Hard to start when hot part III
Hard to start when hot part III
okay you can read part II here https://www.thirdgen.org/messgboard/...ML/006271.html
basicly I'm losing pressure when the pump isn't running and it's not coming out the injectors or the return side of the regulator so it seems to be losing it back the way it came from the pump.
with the key on the pressure is on up there till the pump kicks off after a few seconds and with the oil pump switch jumped it's 46#'s steady, and with the engine running it's 36#'s.
So is there a check valve inline that could be bad? Is the pump responsible for holding the pressure even when it isn't running?
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basicly I'm losing pressure when the pump isn't running and it's not coming out the injectors or the return side of the regulator so it seems to be losing it back the way it came from the pump.
with the key on the pressure is on up there till the pump kicks off after a few seconds and with the oil pump switch jumped it's 46#'s steady, and with the engine running it's 36#'s.
So is there a check valve inline that could be bad? Is the pump responsible for holding the pressure even when it isn't running?
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Senior Member
Joined: Nov 2000
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From: Charleston, WV, USA
Car: '86 IROC-Z + Misc. project cars.
Engine: Supercharged + Nitrous TPI 355 CID
Transmission: Art Carr built Th700r4
OK...
Is the running pressure of 36 PSI measured with the vacuum hose on the regulator attached or disconnected from the regulator? If that is the pressure with the hose attached you are good enough to start, with that fuel pressure. The best way to measure and compare fuel pressure is with the vacuum hose off the regulator. The pressure doesn't vary as much that way. It is a good idea to also compare measurements with the hose both on, and off. There should be an increase in fuel pressure (up to some where between 39-47 PSI depending on year made) when the hose is off.
Anyway, as I said if it is maintaning 36 PSI with the hose on, then that is enough to start the engine. However you do have a problem at the pump if pressure is bleading off immediateley when the pump is turned off. It is probably the pump itself. If it was the pulsator or rubber hose connecting the pump to the hard line leaking it should have low pressure even when running. Those leaking mildly are still a minor possibility though.
If you jump the oil switch and still have hard starts, and your fuel pressure is good enough, then even though you do seem to have a pump problem, that doesn't seem to be the cause of the hard starts.
You may have a fuel related ignition problem.
The ECM gets a signal from the ignition to pulse the injectors. When the cranking speed is under (I think) 500 RPM the ignition module sends a signal to pulse the injectors. Or at least it is supposed to. Yours might not be sending the pulse like it is suposed to. You can try another "known good" module. Or you can use what is known as a "node light". It plugs into the injector harness and lights if the injector is getting a signal pulse from the ECM. If it is lighting durring cranking then the injectors are getting pulsed. You would want to watch very closely to see that it pulses from the time the engine begines to turn over. If it turns over for a while without pulsing the injectors and then begins to pulse them and it starts then it is likely the ignition module not sending the signal.
Have you tried using starting fluid to see if it starts OK when you spray some in the intake first.
If it starts good if you spray in starting fluid first then that verifies that it is not getting enough fuel durring cranking.
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Tracy /AKA IROCKZ4me
'86 IROC-Z Camaro
"Cogito ergo zoom"
EFI Performance Club on Yahoo
Club IROC-Z
Is the running pressure of 36 PSI measured with the vacuum hose on the regulator attached or disconnected from the regulator? If that is the pressure with the hose attached you are good enough to start, with that fuel pressure. The best way to measure and compare fuel pressure is with the vacuum hose off the regulator. The pressure doesn't vary as much that way. It is a good idea to also compare measurements with the hose both on, and off. There should be an increase in fuel pressure (up to some where between 39-47 PSI depending on year made) when the hose is off.
Anyway, as I said if it is maintaning 36 PSI with the hose on, then that is enough to start the engine. However you do have a problem at the pump if pressure is bleading off immediateley when the pump is turned off. It is probably the pump itself. If it was the pulsator or rubber hose connecting the pump to the hard line leaking it should have low pressure even when running. Those leaking mildly are still a minor possibility though.
If you jump the oil switch and still have hard starts, and your fuel pressure is good enough, then even though you do seem to have a pump problem, that doesn't seem to be the cause of the hard starts.
You may have a fuel related ignition problem.
The ECM gets a signal from the ignition to pulse the injectors. When the cranking speed is under (I think) 500 RPM the ignition module sends a signal to pulse the injectors. Or at least it is supposed to. Yours might not be sending the pulse like it is suposed to. You can try another "known good" module. Or you can use what is known as a "node light". It plugs into the injector harness and lights if the injector is getting a signal pulse from the ECM. If it is lighting durring cranking then the injectors are getting pulsed. You would want to watch very closely to see that it pulses from the time the engine begines to turn over. If it turns over for a while without pulsing the injectors and then begins to pulse them and it starts then it is likely the ignition module not sending the signal.
Have you tried using starting fluid to see if it starts OK when you spray some in the intake first.
If it starts good if you spray in starting fluid first then that verifies that it is not getting enough fuel durring cranking.
------------------
Tracy /AKA IROCKZ4me
'86 IROC-Z Camaro
"Cogito ergo zoom"
- 355 cid
- AFR heads
- Arizona Speed & Marine hydraulic roller cam w/ AFR hydra-rev kit
- modified SLP runners
- TRW forged pistons/ceramic coated
- fully balanced
- Edelbrock headers/ceramic coated
- SLP cat-back
- Paxton supercharger
- Nitrous Express nitrous oxide
EFI Performance Club on Yahoo
Club IROC-Z
That 36psi is with that vacuum still attached.
My usual cranking procedure would be to turn the key on and wait till the fp stopped buzzing to even start cranking , which means 0psi now that I have a gauge. But today I tried cranking it immediately while the pump was still on and I still had pressure at the gauge. It seemed to make a world of difference in that one time (It was all I had time for).
I haven’t actually tried cranking the engine with the oil pressure switch jumped I just used that for a pressure reading. I’ll try starting with the switch jumped tomorrow so the pump just runs constantly and see how that goes. So the pump IS responsible for holding pressure on its’ side even when it’s off? What else could it be? If this little test turns out poorly where can one get a node light? Can a test light be substituted by any chance?
Thanks for all the help.
My usual cranking procedure would be to turn the key on and wait till the fp stopped buzzing to even start cranking , which means 0psi now that I have a gauge. But today I tried cranking it immediately while the pump was still on and I still had pressure at the gauge. It seemed to make a world of difference in that one time (It was all I had time for).
I haven’t actually tried cranking the engine with the oil pressure switch jumped I just used that for a pressure reading. I’ll try starting with the switch jumped tomorrow so the pump just runs constantly and see how that goes. So the pump IS responsible for holding pressure on its’ side even when it’s off? What else could it be? If this little test turns out poorly where can one get a node light? Can a test light be substituted by any chance?
Thanks for all the help.
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