A week ago I had to get towed home because the car would not start it had weak spark ( yellow ). The second I got it off the tow truck it started just fine. The next day I had the modual tested 3 times and it was fine my fuel pressure was fine. I was not sure what the issue was I attached a new ground wire from the battery to the intake just to make sure it was not a ground issue and I changed the coil. Car was running fine but it did it again today. I went to a friends house and the car is cool but I have weak spark again and can't get it to run. I have 12v to the bat side of the dist. I do not want to pay another tow charge guys so what am I missing????????????????

 

Try pulling the car into the garage, turn off all the lights, unplug the fuse for the under hood lights and crank it up. Look for any sparks jumping from the wires or the cap. Check the cap for cracks, and look for wetness inside he dist. cap.

 

This is just me but some things there are not tests for under all cases and I fully think a module is one of them. You took the time to take it out have it "tested" and put it back in. For about $25 you could have a new one in and more or less crossed that off your list. I do not like throwing parts at things but you have it out and for the cost it would not be worth it for me to not replace it. I do not think you have ruled out the module

 

I bought a new modual, new cap, new rotor, new coil and I still have a weak spark. The car started after a while so I drove home but I had to stop 5 blocks from the house for fuel. I had to shut the car off to get gas cap key and it would not start again. This is when I bought everything new and still no dice, so now I am sitting with my family waiting for the car to start so I can drive it home 5 blocks.

 

How are you testing spark?

 

I pulled a wire off the dist and watched the spark jump to my test light.

 

I also put all new injestors on the car yesterday from FIC, my fuel pressure is 42#. My fuel pump is new, the sock in the tank is new, the fuel filter on the frame is new, and the spark plugs are new.

 

Sorry I am not understanding how you are testing for spark I am trying to visualize it but I cannot. Next time can you pull a wire off pull the boot back and hold the end about 1/8 in or so from exhaust manifold. If all is good you will get a good crisp spark. You can also by a spark tester at just about any parts store ground one end the other the plug wire goes into and watch to see if you have spark. They are dirt cheap. I am thinking hard on all you have said you have replaced or covered a lot of things. The only thing I can think fo that you have not touched that will effect spark if indead that is what is going on is your pick up and coil ***.

 

I pulled a wire off the distributer then I took a test light and put it close to the post and turned he car over. Spark will jump a good inch but it is a yellow spark not a blue spark. When the car does run it will ark a nice blue spark. This is the craziest thing I have every seen. I know I have 12v to the bat side of the dist, I know the alt is working just fine also. This is my first Vett and I got it last week so I am not real well versed in what makes them tick. At this point I just want to get it started so I can get it home and take it to a Houston area Corvette shop. I bought the car for my wife and she is scared of it now and will not drive it.

 

I would just replace the whole thing with a MSD distributor. Could be the ICM, just check everything else in the dist.

 

I am trying to relate heat and poor spark and there are a few things problem is you covered most of them. It does not take much to get a good spark out of HEI. You know you have 12 volts what about a good and clean ground inside the dist. Like I said off hand the only other thing that comes to my head is the pick up coil ***. It is inside the dist. it is the peice that has 8 nipples and 2 of the wires coming out of the dist are connected to just incase you did not know. This is needed for a spark and the do break down under heat. come on guys jump in if you can think of anything save this guy from his wife LOL

 

I just got my first vett a month ago, and I haven't even got to drive it yet! My dad drove it home, then the fuel problems started! Let's hope we get them fixed soon!

