96 Cobra, Weird No start issue.

[Tyler72]

Hey guys, I'm posting this for a good buddy of mine who has a Cobra that's almost exactly like my old one. A little background on the Car. It's got an MMR engine with around 8.5:1 and a D1 procaharger running 17lbs if boost. Everything was going good, he was driving home and got on it just a little, not full throttle blast or anything like that. He said the car started missing and back firing out the exhaust and continued to loose power. He pulled over and the car died and would not restart. While turning it over, everything sounds normal except for it will randomly pop out of the exhaust. I've got quite a bit of experience with these things but so far I'm stumped. It has no codes at all. My first thought was that a tensioner or guide broke and it jumped time, so we pulled the valve covers and inspected everything. It's in time, and all the velve springs and followers appear to be in good shape too. The crank reluctor looks fine, and obviously the upper cam gears are good too. We did a compression test, and everything looks good there. The number 8 cyclinder is a lower but it appears to be a sticky valve issue, maybe some carbon on it or something, but nothing to keep it from starting. Fuel pump comes on, but we didn't check fuel pressure. But the way it happeded, I don't think its a fuel issue.

Any ideas?

 

[Attaus]

This happened to me before.. same setup on slightly less boost.. pulled over, scratched my head, and it started again 5 minutes later. I have no idea what caused it. A month later my tensioner jumped off my head.

 

[Tyler72]

Update:
Still no luck. After seeing that everything mechanical was ok, he decided to have the upper intake manifold and valve covers powder coated. We finished putting the car back together this morning but still no dice. This time however, I had my x-cal so I did a quick data log of the rpm while cranking. It's pretty erratic... it jumps al around from as low as 30 rpm to as high as 80 rpm, sometimes it hangs at an exact amount such as 30.00 or 40.00 and once it even hung at 00.00 for a few seconds while the engine was turning over. I also noided the injectors and got inconsistent fire on them. The coils don't really fire at all. I mean, every now and then you'll get a spark, but it's not good. We replaced the crank sensor, and the cam sensor, and checked all of the main harness connections (at the computer and at the passenger side bulkhead connector at the firewall) as well as checked the CKP connector itself. Didn't notice any obvious issues at any of those. I even pulled the chip out and inspected that. The theft light flashes when the door is open but goes off when the key is turned on, just like it should.

I'm really at a loss.

I guess the next step is to find wiring diagrams and check all if the pcm grounds and powers and then ohm out the wires that go to the crank sensor.

Any other ideas that I might have over looked?

 

[Tyler72]

So I hate it when someone starts a help me figure this out thread & never replies when they figure it out... Turns out the crank reluctor broke! It cracked all the way around the "hub" that fits around the crank and the ring was no longer attached. When we pulled the timing cover off, the outer portion of tge reluctor hit the ground... Replaced it and all has been well now.

 

[98BABCobra]

So I hate it when someone starts a help me figure this out thread & never replies when they figure it out....

I also hate when this happens so thanks for posting what the problem was.