Truck died and won't restart - the diagnosis begin

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I looked again at your fuel pressure test you posted earlier, and now manipulating the throttle gets some attempts of firing. I think the fuel pressure could be the problem. The fuel pressure is low and dropping too fast. Those engines often won't run without the right fuel pressure. It's really the only thing so far that's known to be off.
 
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It should basically run briefly on starting fluid or continue running as long as your spraying if it is a fuel supply problem.
 
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OK try spraying a good spray or two into the throttle and see if it tries to fire up. I don't mean to seem to say to spray it while the engine is cranking or running. Don't want to over do it and get a backfire smile.
 
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Originally Posted By: another Todd
Originally Posted By: SteveSRT8
timing chain breaking will kill it right in the middle of the road. Is this an interference engine?
If it was this the engine would not sound normal when cranking. It would sound like a drill motor, constant speed with no lopieness from each cylinders compression. Soooo, does it sound normal when cranking?
No matter where the cam stops there will be a few cylinders with the valves closed. Still SOME compression. Pull the dist. cap to verify rotation.
 
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couldn't he notice cam rotation if he takes off the oil filler cap and watches it while being cranked?
 
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We know he has cam rotation because he was getting spark at plugs (maybe weak spark though). We don't know if the timing might be off. We know his fuel pressure is about 10-20 psi low and drops fast, so that's a place to start.
 
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1) Check your timing. Run #1 cylinder to TDC on your vibration damper, remove distributor cap and see if the rotor is pointing at #1 on your cap. 2) Give just a whiff of ether directly into the throttle body. 3)Check for spark with your timing light across all 8 plug wires. 4) Trouble shoot from there.
 

rationull

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Originally Posted By: Vikas
couldn't he notice cam rotation if he takes off the oil filler cap and watches it while being cranked?
Nope -- oil filler goes into the cylinder valley, not the valve cover.
 
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Originally Posted By: mechanicx
We know he has cam rotation because he was getting spark at plugs (maybe weak spark though). We don't know if the timing might be off. We know his fuel pressure is about 10-20 psi low and drops fast, so that's a place to start.
Starting with what you know isnt right is always a good place to start. Common sense right.
 
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I think so too. At first I'd suspect the ignition (spark quality or timing) would be the most likely culprit, and he has some fuel pressure that you'd think it would at least try to fire up. But he's reported spark, and the fuel pressure reported is so far off that the engine wouldn't run right or maybe not at all and is worth looking into there.
 
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Originally Posted By: Trav
Originally Posted By: mechanicx
We know he has cam rotation because he was getting spark at plugs (maybe weak spark though). We don't know if the timing might be off. We know his fuel pressure is about 10-20 psi low and drops fast, so that's a place to start.
Starting with what you know isnt right is always a good place to start. Common sense right.
Originally Posted By: mechanicx
We know he has cam rotation because he was getting spark at plugs (maybe weak spark though). We don't know if the timing might be off. We know his fuel pressure is about 10-20 psi low and drops fast, so that's a place to start.
Agreed. Spec is 55-62psi after cycling the key a few times and his lower than that. Cranking results in it dropping to what? 35psi? These things will typically have 45+ psi at idle.
 
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Still should have enough F/P to at least run, though maybe poorly... Seen plenty of engines idle fine at 25psi, just go lean and bog down on acceleration...
 
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Originally Posted By: TFB1
Still should have enough F/P to at least run, though maybe poorly... Seen plenty of engines idle fine at 25psi, just go lean and bog down on acceleration...
These seem to be different... Can't explain.
 
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Originally Posted By: TFB1
Still should have enough F/P to at least run, though maybe poorly... Seen plenty of engines idle fine at 25psi, just go lean and bog down on acceleration...
My brothers Yukon Denali 6.0 died one day with pretty much the same symptoms. Pop and fire once in a while but wouldn't run. He had 35 PSI. Fuel pump.
 

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Not leaving this hanging, just haven't touched the truck again until today! Went out this morning and did the following: Sprayed starting fluid in past the throttle body and then tried to start it. Got some pops (maybe 1 per 3-4 seconds) and some vapor out the tailpipe while cranking but no start. So, different behavior but different enough to point to fuel as the problem? Doesn't seem like it to me but I don't know. Then I checked compression on cylinders 1 and 2 (front cylinder from each bank). The book I have inexplicably doesn't seem to contain the compression test specs but I got a solid 150 PSI on both cylinders which seems fine to me (9:1 compression ratio) and probably rules out valve timing. The plugs I took out looked fine I think (a little wet from the cranking) but the gap is a little wide (0.065 vs spec of 0.060). Not sure if that could contribute but I'm sure it doesn't help. Not looking forward to it but I should probably just replace them all. Then, I hooked up my timing light to a variety of cylinders and noted that while they were all firing, some of them seemed less frequent than others and one was firing at probably twice the rate of the others. Seems to me this is the clearest piece of evidence yet and it points to either the cap or the rotor. My current thinking is, then, that I should take off the upper intake and pull/inspect the cap and rotor. I feel like I should probably replace both of those, and the plugs and possibly the wires while I'm in there (although the wire sets can get kind of pricey so maybe I should test them instead). Not sure about the coil.
 

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You don't have to pull the upper intake to replace cap + rotor. Just lay on top of intake and you can get to them. I would replace the plugs. A lot of people say this engine runs better with a spark plug gap of .045 which is what I run on my 98 7.4L I have also replaced my wires and coil. You can do the same to rule those out as problems. Wayne
 
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