Shakoba

Hey everybody i just was looking for some advice on a no start condition on an 89 formula that has a 5.0 TPI setup. One day i went to start it up and let it run for few minutes then it just cutoff and now wont start. it has fuel to the rail with good pressure, it has spark and timing. I checked for injector pulse and it does not have it, but rather the noid light just stays on. I checked the V.A.T.S going to the ecm and it has a good 2.5v into pin B6. The car has brand new injectors, new fuel pump, new FPR, and recently a new ICM. I was thinking it could be the distributor not giving the reference signal but im not sure yet. a suggestion on how to test the dizzy and Any advice is appreciated

Rolling Thunder

See the attached photo of the ignition control module wiring. You'll see the ICM on the left and the ECM on the right. On the left you see the item labeled "pick up coil". That induces pulses as the distributor rotates that are sent to the ECM. This is what the ECM uses to trigger the fuel injectors and time the ignition. If your volt meter measures frequency, you could try and measure this signal directly. Also, this same signal can be used to trigger the ignition. If you disconnect the electronic spark timing (EST) line, the distributor will trigger off this signal. If you have spark, this signal must be present (not to say that its getting to the ECM).

Shakoba

Thanks for replying, and i appreciate the diagram. its certainly getting printed and filed. Do you happen to know the frequency that i should be looking for? I have also read that you can just check the resistance of the pickup coil through the two wire leads and if its between 500-1500 then it is good. mine read out at 759 ohms. also if it means anything my bank 2 injector fuse was blown; it was replaced and still nothing.

Rolling Thunder

Frequency output will be relative to engine RPM (revolutions per minute). There will be four pulses per rev. Frequency is cycles per second. so 500 RPMs = (500 RPMs * 4 pulses per rev ) / 60 (to convert from minutes to seconds) = 33 Hz.

Now a word of caution, because of how meters work and how impure the signal will be your meter reading may bounce around or not be 100% accurate to the engine RPM. The key is you should see something and short of looking at it with an oscilloscope will be able the best you can do for the moment.

Also their is one other thing i meant to ask. When you say you checked it with a noid light how did you check it? One side of the injector will remain at 12V while the other side gets grounded to trigger the injectors. Set your noid light up on the +12V side and it will never blink even if it is working properly.

Rolling Thunder

Also one other thing, while your coil may ohm out which is a good sign that signal is conditioned in the ignition control module before being sent to the ECM. Even if you have a good pulse from the coil, if your ignition control module is bad you may have no output to the ECM. That is the point I would try to measure. Unfortunately ignition modules are not particularly reliable in these cars.

Shakoba

The noid light i used was a two pronged device that plugged directly into the harness clip. i turned the engine to prime with the key and it lit up bright, then while cranking it dimmed slightly i think because of current draw. there was no pulse however, it just stayed on. I also have a new ICM so i don't think it that would be the source of the problem. is there a good way to check for a short to ground in the injector harness? i am wondering what caused the bank 2 fuse to blow in the first place.

Rolling Thunder

First if the ICM was recently replace I would still be suspicious of it. If for example the thermal paste was not applied properly it will fail in fairly short order.

As for as why the fuse blew? The circuit is fairly simple. Its simply 12V from the fuse block to the injectors and the the ground is grounded by the ECM. If you plugged a new fuse in and it did not fail the +12V side is ok (unless there was an intermittent short). If an injector coil was shorted that may cause a blown fuse? Could ohm out the injectors and wiggle the wiring harness.

bwiencek

That means that the ground side has a short - remember the computer is simply "grounding" each of the wires for the injectors to switch them on/off - if the noid light is lit up solid then you've either got a short somewhere between the injectors and the computer or a bad computer - try unplugging the computer - if your noid light still lights up then you have a short - if not then you might have a bad PCM.

Shakoba

I unhooked the computer and turned the key to prime. I plugged the noid light into each harness clip on the driver side bank and all of them illuminated the light constant. I then plugged the light into each clip on the passenger side bank and it had nothing. no light.

bwiencek

Well there you go - short on the ground wires leading back to the computer driver's side bank - just start tracing the wires back towards the computer and I bet you'll find the harness pinched/smashed or chaffed somewhere along the way. Without the computer to complete the ground circuit the grounding has to come from somewhere...

Shakoba

Thank you so much! I'm gonna start the hunt when the weather decides to not be cold. You wouldn't happen to have a wiring diagram handy, would you?

bwiencek

Google is your friend... lower left corner are the injectors - note the two fuses feed the + side of the injectors which get switched hot, the other sides are connected together and go to the computer - this is a "batch fire" injection and not a sequential injection - so all the injectors on one bank are tied together and fire at the same time.

Shakoba

Thanks so much! turns out the driver side harness bracket that mounts to the transmission worked its way through the harness and into the wire.. after repairing it, changing the oil and pulling an additional 5 quarts of fuel from the oil pan, it starts right up. I appreciate all of the help!

bwiencek

Glad to hear it's back up and running - that's a LOT of fuel washing down the cylinders - I'd make sure to run it and get the engine oil hot to evaporate any remaining fuel out of the crankcase