Truck died and won't restart - the diagnosis begin

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Sorry but this is going to be a long one! Short version: Truck died and won't restart. Seems to have fuel pressure and spark. It is a mystery to me, but ignition coil MAY be bad if you can trust a multimeter to measure as low a 0.1 ohms correctly. Should I replace the coil or look elsewhere? Last week when I was setting off in the morning to go get the family tow vehicle's ABS module scanned (light is on), the truck decided it didn't want to go to the shop and died about half a block after I pulled out of my driveway. Would not restart. Of course, we live on a 55 mph highway and on a hill so I couldn't push it back home. Had to call for what seems like a pretty ridiculous tow to get it back up to the house. I'm in the middle of trying to diagnose it, have gone through the first few steps, and wanted to get a reality check before I start throwing parts at it. The vehicle is a 1999 Suburban 2500 w/ the 454. What happened: Started the truck up and idled it for probably 2 mins, checking under the hood to make sure all was well before leaving. Accelerated to probably 30 mph and the engine died. Coasted off the road. The truck would crank at normal speed but not restart. Looked under the hood -- no obvious problems. Plugged in OBD2 scanner, no codes. The symptoms: - Truck will still crank just fine, normal speed. Battery is fine (hooked it up to my battery tender to be sure, but it holds voltage well). Will not start up. There may be an occasional quiet pop but otherwise it seems pretty much completely dead. No backfiring AFAICT, no sputtering or any indication it wants to fire. - Fuel: Measured fuel pressure at the rail's test port. Plugged the gauge in and turned the key on (did not crank) and it immediately hit 45 PSI and stayed steady. I don't know what the spec is but this seems high enough to me that it should at least start and [try to] idle. I can't rule out fuel injector problems (it has an issue with warm starts probably due to leaky injectors but has always run just fine with no sputtering, bucking, or lack of power). I only keyed it on once so the pump ran for maybe 2 seconds. In retrospect maybe I should've cranked or keyed on multiple times to see how high it would get but I did not. I can borrow the gauge again if this seems suspect. - Spark: Put a timing light on the #1 cylinder plug wire and cranked -- the light flashed. Pulled the plug from another cylinder and grounded it to the block and cranked. It did spark. Seemed like it may not have been sparking quite often enough but hard to tell given the ground connection could've been [censored] and it was probably only running a few hundred RPM on the starter. DID at one point see a small flame pop from the open spark plug hole (presumably fumes ignited by the spark) so I guess there is some fuel actually making it into the cylinders. - So spark is there but maybe weak? Tested ignition coil as outlined in the [censored] Chilton's book I have. 2 of the 3 tests passed, but the third technically failed. Resistance between two pins in the harness connector is supposed to be "0.1 ohms". Tested .5-.7 ohms with my Craftsman multimeter and .4-.5 with the (probably not as good) cheap multimeter that came with the loaner fuel pressure test kit I was using. So, technically this is a fail but I'm not sure how accurate consumer multimeters are in the < 1 ohm range anyway. Full disclosure: The day before the incident, I replaced the serpentine belt tensioner. I didn't drive the truck after replacing it, but I did run it and it idled fine (just like it did the morning it died, before I pulled out onto the road). Nothing is wrong with the belt or pulleys AFAICT. There is a thick cable near the tensioner pulley that goes from the positive battery terminal to the alternator (the only connection that goes to the alternator I can see) that is a little worn -- looks like it may have contacted the tensioner pulley at some point in the distant past -- but I can't see bare wire and don't see how that would cause this problem anyway. So at this point I can see a few options: - I can replace the coil. It's a single item that would simultaneously effect all cylinders. But there is visible spark and I'm not confident in a multimeter's ability to measure 1/10 of an ohm. - I can try to to more/better diagnosis related to fuel pressure. - Something else I'm missing entirely? E.g. could it be on the air side? Maybe a failed MAF sensor or something causing the ECU to not inject nearly enough fuel?
 
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How many miles? Sounds like it might have jumped timing ,Did crankshaft timing sensor get bumped when the serpentine belt tensioner was changed?
 
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rationull

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Just under 170k miles. I don't think that's possible .. the crank position sensor is way down toward the bottom of the engine pretty far from the tensioner. Although it is pretty dirty down there (oil and I think some coolant from another problem I need to take care of) and I suppose it could've gone bad. Not sure if that would throw a code or not, considering the truck was running fine right up until it died.
 
