won't start
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Joined: Mar 2010
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From: Cape Coral FL.
won't start
I'm a proud new owner 1988 c4 Z52, po had installed many new parts including new plugs, wires , ect. Just installed pickup coil, no codes from computer except code 53 system voltage high.fuel pressure at 40psi she has spark also. Any help would be very much appreciated
Last edited by jmh 88; Mar 2, 2010 at 10:55 AM.
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Joined: Mar 2010
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From: Cape Coral FL.
she cranks over great just wont fire.it has spark also.and fuel pressure is at 40.there is no power to the fuel pump,but wen i apply voltage with my power probe to the pump it works great when i try to start it with the pump energized it builds to 40psi but still wont fire.
Last edited by jmh 88; Mar 2, 2010 at 11:00 AM.
Race Director
Joined: Dec 2000
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From: El Paso Texas
OK...let me see if I'm understanding this...
When you turn the key on, the pump is not doing the 2 second prime? But when you apply power to the pump manually it comes on and builds 40 psi, correct? Try running 12V to terminal G on the ALDL and tell me if you're getting the same result.
Look at your injector fuses, ECM fuse, and fuel pump fuse before we do anything else.
When you turn the key on, the pump is not doing the 2 second prime? But when you apply power to the pump manually it comes on and builds 40 psi, correct? Try running 12V to terminal G on the ALDL and tell me if you're getting the same result.
Look at your injector fuses, ECM fuse, and fuel pump fuse before we do anything else.
Team Owner
Joined: Mar 2001
Posts: 54,124
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From: Cincinnati, Oh USA
Use your timing light while cranking to see if you have spark at the right time. Connect your fuel pressure gauge and see if you have fuel pressure during cranking. Watch the fuel pressure with the ign off and see how long it holds up. Rapid pressure drop indicates leaky injectors and too rich to start. Buy a noid light from a parts house or make one with an LED and a series 680 ohm resistor (homemade must have property polarity connection to work) and see if the injectors are being pulsed during cranking. Unplug an injector and connect the noid light to the injector plug. Measure compression.
Race Director
Joined: Dec 2000
Posts: 17,551
Likes: 26
From: El Paso Texas
Use your timing light while cranking to see if you have spark at the right time. Connect your fuel pressure gauge and see if you have fuel pressure during cranking. Watch the fuel pressure with the ign off and see how long it holds up. Rapid pressure drop indicates leaky injectors and too rich to start. Buy a noid light from a parts house or make one with an LED and a series 680 ohm resistor (homemade must have property polarity connection to work) and see if the injectors are being pulsed during cranking. Unplug an injector and connect the noid light to the injector plug. Measure compression.
Crash course in EFI Troubleshooting 101 in one paragraph.
They need 3 things to run.
1. Suitable Compression
2. Suitably strong spark delivered at the correct time.
3. Correct mixture of fuel and air.
One of them is missing or deficient. Find out which one and why, and then correct the issue.
One minor correction to JFB's post....rapid dropdown of fuel pressure can indicate leaking injectors, a leaking regulator or fuel pump check valve....all of which we can test for.
Last edited by Frizlefrak; Mar 2, 2010 at 02:05 PM.
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From: Cape Coral FL.
OK...let me see if I'm understanding this...
When you turn the key on, the pump is not doing the 2 second prime? But when you apply power to the pump manually it comes on and builds 40 psi, correct? Try running 12V to terminal G on the ALDL and tell me if you're getting the same result.
Look at your injector fuses, ECM fuse, and fuel pump fuse before we do anything else.
When you turn the key on, the pump is not doing the 2 second prime? But when you apply power to the pump manually it comes on and builds 40 psi, correct? Try running 12V to terminal G on the ALDL and tell me if you're getting the same result.
Look at your injector fuses, ECM fuse, and fuel pump fuse before we do anything else.
fuel pump fuse was replaced and working properly, still no start
Last edited by jmh 88; Mar 2, 2010 at 04:32 PM.
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Thread Starter
Navigator
Joined: Mar 2010
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From: Cape Coral FL.
im leaning toward a bad ecm,any pointers on determining that or tests to confirm? again the only code is 53
the fuel pump is working properly now with the key turn on, i replaced the fuse for the pump and the 2 second prime is working. But she still will not start!
the fuel pump is working properly now with the key turn on, i replaced the fuse for the pump and the 2 second prime is working. But she still will not start!
Last edited by jmh 88; Mar 2, 2010 at 07:41 PM.
