Thread: help diagnose engine dying

sounds like a bad crank sensor.

ever notice if the tach dropped to zero before it stalled out?

Could even be a failing MAF, weirder things have happened.

You can tap the sensor with a screw driver end or something when it is running good to see if it starts to stumble and die.

+1 on crank sensor.
Also, Autozone or O'Reilly will rent you a fuel pressure gauge for free if they have one.

I tried to narrow it down, although I didn't have an oscilloscope to hook up. I couldn't get it to stumble or die idling or driving normally, but if I rev the engine up to 4,000 RPM it would start to cut out like a rev limiter. But I don't think the PCM will rev limit at 4,000 RPM even in neutral. I put it in first gear and floored it and would get cutouts that were sharply on-and-off, not at all like a fuel pump getting weak which in my experience is more like running into a pillow as engine power falls off. Also I had my son sit in the back with his ear to the pump. There wasn't an audible indication the fuel pump was having trouble.

So I do think the CKP (service manual term) is a likely candidate. Service manual also shows it is a PITA to replace, requiring one pull and re-install the harmonic balancer. And if one pulls it, it should probably be replaced with a new unit as the rubber often fails with age. And belts. Maybe the tensioner too. Guess I should change the water pump while I'm in there . . .

I'm thinking I should be absolutely sure it is the crank position sensor first, given the work and expense involved. I was thinking of bringing an oscilloscope home from work and probing the 3X and 18X signals while revving the engine to 4K. I don't suppose there is an easier way to confirm the failure.

Originally Posted by Lifespeed

I tried to narrow it down, although I didn't have an oscilloscope to hook up. I couldn't get it to stumble or die idling or driving normally, but if I rev the engine up to 4,000 RPM.

This is because there is a rev limiter at 4k to keep you from over reving it and blowing it. The limiter is increased when in gear.. but there's still limiters

Originally Posted by BillBoost37

This is because there is a rev limiter at 4k to keep you from over reving it and blowing it. The limiter is increased when in gear.. but there's still limiters

Is there anything I can do to confirm the cause of the problem before spending time and money on this repair? It doesn't appear to reproduce on demand, but I know if I my son takes it out driving around it will leave him stranded.

Originally Posted by bonerjamz03

If a wannabe shade tree mechanic like myself can change the crank sensor I'm sure you'll be fine lol

I'm sure I will be, that wasn't the concern. I really prefer to diagnose rather than change parts based on a guess as to what is causing the car to die, likely as it may be.

thats just what a bad crank sensor does, stalls out driving randomly, it might fire right back up or it might fire up 30 minutes later, or once its real bad stalls and dont fire back up, you could try every morning for a week, then on day 7 it just fires up.

and the best part....it hardly ever sets a code for it. but we all know what it is here.

Originally Posted by Scottydoggs

thats just what a bad crank sensor does, stalls out driving randomly, it might fire right back up or it might fire up 30 minutes later, or once its real bad stalls and dont fire back up, you could try every morning for a week, then on day 7 it just fires up.

and the best part....it hardly ever sets a code for it. but we all know what it is here.

OK. Intermittent problems are difficult by their nature, so methodical diagnosis will probably elude me. For this job I'll likely change the harmonic balancer, tensioner, idlers, belts, water pump and supercharger coupler while I'm in there. The car has 173K miles and none of this stuff has been changed. But the engine has had synthetic oil it's whole life and burns very little. The transmission has had regular fluid changes and is showing no signs of trouble. The suspension was completely rebuilt with Bilstein struts, new springs, control arms, tie rods, sway bar links, etc.

The plan is for my son to drive it until he graduates college, which could be six years as he starts his senior year of high school this fall. Hope I don't kick myself for diving in and replacing all this stuff, about $500 in parts from the online GM dealer.

im a huge fan of dont fix whats not broken, no need to replace the balancer either. mines got 242,000 on it gaining daily.

if you got a pulley or two that dont spin free, or feel gritty when hand turned, change em. other then that let em roll till they squeak.

oh, free check here, crank related. its harness, make sure the belt has not hit it and rubbed a spot through. that harness does go bad, but your cars on the newer side for that to be failed. but its possible.

Originally Posted by Scottydoggs

im a huge fan of dont fix whats not broken, no need to replace the balancer either. mines got 242,000 on it gaining daily.

if you got a pulley or two that dont spin free, or feel gritty when hand turned, change em. other then that let em roll till they squeak.

I'm a huge fan of not digging in to things a second time, or having them fail out on the road. Water pumps all die, just a matter of time and miles. And 173K is a lot of miles. You may be right about the balancer, although I've seen lots of separate at the rubber. Idlers and tensioner are cheap and they always fail as well. Removing the balancer from the list brings it down to $340, pretty reasonable for maintenance. My labor, OTOH, I'm not at all happy about. Gonna make this a learning experience for my son. You want to drive, you have to pay one way or the other.

wow, this would be a 40 dollar repair for me. aka the cost of the new delco crank sensor.

this cost me 400 bucks, lol

My son and I replaced the crank position sensor, harmonic balancer, water pump, supercharger isolator and belts. The balancer had a long crack in the rubber, and we all know how noisy the supercharger gets over time. The old water pump bearing was starting to feel gritty, I'm amazed it lasted this long.

So . . . it hasn't died since replacing the crank sensor, but I've only driven it for an hour. My son is out of town for a week so it may not get much drive time. When I tried to get it to fail again (before replacing the sensor) one thing I noticed was the engine would sometimes cut out for less than a second under acceleration. It still does this with the new sensor. Does the engine die leaving the driver stranded with the new sensor? I don't know yet.

Is it likely the lack of crank sensor calibration procedure being performed could be an issue? Other thoughts on this momentary engine cut out under acceleration? Any way to do the CKP calibration with non-professional-price tools? I have a 2009 Cadillac also so willing to invest in a capable GM scan tool, right now all I have is MXTools OBDII scanner.