weak spark bad ecm?
#1
weak spark bad ecm?
can a bad ecm cause weak spark i have just done a rebuild and i am getting weak spark when trying to crank over. i have all new wires pulgs cap and rotors tried 2 distributors 3 coils
does the ecm have have anything to do with giving spark?
does the ecm have have anything to do with giving spark?
#2
Supreme Member
Join Date: Jul 2005
Location: North Central Mass.
Posts: 2,123
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1985 Berlinetta
Engine: Megasquirted TPI
Transmission: Transgo 700R4
Axle/Gears: 3.42
Re: weak spark bad ecm?
no. It just triggers the spark. The ignition control module and the coil are responsible for the actual spark.
#3
Supreme Member
![](https://www.thirdgen.org/forums/images/ranks/tgo10.gif)
iTrader: (8)
Join Date: Feb 2007
Location: Newburg, MD
Posts: 1,091
Likes: 0
Received 18 Likes
on
18 Posts
Car: '89 RS, '89 Iroc
Engine: L03, LB9
Transmission: 700r4, T5
Axle/Gears: 2.73, 3.08
Re: weak spark bad ecm?
and yet it could be the ecm, if you have replaced the coil and the ign. module, possibly the wires from the ecm to the ign. module. idk exactly what you have done, but if you have replace the ignition components then it could very well be the ecm, my car starts, but stumbles oftenly, and even stalls, i am suspect of a bad ecm, as i have checked the wires many times over, and have had 3 ign. modules, only thing left would be the ecm for me, but i have a code 42, gotta hate the code 42!
#4
Re: weak spark bad ecm?
Try unpluging the tan with black trace wire ( EST bypass) it is the same wire used to check timming , and is located in the main engine harness near dist. this will make ignition system stand alone.Check to make sure you have 12v or more at the ignition system and a good ground.Also make sure you are checking spark a coil, it should jump 1 to 2 inches.If its good there but not at plug check cap and rotor for carbon tracking or holes.Good luck.
#5
Supreme Member
Join Date: Jul 2005
Location: North Central Mass.
Posts: 2,123
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1985 Berlinetta
Engine: Megasquirted TPI
Transmission: Transgo 700R4
Axle/Gears: 3.42
Re: weak spark bad ecm?
+1.
Although IIRC the ECM does not control cranking timing.
Although IIRC the ECM does not control cranking timing.
#6
Moderator
![](https://www.thirdgen.org/forums/images/ranks/tgo10.gif)
iTrader: (1)
Join Date: Mar 2002
Location: Chasing Electrons
Posts: 18,428
Likes: 0
Received 220 Likes
on
206 Posts
Car: check
Engine: check
Transmission: check
Re: weak spark bad ecm?
{edit: note, bad advice follows, it will prevent the ECM from firing the injectors. This is from the DRP's also being disconnected from the ECM.}
To completely take the ECM out of the ignition picture, disconnect the 4-wire connector at the distributor. The distributor will still fire the coil to crank, start, and run the engine.
But with that connector disconnected even a bad ECM can not have an affect on the ignition system.
Note: leave the 2-wire connector between the coil & distributor connected. This advice is for the small cap remote coil setup. I am not sure which connector to disconnect on a large cap distributor.
RBob.
To completely take the ECM out of the ignition picture, disconnect the 4-wire connector at the distributor. The distributor will still fire the coil to crank, start, and run the engine.
But with that connector disconnected even a bad ECM can not have an affect on the ignition system.
Note: leave the 2-wire connector between the coil & distributor connected. This advice is for the small cap remote coil setup. I am not sure which connector to disconnect on a large cap distributor.
RBob.
Last edited by RBob; 12-23-2007 at 10:49 AM.
#7
Supreme Member
![](https://www.thirdgen.org/forums/images/ranks/tgo10.gif)
Join Date: Apr 2002
Location: New Jersey
Posts: 3,552
Likes: 0
Received 5 Likes
on
5 Posts
Car: 86 Corvette, 89 IROC, 1999 TA
Engine: 350, 350, LS1
Transmission: 700r4, 700r4, T-56
Axle/Gears: 3.07, 373, 4.10
Re: weak spark bad ecm?
are you sure your battery has a good charge? A low battery can result in a weak spark.. I know it's kinda obvious but just thought I'd ask
Trending Topics
#8
Supreme Member
Join Date: Jul 2005
Location: North Central Mass.
Posts: 2,123
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1985 Berlinetta
Engine: Megasquirted TPI
Transmission: Transgo 700R4
Axle/Gears: 3.42
Re: weak spark bad ecm?
Rbob, With that wire disconnected the car wont run if it is EFI.
#9
Moderator
![](https://www.thirdgen.org/forums/images/ranks/tgo10.gif)
iTrader: (1)
Join Date: Mar 2002
Location: Chasing Electrons
Posts: 18,428
Likes: 0
Received 220 Likes
on
206 Posts
Car: check
Engine: check
Transmission: check
Re: weak spark bad ecm?
Brain fade on my part. Yes, you are correct. No DRP, no injector pulses. Sorry about that, it will take the ECM so far out of the picture that it won't even fire the injectors (unless it is TBI in async mode (a rare calibration setup)).
RBob.
RBob.
Thread
Thread Starter
Forum
Replies
Last Post