My motor makes a very strange noise after it high ideals for a minute
 

When I cold start my truck it creeps up to 1200 rpm and high idles till I drive it. Then after a minute of that it makes a very strange noise in the exhaust. Like it's retarding itself. Then the egts drop to about 30 degrees Celsius . It doesn't smoke or shake What's it doing ?

3 cylinder high idle?

That's what I was thinking. Would mine do that ? It's a 2001. Unless the edge does it

The "3-Cylinder High Idle" shouldn't kick on unless the ambient outside temperature is below 19* (I think...). If it's that cold or below, that could be it. Someone feel free to correct me if in wrong, but I think I read that somewhere. At any rate, it should cause EGTs to rise, not fall...

It could also be "injector knock" from cold fuel?

Injector knock sounds possible. But I have a manual high idle also and when I use that one Thers no strange sound

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Id like to take a video of it and post it. It sounds very odd

3-cyl high idle will come in when the IAT sensor reads below 15*F

6-cyl high idle will come in when the IAT sensor reads below 32*F

(note high idle must first be enabled by a dealer or smarty programmer in your ECM)

3-cyl high idle will raise EGT's to around 500-600*F unless you have a timing box turned on, then EGT's will drop with the advanced timing.

what 3-cyl sounds like....


(not my truck, but best video as far as sound goes to hear 3-cyl high idle come in)

That's exactly what it sounds like ! How do I get my egts not to drop so much then ?

set your performance box to stock before high idle comes in.

I have to do the same with my adrenaline...

if I leave it on PL1 or higher, the EGTs drop to 175*

if I set to PL0 they raise to almost 600*

now if your egts still read low with your timing back to stock, then you probably have your EGT probe in the front half of your exhaust manifold and not the rear half. (3-cyl high idle cuts out the front 3 cylinders and only fires on the rear 3)

Ok I'll try that

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Is it the edge that makes it 3cyl high idle or is that stock ? I didn't notice it doing this last year

You are exactly right ! My probe is in the front. !