This problem only occurs when I first get into the car. If it does start, the check engine light is lit. If I turn off the key and listen for the fuel pump to turn off (just a few seconds), the car will start just fine. So,... Why does the fuel pump not turn on the first time I try to start it, AND, Is the fuel line draining when it sits but the system thinks there should be fuel pressure from the last time it was run. The car runs great after I turn it over 10 seconds which turns on the pump.
Help! Fuel pump does not turn on when key is turned until motor turns over about 10 seconds
- Thread starter tigerdan
- Start date
vetteoz
Well-known member
ECM should run the pump for two seconds when key turned to prime fuel rail then stop.
Possibly bad relay or connectors at relay plug ( very common on the older non - weather pak connectors )
Pump running when you crank engine is by the oil pressure switch in block which powers the pump independent from the relay.
That is the way it is intended; to let you start and drive car if relay goes out .Just takes longer cranking until engine oil pressure closes the OP switch
It runs the pump for 2 sec everytime key is turned on ( assuming relay / wiring are working )
If you turn key on then off then on again;
it won't re-prime if less than 30 sec between key being on
Possibly bad relay or connectors at relay plug ( very common on the older non - weather pak connectors )
Pump running when you crank engine is by the oil pressure switch in block which powers the pump independent from the relay.
That is the way it is intended; to let you start and drive car if relay goes out .Just takes longer cranking until engine oil pressure closes the OP switch
There is no monitoring of fuel pressure by ECM.
It runs the pump for 2 sec everytime key is turned on ( assuming relay / wiring are working )
If you turn key on then off then on again;
it won't re-prime if less than 30 sec between key being on
boomdriver
Well-known member
That relay/plug look familiar....
Heres a link to a place that sells pigtails for the fuel and many others...reasonable too...
> @ Davies Corvette Parts & Accessories
Heres a link to a place that sells pigtails for the fuel and many others...reasonable too...
> @ Davies Corvette Parts & Accessories
- Thread starter
- #4
Fuel Pump Relay bad will create random hard starts
vetteoz & boomdriver,
BINGO!! ECM signal is there, but the coil side of relay itself was open. Time for a new relay. Thank you for the assistance! Having the wiring diagram says it all... tigerdan
vetteoz & boomdriver,
BINGO!! ECM signal is there, but the coil side of relay itself was open. Time for a new relay. Thank you for the assistance! Having the wiring diagram says it all... tigerdan
boomdriver
Well-known member
If you look at the drawing, you see that the oil pressure switch is your back-up in case the fuel relay fails. That oil switch is often refered to as the fuel "back up" switch. It offers an alternate route for power.
Glad you got it figured out.
Peter Stofregen
Member
Hard Starting when parked for a week
I have the same problem with my '96! Will check for fuel pressure ( ordered fuel pressure tester). For the last 3 years, car seemed to start better if the starter was 'bumped' for a second, released and then car started immediately on second cranking.
Some one said fuel should shoot out, I am finding more of a weak stream. First step; Will listen for fuel pump, (2 seconds)
I have the same problem with my '96! Will check for fuel pressure ( ordered fuel pressure tester). For the last 3 years, car seemed to start better if the starter was 'bumped' for a second, released and then car started immediately on second cranking.
Some one said fuel should shoot out, I am finding more of a weak stream. First step; Will listen for fuel pump, (2 seconds)
Peter Stofregen
Member
I found the 10 amp fuel pump fuse on the passenger side dashboard fuse panel (FP 1 fuse 14 IP Fuse Block).
The fuse is good, and there is the 12 Volt, 2 second pulse on the fuse when the key is turned to 'run'. I have the GM service manual, and it looks like no other controls between that fuse and the pump. I do not hear the pump run, even with the gas cap off. If the pump is bad, why would it run fine once it starts?
I see that the oil switch would power it, once the engine is cranked long enough, but that power has to go through the above mentioned fuse also, if I am not mistaken.
Is the $80.00 (Canadian) fuel pressure worthwhile? (Pro Point, Princess Auto, probably made in China, like everything else)
The fuse is good, and there is the 12 Volt, 2 second pulse on the fuse when the key is turned to 'run'. I have the GM service manual, and it looks like no other controls between that fuse and the pump. I do not hear the pump run, even with the gas cap off. If the pump is bad, why would it run fine once it starts?
