Flywheel ring gear

[johnb]

When you ask how the screw lines up -- you mean the relationship between the ref sensor pin and the ring gear teeth? Other than accommodating other models, nothing obvious comes to mind about the half-tooth delay. The phase seems to be fixed by the hardware, so I can't think up an scenario where it would change on a running car...? I'll have to read your write up to understand the other quirks you mention...

Yes that's what I'm asking.

I suppose the same Motronic system was used on other cars too, and maybe some of those cars has press-fit ring gears without any particular timing guarantee.

The diagnostic pin thing is interesting. Does that have something to do with that other sensor, with the connector on the back of the cam tower? I always wondered what the deal was with that. I tried checking it for a signal before and didn't get anything.

[Tom]

When you ask how the screw lines up -- you mean the relationship between the ref sensor pin and the ring gear teeth? Other than accommodating other models, nothing obvious comes to mind about the half-tooth delay. The phase seems to be fixed by the hardware, so I can't think up an scenario where it would change on a running car...? I'll have to read your write up to understand the other quirks you mention...

Yes that's what I'm asking.

I suppose the same Motronic system was used on other cars too, and maybe some of those cars has press-fit ring gears without any particular timing guarantee.

The diagnostic pin thing is interesting. Does that have something to do with that other sensor, with the connector on the back of the cam tower? I always wondered what the deal was with that. I tried checking it for a signal before and didn't get anything.

I'll take a look (and some pics) in the morning. Yes, the extra pin on the flywheel is for that diagnostic connector -- vestigial hardware of no use outside the basement of the Bosch diagnostic equipment museum...

[soxnail]

I am chasing an issue that has me pulling my remaining hair out....
Back ground: The car will get a tiny stumble while sitting at idle, in the dash I will see the rpm nudge down and then up (higher than idle) and then settle down.
It does it with or without the ICV being used to control the idle.

Here is a bench test pic of the idle timing for my DME.

Idle timing.jpg (140.95 KiB) Viewed 33 times

Sorry still trying to figure out how to embed pics with text...

[soxnail]

Now in the car I have been able to isolate this occurrence to an extra tach pulse showing up just before actual tach pulse, it also a lot shorter in time than the regular pulse. (just before the second tach pulse)

F0004TEK.JPG (135.41 KiB) Viewed 32 times

[soxnail]

My last post did not happen so here it is again.
This pic has the speed and ref sensor shown, I could not find any noise in those lines.
Any ideas would be helpful, Tia Sox.

Ps. sorry about the 3 posts trying to figure out how to get the in line pics to agree with the text.

Ign glitch.jpg (140.71 KiB) Viewed 28 times

[Tom]

Is this a factory 951 DME and KLR? If so, are you acquiring those signals from the PCB itself or in the harness?

If you are probing/logging directly off the DME board, the probe wire can itself introduce or alter fast transients, especially with a loose lead on a sensitive 8051 interrupt pin. That loose wire can act like an antenna. I would not conclude that “no spikes visible on the scope” definitely means there are no spikes affecting the circuit. Probably not, but not definitely not.

Where exactly are you picking up the ignition pulse in that scope shot? Assuming it’s the DME pin 21 tach signal, that would suggest the glitch occurs before the ignition signal splits off inside the DME to the coil driver, since you see it in the logs and feel an actual stumble.

I see that the short glitch pulse appears to starts where you would expect the full ignition pulse to start, but then stops quickly, before the full pulse appears seemingly late. That sequence would make me suspect the KLR first. One of its main jobs is to delay timing, so if there is an issue with that circuitry, I could imagine it causing your symptoms. I’d be tempted to bypass the KLR as a short diagnostic test (no hard driving) to see if that’s the source of the issue. If the problem goes away with the KLR bypassed, I’d start by looking for cracked solder joints in the KLR. Let us know. Sorry it's frustrating, but hopefully we can help think it through.

[whalenlg]

How wide is the transient tach pulse?

I can look at my dme simulations to see any similar behavior.

[whalenlg]

My simulations don't show any extra tach pulses at idle.
I do see some idle variations with engine warm for cases where tps has failed, coolant temp fail, air temp fail, afm open circuit, high altitude enabled.
They all kind of look like the 2nd picture.

The 1st pciture is a case where o2 is stuck lean and the simulation shows rpm going to 0 at about 13 seconds after start (see 2nd pic)

Does this happen at cold or warmed or all the time? How long is it between the idle slowing?