 

Personal opinon ECM will not usaly cause weak spark. In fact I am almost positive that as long as the dist is in working condition and you have the 12 volts and ground that you need you do not even need an ecm you just wont have timing control

 

Everything is suspect when it comes to this. What year is your car. Interesting fact about ECUS that I just found out and will make a separate post about soon. Ive been chasing a no start for a month and I have performed all the tests new opti new coil new ICM and still no spark. This is what my problem was

Q. I heard that several GM computers that employ surface mount technology (SMT) may
become intermittent in operation over time due to manufacturing defects. Realizing
this, I replaced the ECM in my customers’ vehicle after performing a Tap-test to make
sure that the intermittent problem was in fact due to a defective ECM. However, the
vehicle still has an intermittent miss, even with the rebuilt ECM. Can this problem be
fixed?
A. This problem can be fixed, and it is fixed with every Blue Streak remanufactured GM
SMT computer. The reason that some SMT computers become intermittent is due to
the conformal-coat that is applied to the ECM circuit board. The conformal-coat is
applied to the circuit board to help protect the ECM from corrosion and the elements.
However, after some time, the conformal-coat may shift, swell, or spread, causing the
movement of certain electronic components on the board. This creates the potential
for intermittent contacts between these electronic components and the circuit board.
At Blue Streak, all remanufactured GM SMT ECMs have the original conformal-coat
removed, all solder joints are then re-flowed and the ECMs are exhaustively tested. A
new conformal-coat is then applied using a process that virtually eliminates the reoccurrence
of an intermittent ECM, and the ECM is tested once again. If after
installing the remanufactured ECM you still have an intermittent miss in the vehicle
and you have checked the wiring harness for chafing and shorts, chances are pretty
good that you have a problem with the vehicle wiring harness connector at the ECM.
If you remove the pins from the harness connector and cinch them down, they will
have a stronger grip on the ECM pins. This should eliminate your intermittent engine
miss.

My ECU is in this companys hands and it is obvious they know what they are doing. The company is called blue streak and my parts rep is getting this whole job done for a lousy 127 dollars talk about cheap and thats shipped both ways. wow I got lucky on this deal and like I said knowing this now everything is suspect. I was getting the opti spark code and the problemisnt the opti but the ecu. Check your codes

 

Mike I am not a great opit guy. but I am sure he has a 1990 that should have just a plain old HEI dist. I had to go to his profile to find that out. keep the idels coming his wife is going to beat him LOL

 

Holy god the poor man lol wow! I dont know why they just did not leave the HEI Id prefer it. You can adjust timing by hand also and it was in my opinion good enough. Ok well that changes things

 

Well I just drove back to the gas station and tried to start the Vet ( 1990 vet zz4 crate motor HEI dist ) and it fired right up. When I got it home and shut it off it fired right uo again no problem. Guys I am not a retard, I have a 530Ci 780hp cadillac stroker motor on my airboat that I have 20K in. Last Saturday I built a 496 in my garage for a friend and installed it on his airboat in 12 hours. I know how to turn wrenches but when it comes to electronics I am limited. This is why I did not go with a fuel injection system on my boat because of these type of problems. I had the same kind of issues last year when I ran a digital 6 ignition box, I had to run this ignition because I installed a nitrous express two stage fogger plate. The ignition box freaked out causing my motor to go lean on the big end and I broke the crank, block, and blew both head gaskets. I swore I would never go high tech again and now I have a Vett with Gremlins. In the two week I have had the car I have replaced the AC compressor, dryer, injectors, computer chip, modual, coil, cap, rotor, plugs, and fuel filter.

The car looks great, new paint 3 months ago, new tires, and now that the injectors are replaced it runs much better. I just need to figure out what is causing it to pull this not starting BS.

 

I would check the ignition switch, and the distributor 4 pin connector right behind the dist.
It sounds like you have a corroded connector that the pins expand with heat, and give an open circuit.
It totally sounds like corrosion on a ground wire, or a plug. and if it's heat related, it's under the hood.
Also check the connector wires from the computer that go through the firewall feed-thru just above the right exhaust pipe.
The feed-thru is injected with some goo that gets soft with heat, and you may have a wire that's chafed through in this area.

 

thanks for all the help guys!! Last night I was so ticked off I was ready to pull the intake and convert the car over to a carb. Today is a better day and I will start trying to figure it out again so keep the advise comming and I will spend the weekend chasing this problem down.

 

Remember, persistence overcomes resistance.