause of a problem, it would have given a code. And then it only shuts off the injectors and fuel pump, not the ignition.

Perhaps you should either look at the actual signal going to the plugs on the plug wire or.
Pull the plugs and see what they look like or.
Monitor the fuel pump pressure or.
Monitor the injector pulses.

My suspicion is the coils are saturating at high speed and can't charge and discharge quickly enough to fire sufficiently. A scope trace like the one above can quickly rule it in or out. But you will obviously have to be on a dyno to do it unless it will do it without a load on it.

 

The dyno isn't a problem, it is on a dyno dynamics chassis dyno right now. That's how I have been data logging it.

SpeedyG, maybe my sig and the rest of my post was confusing with the LS1 PCM thing. The problems that I am troublshooting are on a 97 LT1 hot cam camaro. I am doing this work for another person. On my personal car, I converted my 93 LT1 firebird to use a LS1 PCM with a coil on each cylinder.

I pulled the plugs before there was a tune in the car and it was running super rich. But that was because the AFR was down in the 11:1 range. The PCM was never tuned after the 30Lbs/hr injectors were installed.

I see what you are saying about the DTC 16 and it doesn't look like the fuel is being cutoff. I was just thinking that if the pulse resolution was poor (but not failed) it might not throw a code.

The fuel pressure stays about 43psi at WOT. The coil has just been replaced.

You are right, I could log both the coil discharge and the injector pulses to verify those also.

Thanks for the suggestions.

 

Is it tuned for 30#ers now?

 

Yes, now it is tuned for the bigger injectors. The AFR is right around 12.5:1 at WOT. I have a bunch of logs from the dyno in both EFI live format and an Autotap. The car is being tuned with Jet DST.

The other weird thing is that the commanded spark advance does not match the actual logged spark advance.

 

This is low resolution pulses from my Vette 94

http://web.telia.com/~u33227289/Opti...g_pulses_2.jpg

The numbers represent missing pulses.

PCM looses counting and firing in wrong cylinder


Kjell

 

Confirmation of the signal quality I spoke of. It's looking for the transition not the level.

Interesting, could there be a problem with a pulse dropping out but not enough to trigger a 16.

The definition of a DTC is the PCM detects 720 high res pulses before any low res pulses are detected.

In the above example, such is not the case. How very interesting. A whole new wrinkle on the feedback signal.

 

I'm not sure the low res code is necessary, or that its absence rules out a problem with the low res signals. Code is set when the PCM counts 720 high res counts before it sees a low res rising edge. That represents complete failure of the signal. That's not the case here. The question is the quality of the signal, and what the PCM uses to determine when the pulse has ended. And if it does suddenly see a shorter pulse than it expects, does it default to counting the high res pulses until the correct signal reappears. Obviously from the code diagnostic, the PCM is capable of running the enigne for 720 high res pulses, by counting those pulses, before it decides that its not going to find the low res signal, and shuts it down.

Appears its the 22-degree pulse from Cylinder #2 that has the consistent irregularity. Does the PCM interpret that sudden dip in the middle of the pulse as "end of event"? I don't know. How does it react to seeing a shorter pulse width, when its expecting a 22-degree pulse width?

I have seen an Opti run on a scope, by the shop that built my engine. They did a lot of development work in allowing the MoTeC aftermarket ECU's to accept the Opti signals as the reference cam position signal. But that was 10 years ago, and my failing senior citizen memory does not help me remember how "square" the signals were. [EDIT] I beleive they were closer to V8Fluke's.

The pulse for the 7-degree (#8), 12-degree (#3) and 17-degree (#5) widths look clean. The alternating 2-degree pulses for the other cylinders look OK as well. I'd focus on #2 cylinder and whether the misfire count is higher than the other cylinders.

Great stuff!!!! Much more interesting than "which CAI is the best?".....

Probably qualifies for "Advanced Tech", but no one goes there any more.

 

Thanks Kjell,
So you were not throwing DTC16 code either? Did you replace the opti and the car performed correctly?

In my pics, it looks like in some cases the signal drops out or it bridges to another pulse. It is hard for me to tell if there are missing signals like you indicated. It would be nice to know what size slot corresponds to which cylinder. I might have an old opti laying around that I could look at.

So SpeedyG, you are saying that the DTC16 won't throw unless it doesn't detect a low resolution pulse within 720 High resolution pulses. That could be the case for me.

I am glad to see there are others that enjoy data like me!

 

That's the definition of DTC 16. More than that I don't know for sure.

Correct me if I'm wrong (like I have to ask). But doesn't the hi res pulse have a "trigger" signal that is different than the rest???????

shown here opti encoder wheel

So if you triggered the scope from the high res and showed the low res with it, you could see the start of the event. HOWEVER. I don't think the feedback signals are your problem.

I agree

 

I have the log files and have the data exported to excel so I could use SPC on the data. I can't post attachments here, but could email. It appears that cylinder #1 has the most misfires with #2 in second place. I would really like to post the logs so you guys could take a look.
I've got lots of data!

I can log the high resolution signal along with the low resolution. That might be a good way check for correlation.

 

I posted one of the dyno pull (with 3 runs) printouts to the same link as in post #1. You can see the car breaking up at ~4800RPM. This is the same RPM range that the graphs of the opti output are from.