Dieseling / run-on?

Always something with this damn engine....

So now I have a slight run on whenever I shut the engine down. More so when ECT is at operating temps, than when cool. I have not had this happen before.

Changes that I've done are new ID 1000 injectors, and a complete re-cal of VE and MAF. I haven't touched idle speed, and min air is the same. Trims at idle are under 5%. Idle spark is 18. Idle speed is 900.

I could just start changing things and see what might cure it, but figured I'd get input first. I do not think it is detonation, but run on. My initial thought is to just reduce idle speed to 850. It's at 900 to help get the car rolling from a dead stop without having to feather the throttle so much. (08 Z06 with a healthy cam). It will idle at 800 OK...just a lot of lope.

Viewed 51 times. Either I'm asking a really stupid question, and no one feels compelled to respond to such a stupid question, or no one knows what to do.

Lowered idle speed to 825. Didn't help.

Lowered min air 20%. Helped a tad, but I still get a couple cylinder fires after hitting the stop button. Now fuel trims are off. Need to revisit MAF/VE cal if I leave min air where it is. Sonofabitch.

I can't understand how it's even possible. Once the power is cut to the ECU, it shouldn't be able to pulse the injectors to put fuel in the engine.

If the injectors are spraying more fuel on the wall of the port than the previous ones and the spark plugs are too hot of a heat range this will happen.

You waited a whole day for a response and complained when one didn't come fast enough. Did you bother to search around?

Chris

Pre-EFI cars use to knock on sometimes (cheap gas and/or carbon buildup). The carbon stays hot (glows like an ember). Gulf had the No Nox commercials going 40+ years ago to solve all your problems by having a horse kick the gas pump. EFI, I dunno....your compression is most likely not nearly as high as a diesel so "A THEORY"....maybe leaking/timing of injectors plus hot carbon buildup ????? If it were me, I would check my injectors and probably do a seafoam or equivalent cleaning attempt. cheers

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Originally Posted by granatl

I can't understand how it's even possible. Once the power is cut to the ECU, it shouldn't be able to pulse the injectors to put fuel in the engine.

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That's what I thought too. No fuel, no spark, why the run on. A quick Google search on this brought up a few theories, one being too much fuel on the piston from running too rich at idle. I having trouble buying that one.

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Originally Posted by Rocko350

If the injectors are spraying more fuel on the wall of the port than the previous ones and the spark plugs are too hot of a heat range this will happen.

You waited a whole day for a response and complained when one didn't come fast enough. Did you bother to search around?

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Not sure if these are spraying more or not. Plugs are NGK TR7IX, which are supposedly one range cooler than OEM. I'm also using MSD coil packs, with 12v direct wiring harness.

It isn't the "one day" that matters, it's the "over 50 views" without any comment. And yes, I did search. Both this site, and the ol' interweb. Not too many discussions about this happening with EFI.

Chris[/QUOTE]

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Originally Posted by seven ends

Pre-EFI cars use to knock on sometimes (cheap gas and/or carbon buildup). The carbon stays hot (glows like an ember). Gulf had the No Nox commercials going 40+ years ago to solve all your problems by having a horse kick the gas pump. EFI, I dunno....your compression is most likely not nearly as high as a diesel so "A THEORY"....maybe leaking/timing of injectors plus hot carbon buildup ????? If it were me, I would check my injectors and probably do a seafoam or equivalent cleaning attempt. cheers

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I ran a 100psi pressure test on the fuel system when I installed it (rails and AN hose). Probably wouldn't hurt to do that again, to make sure the injectors aren't leaking. I have not used Seafoam on a fuel injected engine before, and did not even think of doing that...Thanks.

Whether or not you found it occurring in efi makes no difference. I usually drop 2 heat ranges when running long tubes , if that's what your running, so the added timing needed when running them doesn't cause a heat issue. Research the Tau fueling. It is the fuel that adheres to the port wall. The 1000's may generate more of that. Its like putting ford 30lbs in a cathederal port motor. Spray pattern to wide. Im not familiar with those injectors, but that's about the only explanation of fuel and ignition source in the chamber. Shut it off in gear and I bet it wont do it.

Chris

Michael, I doubt your ID1000's are leaking, but still needs to be double checked... Most likely it's one of two things. Either your injection timing is so far off that your puddling up fuel on the back side of the intake valves that's continuing to burn in the hot combustion chamber after shut down "happens if too advanced or retarded where fuel actually puddles in the combustion chamber" or you need to go to - Fuel - Transient - Transient Fuel Mass Evaporation - Fuel from Wall Stabilization and play with that setting a little. All though I have never heard of ID injectors having spray pattern change issues and that particular fuel from wall setting is usually for transient fueling? Either this or something is off in the injector data. DSTEK does a lot of these and can hopefully chime in or PM you. I didn't think when you posted having to change your "air tables by increasing them 20%" to fix your fuel trims as much as you did that things were "exactly" right? Usually ID's data is very close... The timing is where I would start after verifying no leakage.

