Dieseling

[eboggs_jkvl]

We installed the E-force supercharger. My car diesels when I turn it off. What can be done to eliminate this?


Elmer

[eboggs_jkvl]

Should I have put this in the Diesel forum? :D

[eboggs_jkvl]

We're still struggling on this. Any ideas at all???????

[nevinsb]

What are you running for fuel? Does this happen every time you shut it off, or only right after a run? How bad does it chug after you shut it off?

I'll be honest, I've never had it happen to me. Maybe fuel is pooling inside the intake from wrong shape or injector timing at idle?

What else has been modified?

[eboggs_jkvl]

Shell 93 octane with ethanol (10%). It diesels every time I drive the car and shut it down. At the most, it is 1-2 seconds of sputtering but it won't just flick off like it used to do. As far as what else has been modified, are you referring to the tuning? I have all of my mods listed in my SIG. If it is tuning, I'll have to ask my tuner.

Elmer

[swingtan]

Going back to basics, dieseling can only occur when fuel is still being fed into the engine and there is something hot enough in the combustion chamber to ignite the charge. so there are a couple of things to look at here.


Fuel source: Where is the fuel coming from? Normally the injectors and fuel pump are powered down as soon as the key is turned off. This should be pretty fail safe and normal faults to the injectors ( like being stuck on ) would be very obvious. We can assume that for a short time after power off, there is still some pressure in the fuel lines, so it makes me think that one or more injectors may be leaking. This would not be too obvious when the car was running, especially if the leak was quite small. Another option for the fuel source is if you are injecting into the supercharger, which would result in a significant amount of fuel and air in the intake system. It's unlikely given your engine setup, but you may find that at idle, where boost levels are low or non-existent, that some fuel vapor is finding its way back into the charger. The amount of fuel may be low but may be enough to support a short period of dieseling.
Ignition source: If we assume one or more leaking injectors, then the ignition source might just be the hot combustion chamber and a very lean mixture on the intake. as the very lean mixture is compressed, it might be detonating from the heat buildup alone. The other option would be that there are hot debris in the combustion chamber ( soot, carbon, sharp edges, plug tips ) that are igniting the charge. Normally the liquid fuel injected into the intake would cool these to some degree, but with a very lean charge, the cooling effect is not there.


I doubt it's tuning, as when the ignition is off, the tune is also.

Simon

[joecar]

Elmer,

Are you using a manifold-referenced FPR...? If so, check to see if the diaphragm has ruptured...

if it has ruptured residual fuel pressure will push fuel past the diaphragm and into the manifold.

[eboggs_jkvl]

Someone asked me to check the stock 2007 LS2 spark table and compare it to the one that was loaded into my car. The stock tune called for 13 degrees at idle whereas my loaded table was calling for 23 degrees. I highlighted the stock tune about 6 columns across and 5 rows down and pasted the collection into my current tune. I ran the car today and the dieseling is gone. The rest of the spark table seemed to be the same as the rest of the stock table so I am not going to change the spark table unless it is absolutely called for.

I'm investigating my "High Octane Spark Table" numbers now.

Thanks for the help!

Elmer

[nevinsb]

That's kind of weird, but at least you are making progress. Thanks for updating us, it really helps others when they encounter a similar issue.

[eboggs_jkvl]

OK, 6 months of this and I still have an issue. Would you smart guys look at this link http://forums.corvetteforum.com/c6-forced-induction-nitrous/2690856-dieseling-condition-with-e-force-8.html

Go to page 8, post 150.

Does EFILive give access to the Throttle position?


I've changed injectors, pumps, removed the BAP, replaced the intake manifold gaskets, and Friday we're swapping out the SC itself. I'm chasing my ass here and I don't think the SC swap is going to fix my issue.

Elmer

[swingtan]

I can't see those images on LS2.com without being a member........

RE: the throttle opening, is this just the standard "shutdown" positioning of the electronic throttle? The ETB has an "at rest" position of about 20% opening, it's not closed like on a traditional cable unit. The reason is that this is where most of the driving is done, so it uses less power to hold the throttle at this position. If you log the throttle blade position, you will see that when the key is turned to the accessory position, the TPS % will be around 20%, then when the key is turned to "on" the TPS will drop to between 6% and 12% (depending on engine temp). So the ECM applies power to close the throttle as well as open it past 20%. On shutdown, the ECM should close the throttle completely till the RPM's drop below a set point, maybe 150-200 RPM. Then the ECM release the ETB to allow it to return to it's "at rest" position.

I do not believe any software provides access to this type of throttle control. But I don't think it should be needed to stop dieseling. I think you would need to check how long after the key is turned off, that the ECM still tries to manage the engine. If the ECM stops managing straight away, then no "tune" settings are going to help. I keep returning to the question of "where is it getting fuel from?" Stop the fuel and you stop the dieseling, perhaps there is a build up in the SC, or maybe the PCV system? Here's a thought.... try logging with a wide-band in place while it's dieseling and look at the AFR's.

Post any logs you have as well, there may be something in there that will help.

Simon

[eboggs_jkvl]

The RPMs surge back up after key off






http://www.ls2.com/boggs/eforce/diesel05.jpg

[eboggs_jkvl]

Here's just a start, idle and shutdown.