djmacc

I have a GM OBD1 system controlling fuel and spark in my 82 J10 with a Ford 460. The ECM and wiring harness came from a 91 Camaro so I thought you guys might be able to help me with my no spark issue. I had trouble with my IAC and found that the stock wiring pinout was wrong for my new Holley Tbody. I reversed the wiring and corrected that issue but ended up with no spark. I have an MSD 6A ignition box and jumped the test terminal and got a very strong spark out of the coil. With the key on I have no voltage at the coil + terminal but I understand that is normal with just the key on. My issue is I don't know the sequence of operation between the ECM and Ignition Control module and coil. I disconnected my ecm to troubleshoot the IAC so I could have disturbed a connection there. I replaced the Ignition Control Module no luck. So does anyone know with the key on what voltage I should be reading at the wiring harness connection to the ICM? How about when cranking? My module has a 2 pin and 4 pin connection on one side and a two pin (input?) connection on the other. I believe if I knew what 8 terminal should read voltage wise with the key on I could track the issue down. Like I mentioned this system came out of a 91 Camaro if that helps and I have a standard billet dizzy with the computer controlling spark. This link has a ICM similar to mine. http://www.fieros.de/en/v6help/code42.html
Thanks in advance for any ideas

Drew

iTrader: (58)

Just a shot in the dark, because this scenario is WAY off the reservation, and I really don't want to get any on me... Positive at the coil should be battery voltage with the key on. The other side of the coil is triggered by the module and pick-up. Fix the lack of power to the coil.

djmacc

Thanks for the help I will check that out.

djmacc

Looks like it's back to the drawing board. I found this on on the MSD site:

No 12v present at Coil +

1. One common question in regards to MSD Ignition controls is “Why isn’t 12V power on the orange (COIL +) wire?”
   The main reason 12V won’t be present at coil + is because your MSD ignition is a Capacitive Discharge Ignition. Like all CD ignitions they use a large capacitor to discharge 420-480 Volts to coil + and coil – will normally be connected to ground. (That’s why you wont see +12V on coil +)

I don't have 12v at the coil but it appears like that is a normal condition. Any other suggestions are welcome. I am concerned that I disturbed a splice that is between the ignition system and the ECM but I can't really check it out because I don't know what voltages to expect at the wiring harness from the ECM to the ignition control module with the key on and when cranking.

RBob

iTrader: (1)

At key-on, engine-off the 4-wire connector wires should all be at 0 volts. Note that during cranking the ECM doesn't control the spark, it is done internally to the ICM.

With the exception of REF HI they should remain at 0 volts while cranking.

On the 2-wire connector, the + terminal needs to be powered during key-on. Engine off, cranking, or running.

Also, be sure to ground the base plate of the ICM to the engine.

RBob.

djmacc

Thanks very much.

djmacc

RBob
One more question should there me any voltage at the male spade pins on the opposite side of the ICM? I believe they connect to the pickup in the dizzy.

Tuned Performance

iTrader: (92)

RBob

iTrader: (1)

The pickup coil will only generate an AC voltage when the distributor is turning. Can also measure the pickup coil resistance with it unplugged from the ICM. IIRC, should be in the 900 - 1100 ohm range.

RBob.

djmacc

Yes, and the article explained how the whole system works very clearly. I read some where that the ICM control the ignition until the the ECM is in closed loop. Is that true? I got the impression from the article that the ECM took over at 400 rpm?

djmacc

Understood I will check out the pickup coil as well. I have 12 volts at the 2 pin connector with the key on, I know the MSD work cause I can get a spark when I jump the test terminal so I am narrowing it down.

Tuned Performance

iTrader: (92)

djmacc

got it

djmacc

Well, we had a big heatwave in Michigan. It went up to 37 degrees so I went out to give all the tips you guys gave me a try. The original problem was the ICM. My mistake was not grounding the new one when I tested it. I just unplugged the old into the new without mounting it. As soon as I took RBob's advise and grounded the ICM with a jumper she fired right up. Thanks for all the help guys.

IROCZman15

iTrader: (25)

how do you go about grounding the ICM ? Is it grounded via the two machine screws that hold it to the base plate of the distributor or am I missing something here? it cant be grounded by its underside because we are supposed to put that thermal-insulation gel there right?

my ICM tested as PASS at autozone three times in a row and i bought a new one to test out and return later but still getting no spark. I just typed up a thread on TGO here about it in the general tech section. something went awry in my ignition system and melted my cap/rotor and no no spark while cranking. this is the first im hearing of "grounding the ICM".... ?

djmacc

Just bolting it down worked for me. I assume the 2 screws work as the ground path. You could run a jumper to the negative battery terminal to confirm.