Truck died and won't restart - the diagnosis begin

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rationull

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Hooked up a fuel pressure gauge again just now. After a few key-on cycles it read close to 50 PSI so that seems fine. When cranking the pressure dropped into the 30-40 PSI range and would cycle a bit as the engine cranked, so it seems like the injectors are firing. Not sure if 30-40 PSI while cranking is "good enough" but it seems like I'd get something from the engine at that pressure. Right?
 
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Can you pinch the return line and see if you can keep fuel pressure higher. Unless you have really weak spark. It's starting to look like a compression check to see if valve timing is right might be in order.
 

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I don't think I can pinch the return line, it's all metal, fuel line to rail is connected with a flare nut. It seems like the pressure was still high enough while cranking to make SOMETHING happen in the engine bay. So it could be spark timing (bad distributor rotor) or cam timing. In order to check valve timing via compression, would I even need to check multiple cylinders or just one?
 
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There should be a rubber hose section in the return line under the truck that you can get to #6 here http://www.genmotorinfo.com/FullImage.as...=970825TC03-151. Your fuel pressure seems low, but seems like there's enough pressure it would attempt to fire. I wouldn't worry about starting fluid harming anything. Or if you want to get adventurous carefully pour a little gas past the throttle body. Use caution. I think you'd want to test at least two nonadjacent cylinders maybe on different banks to see if all cylinder are too low because of valve timing.
 

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The fuel that came out when I drained the pressure gauge sure smelled like fuel, and considering the truck ran and drove fine the day before it died (and just died w/out sputtering) isn't timing (either ignition or spark) more likely than fuel (pressure or contamination) at this point? If fuel is still a question and I can do starting fluid safely, maybe that's the best option to rule it out once and for all, because everything I've seen so far from fuel seems "good enough" not to be causing the no-start at least in my view.
 
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Given that you need air, fuel, spark, compression, timing to start the vehicle, which one have you *completely* ruled out so far? The only thing that has been ruled out is compression because the car was running fine and died in the middle of road. You won't lose compression in all cylinders like that with zero warning. You think it has fuel and spark or at least some fuel and some spark. I just got an idea. Can you disable the ignition completely by taking the fuse out or by disconnecting the coil input or something like that? Then crank and see if you feel difference. I also think that if the timing was very bad, you would have misfire galore if the air/fuel mixture was igniting. Have somebody put his hand on the tail pipe and see if he can feel the pulse of air coming out when you are cranking. Everything else is still suspect. If you want to spend/waste some money, why not new rotor and cap if the old one has many miles on it? I know it is frustrating but I think you really need to approach this rationally and methodically.
 
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Right if the valve timing (and ignition timing and compression) is off enough the engine won't start and won't necesarily backfire either. His fuel pressure is a little low, we aren't sure about spark quality, timing, compression or much of anything really at this point. Another question (although I'm sure he tried it) has the throttle been open to mid throttle when cranking? Sometimes that will alter the A/F ratio to get some cylinder firing when fuel supply is off.
 
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Originally Posted By: Vikas
But in that case, giving 1/4 gas pedal could have started the car. It turned out that most of us have now forgotten the old tricks of starting cars when we had chokes and carburetor but sometime they are useful in diagnosis!
Already suggested that!
 

rationull

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Originally Posted By: Vikas
Given that you need air, fuel, spark, compression, timing to start the vehicle, which one have you *completely* ruled out so far? The only thing that has been ruled out is compression because the car was running fine and died in the middle of road. You won't lose compression in all cylinders like that with zero warning. You think it has fuel and spark or at least some fuel and some spark. I just got an idea. Can you disable the ignition completely by taking the fuse out or by disconnecting the coil input or something like that? Then crank and see if you feel difference. I also think that if the timing was very bad, you would have misfire galore if the air/fuel mixture was igniting. Have somebody put his hand on the tail pipe and see if he can feel the pulse of air coming out when you are cranking. Everything else is still suspect. If you want to spend/waste some money, why not new rotor and cap if the old one has many miles on it? I know it is frustrating but I think you really need to approach this rationally and methodically.
No disrespect, but I am trying to go at this rationally and methodically, and honestly it's not that frustrating -- I just don't have that much time for this right now and the truck sitting doesn't cause me any problems so I'm taking my time. I don't think compression has been ruled out at this point, but a compression check (at least of easily accessed cylinders which should be enough for this purpose) is on the list now. The reason I thought cap/rotor was a good idea was because they are probably old as the hills and are apparently a known problem on these engines. With the talk of a broken timing chain messing up valve timing, a compression check makes sense before taking the time to do the cap/rotor (only because they're a PITA to get to). But the compression check hadn't been suggested and hadn't occurred to me before the cap/rotor talk. I realize that fuel is still suspect at this point, but I have verified fuel pressure at the rail that is affected by cranking. It seems unlikely that fuel pressure is the cause, then, because it seems like after a few cranks there'd be enough in at least a few cylinders to attempt to fire -- and if low fuel pressure were the problem I would've expected the engine to at least sputter rather than die suddenly. Water in the fuel is still a possibility I suppose, and I could throw a new filter on but I think the evidence is stronger for ignition. Agree/disagree? If I'm just over-complicating this or ignoring the obvious then starting fluid would probably be a good way to close the case on fuel. I initially didn't think a busted timing chain was likely because it seems like the engine would crank more quickly without having to drive the valve gear and work against compression in all cylinders, and it cranks normally AFAICT. My expectations could be wrong here, though. If I take the upper intake off to get to the ignition parts, I will also be able to see whether valves are moving (or the dist rotor for that matter) when the crankshaft is turned manually, which would rule out a broken timing chain (but not a sufficiently jumped one).
Originally Posted By: SteveSRT8
timing chain breaking will kill it right in the middle of the road. Is this an interference engine?
I would've assumed it's not (given it's a big, low compression engine) but I've found contradictory info online. According to some it is interference on the intake side.
 
