Where to look next? Feedback/advice?

[johnb]

It should be close to 30% when up to temp, since that's the duty cycle when closed loop control is disabled.

Do you happen to know the frequency of the PWM -- I'm tempted to check how open/closed the valve actually is at 30%...

Its approximately 87Hz

[johnb]

It should be close to 30% when up to temp, since that's the duty cycle when closed loop control is disabled.

Do you happen to know the frequency of the PWM -- I'm tempted to check how open/closed the valve actually is at 30%...

Its approximately 87Hz

Some more info...here's the open loop PWM map. Weirdly there does appear to be different versions of this in different bin files but I'm not sure why. Anyway the map I showed at the end of this[1] is the more sensible looking one:

Screenshot_2025-11-12_08-22-47.png (42.21 KiB) Viewed 789 times

When not at idle, this map fully determines the duty cycle. When at idle, this is the base value that gets modified by the closed loop logic to try to keep the idle at the target rpm.

[1] https://jhnbyrn.github.io/951-KLR-PAGES ... utine.html

[spacecad3t]

That is your repo? Cool stuff, thank you for creating that.

[johnb]

Any progress? You mentioned it was getting up to 1400. I don't know why I didn't think of this before, but that should be above or pretty close to the fuel cut off threshold for a fully warmed up engine. The map value is 1200rpm but there's some other logic involved that I haven't untangled yet, so the rule might not be exactly 1200rpm. Even so I know from my AFR gauge that fuel should be cut somewhere in that neighborhood.

I can't check on my car right now but maybe someone with an AFR gauge can check if fuel is cut when you release the throttle at 1400?

Can you get it to go higher? Do whatever you have to - clamp the fuel return line, pull a hose to induce a vacuum leak etc. If you can get the "idle" rpm above the fuel cutoff, and fuel isn't cut, that will prove definitively that your DME is not seeing the idle signal or at least not handling it correctly.

[Tom]

Any progress? You mentioned it was getting up to 1400. I don't know why I didn't think of this before, but that should be above or pretty close to the fuel cut off threshold for a fully warmed up engine. The map value is 1200rpm but there's some other logic involved that I haven't untangled yet, so the rule might not be exactly 1200rpm. Even so I know from my AFR gauge that fuel should be cut somewhere in that neighborhood.

I can't check on my car right now but maybe someone with an AFR gauge can check if fuel is cut when you release the throttle at 1400?

Can you get it to go higher? Do whatever you have to - clamp the fuel return line, pull a hose to induce a vacuum leak etc. If you can get the "idle" rpm above the fuel cutoff, and fuel isn't cut, that will prove definitively that your DME is not seeing the idle signal or at least not handling it correctly.

The DME/KLR test plan says the injectors should turn off until RPMs drop to 1200-1300 (when the engine is warmed up). I seem to recall earlier in this thread he did get the RPMs to go up higher and it started bouncing off the cut off, but I may have misinterpreted that comment.

[spacecad3t]

No progress, no time these last few days. Also getting colder/darker.

I dont follow you two here. Im aware of decel fuel cut off, the car seems to do that. If I am cruising and I let off the gas and engine speed starts slowing, around 1400-1600 you can hear the engine speed and tone change. From that git repo, It seems like this is that "flare" period, intended to dampen returning to idle?

Either way- maybe Im wrong here... What I do not follow is "fuel cut off with a warm engine". When Im not decelerating, the engine is static and idling, why would there be a fuel cut off?

Im not sure I have seen any bouncing off the cut off. The original 1200 warm and now 1400 all temps is steady, not surging or bouncing.

And just to recap. The car is an NA not a Turbo. And with the ISV out of the loop, car is idling correctly, just cold starts rough, as expected.

Next steps: Testing the DME plug for Temp and TPS signals. Smoke testing again. I also want to test restoring the venturi and y-pipe to the ISV loop.

[spacecad3t]

Updates...

- Disconnected TPS, idle goes higher, 1800.
- Disconnected ICV, no change.
- Open the bypass screw, eventually causes the car to surge very badly. This never happened before actually... I could open the bypass alot and it would just rev.
- I pulled the TB again... Seal does not look pinched, no bolts were loose. (photo)
- I swapped to another TPS that I have. No change, 1400 idle.
- Put a vac gauge on it... 18-19

Somehow I introduced a-lot air since changing my o-ring.