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Joined: Dec 2000
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From: El Paso Texas
The ECM should be giving the fuel pump the 2 second prime signal at key on, and then should energize the pump during cranking. Probe terminal G with a voltmeter +. Now turn the key on....you should get 12V for approx 2 seconds (assuming a good relay), then it should fall to zero. During this prime, you should have around 40 psi on the rail and it should hold for several minutes.
Do you have 12V AT the pump harness with terminal G energized? I'm trying to determine if you have an open fuel pump circuit, or if the ECM is laying down and not sending the fuel pump signal.
With terminal G energized, the pump should run continuously. If it's not, the pump is either dead or there is an open circuit. If voltage is present and the pump doesn't run, either the pump is bad or the wiring south of the harness has an open circuit.
Thread Starter
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Joined: Mar 2010
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From: Cape Coral FL.
None that I know of to test an ECM other than eliminating everything else first. I had a bad ECM on my 84 that was causing one injector to not squirt....drove me nuts troulbeshooting it....finally, everything else tested OK and there was nothing else left.
The ECM should be giving the fuel pump the 2 second prime signal at key on, and then should energize the pump during cranking. Probe terminal G with a voltmeter +. Now turn the key on....you should get 12V for approx 2 seconds (assuming a good relay), then it should fall to zero. During this prime, you should have around 40 psi on the rail and it should hold for several minutes.
Do you have 12V AT the pump harness with terminal G energized? I'm trying to determine if you have an open fuel pump circuit, or if the ECM is laying down and not sending the fuel pump signal.
With terminal G energized, the pump should run continuously. If it's not, the pump is either dead or there is an open circuit. If voltage is present and the pump doesn't run, either the pump is bad or the wiring south of the harness has an open circuit.
The ECM should be giving the fuel pump the 2 second prime signal at key on, and then should energize the pump during cranking. Probe terminal G with a voltmeter +. Now turn the key on....you should get 12V for approx 2 seconds (assuming a good relay), then it should fall to zero. During this prime, you should have around 40 psi on the rail and it should hold for several minutes.
Do you have 12V AT the pump harness with terminal G energized? I'm trying to determine if you have an open fuel pump circuit, or if the ECM is laying down and not sending the fuel pump signal.
With terminal G energized, the pump should run continuously. If it's not, the pump is either dead or there is an open circuit. If voltage is present and the pump doesn't run, either the pump is bad or the wiring south of the harness has an open circuit.
Race Director
Joined: Dec 2000
Posts: 17,551
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From: El Paso Texas
Two things I would do next assuming you have a constant 40 psi on the rail that holds after key off......
Attach a timing light and check spark and timing while cranking.....install a noid light and see if the injectors are pulsing. I'm really curious to see if the ECM is triggering the injectors. If it has fuel and fire and won't light off, check compression next. As I love to say...they only need 3 things to run.
Attach a timing light and check spark and timing while cranking.....install a noid light and see if the injectors are pulsing. I'm really curious to see if the ECM is triggering the injectors. If it has fuel and fire and won't light off, check compression next. As I love to say...they only need 3 things to run.
Thread Starter
Navigator
Joined: Mar 2010
Posts: 9
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From: Cape Coral FL.
won't start
Two things I would do next assuming you have a constant 40 psi on the rail that holds after key off......
Attach a timing light and check spark and timing while cranking.....install a noid light and see if the injectors are pulsing. I'm really curious to see if the ECM is triggering the injectors. If it has fuel and fire and won't light off, check compression next. As I love to say...they only need 3 things to run.
Attach a timing light and check spark and timing while cranking.....install a noid light and see if the injectors are pulsing. I'm really curious to see if the ECM is triggering the injectors. If it has fuel and fire and won't light off, check compression next. As I love to say...they only need 3 things to run.
Yes rail pressure hold constant 40 psi after key off.
I will continue in the morning with the other tests. Thanks in advance for the help today guys
Instructor
Joined: Jan 2003
Posts: 165
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From: Marianna FL
just because you see a spark does not mean the ign system is correct. your first post said the PO changed plugs and wires and who knows what else. your trying to diagnose to many things at once. you got fuel psi, great. you got spark but you dont know if it is at the right time. if you give it a shot of starting fluid and it does not bark, than you have ign timming problems could just be the firing order. if it does bark with starting fluid than you got a fuel problem. but take it 1 thing at a time its easy to start guessing and throwing $$ at it. start with the ign system that was messed with by the PO hit it with starting fluid and lets see what happens. GOOD LUCK!