Dans69LS1velle

I have an LS1 with LS2 heads, hot cam, 770 holly carb. MSD 6LS box and a TCI trans controller. My problem is that it diesels when I shut it off. I had the timing all the way from 6 degrees initial to 22 degrees at idle and it still diesels. There is no carbon build up and the plugs are new. I don't believe also that it is running to lean but not sure... When I fattened up the mixture it seemed to make it worse. Idle is set about 850 rpm's. Any lower then that and it wants to die in gear. Any help why my LS1 diesels or wants to continue to run would be great...

Pop N Wood

iTrader: (1)

Do you know what compression ratio you end up with? I would double check the idle mixture with a wideband. Keep it as lean as possible.

Back when I was a kid cars use to diesel due to low octane gas. Run a higher octane gas if you aren't already.

The other trick we use to do is leave it in gear when turning it off.

Just noticed Wikipedia has some good info. The last link has some good suggestions.

http://en.wikipedia.org/wiki/Dieseling

http://www.jeepster.org/swchapter/dieseling.html

http://mgaguru.com/mgtech/engine/ro101.htm

speedtigger

iTrader: (16)

Carbon deposits in the combustion chamber can also cause this.

Dans69LS1velle

Ya heads are new, and the tops of the pistons were cleaned. No carbon build up.

Dans69LS1velle

Great! I do shut it off in gear but the problem is still there. It surges at idle in gear. Talked to MSD tech and they said there were problems with carbed manifolds sealing properly to the head. They suggested felpro's thicker gaskets.
It raised the comp ratio going to the LS2 head which is the same chamber as the LS6 head. LS2 head has a 5cc smaller chamber. Not sure how much that raised the comp ratio from the stock 10-1.

jimmyblue

iTrader: (11)

I wonder if that hotcam isn't the problem, maybe you want one
with less overlap and better idle vacuum so it doesn't have so
much feeding it, to (barely) run without spark.

But I wouldn't ignore engine cooling either. Sure there is no steam
action? Seeing any coolant puking? Getting an aluminum head hot
enough to diesel seems to take some doing, there are lots more
extreme setups than yours that don't.

Dans69LS1velle

My temp is at 185 for the most part. Sitting in the garage at idle it will get to 190-200. But no coolant is puking, I bleed all the air from the cooling system and I have the steam line hooked up properly to the radiator. Maybe the pcv system isn't right. Since that is changed from when I had the EFI set up.

Dans69LS1velle

Oh, about the hotcam. Vacuum isn't problem. It produces between 7-10 inches at idle and I have great brake pedal feel as well.

speedtigger

iTrader: (16)

There is another thread about this LS1Tech somewhere. I remember reading it a couple months ago.

Oh, and one more thing to consider. My head steam vent tube was completely clogged to the point that it had to be drilled out. Fortunately I noticed it when I was painting the item. I would be worth a look to make sure the passage is clear.

tennerv8

iTrader: (7)

Mine does this also. See sig for specs.

butler

That is very low vacuum. I say you have a vacumm leak and the idle is turned up to compensate. With that small of a cam it shouldn't diesal.

Dans69LS1velle

Yes, I'm changing to thicker intake gaskets and carb gasket. This is what I narrowed it down to is a vacuum leak. I'll change out the gaskets and will get back with the results...

speedtigger

iTrader: (16)

Which intake do you have?

Gray86hatch

iTrader: (83)

More timing. I run almost 40 at idle. Idle is smoother and dosn't run on. Try lowering the idle just a touch also.

Tim

Dans69LS1velle

I have the edelbrock performer carb intake. With LS2 heads. Which raised the comp ratio. Not sure if thats a factor in dieseling. I've tried more timing. That makes the starter kick back, didn't help. I'm sure it's a vacuum leak, cause it doesn't want to idle in gear so I have to turn the idle up a little. I'm sure all my problems are related to a vacuum leak. I have some plugs that are burning leaner that others. That's also a sign of a leak. Hoping this will fix the problem is a gasket change. I'm trying the felpro extra thick gaskets .120 thickness.

Na306StAnG

If that doesn't fix it. Does it do this no matter how hot or cold it is? Hows the cooling fan's wired? I've seen cooling fans wired incorrectly and cause problems like your having.

Goodluck!

Dans69LS1velle

It does this once it reaches about 140 degrees. I have a dual fan set up on a relay with a thermostat. Big two row aluminum radiator. Fans kick on at 185.
Never had any over heating issues. Never seen the temp go above 200. And that was at idle in the garage.

speedtigger

iTrader: (16)

If you pull off your cylinder head steam vent hose, does coolant squirt out when it is running?

rojs234

iTrader: (5)

I know this is a dumb question, but both *speedtigger* and myself had a lapse on this just recently. The Performer RPM has a 10/32 threaded hole on one of the front runners to bolt MSD box on. You would think this would be a blind threaded hole, but it goes through into the runner. If you don't use it to bolt the box on, it needs a 10/32 screw in it. Just a thought, Ron

speedtigger

iTrader: (16)

Crazy design for sure. Once Ron pointed this out, I put a screw in the hole and it cleaned my idle right up.