MSD Cap and Rotor

[96z28SideSwype]

File sent at 4:18 PM, EST.

Fred

Got it thanks. The engineer I sent it to said that it was strange the readings he's going to look into it more but did ask if you can get another reading if possible and have him disconnect the iac on his car


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[SSlowBoat]

Got it thanks. The engineer I sent it to said that it was strange the readings he's going to look into it more but did ask if you can get another reading if possible and have him disconnect the iac on his car


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The iac isn't gonna change a faulty sensor in the opti from sending a proper signal to the pcm.

"Engineers......"

No offense Fred, ur structural and stuff, that's different than electrical lol

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[Injuneer]

As I noted in the email, the trigger is the single frame of data, where RPM jumps as much as 5,000 RPM, to a reading as high as 7,000 RPM+. This happens in less than 1/2-second, and the next frame the RPM returns to the actual RPM, 2,000 - 2,500 RPM. At no time does the TPS% change from 0. At no time does the indicated MAF reading in grams/second increase, even though indicated RPM jumps to 5,000 - 7,000 RPM. And MAP does not increase, so the throttle really hasn't moved, and no indication of a sudden vacuum leak.

In response to the erratic high RPM trigger, the PCM advances the ignition timing, and then increases the IAC counts. This is a somewhat normal response from the PCM, because it appears it opens the IAC so that the engine doesn't stall if the throttle blades suddenly close. Increase in timing is normal, because as RPM goes up the timing table increase advance. But as the idle RPM comes back down to the actual number (2,000 - 2,500 RPM), the PCM should pull the IAC counts down to match actual idle RPM to target idle RPM. But the next erratic indicated RPM jump comes so frequently that the IAC keeps getting opened back up, and idle can't come down to target. Appears that the increase rate for IAC counts is delayed slightly, maybe tow frames after the RPM spike.

In Tubby's case, the erratic jumps to high RPM was not as severe, and much less frequent. So his IAC counts did not elevate so much, and as I recall he had an idle surge from less than 1,000 RPM to 2,000 RPM.

I can ask the owner to disconnect the IAC, but that just subverts the PCM from doing what it is supposed to do. He will have to wait until the IAC counts drop to the 20 - 40 range, where they should be. Then unplug the IAC. The idle should stabilize, and it will be interesting to see if the erratic RPM reading continue or stop. I can't see how the IAC could drive the RPM feed, but we will see.

I'm not a structural engineer, I have a BS in mechanical engineering, an MS majoring in management (industrial) engineering, and a Professional Engineer's license. My first job was 7 years with the Exxon Research & Engineering. Spent a lot of time designing instrument and control system for refineries and chemical plants. I will admit I rely on member GaryDoug (graduate electrical engineer) for electronics help

[Injuneer]

Sorry.... tried to edit above and it resulted in a duplicate post.

[96z28SideSwype]

Im just relaying what im being told to try and figure out the issue and to try to see if it is in the sensor in the optispark.

[Injuneer]

I understand.

[SSlowBoat]

As I noted in the email, the trigger is the single frame of data, where RPM jumps as much as 5,000 RPM, to a reading as high as 7,000 RPM+. This happens in less than 1/2-second, and the next frame the RPM returns to the actual RPM, 2,000 - 2,500 RPM. At no time does the TPS% change from 0. At no time does the indicated MAF reading in grams/second increase, even though indicated RPM jumps to 5,000 - 7,000 RPM. And MAP does not increase, so the throttle really hasn't moved, and no indication of a sudden vacuum leak.

In response to the erratic high RPM trigger, the PCM advances the ignition timing, and then increases the IAC counts. This is a somewhat normal response from the PCM, because it appears it opens the IAC so that the engine doesn't stall if the throttle blades suddenly close. Increase in timing is normal, because as RPM goes up the timing table increase advance. But as the idle RPM comes back down to the actual number (2,000 - 2,500 RPM), the PCM should pull the IAC counts down to match actual idle RPM to target idle RPM. But the next erratic indicated RPM jump comes so frequently that the IAC keeps getting opened back up, and idle can't come down to target. Appears that the increase rate for IAC counts is delayed slightly, maybe tow frames after the RPM spike.

In Tubby's case, the erratic jumps to high RPM was not as severe, and much less frequent. So his IAC counts did not elevate so much, and as I recall he had an idle surge from less than 1,000 RPM to 2,000 RPM.

I can ask the owner to disconnect the IAC, but that just subverts the PCM from doing what it is supposed to do. He will have to wait until the IAC counts drop to the 20 - 40 range, where they should be. Then unplug the IAC. The idle should stabilize, and it will be interesting to see if the erratic RPM reading continue or stop. I can't see how the IAC could drive the RPM feed, but we will see.

I'm not a structural engineer, I have a BS in mechanical engineering, an MS majoring in management (industrial) engineering, and a Professional Engineer's license. My first job was 7 years with the Exxon Research & Engineering. Spent a lot of time designing instrument and control system for refineries and chemical plants. I will admit I rely on member GaryDoug (graduate electrical engineer) for electronics help

Haha thanks man, just busting chops. Your knowledge has helped/saved many of us.

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[SSlowBoat]

Im just relaying what im being told to try and figure out the issue and to try to see if it is in the sensor in the optispark.

I understand that, but why would a new opti from delco fix that immediately and not have the issue any more?

Optical sensor.....that's why

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[96z28SideSwype]

I understand that, but why would a new opti from delco fix that immediately and not have the issue any more?

Optical sensor.....that's why

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And ive told them that thats why they want to check every possible avenue to look and see what could effect the sensor.

[Injuneer]

And ive told them that thats why they want to check every possible avenue to look and see what could effect the sensor.

I have to find your file. I think it was DataMaster, not Scan9495. Your erratic RPM jumps were smaller and less frequent, harder to even find. The current file is much larger jumps and much more frequent. But the end results were similar.