What's up gurus,

I just bought (for $500 I might add):
1987 Formula Firebird
5.7L TPI 350
Auto Tranny

She has an external coil distributor.

She will not start. She cranks, and has fuel pressure to the rails, but she gives no spark off the coil and I'm not certain if the injectors are firing (haven't checked, because I have no spark. One thing at a time, ya know?).

I tested:
Three different resistance values on the ign coil by the book (including secondary ignition) and received results corresponding with a good coil.

I have 12V to the coil with ignition in the 'on' position.

From the pickup coil (connector to the ignition control module) I read about 840 ohms. I understand that anything between 500 and 1500 ohms is fine.

The Ignition control module tested bad. I replaced it with a new, tested module (used heat sink grease).

I am not receiving voltage from the ignition control module to the coil while cranking (or otherwise).

From the harness to the dizzy/ignition control module, Black/Red wire reads about 1 volt with the ignition on (or cranking - does not change), other three wires (tan/black, white, pink/white - I think those are the colors) show less than .5 volts. Not really sure what I'm looking for here, but I figured I'd see if I'm getting any sort of signal from the pcm and it doesn't look like I am.

I'd replace the coil, but it doesn't look like I'm even getting a signal from the pcm so I don't see the point.

ECM 10 amp fuse is good. So are all the others in the fuse box. I checked for empty fuse holes against my chilton's manual (since it's a new car to me and I have no idea what's up with it) and they're all there and good. Though come to think of it I only checked the fuses with my eyes, I suppose I could go check for resistance. But that wouldn't make sense because - >

Trouble codes read 12. Flashes 12 three times then flashes it three times again. And again. All systems normal. Even when the dizzy is unplugged (after cranking it).

Sooooooooooo..... I'm thinking the pcm is toast? But I find it hard to believe. Everything else seems to work fine.

It is my understanding that the previous owner was driving the car and it suddenly just cut out and would not restart three months ago.

I don't know what to check next. I would love a pinout of my ecm, or if you could tell me how to know which ecm I have to I can go find one. I would love to know how I test for signal from the ecm to the distributor, or any way to find out whether my pcm/ecm/ecu/computer is in fact bad.

I would swap it with another, but I haven't got one. I'd go buy one of Craigslist or something but there don't appear to be any.

Help! Thanks for your time. Is there anything I missed?

 

Oh, and I looked for like an hour for a problem similar to mine and couldn't find what I needed. I'm not a fan of posting new threads, (especially no start threads), but I feel my situation makes it okay. Thanks again guys! (gals?).

 

want to sell it to me... haha just kidding. try taking a wrench to the crank shaft turning it until the timing mark on the harmonic balancer meets up with the timing tab under the water pump to 0*. next open up the cap and look to see if the rotor is pointing to #1 terminal on the dizzy cap. im guessing you did good check everything but timing could be an issure, the code 12 is normal. that means nothing. and i think you said that the fuel pump is ****. so id assume its an ignition problem. makes me wonder like that movie with robin williams during the holacaust. sad, makes me sad. but try that. perhaps the dizzy bolt got loose and the dizzy retarded. did u test the injectors should be ohm listed in the book haynes.. turn key to on position test to see if the fuel pump is making noise/priming (noise=good) and the pickup coil may be ok in ohms but it has a permenant magnet that could throw the readings off, but you could also try take a spark plug wire off putting it next to a good ground (alternator bracket) and look for a blue spark when turning the engine over. if youre getting pressure to the rails then its not a fuel problem, even in the worst conditions without a prom i could start my car, it runs like crap but its run, so your situation should be a snap. too bad youre not in my area. ive resurrected vw bugs, buses, trans am, camaros, and ever lawn mowers

 

And the check engine light comes on while ignition is in the on position.

 

Lol lawn mowers are easy! But it's true.

Yeah, distributor is tight on there, though I will check to see if it's in correctly. Even if it isn't though, it should still be firing. Just at the wrong time.

My problem is I don't think I have power to my distributor/ignition control module. I'm looking to find out what kind of readings I should be getting from the pcm/wiring harness to the ignition control module?

Damned electronic distributors. Why can't I just have a good old fashioned points dizzy? lol.

Will test injectors when I have spark lol.

 

thats proof your ecm is working its ok

 

whats a pcm hhha you mean ecm rite? im confused. its saturday, im breakin open a bottle of jack.

