6.2 timing chain stretch or Fast idle switch causeing rough starts.

AECS

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Munford, TN
I know that the timing chain on the 6.2 can stretch and retard timing. I am having problems when the M1009 starts cold, it smokes a lot, and idles very rough for about 5 seconds at the first start of the day. Once warm it is great. Once it cools down to about 100 on the gauge the fast idle and cold advance do not cycle on, it is worse, lots of smoke and rough for the first 10 or so seconds.

The IP was just rebuilt last month, the timing marks are lined up exactly. I don't know if I should look at the fast advance switch or the timing chain has stretched. Is there a way to check the slack in the chain without tearing it all down? I was thinking I might be able to see it through the oil fill hole?
 

Hasdrubal

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Sounds like your fast idle/cold advance is not operating. Check to see if there is power to the sensor at back of passenger head. The smoke sounds like unburnt fuel, check that all your glowplugs are working.
 

AECS

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Location
Munford, TN
Glow plugs are all good, by the DMM, 2.1 or so Ohms. The fast idle is working when dead cold, checked that, but there is a spot where is not coming on but the motor is not warm enough. Maybe the switch on the head is not closing at the right temp anymore? The switch is pricy, and the chain is a pita to change, I just want to get the right fix the first time.
 

gringeltaube

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You said the marks are perfectly aligned. What if you advance the pump a tad?
Try and see what it does having the marks offset about 1mm; that is, the pump's mark moved to the drivers side.


G.
 

Chaski

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Your timing is too retarded. Correct timing is NOT having the marks alligned. The pump mark should be offset to the drivers side. If you download "The 6.2 Liter diesel engine" GM training manual 16015.05-1C there is a nice illustration (4-166) on page 4-99 that shows that the correct adjustment range is an offset of 2.5-4mm tward the drivers side (exact offset depends on your pump model). Get out a 15mm wrench and move your pump to where it is offset 2.5mm. Give that a try and see how you like it.
 

AECS

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Munford, TN
Well that may explain it. I was always under the impression that lined up was right, and some bumped it to get better performance and to make up for a worn timing chain. Project for the weekend.
 
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AECS

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305
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Location
Munford, TN
Is it normal for the pump to be very difficult to turn? All three nuts are loose, but it does not want to turn...
 
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AECS

Member
305
3
18
Location
Munford, TN
Don't think that the issue, I just installed it a week ago, I am wondering if I need to loosen the injector lines a bit to let it rotate.
 

Chaski

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If you can't wiggle it at all by hand the gasket is stuck. If you can move it by hand get a second helper or pry it over to where it needs to be and tighten it down. You should not need to loosen the injector lines.
 

Keith_J

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Schertz TX
Timing chain stretch is only a problem when you hear it slapping around at idle. No fun to change. Interesting on the timing mark alignment, the last 6.2 timing chain I did, the timing marks were aligned before removal. The engine was hard to start and made noise. After timing chain replacement with new cogs, timing marks were aligned as originally. The engine started and ran fine.
 
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