I see that the oil switch would power it, once the engine is cranked long enough, but that power has to go through the above mentioned fuse also, if I am not mistaken.
Is the $80.00 (Canadian) fuel pressure worthwhile? (Pro Point, Princess Auto, probably made in China, like everything else)
E
ecss
Guest
Why are you trouble shooting the fuel pump circuit if the engine runs?
Long crank time before the engine starts could indicate a bad fuel pump relay.
The relay output contacts could be pitted allowing current to flow but the contacts could break down under
a load so not enough current could flow to operate the fuel pump.
if you want to disable the oil pressure switch, unplug the connector at the oil pressure switch.
That removes it from the circuit.
If the PCM sees no low resolution pulses from the Optispark which would indicate the engine is not rotating it will
only enable the fuel pump relay for around 2 seconds to prime the fuel rail when you turn the ignition On.
When the engine is rotating the PCM will always enable the fuel pump relay as long as it sees the low resolution signal.
As you mentioned the oil pressure switch will also provide the fuel pump fuse with 12 volts if the
oil pressure exceeds around 4 psi. This is a backup circuit if the fuel pump relay ever fails.
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Peter Stofregen
Member
Thanks ecss;
I am completely new to the c4, pardon my stupid questions. I found oil switches, there are 2. Can you tell me if I should unplug the single wire sensor or the 3 wire? Can I assume if the car will start and run with it unpluged, it means PCM is working fine?
FYI The starting is only a problem when it sits for a few days, however, last summer, it did not start after some city driving on a hot day. (Reminded me of the old days with vapour lock) I waited half an hour, gave it one more try knowing that the battery was almost flat, and it finally started.
I appreciate your help and patience. I am determined to fix this. The fear of being stranded or having it towed is taking the fun out of driving.
I am completely new to the c4, pardon my stupid questions. I found oil switches, there are 2. Can you tell me if I should unplug the single wire sensor or the 3 wire? Can I assume if the car will start and run with it unpluged, it means PCM is working fine?
FYI The starting is only a problem when it sits for a few days, however, last summer, it did not start after some city driving on a hot day. (Reminded me of the old days with vapour lock) I waited half an hour, gave it one more try knowing that the battery was almost flat, and it finally started.
I appreciate your help and patience. I am determined to fix this. The fear of being stranded or having it towed is taking the fun out of driving.
E
ecss
Guest
I was under the impression in 96 they only used one oil pressure sender/fuel pressure switch and got rid of the separate oil pressure sender for the dash cluster gauge.
I know the service manual at least for a 95 shows both which I think is wrong. :ugh
Schematics shows the wires that go to the oil/ fuel pump switch as Red and Yellow and a Tan/White for the dash cluster gauge.
Can you verify those are the wire colors?
If they are, disconnect the plug which will disable the oil pressure fuel switch and oil pressure gauge sender
This will cause the fuel pump relay to run the fuel pump.
If I were you, I would just swap the fuel pump relay to eliminate it. All the relays in that area are interchangeable.
Attach a fuel pressure gauge and monitor the fuel pressure. Many people will tape the gauge to the windshield as long as the hose is long enough.
When the problem occurs and the fuel pressure is good, verify there is spark to the plugs.
Purchase a OBDII reader and verify no PCM codes are set.
Short pin 4 to pin 12 on the OBDII connector and turn the ignition On.
The speedometer area of the LCD will display CCM codes (Module 1) if any are set.
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Peter Stofregen
Member
Hi ECSS;
I disconnected the sensor (top rear of block) It has a red, a yellow, and a tan and white, as you mentioned. The other sensor has a green(I think). The single wire sensor was left connected. The car started reluctantly as usual but idled fine once it started. Oil pressure gauge in dash was pegged max.
I have a OBDII reader, never found any codes. Will be getting a Pressure gauge. I hear the fuel pump run for 2 seconds, but my ear has to be over the tank with the gas cap off. This time, I heard an electric whine 'pump' sound, about every third or forth time that the key was cycled, from off to run.
I disconnected the sensor (top rear of block) It has a red, a yellow, and a tan and white, as you mentioned. The other sensor has a green(I think). The single wire sensor was left connected. The car started reluctantly as usual but idled fine once it started. Oil pressure gauge in dash was pegged max.
