V2Rocket

Yesterday I was driving along and came off a light, accelerated in 1st to about 6000RPM and suddenly the car went dead, instantly. Like 6000-0RPM in under a second.

At first I thought I might have popped a timing belt but I pulled to the side of the road and used a pencil to put a mark on the belt and turned the key and the marks went away, so the belt was good. I used my tire wrench to loosen the fuel rail cap, it had fuel pressure and some fuel in the tank. Pump was coming on. I swapped DME relays, still nothing. It just cranks and cranks and sprays fuel.

Towed it home last night and today been trying to diagnose a no-spark condition.

There is no spark from any of the plugs, and no spark when a plug is connected directly to the coil output. I swapped with a spare DME, still nothing. Rotor was on tight, cleaned off some dirt from the rotor and the contacts but nothing.

Getting 12v on both sides of the coil and primary and secondary resistance tests passed. Checked the speed/reference sensors, one was kind of wonky in readings on oscilloscope and so that was just replaced with a spare, still nothing. The other one tested fine for voltage and resistance.

Tach bounces, but on first crank it will go up to like 3000RPM indicated (not really though) and after that it will bounce. Tried switching them still does the jumping still no start.

Seems that the coil is getting power but is not pulsing. Cam timing is bang on. Ideas?

Once again I have replaced already:
DME Relay
DME
Ignition coil
Speed sensor

blown 944

check the rotor

V2Rocket

rotor is fine. the issue is for whatever reason the coil is not pulsing voltage. like i said, even hooking a plug directly to the coil doesnt get a spark.

blown 944

Are getting power to the coil while cranking??

V2Rocket

yea constant 12v

boostskillz

Crank position sensor or wiring for it, mine did this several times, turned out to be a loose wire in the crank sensor connector.

blown 944

obviously difficult to diagnose over the net

Not sure if the signal is being interupted for the coil. I am guessing not.

The carbon button could be bad in teh cap, the coil wire could be bad too

V2Rocket

dunno how this would be relevant but it died immediately after i hit the clutch to change gear. didnt even have time to do the 1-2 shift. makes me think maybe the clutch action jarred something? could a bump be enough to alter the gap or something of the sensors? they still test within spec though.

V2Rocket

the coil has 12 v as it should on either terminal but for whatever reason is not getting a pulse signal. based on my searching here, the black wire is constant power and the green wire is a switched ground. the green can either be a "floater", with no flow or ground through it, or a ground when the DME tells it to be. when the dme tells it to ground that is when the coil will pulse.

at this point i have checked as much of the wiring harness as i can (excepting the part that is hidden on the front frame member) but all the other electrical systems that run parallel to the coil's power (within the same wire bundle) work, including the rad fans (controlled with AC switch), headlights, HL motor.
all i can think of now would be to run a new wire between the coil and the main wiring harness, bypassing the factory coil wiring altogether and seeing if that works.

PeteL

I would keep looking at the ref sensors. They can fail just like that.
Probably a break in the wiring, or a bad connector.

KuHL 951

I was going to say the same thing until I re-read where he says it sprays fuel. A bad or disconnected ref sensor won't allow the fuel pump to engage similar to a bad DME relay. Sounds more like he lost a ground connection or DME failure.

V2Rocket

checked the ref sensors at the connectors for voltage oscillation and resistance and stuff and they checked out, swapped in a spare speed sensor because it seemed a little wonky and it was good.

connectors were cleaned and are in good shape.

i swapped to a spare DME almost first thing, still no spark unless both dme's have fried ignition circuits, then i will try my 3rd dme for kicks.

im thinking i might just try to dig into the wiring harness, find the pin-1 wire (pulse to coil) and run a new wire between the DME and the coil and see if that fixes it.

m73m95

Ignition system troubleshooting

V2Rocket

the dme must be getting a start signal because the fuel pump runs and the injectors all fire completely fine. does this mean that the problem is probably the ground for the coil?

m73m95

You checked both the primary and secondary resistance of the coil?

Can you check the voltage of the DME to coil wire for pulsing? unhook the wire from the coil, then test (with a testlight) between it and ground. Should pulse.

You can also check to see if that wire is grounded with a continuity tester (the "BEEP" setting on your multimeter). One lead on the wire, the other lead to the body of the car.