Dieseling / run-on?

[Michael_D]

I thought I had fixed it till last night. ...grrrrrr

I spent some more time calibrating VE under 1000 rpm after lowering min air flow. I used the scanner to force idle down to 600. Got VE under 2% error. It stopped the run on for several hot stops. Then it ran on again last night. I need to pressure test to rule out a flaky injector.

[twistedpixels]

Ya min does run on here and there when hot and it is an 07 H/C/I with e85 mix. My tuner has taken several tries to get rid of it but to no avail. It seems to be something that is really a big issue with the 06-07 cars and the ECU and programming. He said it may go away with a ECU from a 2010 since he has seen many issues go away once the ECU is changed to a newer year. OF course that is kind of an involved process and not cheap. I have LS9 injectors and it did it with my stock ones as well. So it is not isolated to injectors.

[Michael_D]

Interesting thought about the newer ECM. Not sure if that's what I'm seeing, cause it's a new problem. I would however like to go with a new ECM to get some O2 tables.

Leak test was good.

So the run on definitely is improved. Still does it a bit, but not nearly as bad as before. I'm thinking it was VE being too rich in the <800 rpm rows. I probably moved those cells 15%. I still don't understand how the engine could fire without spark. Unless I have a build up of carbon on the pistons, or the plug is glowing..... I need a bore scope. This might be a good opportunity to buy a new toy.

[07GTS]

is it the same sort of run on u get when u first start up and its cold so there is more fuel going in and after bout 20-30 seconds u turn it off and because its so rich it runs on a little..? thats the only time mine does it now and u would think since the spark is cut it wouldnt do it and if it was self combusting then thats just not right for petrol so something must be keeping the spark there just a bit after shutdown, can u see it in a log..? when i turn off to accessory's my log keeps going if yours does too u could see maby whats still happening

[Michael_D]

It only occurs when the engine is up to operating temp. I have logged shut down and can't find anything unusual, but to be honest, I'm not sure what to look for?

[07GTS]

i wasnt sure if u know the exact time it stops running and then if u can see if any spark still there just after it, couldnt have anything to do with dwell time if thats been increased at low rpm could still hold some charge..?

[Sébast19X]

I have already experienced this with a customer car. And a similar cam that you have.

When you log the shut off, look carefully, at around 200 rpm or so the MAP should be close to 95 kpa, the timing return to crank mode and the tps reopened up.

I think if the engine run more compression, lower mass flywheel, and shutoff more rapidly, that trouble should goes away.

BTW I don't find how to eliminate it. The 2006 Z06 with almost the same cam, never reopened the TPS on shut off like the 2008 and newer.

Seb

[Michael_D]

I'm not gunna hold my breath too long, but I've probably shut the engine off twenty - thirty times now, and it did not run on at all. I'm beginning to beleave my hypothesis that VE was part of the problem.

[10_SS]

Thought I'd share my story of running an engine backwards for 2-5 seconds... could be related. If not, something to think about.

82 Firebird carburated.. 305. Rev it up to 2500rpm then shut off the key and hold the gas to the floor... (fill the exhaust with air fuel at the right ratio)... then right when the engine stops, turn the key back on.. it would fire up backwards (and smooth)! Run about 1500rpm for 2-3 full seconds before stalling.. it would sound weird like tons of air was being pushed through the carb... and it would stink. Restarting normally would take a bit and no oil pressure for ~5 seconds... lol.

So, point is, with a cam yes there could be more un-burned fuel in the intake from the cam at idle pushing cylinder air/fuel back into the intake, or air/fuel in the exhaust. Leaning it out at idle like you have done may help things.

[Michael_D]

Still no issues with run on....this is kinda exciting. I think I may have actually fixed something, for once. What an odd feeling.

[schpenxel]

Still no issues with run on....this is kinda exciting. I think I may have actually fixed something, for once. What an odd feeling.

What did you end up doing? Lowered the very low areas of the VE table?

And I know what you mean there.. haha. I get the same weird feeling once every 10 tries or so to fix something lol

[Michael_D]

That's the only thing I've done that made a noticable difference.