Carpokes Porsche Forum

Latitude48 wrote: Mon Oct 31, 2022 6:45 pm Implementing the ignition advance feature wasn't easy as TDC had to be determined, which was a bit of a chore to do in code since the "Mark" sensor outputs a signal way in advance of TDC. This is still Beta code as it was to be verified by comparing to the ignition advance of a client's car with a standalone system on the dyno, and I don't know if that happened yet.

FWIW, the average advance of my 951 at idle in the recent run I recorded was 5.38, which IIRC is within the spec range of 5 +/- 3.

Yes, I went through that making my own monitor. Making it harder, none of offset values people quote for stand-alone systems seemed to line up exactly with what I was seeing. I have a zillion notes somewhere if they would be of any help.

Something to add to running issues.

When troubleshooting clean and then air dry your contacts with isopropyl alcohol.

We continually do this with the systems I work on when we overhaul them and then run them up and test system functions…..long process. Cleaning connections that already appear clean sometimes leads to correcting faults.

I checked the resistances from the throttle switch to the DME and KLR:
1) DME Test
Throttle switch at idle - measure resistance between DME connector terminal 2 (throttle switch idle contact terminal 6), and DME terminal 19 (my choice for Ground). Result: 0.4 ohm.  Spec value, 0-10 ohm. PASS
Throttle switch above idle - same test points. Result: open circuit. Spec value, infinite resistance. PASS
2) KLR Test
Throttle switch at idle - measure resistance between KLR connector terminals 22 & 23. Result: 607 ohm. Spec value 320-670 ohm. PASS
Move throttle slowly to full load, resistance should continuously vary. PASS
Move throttle to full load position. Result: 4.1xx Kohm.  Spec value, 2.7-4.7 Kohm. PASS

So, it looks like I now have a new throttle switch to add to my spare parts stash

Latitude48 wrote: Wed Nov 02, 2022 11:47 am I checked the resistances from the throttle switch to the DME and KLR:
1) DME Test
Throttle switch at idle - measure resistance between DME connector terminal 2 (throttle switch idle contact terminal 6), and DME terminal 19 (my choice for Ground). Result: 0.4 ohm.  Spec value, 0-10 ohm. PASS
Throttle switch above idle - same test points. Result: open circuit. Spec value, infinite resistance. PASS
2) KLR Test
Throttle switch at idle - measure resistance between KLR connector terminals 22 & 23. Result: 607 ohm. Spec value 320-670 ohm. PASS
Move throttle slowly to full load, resistance should continuously vary. PASS
Move throttle to full load position. Result: 4.1xx Kohm.  Spec value, 2.7-4.7 Kohm. PASS

So, it looks like I now have a new throttle switch to add to my spare parts stash

Well, it did seem to be intermittent so you never know. Not a bad spare to have handy either way. They were back ordered for a long time too, so you never know when the supply might dry up.

Tom wrote: Wed Nov 02, 2022 1:15 pm Well, it did seem to be intermittent so you never know. Not a bad spare to have handy either way. They were back ordered for a long time too, so you never know when the supply might dry up.

Good point Tom. I'm still not convinced that my issue has been solved. Joe has stated that the DME won't go into Full Load mode until the throttle switch is in the Off Idle mode, AND the throttle is pushed enough to be beyond the angle (potentiometer resistance) that the DME considers WOT.

I don't see how that can happen with the throttle in the idle position unless there's a double failure: the throttle switch internal microswitch fails and reports an open circuit to indicate to the DME the throttle is Off Idle, AND there's enough corrosion on the KLR contacts in the throttle switch (or at the KLR) to make the DME and KLR think these two conditions have been satisfied. But my throttle switch tests fine, so something else must be triggering the Full Load signal such as an intermittent KLR? It might be time to open it for an inspection.

On the positive side, I got a new multimeter to play with

Latitude48 wrote: Wed Nov 02, 2022 3:46 pm

Tom wrote: Wed Nov 02, 2022 1:15 pm Well, it did seem to be intermittent so you never know. Not a bad spare to have handy either way. They were back ordered for a long time too, so you never know when the supply might dry up.