Hope this helps you out.

It would also need an ignition source since he is not high compression like a diesel unless you have a turbo cool down (i.e. like in some after-market alarms) and it runs a couple of more minutes after you take the key out.

Thanks.

To clarify, it doesn't cough and run on for an extended period. It's more like a couple extra half fires after the stop button is hit. Whereas prior to this occurring, it would shut down immediately.

My injection timing has remained unchanged, since I moved boundary several weeks ago. I was just trying to note things that have changed very recently that might be causing this.

My min air was something I've been playing with, trying different things to see the effect it has while cruising at low rpm. I had it artificially high, and that started causing too much hang when in first gear, so now I'm backing it down again. (which is why I was able to lower it 20%).

Could these MSD coil packs be holding a charge, and providing voltage to fire the plugs, with the ignition off???

if u change your "min inj pulse width" in the zero rpm column to 0.00 does that help at all..? think i remember reading bout it somewhere and mine was doing a similar thing so i changed that and its fine now, or i was doing some big changes at the time so it could have been a coincidence but thought id mention it anyway cant hurt to try...

Thanks for the tip. The ID data did have a value for zero rpm, so I plugged it into the table. I reviewed a stock tune file and there is no value at zero rpm, so I think your idea is a good one to try. I'll report back what the result is.

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Originally Posted by GHuggins

Michael, I doubt your ID1000's are leaking, but still needs to be double checked... Most likely it's one of two things. Either your injection timing is so far off that your puddling up fuel on the back side of the intake valves that's continuing to burn in the hot combustion chamber after shut down "happens if too advanced or retarded where fuel actually puddles in the combustion chamber" or you need to go to - Fuel - Transient - Transient Fuel Mass Evaporation - Fuel from Wall Stabilization and play with that setting a little. .

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Zero'ing out the min pulse width Zero rpm cell didn't fix it.

I also re-visited EOIT. The ID's pulse width is shorter, so I tweaked that a bit to compensate. I had already moved EOIT to fire after the exh valve is shut. Regardless, that didn't help.

So I got to thinking and looking at the last few calibrations. Sometime within the last few cals, I changed Fuel from Wall Stabilization from 1, to 2. Not real sure why I changed that either....I was experimenting with transients I think, and just forgot to move it back. I'll move it back to 1 and see what happens.

I'll pressure test the system this weekend, if this last change doesn't help.

So, when exactly did the problem start?

About a week ago I started noticing it. I take care to give every calibration and log a unique name and date/time stamp, so I can go back and compare to previous cals. But what I do not do, is keep really good notes detailing exactly what changes I make. I need to get into the habit of doing that.

I tried moving the fuel from wall stabilization back to "1" last night. Didn't help.

If you saved your different tunes and know when it started, just do a compare. Should show exactly what was changed. Just make sure to go through all of the different sections :)

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Originally Posted by Michael_D

Always something with this damn engine....

So now I have a slight run on whenever I shut the engine down. More so when ECT is at operating temps, than when cool. I have not had this happen before.

Changes that I've done are new ID 1000 injectors, and a complete re-cal of VE and MAF. I haven't touched idle speed, and min air is the same. Trims at idle are under 5%. Idle spark is 18. Idle speed is 900.

I could just start changing things and see what might cure it, but figured I'd get input first. I do not think it is detonation, but run on. My initial thought is to just reduce idle speed to 850. It's at 900 to help get the car rolling from a dead stop without having to feather the throttle so much. (08 Z06 with a healthy cam). It will idle at 800 OK...just a lot of lope.

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Michael_D,

I don't have any answers for you, but I can tell you I started experiencing the exact same issue when I switched from stock injectors to ID1000's on my full bolt-on 2007 Z06. The exact same time that I switched the injectors, I also switched to E85. I wasn't sure which of the two was more influencing the problem. However, other than this issue my car runs excellent. Good fuel trims, great idling/street manners (stock cam). My only issue is when shutting the car off it does this quick dieseling (more like a quick stumble).

I hope you're able to nail down the issue!

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Originally Posted by GHuggins

If you saved your different tunes and know when it started, just do a compare. Should show exactly what was changed. Just make sure to go through all of the different sections :)

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That's exactly what I've been doing, but it's been painful due to my lack of note taking. I have learned the value of doing that! Lol

Does the 12v direct wiring harness have a separate relay? If so its probably taking longer to power down and that's why it's running on.

any news? I have an )7 with bolt ons and ls9 injectors, runs great, strims are great but it is doing the same thing as yours. I thought it may be the injector spray pattern but you have after market injectors and its doing the same.

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.

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.

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.

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

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?

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..?

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

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.

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.

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

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Originally Posted by 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.

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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

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