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Hi. '86 2.8L Firebird. Does anyone know a way of testing the Ignition Control Module? Would like to confirm it's bad before buying a new one. My problem is that I think my spark is weak. It has spark but doesn't seem bright and blue like it's supposed to. Right now the car is a crank no start. Replaced and checked many things so far. Hoping new ICM will fix the weak spark.
thanks
Most of the major auto parts stores used to have ignition module test benches in store. I would call an AutoZone or an advanced auto parts near you if you have one and ask them. There isn't much you can do from home.
AHHHHH! Dammit. I just spent $50 on a new ICM and it didn't fix anything. Still cranks but won't start.. still have weak spark. Checked the coil with ohmmeter per the book.. checked out fine. All new cap rotor plugs wires. Fuel pressure good. I have no idea what's wrong. Been working on this for 3 months. This is my daily driver. Can anyone help?
First thing, resistance isn't a definitive answer on a coil, but let's ignore that for now. Do you have access to a noid light set or an old school, incandescent test.light? We need to see if you're getting injector pulse. Also, have you performed the basics like a compression test?
First thing, resistance isn't a definitive answer on a coil, but let's ignore that for now. Do you have access to a noid light set or an old school, incandescent test.light? We need to see if you're getting injector pulse. Also, have you performed the basics like a compression test?
The car periodically runs/drives.. so compression i xan assume is good. I've checked inj pulse with test light.. All good.
for a while i was thinking it was air/fuel ratio prob. It was like trying to start a lawnmower cold without closing the choke. Just cranked and cranked.. sometimes would eventually start.. then once warm it would start back up perfectly.
I've checked cold start injector too. All good.
So if coil resistance checks out.. it might still be bad?
It could be but it usually is in an intermittent type of thing. Are the spark plugs fuel fouled? Have you pulled them to inspect them?
yes. Pulled the plugs many times. After a lot of cranking they are black and wet with gas. I'd clean them with a map gas torch to burn off the carbon before reinstalling.
It would be great if you could get a scanner on there and see data. Could be the pickup coil failing, could be a coolant temp sensor reporting extremely low temp and making it run extremely rich.
no dtcs when it won't start?
It would be great if you could get a scanner on there and see data. Could be the pickup coil failing, could be a coolant temp sensor reporting extremely low temp and making it run extremely rich.
no dtcs when it won't start?
ok.. no codes. No cel. I just got a scanner Bosch 1300 obd1. Will it tell me much if engine not running? Plugged it in yesterday.. coolant temp was -40 but I have replaced the coolant temp sensor. speed read 192 mph.. not sure why bad data unless it needs to be running. I'll hook it up again tomorrow see what i can figure out.. thanks
-40 is the default value for an open circuit. Id be willing to bet that's where your issue lies. Possible bad wire between ECM and ect. Are you familiar with continuity tests? The next thing I would do before you replace another part is check both wires end to end.
while you were replacing the ICM and distributor parts, was the pickup coil (not the ignition coil) visually inspected or replaced? they are well known for corroding and disintegrating/wires covered in green oxide and losing connection. I would make sure that is sound before looking at other items... also check battery voltage and condition, even though it cranks it could be low
while you were replacing the ICM and distributor parts, was the pickup coil (not the ignition coil) visually inspected or replaced? they are well known for corroding and disintegrating/wires covered in green oxide and losing connection. I would make sure that is sound before looking at other items... also check battery voltage and condition, even though it cranks it could be low
did not replace pickup coil.. you might be right about it needing to be replaced. Batt is good.. after much cranking i throw the charger on it to make sure it's full.
Just did spark test again.. looks like good spark between coil and cap.. but little to no spark between cap and plugs. So i guess now i can focus inside the distributor. Also thanks to you all for helping. I'd be pretty lost on my own.
That's a pretty strong indicator of 'no spark"....or bad timing (wrong plug wire routing?)
With all of your spark plugs installed, wires hooked to them, take a spark plug...any spark plug -it could be from your lawn mower, put it in your coil wire, then ground the body of that plug, to the center post on your distributor cap. Have someone crank the engine, you should see 3 sparks across the spark plug/engine revolution.
What you're doing here is using a "spark tester" (your 'lawn mower' spark plug) to see if you have spark. You're also confirming if your "weak spark" is actually weak or not, by forcing the spark to happen when it's most difficult; under compression. If the spark jumps the gap on your test plug, then it also HAS to jump the gap inside the cylinder, under compression...no other way for the spark to get to ground (unless all of your plug wires are bad). I'd try that next b/c it's free, easy, and conclusive.
I did another spark test with a spark plug grounded against the exhaust manifold.. it did spark but might have been a little weak.. looked a bit more orange than blue but kinda hard to tell. Is it possible the ign coil is putting out a spark that's just a little too weak to ignite the combustion?.. cause i have spark and fuel but still just cranks and won't fire. Any additional thoughts or help is super appreciated.
it did spark but might have been a little weak.. looked a bit more orange than blue but kinda hard to tell. Is it possible the ign coil is putting out a spark that's just a little too weak to ignite the combustion?.. Any additional thoughts or help is super appreciated.
I have some thoughts. YES, it's possible that the ign coil is putting out a spark that's just a little too weak to ignite the combustion. So what we need is some kind of test to check for that. We need some way, to determine if your spark, which appears to be present in open atmosphere, is actually sufficient to jump a gap inside the cylinder! How can we accomplish that? We know that judging a spark's quality/strength by viewing it jump a plug gap in the daylight, is kind of like judging horsepower, by how long a car a peel out. It don't work. So we need a test that conclusively shows us if the spark that you do have, is sufficient and actually working, inside the cylinder. It turns out that there IS such a test! After doing some extensive internet research, I came up with this test:
Originally Posted by Tom 400 CFI
With all of your spark plugs installed, wires hooked to them, take a spark plug...any spark plug -it could be from your lawn mower, put it in your coil wire, then ground the body of that plug, to the center post on your distributor cap. Have someone crank the engine, you should see 3 sparks across the spark plug/engine revolution.
What that test does, is confirm if your "weak spark" is actually weak or not, by forcing the spark to happen when it's most difficult; under compression. If the spark jumps the gap on your test plug, then it also HAS to jump the gap inside the cylinder, under compression...no other way for the spark to get to ground (unless all of your plug wires are bad). I'd try that next b/c it's free, easy, and conclusive.
....and it's not just re-doing a test that you've already done that didn't give you conclusive information.
My only problem is having someone crank the engine while i look for spark. Kinda hard to see from inside the car if I'm cranking.. and I'm by myself here.. don't have anyone to crank for me. If i can figure something out I'll def do that test.
... yes,, that's exactly what i did yesterday.. took 2 long wire leads, clipped them to the starter posts then held the other ends of the wires together.. was a little tricky but I made it work.
also.. UPDATE: sometimes I would get spark from the coil and sometimes not.. so i took a used ign coil from a monte carlo and hooked it up just temporary.. my car instantly fired up!
So i'll conclude the problem the whole time was just a weak ign coil on it's way out.
Thanks to everyone who helped with my diag on this. I'm so relieved, now just have to get the monte carlo coil onto the bracket for my engine. I can't believe it took me 3 months to figure that out.
03-05-2024, 09:40 PM