Good point Tom. I'm still not convinced that my issue has been solved. Joe has stated that the DME won't go into Full Load mode until the throttle switch is in the Off Idle mode, AND the throttle is pushed enough to be beyond the angle (potentiometer resistance) that the DME considers WOT.

I don't see how that can happen with the throttle in the idle position unless there's a double failure: the throttle switch internal microswitch fails and reports an open circuit to indicate to the DME the throttle is Off Idle, AND there's enough corrosion on the KLR contacts in the throttle switch (or at the KLR) to make the DME and KLR think these two conditions have been satisfied. But my throttle switch tests fine, so something else must be triggering the Full Load signal such as an intermittent KLR? It might be time to open it for an inspection.

On the positive side, I got a new multimeter to play with

Every 944 owner needs a good multimeter! Your logic makes sense about needing two failures if the DME used yes/no logic for the throttle state (they way we all think about it), but your post earlier in this thread educated me about those inputs actually going through voltage dividers to create 3 different voltages. I'll noodle the DME circuit a bit, but I think Joe's theory was that an unexpected input from the idle contact (i.e., some resistance rather than all open or closed) might create 3.8 volts after the resistor network (where it does the AD conversion) even though the TPS isn't actually open at all. No idea if that's true, so may try to model it and see, but if it is true, I could see that one failure creating a false full load signal.

As an aside: what's the best (correct) way to disconnect JPT (Junior Power Timer) connectors, such as used on the throttle switch?

Also, Joe confirmed he signed up for Carpokes and looked around, but he doesn't have time to support another forum at this time, but hopefully in the future.

Best way to disconnect?

1. Picked the little spring clip out using an awl or tiny screwdriver.
2. Spend 30 minutes to 3 days looking for that clip after it flies across the garage.
3. Pull/wiggle the connector off (holding the connector, not the harness wires).

Or am I missing the point of your question? On the spring clips, I usually don't take them all the way off, put rather pick them out enough to the sit cock-eyed enough to free the connector. I use a tiny pair of electronics needle nose pliers to grab onto to them when I remove them completely -- it helds avoid step 2 above.


Thanks very much for working on Joe. Very much appreciate that!! We'll be here with open arms whenever he (and others) are ready. No sponsorships needed, and no fighting with Viagra ads for screen space....

Latitude48 wrote: Wed Nov 02, 2022 3:46 pm Good point Tom. I'm still not convinced that my issue has been solved. Joe has stated that the DME won't go into Full Load mode until the throttle switch is in the Off Idle mode, AND the throttle is pushed enough to be beyond the angle (potentiometer resistance) that the DME considers WOT.

I don't see how that can happen with the throttle in the idle position unless there's a double failure: the throttle switch internal microswitch fails and reports an open circuit to indicate to the DME the throttle is Off Idle, AND there's enough corrosion on the KLR contacts in the throttle switch (or at the KLR) to make the DME and KLR think these two conditions have been satisfied. But my throttle switch tests fine, so something else must be triggering the Full Load signal such as an intermittent KLR? It might be time to open it for an inspection.

I mocked up a circuit on my iPad that shows the theory I think Joe had about the extra resistance in the idle contact. This is based on the concept you/Joe pointed out earlier -- i.e., that the idle contact and full load signals are not used directly by the CPU, but instead go through some circuitry to create three voltage levels which are fed to an analog to digital converter (ADC). Going off your post, the ADC should see 3 volts at idle, 5 volts at part throttle, and 3.8 volts when the KLR triggers the Full Load signal. (The DME doesn't see the TPS potentiometer values -- it just gets the yes/no Full Load signal from the KLR.) This circuit mock-up does not replicate the DME really, but is similar (scaled down to basic voltage dividers) and is just set up to show how that one failure (extra resistance in the idle contact) could cause the DME to see the Full Load signal when the throttle is shut. Whether this actually happened in your case, or could ever happen with the actual DME circuitry, I don't know. This just demonstrates that the theory 'could' explain it. You may need to pause each scenario to see what's really happening (and google voltage dividers if needed).

Very cool video, Tom. I sent the link to Joe.