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Help - 91 C4 does not want to go

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Old 01-07-2018, 03:27 PM
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wdsj
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Default Help - 91 C4 does not want to go

Base 91 C4; cranks, give gas and it dies; no codes.

Checked pressure at fuel rail; ~32 PSI.
Replaced gas filter and car ran ok again. But fuel pressure a little low.
Replaced fuel pump and strainer.
Now I have 38-40 psi fuel pressure but car is back to where I started.

Cranks idles few seconds and dies. Apply gas when running and it dies.

No drop in fuel pressure as it dies. Pressure holds steady 38-40.

Car is a daily driver and running fine before this started.

Any help/hints appreciated
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Old 01-07-2018, 04:10 PM
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couple other things to consider
Fuel does not prime when key to ON position. Pressure comes up when she tries to crank.

Checked all elect connections to tank, all appears good.

Also noticed when I release fuel gauge pressure, I get some air bubbles. Can you get air trapped in the fuel rails?

dell

added:Can someone answer this?
Even if the fuel pump is erratic, if there is pressure (~40psi) at the rails and the car won't run; it is not due to not getting gas?

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Old 01-07-2018, 07:57 PM
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The ecm controls pump prime koeo via the pump relay.
Have you ohmed your injectors ?
If they are stock multecs the coils are prone to short out.
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Old 01-08-2018, 06:08 PM
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have not checked injectors, replaced them with bosh 3's last year.
cranks, runs at idle a few seconds and dies. while in that few second idle period if I press the gas it dies.

If I try to crank with gas pedal depressed, it coughs and dies like a timing issue

guess i'm stumped for the moment. Acts like it is not getting gas, but fuel deliver up to injectors looks ok

Last edited by wdsj; 01-08-2018 at 06:44 PM.
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Old 01-08-2018, 07:45 PM
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ddahlgren
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Did you try pulling codes?
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Old 01-09-2018, 12:22 PM
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91fora93
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Originally Posted by wdsj View Post
have not checked injectors, replaced them with bosh 3's last year.
cranks, runs at idle a few seconds and dies. while in that few second idle period if I press the gas it dies.
Fuel Pump Relay is under the passenger glove box, I would test that relay first to make sure it's good. Also this thread here: http://www.digitalcorvettes.com/foru...d.php?t=250905 has some good info on the fuel pumps not priming.

When it runs in that short period what is the fuel pressure?

Sounds like the fuel pump isn't keeping enough pressure in the rails to sustain combustion. Have you checked vacuum hose on the fuel pressure regulator to see if it's full of gas?

Originally Posted by wdsj View Post
couple other things to consider
Fuel does not prime when key to ON position. Pressure comes up when she tries to crank.
I think the main problem here is that the new fuel pump doesn't want to prime when you turn the key. If everything was working before this started, then it probably wasn't spontaneous ecm failure. If the fuel pump relay is fine, then my guess is hardware failure on the old fuel pump, and you replaced it with a defective pump. That, or the connectors on the sender unit aren't installed properly. When I replaced the fuel pump on my 91' a year ago (http://amzn.to/2m92LjE), I remember making sure that the connector matched and I didn't have to solder in a new one. There's also the fuel pulsator(someone correct me on the name if I'm off) that sits right above the fuel pump, you can remove that and replace it with an airplane clamped high psi hose.

Could also been oil pressure switch off rear china wall/intake manifold not showing enough psi to prime the fuel pump. I believe it needs 4psi.

Keep us updated on how it's going.

Last edited by 91fora93; 01-09-2018 at 12:53 PM.
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Old 01-09-2018, 01:22 PM
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Originally Posted by 91fora93 View Post
I think the main problem here is that the new fuel pump doesn't want to prime when you turn the key. If everything was working before this started, then it probably wasn't spontaneous ecm failure.

If the fuel pump relay is fine, then my guess is hardware failure on the old fuel pump, and you replaced it with a defective pump.

