1984 troubleshooting fuel system
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Cruising
Joined: Oct 2013
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1984 troubleshooting fuel system
The vehicle starts but does not run for long. Have not checked the fuel pressure yet. There is spark but check the plugs and they were covered in soot.
Unfortunately, the person we purchased the car from did not take the time to fix issues just found ways around them, it is such a headache trying to make heads or tails of the mess left. Basically the previous owner hot wired the fuel pump to the fan relay which was set to always be on, this way he by passed the computer. I know the car was over heating I am assuming this is why he did that "fix". Oh and the thermostat had been removed as well. Replaced thermostat, 2 cracked heads, rebuilt the TB, all new gaskets, and wired it correctly.
When the car does run it seem as though there is just way too much fuel being sprayed out. Did an oil change not to long ago and found gas in the oil pan and I have a feeling there is gas in the oil again. Also it took about and hour and a half to go through 5 gallons of gas with the vehicle idling. Thought there might have been a problem with the injectors but was told the voltmeter readings were ok. Maybe the problem is in the computer.
Any information is appreciated. Thanks in advance.
Unfortunately, the person we purchased the car from did not take the time to fix issues just found ways around them, it is such a headache trying to make heads or tails of the mess left. Basically the previous owner hot wired the fuel pump to the fan relay which was set to always be on, this way he by passed the computer. I know the car was over heating I am assuming this is why he did that "fix". Oh and the thermostat had been removed as well. Replaced thermostat, 2 cracked heads, rebuilt the TB, all new gaskets, and wired it correctly.
When the car does run it seem as though there is just way too much fuel being sprayed out. Did an oil change not to long ago and found gas in the oil pan and I have a feeling there is gas in the oil again. Also it took about and hour and a half to go through 5 gallons of gas with the vehicle idling. Thought there might have been a problem with the injectors but was told the voltmeter readings were ok. Maybe the problem is in the computer.
Any information is appreciated. Thanks in advance.
Melting Slicks
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Check the coolant temp sensor, its in the front of the intake below the a/c comp. & air pump. If it has the older style sensor (looks like a knock sensor connector) then up date it with a newer sensor & pigtail. A bad cts can make it run real rich, as well as a map sensor thats not hooked up to the right port. Check the ign. timing (follow label) & all the grounds carefully.
Safety Car
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http://www.corvettephotographs.com/c4vettes/codes.htm
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Cruising
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Fuel pressure is ok. Engine is getting spark. However I have 2 ECMs the old one fires the injectors but wont run the fuel pump. The guy that had it before me hot wired the fuel pump to be on at all times by wiring it to the fuel pump relay from the cooling fan that was also wired to be on at all times when the key was on. I fixed the wiring problem by putting it back to factory wiring specs, replacing the cooling fan sensor, and the fuel pump relay. Still the car wont run the fuel pump even with the new relay so I still have to hot wire the pump to get the car to start. Of course the car runs like crap when done this way. The injectors seem to just dump fuel into it, which most of it seems to end up in my oil pan or out my exhaust as white smoke.
I bought a used computer that I was told worked, that computer primes the pump by itself when I turn the key to the on position but wont run the injectors when I try to start the car. I know this because I checked both injectors with a noid light with each of the ECMs.
Somebody please tell me there is an easy and cheap fix for this or that there is just something simple and stupid that I am over looking.
I bought a used computer that I was told worked, that computer primes the pump by itself when I turn the key to the on position but wont run the injectors when I try to start the car. I know this because I checked both injectors with a noid light with each of the ECMs.
Somebody please tell me there is an easy and cheap fix for this or that there is just something simple and stupid that I am over looking.
Safety Car
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There is a independent switch (wired in parallel ) operated by oil pressure as a backup that does powers the pump direct
from the battery as soon as the engine is cranked over and OP builds
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Racer
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You mentioned rebuilding the throttle bodies - did you set minimum air, sync. the throttle bodies, and set tps voltage? Also make sure you hooked the vacuum line from the map sensor to the right port on the throttle body. (max vacuum at idle) Being out of sync will make idle and part throttle funky , but tps adjustment and map sensor can make it guzzle fuel if not right. TPS should be .525 volts throttle fully closed, and needs to be set after other adjustments. No matter how the fuel pump is powered, as long as it pumps fuel, it won't affect how it runs, the computer can't tell the difference. The 2 second prime is to help starting, and after that the oil pressure switch sends power to the pump when oil pressure builds up. (done this way as a safety feature to prevent pump from running when engine is off or loss of oil pressure) Being wired in direct isn't the best or safest way to be hooked up, but is fine for testing or troubleshooting.
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Cruising
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Is there a way to check if the oil pressure switch is functioning properly?
Thank you everyone for all of your suggestions, I really appreciate all of the valuable information.
Thank you everyone for all of your suggestions, I really appreciate all of the valuable information.
Last edited by dvargas; Oct 27, 2013 at 01:40 AM.
Safety Car
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Look at the circuit diagram ;
if the ECM is operating the relay which it does as long as the ECM is seeing ref pulses from the dist showing the engine is turning over then the pump will still run off the relay regardless what the OP switch is doing
The OP switch is a backup wired in parallel with the relay that allows you to start
your car should the pump relay fail
Last edited by vetteoz; Oct 27, 2013 at 02:27 AM.
Safety Car
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Jumper the 2 terminals in the switch connector ; the pump should run full time.
( checks the wiring to pump from switch )
Racer
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Wrong
Look at the circuit diagram ;
if the ECM is operating the relay which it does as long as the ECM is seeing ref pulses from the dist showing the engine is turning over then the pump will still run off the relay regardless what the OP switch is doing
The OP switch is a backup wired in parallel with the relay that allows you to start
your car should the pump relay fail
Look at the circuit diagram ;
if the ECM is operating the relay which it does as long as the ECM is seeing ref pulses from the dist showing the engine is turning over then the pump will still run off the relay regardless what the OP switch is doing
The OP switch is a backup wired in parallel with the relay that allows you to start
your car should the pump relay fail
Thread Starter
Cruising
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Just to verify the information from Vetteoz will still allow for the computer not running the fuel pump and allowing the car to function correctly?
"You don't need the ECM to run the pump relay ;
There is a independent switch (wired in parallel ) operated by oil pressure as a backup that does powers the pump direct
from the battery as soon as the engine is cranked over and OP builds"
"You don't need the ECM to run the pump relay ;
There is a independent switch (wired in parallel ) operated by oil pressure as a backup that does powers the pump direct
from the battery as soon as the engine is cranked over and OP builds"
Last edited by dvargas; Oct 28, 2013 at 02:02 PM.
Thread Starter
Cruising
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My switch has 3 terminals. Which 2 terminals do I check?
Safety Car
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Safety Car
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Team Owner
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From: Park City Utah
In addition to what Vettoz has provided you;
1. How do you know that your "fuel pressure is ok"? What is it?
2. In the quote above...none of that is right. "Hot wiring" the fuel pump" in now way condemns the car to run poorly; if the every thing else is functioning reasonably well, car should/could run perfectly fine, with a hot-wired pump.
3. Have you checked for vacuum leaks?
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