86 951 randomly shutting off.

jamess2 · 06-02-2014, 09:58 AM

I went out to go to lunch on Friday and the car refused to start. It would crank and idle for just a second and die. I finally got it going and while running could here a huge air leak under the intake. I know if its bad enough a boost leak will cause weird cranking and running issues. Once it started I was able to crank it over and over and it was fine. After my shift ended I cranked it let it idle for about 10 minutes and drove it around in my parking lot. I get out on the road to go home and it dies and wont restart. I finally get it going again and make it back to my work and leave it in the parking lot over night. The next day I pull intake in parking lot and find a broken nipple on the cycling valve and find a few minor leaks at the AOS. I fix them all. The car cranks, idles smoothly and ran fine all evening. I drive it over the week end, everything fine. I head out for work this morning and the worst place possible it just shuts off. I jumper the dme relay and still no start but I can hear fuel running through the rail. I pull the jumper reinstall the dme relay and the thing cranks and I'm able to drive it back home. When I got the car it was non running and I have repaired the computer,bypassed alarm, installed a new injector harness, new dme relay, new timing belt, new tial waste gate, tie rod ends, replaced the oil pan, replaced the turbo and all kinds of other random bits and have daily driven the car pretty much since March with no problems until now. It had Lindsey chips,3.0 bar regulator, manual boost controller and tial waste gate for mods other than that the car is stock. Any ideas of what I can check?

Lapkritis · Lapkritis's Garage

Quote:

Originally Posted by jamess2

Once it started I was able to crank it over and over and it was fine.

I'm confused. Cranking generally means the engine not starting but the starter just cranking without the engine firing to life. See here for how to describe this accurately:

jamess2 · 06-02-2014, 12:34 PM

It would crank stumble and die then went to just spinning over with no stumbling or any thing the starter was turning and the car wouldn't crank

Lapkritis · Lapkritis's Garage

Starter turning but car won't crank is a contradiction unless your starter has fallen off the transmission but maintained electrical contacts through some miracle or your starter/flywheel have stripped teeth.

I believe what you're describing is a "crank, no start." The engine spinning is the engine cranking but not reaching running condition (the show stops entirely if you stop the starter from cranking).

No crank, no start is when the engine does not spin when requested at all (not cranking)... essentially nothing happening when the key is turned to the starter engagement position. This is the same result from the starter as when you have no battery in the car at all. Completely dead.

Crank but no start? I would check fuel pressure at the rail and also confirm spark from the injectors. Nothing else to check until you know what those two things are doing when you have a no-start condition.

jamess2 · 06-02-2014, 01:39 PM

Ok let me see if I can be more specific. When I tried to command the car to start with the ignition key, the engine under the hood cranked over and started. It immediately stopped as if I would have commanded it to with the key. Then when I tried to crank again it would spin over ( the crank in the engine was turning) and it would refuse to start. I eventually got it to run...and it seemed fine after that then when I tried to get it home after idling in the parking lot and driving around in the parking lot for quite a while I tried to make the commute home. As soon as I pulled out in the road I made it about a 1/4 mile before it stopped running. After setting for a minute it cranked (as in it was running under its on power) and I was able to get it back to my work it shut off again and I coasted into the parking lot. The next day I pulled the intake and fixed a large vacuum leak and put it all back together and the car ran fine all week end then on the way in this morning it shut off with out warning. I tried cranking the engine and it would not. It would spin over but not start. I jumped out of the car and bypassed the dme relay, still would not run and I could hear fuel rushing thru the rail. I then removed the jumpers and reinstalled the dme relay and the car cranked as in the motor sprung to life and I was able to drive the car back home.

Lapkritis · Lapkritis's Garage

Ah yes, there is the confusion. Cranking does not mean the same as running as a general rule. Cranking is only when you are operating/commanding the starter to turn with the key.

I would check for spark at the injectors, fuel pressure at the fuel rail and also signal to the fuel injectors (LED test only - regular test light will blow your computer). I would guess the problem is with your reference sensors but that is what the tests will help isolate.

kdollar · kdollar's Garage

Possible faulty AFM. I had one that would start cold just fine but after warming up it would
cut off similar to yours.

jamess2 · 06-04-2014, 01:04 PM

Thanks for the useful reply. I really appreciate the suggestion and will try and test the afm.

DannoXYZ · 06-06-2014, 03:25 PM

1. Manually test AFM wiper-track with voltmeter by moving flapper-door by hand slowly. Voltage should increase smoothly with no drop-outs. Should be around 0.75-0.85v at idle to 4.5v at max opening. If you find dead-spots, it may need bending the wiper-needle over to an unused area. I find it's easier to just slot the holes for the circuit-board and slide the board over.

2. test speed/reference sensors. Use oscilloscope and measure waveforms. Should match the following image.

3. also a good idea to go through each test in the DME/KLR Test Plan manual in order. Some issues may point to a certain symptom & component, but the actual problem may be caused by something else up the chain.