Chris

How you connect your probes ?

I backprobing this way and have no noise in the signal.

Connector under right fuel rail cover:

http://web.telia.com/~u33227289/opti_connect_1.jpg
http://web.telia.com/~u33227289/opti_connect_2.jpg

Kjell

 

Kjell,
I cut the insulation on the wires and used alligator clips on the scope to get the signal. The signal at idle looked pretty good, but in the problem RPMs the signal was as shown in the graphs. I am still on the fence about the opti being the problem. I am looking for some more input.

 

hot damn this sounds identical to my problem. 4500rpm+ she just falls flat on her face

 

thats the way mine is acting. i just found a guy , thanks to 96capricemgr, that sells the optical sensor by itself. if you want a link i'll throw it your way.

 

Thanks for the help, If im going in there just for the sensor i might as well replace the entire 117,000 mile opti anyways. i've been dealing with this high rpm studder for a year now. And the entire opti is covered in a black goo thanks to my waterpump seal leaking like niagra falls.

Unfortunately I also have no budget at the moment for a $300 opti and will most likely replace it when it finally dies for good. Most likley leaving me stranded somewhere.

 

I found out today that the opti was in fact replaced this spring with a GM opti. The owner was experiencing the same symptoms (miss at 4800rpm)before the opti was replaced. I checked resistance and continuity on the opti harness and to the pins at the PCM...everything checks out. Huh.

 

Did the original owner replace just the base, or the cap and rotor as well? Have you checked the wires for arcing?

 

The whole opti was replaced. I just put new wires and plugs in...no arcing

 

That signal looks pretty rough. The pulses should be fairly square. The low res pulses with be spaced differently because the wholes are different lengths. The high res should be a bit more even.

The falling edge on the low rez should be evenly spaced. I have used this for megasquirt triggers before.

 

Well, I hooked up the scope again, this time using the ground wire to the opti instead of a chassis ground. I posted the pics here

http://s819.photobucket.com/albums/zz117/wilsoncd2/

They are labeled #2 scope pics 1-6.

This time it appears that there are pulses missing from the opti. I am going to replace the opti since it looks like the low resolution output is malfuntioning.

What do you guys think?

-Chris

 

If you're referring to the pink/black wire as ground. That's not a ground to the opti. It may measure close to ground but it's listed as reference. Never the less, wouldn't that only confirm that you have a signal reference issue? Which could be merely a wiring/contact issue.

As far as changing the opti:
Which according to you didn't fix the SAME problem.

I'de have to say you're spinning your wheels.

I only hope you thought of this before you started your repair.

 

You are right that the pink and black wire is the low reference wire. I guess technically it isn't a ground. But, that wire is the low reference to the opti and by connecting between that and the low resolution signal I should see exactly what the PCM is seeing. I did test from the low resolution signal to a chassis ground and basically got the same results.

I also checked the source voltage (to the pink/black low reference wire) during a run and the voltage stayed perfect. This lead me to believe that the low reference signal and the 12V source were both fine, and the opti was getting the correct inputs...but the output was bad (based on the scope graphs).

I did test the wiring harness for both continuity and resistance and both tests came back fine. I checked all of the connections and they are corrosion free and look to be making good contact. If it was a wiring issue, I don't know why it would only happen at certain RPMs?

I did speak with the owner again in regards to the symptoms of the car before and after the new opti was installed. He said that the car actually ran worse after the opti was replaced. This is information I just got.

I'm not sure what other tests I could have performed to further test the opti?

If it isn't the opti, not sure what else it could be. Like I said earlier, the plugs, wires, ICM, and coil have all been replaced. The fuel pressure was tested at WOT, A/F is right on (using a wideband), I checked and there are no leaking injectors.

 

What are the odds that the first opti went bad and the replacement was bad in the same way? Not good in my book.

I think either the item you are looking at is not the problem or something else is causing it, if it is the problem.

Do you have another opti? Why not plug it into the harness and spin it by hand and look at the signals in the same way?

Also try looking at the same signals you been looking at but at lower speeds where you don't experience the missing. If the signals don't look much different at low speeds, chances are something else is causing the problem.

 

You think just like I do...

I tested the low res pulse from the opti at idle and the output looked pretty much perfect. It just seems to break up at the higher RPMs (which is where I see the misfire). I only posted the pictues of the portion of the graphs where the problem appeared.

I am also unsure if the original opti was bad. I found multiple other issues with the car when I got it. Two injector harnesses were switched, it had old plug wires on it, TPS was throwing a code and had to be adjusted, and other small issues.

I am making my diagnosis based on where the misfire occurs, the low resolution signal is poor (at best).

 

Well, I replaced the opti with another new GM unit and the same problem is there. I also tried another opti harness...same problem. Another PCM...same problem.

Any other ideas?