# 2013 1.4T engine diesels or runs-on when turn key off



## jblackburn (Apr 14, 2012)

I've never seen this on a fuel injected car, but it happened on an old carbureted piece of crap I used to have. A top end cleaning solved it for that car.

Do you see a lot of oil under the throttle body and on top of the transmission? This would be a result of a failed intake manifold PCV check valve, and can cause a lot of crud and oil to build up in the intake system and tops of cylinders.


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## roundy (Sep 25, 2017)

Update on engine run on problem.
Switched with a known good car: the main relay in the underhood fuse box, valve cover with PCV, throttle body, canister purge valve, and looked at top of pistons for excessive carbon build up. No joy so far. I haven't done anything with the actual intake manifold, going to spray around it for vacuum, but I'm not getting any lean codes. Next item I'm going to try is the electrical portion of the ignition switch as it is a relatively low-cost part. Still looking for ideas if you have one. I would be glad to link to a short video of the condition if you think it would help.


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## Tomko (Jun 1, 2013)

Dieseling, or run-on, in a gasoline engine is almost always caused by carbon build-up in the combustion chamber. 

Regular, effective and ongoing use of a Top Tier Gasoline will prevent this. 

In your case I suspect that looking at the top of the pistons is not telling you the whole story. The carbon is likely on the valves and cylinder heads themselves. Maybe even the spark plugs. 

A treatment of GM Top Engine Cleaner introduced through your fuel rail with inert nitrogen gas will likely solve your problem. Do not let anyone use anything else, like seafoam, for example. That will end very badly for you. 

As well, running the highest octane gasoline possible may stop your dieseling as it is less prone to pre-ignition. 

As a first step I would run three full tanks of Shell V-Power through your car. Then reassess. That is if you want to avoid a trip to the dealer for the GM Top Engine Cleaner treatment.


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## Taxman (Aug 10, 2017)

"Dieseling, or run-on, in a gasoline engine is almost always caused by carbon build-up in the combustion chamber."

But it can't happen without fuel, so in a car with EFI, if the injectors don't leak and don't get power after shutdown, it can't diesel.

The last car I can remember experiencing it in was a 1977 Chevy Nova. Fortunately it was a stick (more specifically a 3 on the tree), so you could stop it by engaging the clutch.


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## Tomko (Jun 1, 2013)

Taxman said:


> "Dieseling, or run-on, in a gasoline engine is almost always caused by carbon build-up in the combustion chamber."
> 
> But it can't happen without fuel, so in a car with EFI, if the injectors don't leak and don't get power after shutdown, it can't diesel.
> 
> The last car I can remember experiencing it in was a 1977 Chevy Nova. Fortunately it was a stick (more specifically a 3 on the tree), so you could stop it by engaging the clutch.


Correct. Needs fuel and oxygen. The heat retained by the engine and increased compression due to the carbon build-up allow the dieseling. 

However, if the carbon and other crud built up in the combustion chamber have absorbed fuel, that can be enough to permit the dieseling.


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