 

PCM = ECM = ECU = Computer.

OBD1 GM is often referred to as PCM I believe. My chilton's calls it PCM. I hate to rely on that thing though... I often find that it's a waste of time reading that book and I should just do what I know is right in the first place.

Anyway, if the CEL is on with ignition on the ecu is guaranteed good?

 

And where in Cali are you? I'm in Davis. Near Sacramento.

 

During cranking the ECM doesn't have anything to do with the spark control. At this time it is all between the distributor and the ignition coil.

To make sure that the ECM isn't interfering with the distributor unplug the 4-wire connector on the distributor. That one carries the signals between it and the ECM. Note: with this unplugged the ignition system will still spark. However, the ECM won't fire the injectors.

Can still unplug this connector while trouble shooting the ignition system. Will also prevent the engine from being flooded while cranking to test the ignition. The ECM may still be firing the injectors while the ignition isn't producing spark.

There are ECM wiring diagrams over on the diy-efi.org/gmecm site. These also cover the ignition set up.

With the original module being bad the ignition coil may also be bad.

Some notes on the wiring: the large pink wire going to the coil is the ignition switched +12 volts. The 2-wire white & pink pigtail between the coil and the ignition module are:

pink is +12 ignition switched to the module
white is the coil - dwell/trigger wire from the module

If you unplug this 2-wire/connector from the coil the pink should have the +12 ignition switch power on it.

The small white wire from the coil goes to the dash tach. Unplug that while trouble shooting. The tach can cause the coil to not fire. Should be a spade connector to open.

If you tie the white wire to ground then remove it the coil should spark. Do not hold it to ground for more then a second. Just tap it on/off ground for a series of sparks. Obviously need to have the ignition on for this to work.

Other checks: remove the distributor cap and set to side so that it is clear of rotor. While watching the rotor crank the engine briefly. Did the rotor rotate with the engine? If so good, if not then bad. That would mean timing chain set up or cam or distributor gear is broken.

Check that the star wheel in the distributor (right under the rotor) is still attached solidly to the shaft. If loose from shaft then bad.

that should get you started on things to look for.

RBob.

 

Not really. Need to look for the blink at key-on, engine-off (KOEO). At KOEO the SES/CEL should turn on, blink off, then turn on solid. Without the blink off the ECM is not running correctly.

To repeat the test key-off for 10 seconds or more.

RBob.

 

So.

Replaced coil.

Cannot get new coil to manually spark. Do I have to tie the pink coil to icm wire to ground?

New coil resistance checks out.

So I'm assuming my pick up coil must be bad. Or somehow my new (as of yesterday) icm is bad again (maybe the ecu shorts it out somehow?).

Going to head back to AZ tonight to have it tested on their wells machine cause they do it for free.

Figure I'll just buy a distributor and pray? From what RBob says, coil and distributor are the only things required. Wiring is good, ground is good. So distributor must be bad, right?

 

Awesome, I was having the exact same problem and stumbled on this thread by mistake. Disconnecting the tach wire fixed it for me. Now the beast runs (just bought mine too) so I'm wondering what the cure for the tach wire is?

 

Victory is mine!

The dizzy was bad. Replaced that and the cap and rotor (cause the rotor wouldn't come off the old distributor lol) and she fired right up, with the computer connected. Haven't tried with the tach connected so I'd be interested in the answer to el_muerte's question as well.

Thanks guys!

 

i think it was two things, either the ignition control module, or pickup coil. glad you got it fixed. made my day kinda, i felt bad you bought a coil and it didnt work..

 

Lol made your day? I'll tell you what made mine: No Rod knock! Engine runs great! Still need to time her, but she plays all eight notes beautifully. I was going to replace the coil anyway after I got her running, as it was stock. Don't need to deal with a roadside breakdown on account of a coil. Screw that haha.

Thanks!

 

What is the fix for the bad tach? Repair, replace, chase down a short...? Don't mean to hijack the thread but figured on a better chance of a reply here (after knowlegeable people have already posted lol) than starting my own. Also, mine runs great at idle but responds very slowly to throttle inputs and will backfire if I open it too quickly. Could this be caused by the tach wire being disconnected? Seems kinda unlikely to me, but then I never would have suspected a bad tach could cause the initial problem either. Could be a plethora of other issues I suppose, vehicle sat for who knows how long and I don't know any of the history but thought I'd rule this out as a starting point.