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Spray some starting fluid, or brake clean (be sure the can does not say "non flamable" like the CRC Red can) into the throttle body and see if it starts. 45 seems a bit low, 55+ would be normal. If it still does not start. Just try putting a new cap and rotor on it... Yes, you said there was spark lol.. The bad cap and rotor problem has bit more than a few professional techs.
 
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One I seen recently on a 4.3L was the Dist Rotor was conductive. You could put a ohm meter on it and see resistance between the center and the plastic! Plastic should not have measurable continuity. it could not be detected with a spark tester or anything, but the spark was jumping to the wrong cylinders while cranking.
 
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Fuel filter ,,or weak fuel pump ,,,If you can get all the plugs out and they are wet from fuel then it is module /coil -spark related
 
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One thing that will keep an engine from starting and not always set a code is the MAF sensor or maybe the MAP sensor. Try unplugging the MAF sensor and starting and then the MAP. also check the vacuum tube to the fuel pressure regulator for leaks as your fuel pressure seems a little low.
 
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Some of the GM v8s have a problem with the gear at the bottom of the distributor shaft wearing out. Pull it and look. Don't just stop with the rotor and cap.
 
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A quick search of the net says FP should be 55-61psi. Also take a mechanics stethoscope or long extension and see if you can hear the injectors clicking (if they're accessible - I can't remember).
 
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I diagnosed several of those Vortec engines back in the day. Starting fuel pressure needs to be 60 psi give or take 5-10%. A crank sensor will cause a no start, but I don't know if it would kill it.
 
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You have verified that there is actual spark at the spark plug. You have verified you have fuel pressure. BUT you have NOT verified that there is fuel inside the cylinder. It seems that the injectors are not firing. Something which allows injector to fire is not set. I am presuming you have already looked at all the fuses etc. Since the car died right on the road while running, you can rule out mechanical issues such as bad compression etc. If only one or two injector were giving you problem, car would still run but badly. In your case, computer is NOT turning on the fuel or something in the wiring has shorted. You are right 45psi should be enough to get it started. When you have fuel pressure gauge hooked up and are cranking the starter, do you see any activity on the gauge? If it stays rock steady, it is likely that the injectors are not firing at all. You can rent/buy tool (noid light??) which tells you if the injectors are firing but even after knowing that they are not firing, you have to find why.
 
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Originally Posted By: heyu
Fuel filter ,,or weak fuel pump ,,,If you can get all the plugs out and they are wet from fuel then it is module /coil -spark related
When was the last time you replaced the fuel filter underneath on the frame? (drivers side IIRC)I had a 99 5.7 that did the same thing which was caused by bad gas (water). Replaced filter and cleaned fuel rail with techron.
 
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Possibly a bad fuel pump. 55-62 psi is spec engine off not cranking. As soon as the injectors trigger that pressure will drop so starting out with only 45 psi is possibly not enough pressure even cranking 200 RPM to feed the multec injectors. Give it whiff of starting fluid. If it fires you will get a better idea whats going on.
 
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Originally Posted By: Trav
Possibly a bad fuel pump. 55-62 psi is spec engine off not cranking. As soon as the injectors trigger that pressure will drop so starting out with only 45 psi is possibly not enough pressure even cranking 200 RPM to feed the multec injectors. Give it whiff of starting fluid. If it fires you will get a better idea whats going on.
Yep. I agree 100% with Trav. If she won't start with ether, you have a non-fuel problem. But I'm gonna agree with most here, it's probably your fuel pump, fuel regulator, fuel injectors, etc. They are all known problems with these truck. My brother has a 1999 K2500 Suburban with the 7.4L (454ci). He just recently replaced all the injectors, FPR, and fuel pump in his @ 135k miles.
 