I have a OBDII reader, never found any codes. Will be getting a Pressure gauge. I hear the fuel pump run for 2 seconds, but my ear has to be over the tank with the gas cap off. This time, I heard an electric whine 'pump' sound, about every third or forth time that the key was cycled, from off to run.
E
ecss
Guest
That is the Low oil pressure switch. The switch is monitored by the CCM. The switch closes when there
is no oil pressure and the Check Gauges indicator on the Dash turns on.
With the three wire plug disconnected only the fuel pump relay is supplying 12 volts to the fuel pump.
You really need to monitor the fuel pressure with a gauge.
Pressure should be around 43 psi and hold for around 10 minutes after the engine is shut off.
Remove the vacuum hose going to the fuel pressure regulator and verify there is no gas in it
which would indicate the fuel pressure regulator is bad.
Try holding the gas pedal to the floor when you start the engine.
That tells the PCM to not pulse the engine. (flooded engine) caused by leaking injector.
Here's a video showing how to remove the fuel pump.
https://www.youtube.com/watch?v=9OMF59hf_B4
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Peter Stofregen
Member
Thanks again ECSS, for the great info;
I removed the vac line from the fuel pressure regulator, then cycled ignition key from off to run, about six times. I heard the pump running for those 2 second pulses. No gas found, coming out of the regulator.
I will pick up a fuel pressure gauge tomorrow; Innova / Equus Fuel Injection Pressure Tester 2-1/2 Inch Dial 0-100 PSI 3640
I removed the vac line from the fuel pressure regulator, then cycled ignition key from off to run, about six times. I heard the pump running for those 2 second pulses. No gas found, coming out of the regulator.
I will pick up a fuel pressure gauge tomorrow; Innova / Equus Fuel Injection Pressure Tester 2-1/2 Inch Dial 0-100 PSI 3640
Peter Stofregen
Member
Can I waste your time with a few more dumb questions;
A; If the fuel filter is dirty; wouldn't the fuel pressure still develop with repeated cycling of the ignition key. If the engine is not cranking, the injectors will not reduce the static pressure.
B; Would blocking the Fuel return line be another valid test? Have these regulators ever failed in such a way as to allow too much fuel to return to the tank?
I am getting the gauge tomorrow, I know I am shooting in the dark, without it
A; If the fuel filter is dirty; wouldn't the fuel pressure still develop with repeated cycling of the ignition key. If the engine is not cranking, the injectors will not reduce the static pressure.
B; Would blocking the Fuel return line be another valid test? Have these regulators ever failed in such a way as to allow too much fuel to return to the tank?
I am getting the gauge tomorrow, I know I am shooting in the dark, without it
Peter Stofregen
Member
Does this mean something to anyone?
I got the gauge, and found the following readings;
Connected the Gauge: 0 psi
Turned key to 'Run': 18 psi
Turned key from 'Off' to 'Run' several times, thing I could "bump up" the pressure with the 2 second pulses: no change stayed at 18 psi, even waited 30 seconds.
Cranked engine, it started with 3 or 4 seconds of cranking: pressure pulsed between 34 and 40 psi at about 'heart rate' frequency
Turned off engine: pressure stayed at 34 psi;
Ten minutes later: 35 psi
30 minutes later: 42 psi
50 minutes later 40 psi
What does this mean?
I got the gauge, and found the following readings;
Connected the Gauge: 0 psi
Turned key to 'Run': 18 psi
Turned key from 'Off' to 'Run' several times, thing I could "bump up" the pressure with the 2 second pulses: no change stayed at 18 psi, even waited 30 seconds.
Cranked engine, it started with 3 or 4 seconds of cranking: pressure pulsed between 34 and 40 psi at about 'heart rate' frequency
Turned off engine: pressure stayed at 34 psi;
Ten minutes later: 35 psi
30 minutes later: 42 psi
50 minutes later 40 psi
What does this mean?
Hib Halverson
Technical Writer for Internet & Print Media
It mreans you've got a fuel pressure problem. Yeah, you can just replace the pump and that might fix it, but it would be better to do a proper diagnosis.
You need the Factory Service Manual for a 96 because it has diagnostic instructions and tests you can run to help you decide what needs to be repaired or replaced, the pump or something else.
Finally, you mentioned that the check engine light is on.
What fault code is set?
You need the Factory Service Manual for a 96 because it has diagnostic instructions and tests you can run to help you decide what needs to be repaired or replaced, the pump or something else.