There's also the fuel pulsator(someone correct me on the name if I'm off) that sits right above the fuel pump, you can remove that and replace it with an airplane clamped high psi hose.

Could also been oil pressure switch off rear china wall/intake manifold not showing enough psi to prime the fuel pump. I believe it needs 4psi.

Keep us updated on how it's going.
Can it not prime but give fuel pressure? Sounds odd to me.

I wonder where he got that new pump?

I wouldn't just shove any hose in there. It better be rated for immersion in fuel. I'd get the kit from Racetronix so you have the gaskets and new bolts and the right hose.

I doubt that matters. That is a backup circuit. IIRC, I pulled that one off just for the hell of it so I wouldn't get any oil pressure reading. Cranked and started so that is kinda the end of the test.
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Old 01-09-2018, 01:41 PM
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Originally Posted by aklim View Post
I wouldn't just shove any hose in there. It better be rated for immersion in fuel. I'd get the kit from Racetronix so you have the gaskets and new bolts and the right hose.


Good to know about the oil pressure switch, one less thing to worry about. Could that redundant loop be the reason why he gets fuel pressure at crank but not when priming?

I can't think of any reason why it would give pressure at crank, and not at ignition, unless an electrical fault (fuel pump fuse, or relay.) It would make sense that if the relay was bad, then it wouldn't receive any signal to prime when OP turns the key to ign on. However if he's cranking the engine and supplying enough oil pressure to turn on the fuel pump (4 psi) then the pump would engage and he would get psi readings. Of course this would mean the pump was only engaged by the oil pressure and not ecm controls, so the pump wouldn't stay on for long and the engine would die. Check me on my logic if I'm off base.
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Old 01-09-2018, 07:04 PM
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Great info folks, now I curious and back at it again.

I checked for codes, no codes.

Here is the whole story.
Car started not wanted to crank and dying at idle. I could nurse it along and get where I wanted to go, but was not good.
I checked fuel pressure and saw about 34 psi, low.
I installed new fuel filter, ran better but still rough at idle; felt like it was not getting fuel.

Replaced fuel pump and strainer. Pressure 38-40 psi with new fuel pump, but noted the pump did not prime (no pressure change) with the key ON Key to crank and the pressure slowly comes up. Also ran no better if not worse.

So yesterday, I reinstalled the original fuel pump. It primes but it is really slow to get up to full pressure.

Now I can't get the engine to run at all. Cranks, runs for a few seconds and dies at idle. Give a little gas in those few running seconds and it dies immediately.

Current status: Original fuel pump with new strainer and fuel filter with rail pressure about 36 psi. Cranks, runs a few seconds and dies. If I apply any gas at the pedal and it wont crank at all. If I apply and pedal while it idles a few seconds it dies immediately. Can't nurse the idle up at all.

I am starting to think the fuel pressure was not the original problem.
I believe it's a fuel problem but maybe not a gas problem.

Currently looking at throttle body and IAS

More information please.

Last edited by wdsj; 01-09-2018 at 07:05 PM.
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Old 01-09-2018, 07:06 PM
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Also, new pump was Delphi from Autozone
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Old 01-09-2018, 08:00 PM
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Can you remove the IA control valve without removing the throttle body?

I have a FSM at home, unfortunately I am not at home and it is.
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Old 01-09-2018, 09:31 PM
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Originally Posted by wdsj View Post
Great info folks, now I curious and back at it again.

I checked for codes, no codes.

Here is the whole story.
Car started not wanted to crank and dying at idle. I could nurse it along and get where I wanted to go, but was not good.
I checked fuel pressure and saw about 34 psi, low.
I installed new fuel filter, ran better but still rough at idle; felt like it was not getting fuel.

Replaced fuel pump and strainer. Pressure 38-40 psi with new fuel pump, but noted the pump did not prime (no pressure change) with the key ON Key to crank and the pressure slowly comes up. Also ran no better if not worse.

So yesterday, I reinstalled the original fuel pump. It primes but it is really slow to get up to full pressure.