It was this post in the thread maybe, where I mentioned a higher idle, 1800 with TPS disconnected and "surging", which must have been "bouncing off the cut off"?

Also, I was reading this interesting book... and noticed in the troubleshooting section it mentions increasing fuel pressure by blocking the FPR vacuum port.

Screenshot from 2025-11-14 09-13-57.png (98.23 KiB) Viewed 731 times

[johnb]

Updates...

- Disconnected TPS, idle goes higher, 1800.
- Disconnected ICV, no change.
- Open the bypass screw, eventually causes the car to surge very badly. This never happened before actually... I could open the bypass alot and it would just rev.
- I pulled the TB again... Seal does not look pinched, no bolts were loose. (photo)
- I swapped to another TPS that I have. No change, 1400 idle.
- Put a vac gauge on it... 18-19

Somehow I introduced a-lot air since changing my o-ring.

It was this post in the thread maybe, where I mentioned a higher idle, 1800 with TPS disconnected and "surging", which must have been "bouncing off the cut off"?

Also, I was reading this interesting book... and noticed in the troubleshooting section it mentions increasing fuel pressure by blocking the FPR vacuum port.
Screenshot from 2025-11-14 09-13-57.png

What I meant was that if the engine is running above the fuel cutoff rpm threshold, and the throttle is closed, but fuel is not being cut, then the TPS is not working. 1200rpm is the point where the fuel is turned back on after the cut, but it might be necessary to go higher than that to activate it. It sounds like it doesn't matter though, if you are able to get it to idle correctly without the ISV. Sorry if I miss stuff you covered - it's hard to keep track of everything.

That's a really interesting book though. Do you know the title/author? The pdf seems to go straight to the contents but I would love to track down a hard copy. I didn't know books like that existed.

[spacecad3t]

I think it's the PDF of this book. I just googled this book +pdf and found that link.

IMG_1256.jpeg (382.88 KiB) Viewed 722 times

[Tom]

No progress, no time these last few days. Also getting colder/darker.

I dont follow you two here. Im aware of decel fuel cut off, the car seems to do that. If I am cruising and I let off the gas and engine speed starts slowing, around 1400-1600 you can hear the engine speed and tone change. From that git repo, It seems like this is that "flare" period, intended to dampen returning to idle?

Either way- maybe Im wrong here... What I do not follow is "fuel cut off with a warm engine". When Im not decelerating, the engine is static and idling, why would there be a fuel cut off?

Im not sure I have seen any bouncing off the cut off. The original 1200 warm and now 1400 all temps is steady, not surging or bouncing.

And just to recap. The car is an NA not a Turbo. And with the ISV out of the loop, car is idling correctly, just cold starts rough, as expected.

Next steps: Testing the DME plug for Temp and TPS signals. Smoke testing again. I also want to test restoring the venturi and y-pipe to the ISV loop.

I must have misinterpreted something you said above about surging. When the TPS idle contact is closed, the DME cuts fuel to the engine somewhere in the 1200 to 1600 rpm range. (The book and the maps say 1200-1300 when warm, but actual experience suggests it's a bit higher.) So, if there is a vacuum leak that is allowing the motor to idle at, say, 1800, with the throttle closed, what happens is the rpms start to climb up until the DME cuts fuel, at which point the rpms drop, then when the rpms are low enough again, the fuel comes back on and the rpms climb again, until the fuel shuts off again, and so on and so on. That's when you see the rpms 'bouncing' back and forth between idle and 1500rpms or so. If that happens, it means the throttle idle contact is working. But it sounds like that's not your situation, so I'd double check the idle contact at the 35-pin dme connector.

I think your next steps are good ones. I can't think of anything that would cause the DME to intentionally command a 1400rpm. A bad temp sensor might cause add a few hundred rpm to the idle (if the DME thinks the motor is at sub-zero temps), but not 1400. You either have a leak somewhere, or your ISV is not working correctly (ISV/wiring to it/DME). The motor is getting extra air somewhere. My hunch is that the ISV will always let a certain amount of air in, and that blocking it off really just cuts off that expected airflow, bring the total amount available to the motor down to idle speeds -- in other words, blocking off that airflow is just masking the problem and not revealing one...