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?
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?
