1989 Grand Marquis ECM removal

[monotonorobo]

Wasn’t the battery. Only other thing I can think of it being is one of the relays or either the ECM harness. Done everything else I could think of.

[gadget73]

ok so lets step through this in a logical manner here. can you measure the following things please?



battery negative to battery positive voltage key off
battery negative to battery positive voltage key on
battery negative to battery positive voltage engine cranking

battery negative to ignition coil + key on
battery negative to ignition coil engine cranking

battery negative to TFI PWR key on
battery negative to TFI STRT engine craking


this should confirm if we have power where it should be, and if the battery is too weak to make all this happen.


again the ignition system is unrelated to the relays or the ECM harness. None of the power comes through any of that.

[monotonorobo]

Yeah I will. My bad if it seemed like I wasn’t listening to what you were saying. I’ve done all of this except TFI start cranking and ignition coil cranking and I’ll check tomorrow.

[gadget73]

no issue, just trying to get all the info together in one spot rather than going through a bunch of posts and possibly missing something.

At this point we're dealing with a mix of old car with old wiring and aftermarket parts that may or may not be bad right out of the box. Annoyingly just because its new doesn't mean it actually works.

[monotonorobo]

TFI power key on was like 11 volts and while cranking the ignition coil went down to 7 volts. I think the lead came out so I’ll do it again for both but I also got codes 23, 14, and 18.

[sly]

Those codes are probably from a low voltage condition or false start (engine started but died quickly).

edit: Thinking about this more... if you haven't changed the distributor, the PIP could indeed be bad inside. Sometimes you can tell easily as it will be getting ground up by the tone ring under the rotor. I had one die that way.

If you have replaced the dizzy, then either it's bad or it's just as I initially thought.

[monotonorobo]

Those codes are probably from a low voltage condition or false start (engine started but died quickly).

edit: Thinking about this more... if you haven't changed the distributor, the PIP could indeed be bad inside. Sometimes you can tell easily as it will be getting ground up by the tone ring under the rotor. I had one die that way.

If you have replaced the dizzy, then either it's bad or it's just as I initially thought.

I believe it’s just as you initially thought. I changed the dizzy, ignition coil, ECM, and ICM. It did start and die a few times.

[sly]

So yeah... stale codes.

[monotonorobo]

Bad wiring was one of my guesses too. I’m thinking maybe the ICM harness, but that’s just a guess.

[sly]

I had that issue on the 88 MGM. The clip wasn't holding the harness snug. I zip tied it to the ignition module (one around the module so the zip tie holds the clip down) and didn't have issues after that. Hopefully if that is the issue, it's as easy a fix.

[monotonorobo]

Tried it last night and I’ll mess around with it some more today. I also had a vacuum leak and the day it died on me was the day I was gonna find it. Think that that may be an issue as well? I’ll also check to see if the engine is flooded.

[gadget73]

so just to confirm, does this have spark or no? Vacuum leaks won't cause no spark.

[monotonorobo]

Yeah when it wants to spark. Sparks sometimes for no reason doesn’t spark sometimes for no reason. In retrospect I don’t know why I mentioned that.

[gadget73]

7 volts when cranking seems awful low. might be low enough that the ignition doesn't work reliably. I don't know what its lower limit is.

[sly]

I think it's 8.5 or 9V. I have a vague feeling I've read that somewhere before. Reliably is probably 10 though. I know I can't get a starter to turn fast enough with less than 10V on crank from the numerous battery replacements I've done with my own vehicles and family/friends cars.