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Discussion Starter #1
I just replaced all the glow plugs in my truck, not knowing if they had ever been done.

Turns out all 8 were good, ac delco 9s (forget the prefix).

Symptom is still the same, very hard to start, like not all the plugs are heating. Is there some part of the circuit that controls the separate banks? The truck started MUCH easier this morning after being on the block heater all night, so I suspect a plug issue.

Any ideas? :help:
 

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use your test light to see if your getting power to each of your GPs.
or atleast test one on each bank to make sure its not a blown fuseable link.
It could also be that the connectors are no good. I replace them often for customers with regular female blade connectors, and I suggest using heat shrink tubing too.
It could be the controller itself too. Are you getting any codes?
Does the truck smoke while your cranking when its hard starting?
Supply pump working? Fuel filter been replaced?
 

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Hard starting

I know I new here and to the Chevy Diesel, But I had the same problem with my other Diesel, it would crank and crank Fast also, well long story short I put new batteries and it fired right up, I couldn't belive the other ones would turn pretty fast but not as fast as the new ones
 

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Discussion Starter #4
use your test light to see if your getting power to each of your GPs.
or atleast test one on each bank to make sure its not a blown fuseable link.
It could also be that the connectors are no good. I replace them often for customers with regular female blade connectors, and I suggest using heat shrink tubing too.
It could be the controller itself too. Are you getting any codes?
Does the truck smoke while your cranking when its hard starting?
Supply pump working? Fuel filter been replaced?
1. I'll see what I can do - not much room in there
2. connectors seemed ok
3. No codes
4. Doesn't smoke until it starts running - then smokes like crazy
5. I can hear the pumps running - not sure on fuel filter

As for the other answer about the batteries, its possible, the current pair of red top optimas are 10 years old, but still have a good charge to them
 

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I had a problem with it not spiining over fast enough with the factory gear reduction starter, so i went and got one for a 6L, bolts right up and starts much faster.
 

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If there's no smoke at the tailpipe while cranking then there's no fuel being delivered. Either because there is a problem with your IP or you don't have sufficient cranking speed for the aforementioned reasons, starter or batteries.
 

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Discussion Starter #7
If there's no smoke at the tailpipe while cranking then there's no fuel being delivered. Either because there is a problem with your IP or you don't have sufficient cranking speed for the aforementioned reasons, starter or batteries.
It does eventually start and runs fine once it does warm up, so it is getting fuel. It runs really rough initially then settles in as it gets hitting on all cylinders.

Thats why I suspected the glow plugs. Starter should be in good shape, it was checked out last year after one of the bolts sheared off - that was expensive :(

Looks like batteries are the thing to check - I guess I can't gripe after 10 years on this pair
 

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#1 cause of hard starting is slow cranking speed, due to bad connections, bad cables, bad batteries, bad starter, not necesarily in that order.

And, guess what? - cold weather only serves to aggravate the problem.
 

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Discussion Starter #9
#1 cause of hard starting is slow cranking speed, due to bad connections, bad cables, bad batteries, bad starter, not necesarily in that order.

And, guess what? - cold weather only serves to aggravate the problem.
Yup - oh joy. And I just put a voltmeter across the batteries, a nice 12.26 volts. Time to trace cables, oh joy.

Although why would it hit on some cylinders, but not all?
 

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Weaker compression in some cylinders, takes longer to get firing in them.
 

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That's unloaded voltage - need to check voltage with a 200amp min load on.

Turn IGN key on, headlites, blower motor, then check again as wait to start lite is on

Inj Pump does not meet inj timing\pressure specs below certain rpm, and PCM does not manage injection properties well on low voltage.

Cylinder operating temps do not stabilize quickly at cold.

Injectors do not deteriorate at same rate.

SS connectors at glow plugs deteriorate, oxidize.

At slow crank, any and all defects will evidence themselves - cold makes it worse.
 

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After changing out my glow plugs last fall, (I only had 3 that were working) I noticed that with all 8 working I could see my volt meter drop down alittle during each glow cycle, I also can see a slight dimming of my running lights. Never saw any of this when only 3 were drawing current. Are you seeing any change in your volt meter during the glow cycle?
 

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Rigwatcher I was looking for a started that would spin the 6.5 faster,is the one from a 6 liter chev that muck faster?
 

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Discussion Starter #14
After changing out my glow plugs last fall, (I only had 3 that were working) I noticed that with all 8 working I could see my volt meter drop down alittle during each glow cycle, I also can see a slight dimming of my running lights. Never saw any of this when only 3 were drawing current. Are you seeing any change in your volt meter during the glow cycle?
Yeah the meter drops to 10v or so while the plugs are pulling current, then back up to 12 once the relay turns back off.
 

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way faster... starts it before the engine has made a complete rev, or seems like it. I dont know how long it will last if you had extended cranking times, but its also a lot cheaper than the G.R. factory model. I think mine was 140 CDN.

Dont take my word for it that its off of a 6 litre, thats just what the parts guy told me when he handed it to me.
 

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Might drop to 10v at the glow plugs, but should not drop below 12v at
battery(s).

With good battery(s)....................
 

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Discussion Starter #17
Might drop to 10v at the glow plugs, but should not drop below 12v at
battery(s).

With good battery(s)....................
Thats at the voltmeter in the dash - I cant run around to the batteries fast enough from the ignition switch, and the relay doestn' stay on long enough after the first cycle to get a good reading - i see around 11.4 at the batteries, but its a digital meter that doesn't track that fast so it might be a bit lower.

The grounds I've found so far are all good and tight, the cables feel ok.

Any good way to test the battery theory without spending $300 for a pair of new ones? I hate to buy new ones needlessly.

At this point it looks like the batteries need more thorough checking, the starter needs checking, and a compression test. I took a few pics for people that are interested in how crazy the hummer engine layout is - I am NOT looking forward to doing the compression - #4 and #7 plugs are nightmares, and 5, 6 and 8 aren't much fun either.

On the plus side I FINALLY found a very annoying rattle that has been driving me nuts for some time - loose heatshield just to the rear of the exhaust manifold heatshield.

I'll put a link up in this thread when I have the pix uploaded.

Thanks everyone for the input so far.
 

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Discussion Starter #18

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Take it to autozone for a free battery-load test.

Turn on everything but the engine, place the red lead on the (+) battery post, black lead on (-) battery post, should measure +12.6v

Place the black lead on the engine, dvm should read the same.

Place the black lead on the body, dvm should read the same.

Place the black lead on the (-) batt post, place the RED lead on the ALT term, should read (+)12.6v

Place the red lead on other successive points of interest, dvm should read (+)12.6v.

What you're tracing is connectivity continuity - find where the voltage reads lower, and you've found a problem.

Dosn't matter whether is is in the ground (black, -) path or the Positive (red, +) path - voltage should not drop more than a few millivolts.
 

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The Inj Pump does not meet inj timing\pressure specs below certain rpm, and PCM does not manage injection properties well on low voltage.
Additionally, low voltage during cranking will also cause LONG CTIMES, and a weak head and rotor that may already be putting up low cranking deliveries will be further lowered by long CTIMES and slow cranking speed. To the point that it may take several rotations before it actually delivers any fuel.
 
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