Finally, you mentioned that the check engine light is on.
What fault code is set?
E
ecss
Guest
:ugh
If you turned the engine off and the pressure was 34 psi are you saying 50 minutes latter
the pressure increased to 40 psi? :eyerole
With the engine running at idle what is the fuel pressure?
What happens when you do a wide open throttle? Pressure should increase around 5 psi.
Sounds like you have a weak fuel pump.
I'd first change the filter on the inside of the passenger side frame rail just behind the front wheel.
Then test again.
If no change in fuel pressure, pull the fuel pump out and examine the sock which is the pre filter. If that looks ok, I'd replace the pump and install a new sock.
I like the pumps made by Delphi.
Peter Stofregen
Member
Should have been more clear;
With the engine running, the pressure cycled between 34 and 40 psi. Opening throttle did not seem to affect fuel pressure. To be honest, I did not have the nerve to put the peddle to the floor, with no load on the engine.
Could I not just disconnect the vacuum from the fuel regulator (and plug the hose)? Would that not perform the same test re; 5 psi pressure increase?
The pressure slowly went up AFTER the engine was shut off. BTW, its 3 hours later and the pressure is still 26 psi.
PS; I have the GM 96 vette service manual, I was just looking for 'short cuts' from fellow Vette owners.
PPS; My car did not have engine light come on, and no codes have ever been found with my OBDII reader
With the engine running, the pressure cycled between 34 and 40 psi. Opening throttle did not seem to affect fuel pressure. To be honest, I did not have the nerve to put the peddle to the floor, with no load on the engine.
Could I not just disconnect the vacuum from the fuel regulator (and plug the hose)? Would that not perform the same test re; 5 psi pressure increase?
The pressure slowly went up AFTER the engine was shut off. BTW, its 3 hours later and the pressure is still 26 psi.
PS; I have the GM 96 vette service manual, I was just looking for 'short cuts' from fellow Vette owners.
PPS; My car did not have engine light come on, and no codes have ever been found with my OBDII reader
E
ecss
Guest
If the gauge reading is jumping back and forth excessively it could be caused by a defective
pulsator.
Watch the you tube video below. He has a 96 and shows a static pressure of 45 when he turns the
key on and 37 psi at idle. His gauge does bounce around but not as much as you describe.
When you purchase a new fuel pump some of the kits include a piece or rubber hose to eliminate the pulsator.
Yes if you pull the vacuum hose off with the engine running you should see an increase in fuel pressure.
No need to plug the hose.
Not sure why the fuel pressure would increase after you shut the engine down. I've never noticed a pressure rise in a mechanical gauge after the engine was shut off.
Click on link below.
https://www.youtube.com/watch?v=_oXLUqE4Sf0
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Peter Stofregen
Member
Thanks again for all the help,everyone, and Happy Easter!
I am beginning to suspect the fuel filter, I have rejected the idea so far because it seems fine, accelerating etc. once it starts.
ECSS; your link above, re; fuel pressure measurement was relevant, same year '96.
This morning there was still some pressure at the shrader valve; 20 psi. I released pressure. Turned key from Off to Run. Pressure went to 22 psi. Turned key to Off, and waited 2 hours. Pressure was 18 psi. Turned key On, pressure only went to 19 psi.
I have read many posts commenting on the fuel filter being a PI the A..
Shops closed today, and being impatient; Is there a trick or easily made jig to remove those (push on or what ever) hose connectors on the stainless braided hose from the frame mounted line to the engine?
Might be a waste of time, but I would like to connect the gauge to the fuel line, before the filter
I am beginning to suspect the fuel filter, I have rejected the idea so far because it seems fine, accelerating etc. once it starts.
ECSS; your link above, re; fuel pressure measurement was relevant, same year '96.
This morning there was still some pressure at the shrader valve; 20 psi. I released pressure. Turned key from Off to Run. Pressure went to 22 psi. Turned key to Off, and waited 2 hours. Pressure was 18 psi. Turned key On, pressure only went to 19 psi.
I have read many posts commenting on the fuel filter being a PI the A..
Shops closed today, and being impatient; Is there a trick or easily made jig to remove those (push on or what ever) hose connectors on the stainless braided hose from the frame mounted line to the engine?
Might be a waste of time, but I would like to connect the gauge to the fuel line, before the filter
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