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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?
 
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rationull

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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?
To my ears, it does sound completely normal when cranking. And I've heard it cranking quite a bit in the past due to hard warm start issues.
 
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I don't suspect that the chain broke entirely, just possibly jumped time. As you seem to have some spark and signs of injector pulsing. That's all speculation at this point though. I don't think you would necessarily be able to hear a difference in a V8s cranking that was out of time. It'd be good if you could get any of a spark tester and timing light on it, spray a little starting fluid in the intake, compression test and maybe if you can constrict return line to kill the suspense smile.
 
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How would you suddenly lose compression in all cylinders to prevent it from starting? A nice long stick in the spark plug hole will tell you if the cylinder is reciprocating. That will at least rule out broken timing chain. Block the exhaust with paper and tape it and see if it gets blown away during cranking (assuming you have no helper around). That will tell you that engine is breathing air which rules out blocked intake passage or zero compression. If you print this topic, you will find probably half dozen or more different ideas and some of them need no new tools or very little work. I still think you have very poor ignition and the spark that you saw is just not enough to fire under the compression as you said the car did not die as if running out of fuel but rather running out of spark.
 
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Originally Posted By: Vikas
How would you suddenly lose compression in all cylinders to prevent it from starting? A nice long stick in the spark plug hole will tell you if the cylinder is reciprocating. That will at least rule out broken timing chain.
No it won't, and don't stick a stick in your spark plug hole. The pistons are going up and down regardles of timing chain operation. I also would rule out ignition (cap, rotor, your suspect coil) before anything else. Just because it sparks outside the cylinder does not mean it will spark in the cylinder. Due to compression pressure it takes much, much, much more voltage to cause a spark inside the engine then outside, even with small gaps. Outside the cylinder, the plug wire should be able to jump a half inch gap or more to a good ground easily.
 
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I have seen condensation from the AC hose dripping on the dizzy cap cause corrosion in the distributor. This caused a no start condition in the truck I was working on. I would replace the cap and rotor just because it probably hasn't had a tune up lately. If the sprak plugs are old might as well complete the tune up. Ive heard of a hole burning through the cap and the spark arcing to the dizzy shaft.
 

rationull

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I just went outside and did a couple things. First, I taped a paper towel over the exhaust pipe to see if it would come off when I cranked the starter -- it did. While I was cranking I varied accelerator pedal position (per suggestions above) because I think I only tried to start it before with the accelerator all the way up or all the way down, and it occurred to me that WOT might be a "flood clear" mode and so useless for diagnostics. When I was varying the pedal position I got a little bit of feedback from the engine. I wouldn't say it was trying to start, but it was definitely a sound of "life". It seems like the cranking sounded a bit different too which could've been caused by whatever pathetic combustion was going on or could just be me being tired. When I went back around to pick up the paper towel I smelled raw fuel in the exhaust. I think this is more evidence that fuel isn't the problem (again, taking into account how it died originally).
Originally Posted By: mechanicx
It'd be good if you could get any of a spark tester and timing light on it, spray a little starting fluid in the intake, compression test and maybe if you can constrict return line to kill the suspense smile.
I already hooked up a timing light just to see if it would flash, but I can't use it to check timing b/c there's no mark on the pulley -- timing has to be checked with a scanner (and not just any scanner). Spark tester might be interesting but won't tell anything about timing.
Originally Posted By: Vikas
If you print this topic, you will find probably half dozen or more different ideas and some of them need no new tools or very little work. I still think you have very poor ignition and the spark that you saw is just not enough to fire under the compression as you said the car did not die as if running out of fuel but rather running out of spark.
I'm trying to go through these suggestions. To take your earlier approach, here's my take on the various possibilities. Please anyone correct me if I'm wrong. - Air: I'm considering this ruled out because the intake is clear and the engine is apparently pumping air. - Fuel: I think the evidence is against this one but if anyone still thinks I need to try starting fluid I will do that. - Spark (strength and timing): Not ruled out, can test with spark tester or just replace components. - Compression: Not ruled out. Will do a compression check on at least a few cylinders as the next step. - Cam timing: Not ruled out but compression check confirm or rule this out too. I won't be able to touch it for a few days at this point but next weekend I should have some solid time in the daylight, when I'll check compression, and I can go get starting fluid and a spark tester if that would still be a good idea. Otherwise I'll probably start taking apart the ignition and at least see how it looks.
 
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