Now I can't get the engine to run at all. Cranks, runs for a few seconds and dies at idle. Give a little gas in those few running seconds and it dies immediately.

Current status: Original fuel pump with new strainer and fuel filter with rail pressure about 36 psi. Cranks, runs a few seconds and dies. If I apply any gas at the pedal and it wont crank at all. If I apply and pedal while it idles a few seconds it dies immediately. Can't nurse the idle up at all.

I am starting to think the fuel pressure was not the original problem.
I believe it's a fuel problem but maybe not a gas problem.

Currently looking at throttle body and IAS

More information please.
Sounds odd. Why would it care whether you have your foot on the gas or not? Cranking should be either way.
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Old 01-09-2018, 09:32 PM
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Originally Posted by wdsj View Post
Also, new pump was Delphi from Autozone
Well, IDK what the specs of that pump is. Hopefully it is right. Testing will tell
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Old 01-09-2018, 09:32 PM
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Originally Posted by wdsj View Post
Can you remove the IA control valve without removing the throttle body?

I have a FSM at home, unfortunately I am not at home and it is.
Yes, depending on how careful you are and if you can get the right wrench around the nut part. Also you need a new gasket. Not sure if what you are having is a problem with the IAC.
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Old 01-10-2018, 12:31 AM
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Originally Posted by wdsj View Post
Current status: Original fuel pump with new strainer and fuel filter with rail pressure about 36 psi. Cranks, runs a few seconds and dies. If I apply any gas at the pedal and it wont crank at all. If I apply and pedal while it idles a few seconds it dies immediately. Can't nurse the idle up at all.
While changing the fuel pumps did you test the fuel pump relay and double check/replace the pulsator? While the pulsator is unlikely, you might as well change it now, since it's prone to failure. I'm wondering if the fuel pump relay is bad. Check that and the fuel pump fuse JIC. I think ruling out electrical is a good place to start.
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Old 01-11-2018, 05:49 PM
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Originally Posted by 91fora93 View Post
While changing the fuel pumps did you test the fuel pump relay and double check/replace the pulsator? While the pulsator is unlikely, you might as well change it now, since it's prone to failure. I'm wondering if the fuel pump relay is bad. Check that and the fuel pump fuse JIC. I think ruling out electrical is a good place to start.
Did not change pulsator or check the relay. I have 36 PSI fuel pressure and the fuel pressure holds constant when the engine cranks and when it dies. Hence I don't think I have a fuel delivery problem; make sense?

Why wont it continue to run at idle and why does it die when I apply any gas pedal? Checking TPS operation next.

Keep you ideas coming, they are all good and it makes me think.

thanks
dell
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Old 01-11-2018, 05:51 PM
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Originally Posted by aklim View Post
Sounds odd. Why would it care whether you have your foot on the gas or not? Cranking should be either way.
Engine turns over and sometimes fires and runs for a few (2-4) seconds then dies. Foot on the gas is nursing it to try and get the rpms up; however just a little press on the pedal and it dies immediately.

Poor use of the word "crank". It cranks (starter turns the engine over), it just will not run more than a few seconds at idle and 0 seconds if gas applied. Make sense?

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Old 01-11-2018, 06:14 PM
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checked codes again, now have
code 22 - TPS low
code 14 - CTS high
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Old 01-11-2018, 10:12 PM
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Originally Posted by wdsj View Post
checked codes again, now have
code 22 - TPS low
code 14 - CTS high
Well, the CTS can explain that it has been seeing it as very hot so it leans out the mixture. I would certainly skip the code reading and get scanning.
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Old 01-12-2018, 03:30 PM
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Checked data with turner pro (version 4, I can't get version 5 to stay connected to my car)

Car has not run in days and coolant temp is reading 152 C. not good
TPS has no output. Stays at 0% then starts bouncing around. not good

added: is there a different temp sensor that sends temp signal to ecu vs the dash gauge? dash gauge shows temperature ok

Last edited by wdsj; 01-12-2018 at 03:33 PM.
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