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C4 spark testing

Old 01-09-2018, 12:21 AM
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Brent Higginbotham
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Default C4 spark testing

This may sound dumb but I bought a 1990 C4 that didn't start. Ok they told me it has water damage and was totaled. When I looked into it the water damage was minimal but the engine had thrown a rod. How do you throw a rod parked at the Beach?? Anyway after a rebuilt engine I've gone through most of the electronics, new ECU, relay's, distributor cap roter wire's +. The engine will crank over, fuel pressure up, but won't start? I've tested voltage to the ECU the Fan's come on the vats light goes off when cranking but have no spark, checked all fuses (twice) in line fuses (twice) power to the distributor cap.
I don't know what else to check, is there something I've missed??
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Old 01-09-2018, 07:57 AM
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Originally Posted by Brent Higginbotham View Post
This may sound dumb but I bought a 1990 C4 that didn't start. Ok they told me it has water damage and was totaled. When I looked into it the water damage was minimal but the engine had thrown a rod. How do you throw a rod parked at the Beach?? Anyway after a rebuilt engine I've gone through most of the electronics, new ECU, relay's, distributor cap roter wire's +. The engine will crank over, fuel pressure up, but won't start? I've tested voltage to the ECU the Fan's come on the vats light goes off when cranking but have no spark, checked all fuses (twice) in line fuses (twice) power to the distributor cap.
I don't know what else to check, is there something I've missed??
I have a friend of mine who was a insurance adjuster. He said a lot of the vehicles he totaled had blown motors. Said a lot of times they would kill the motors and THEN they would suddenly catch fire or end up under water. Go figure.
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Old 01-09-2018, 08:10 AM
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81c3
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You didnt mention the ICM in the distributor. Is it good? Did you have it tested? How deep did the water get?
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Old 01-09-2018, 08:43 AM
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Joe C
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time to dig out the FSM. start with the basics. question - how are you checking for spark?.

Last edited by Joe C; 01-09-2018 at 08:44 AM.
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Old 01-10-2018, 02:55 AM
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You sure all your grounds got reattached?
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Old 01-10-2018, 07:41 AM
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Originally Posted by Brent Higginbotham View Post
This may sound dumb but I bought a 1990 C4 that didn't start. Ok they told me it has water damage and was totaled. When I looked into it the water damage was minimal but the engine had thrown a rod. How do you throw a rod parked at the Beach?? Anyway after a rebuilt engine I've gone through most of the electronics, new ECU, relay's, distributor cap roter wire's +. The engine will crank over, fuel pressure up, but won't start? I've tested voltage to the ECU the Fan's come on the vats light goes off when cranking but have no spark, checked all fuses (twice) in line fuses (twice) power to the distributor cap.
I don't know what else to check, is there something I've missed??
Pull the code and see what the computer is telling you. Since the fans come on when you turn the key that means there is a trouble code. Hopefully that can point you in the correct direction.
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Old 01-13-2018, 06:32 PM
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Brent Higginbotham
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Originally Posted by bjankuski View Post
Pull the code and see what the computer is telling you. Since the fans come on when you turn the key that means there is a trouble code. Hopefully that can point you in the correct direction.
Ok I pulled up the codes and it says the ECM is bad so I ordered a new one and I'll see what that does 🤔.
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Old 01-17-2018, 11:38 PM
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Does it start if you give it a sniff of gasoline in the air intake? If it turns over. Your problem is fuel delivery. Don’t assume spark. Try and eliminate the cheap stuff. Spark is super tricky. What code did you say you got?
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