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rationull

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One thing I didn't mention is that I replaced the lower intake manifold gaskets about 8 months/1200 miles ago. That figures into some of this. Good point on the dist rotor and cap -- they are a pain to get to on this thing but I can replace them if necessary.
Originally Posted By: mechanicx
One thing that will keep an engine from starting and not always set a code is the MAF sensor or maybe the MAP sensor. Try unplugging the MAF sensor and starting and then the MAP. also check the vacuum tube to the fuel pressure regulator for leaks as your fuel pressure seems a little low.
I should be able to try the MAF/MAP unplug. I replaced the FPR when replacing the intake gasket, and I'm pretty sure I replaced that hose at the same time. I can also try to get a mirror back there to check it, or check it if I end up having to pull the upper intake off for some of the rest of this stuff.
Originally Posted By: Boomer
Some of the GM v8s have a problem with the gear at the bottom of the distributor shaft wearing out. Pull it and look. Don't just stop with the rotor and cap.
That gear was in great shape when I pulled the distributor when replacing the intake gasket.
Originally Posted By: FL_Rob
For some reason,in the back of my mind a nagging thought says ECU. The voltages are showing correctly (Batt,alt)?
I did think of ECU as a possibility but it seems less likely than a lot of others. It would be easy to pull -- I wonder if I can get it tested at a dealer. Voltages appear to be fine where I've checked. I have not checked the alternator output voltage though.
Originally Posted By: The_Eric
A quick search of the net says FP should be 55-61psi. Also take a mechanics stethoscope or long extension and see if you can hear the injectors clicking (if they're accessible - I can't remember).
This is a good idea ..there's one or two injectors that are accessible with a stethoscope w/out disassembling anything.
Originally Posted By: Nyquist
I diagnosed several of those Vortec engines back in the day. Starting fuel pressure needs to be 60 psi give or take 5-10%. A crank sensor will cause a no start, but I don't know if it would kill it.
Maybe I need to borrow the test gauge again for some more diagnosis ..
Originally Posted By: Vikas
You have verified that there is actual spark at the spark plug. You have verified you have fuel pressure. BUT you have NOT verified that there is fuel inside the cylinder. It seems that the injectors are not firing. Something which allows injector to fire is not set. I am presuming you have already looked at all the fuses etc. Since the car died right on the road while running, you can rule out mechanical issues such as bad compression etc. If only one or two injector were giving you problem, car would still run but badly. In your case, computer is NOT turning on the fuel or something in the wiring has shorted. You are right 45psi should be enough to get it started. When you have fuel pressure gauge hooked up and are cranking the starter, do you see any activity on the gauge? If it stays rock steady, it is likely that the injectors are not firing at all. You can rent/buy tool (noid light??) which tells you if the injectors are firing but even after knowing that they are not firing, you have to find why.
I think there is SOME fuel getting into the cylinders, because of the pop and flame I saw when cranking for the spark plug test. It could be that it's not firing the injectors at the right time or often enough, but I think the same could be true for spark. I need to get an FP gauge again and check the pressure behavior while cranking. I actually haven't checked any fuses in the passenger compartment. Checked the under hood ones … but I should verify there are none inside that could affect this.
Originally Posted By: Doog
When was the last time you replaced the fuel filter underneath on the frame? (drivers side IIRC)I had a 99 5.7 that did the same thing which was caused by bad gas (water). Replaced filter and cleaned fuel rail with techron.
I replaced it a few years ago. The truck doesn't get a lot of miles but does a lot of sitting. I would do this just to rule it out but it seems like a waste since any problem the filter caused would show up as bad pressure at the rail, wouldn't it?
Originally Posted By: Trav
Possibly a bad fuel pump. 55-62 psi is spec engine off not cranking. As soon as the injectors trigger that pressure will drop so starting out with only 45 psi is possibly not enough pressure even cranking 200 RPM to feed the multec injectors. Give it whiff of starting fluid. If it fires you will get a better idea whats going on.
OK so bottom line right now: - I need to do some better diagnosis on fuel pressure and try some starting fluid (never done that before!). This still seems like the most likely problem to me given what I know so far. - I'm still a little curious about the coil. Gotta decide whether to just put this one back on or get a new one. I may be able to do some more diagnosis in the next few days but it might have to wait for the weekend.
 

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Originally Posted By: Phishin
Yep. I agree 100% with Trav. If she won't start with ether, you have a non-fuel problem. But I'm gonna agree with most here, it's probably your fuel pump, fuel regulator, fuel injectors, etc. They are all known problems with these truck. My brother has a 1999 K2500 Suburban with the 7.4L (454ci). He just recently replaced all the injectors, FPR, and fuel pump in his @ 135k miles.
The first thing that went through my mind when the truck died was "fuel pump" for this reason. I replaced the FPR when doing the intake gasket, but left the injectors alone. Maybe that was a mistake. But, pump seems more likely to me than injectors to cause the truck to go from "running fine" to "not running or starting". I know the pumps are a problem on these and for all I know this one is original.
 
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