Fuel Injection issue

Executioner · Post by **Executioner** » Mon Jul 22, 2013 7:54 pm

I'm and old school guy that knows carburetion. On my 96 Corvette, 2 times out of 4, it will not start and takes several cranks before it does. Once it does, it runs just fine.

Background: I only drive the car once a week (unless the wife and I decide to take it out for a spin). I'm in a carpool, so I only drive it on Monday's when I'm a solo driver.

I checked the fuel pressure at the rail and found it was only 18 psi with the key in the on position (engine not running). I then pinched off the return line and checked again. Still the same at 18 psi. Did this about 10 times with no change in the pressure. I also checked the fuel pressure regulator and there was no gas in the vacuum line. I also ruled the pressure regulator out since the car drives and performs. As for the pressure, it seems to hold even at the low pressure indication of 18 psi.

When I crank the engine over, I get the required 40 psi. I also noted that the pressure holds when the engine is turned off.

Could this be the fuel pump? Forgot to mention that the fuel filter was replaced less that 10 months ago. I only run Chevron 91 octane.

DaMaN · Post by **DaMaN** » Mon Jul 22, 2013 8:11 pm

fuel pump or fuel injection could be going. Is that a 5.3L engine?

Executioner · Post by **Executioner** » Mon Jul 22, 2013 10:41 pm

5.7L. If it was an injection, I would think that it would not hold pressure. Not really sure since I'm not an expert with fuel injection.

EvilHorace · Post by **EvilHorace** » Tue Jul 23, 2013 8:14 am

FP won't go up with just the ign on so 18psi isn't abnormal. The ECU has to see a crank signal before turning on the FP.

Key Keeper · Post by **Key Keeper** » Tue Jul 23, 2013 11:25 am

The fuel pump should turn on for a few seconds when you cycle the key. The 18psi seems to be normal from that cycle. I would start it up with the gauge on the rail and then shut it off and leave the gauge on it. come back a few days later and see if the pressure is still holding. If it is then it rules out regulator and injectors for sure since they are holding. My GF truck does the same thing. I just cycle the key 3 times before starting it and it fires right up every time.

Executioner · Post by **Executioner** » Tue Jul 23, 2013 1:36 pm

Key Keeper wrote:The fuel pump should turn on for a few seconds when you cycle the key. The 18psi seems to be normal from that cycle. I would start it up with the gauge on the rail and then shut it off and leave the gauge on it. come back a few days later and see if the pressure is still holding. If it is then it rules out regulator and injectors for sure since they are holding. My GF truck does the same thing. I just cycle the key 3 times before starting it and it fires right up every time.

According to specs, as soon as you turn the key to the on position, I should have 38-42 psi not 18.

EvilHorace · Post by **EvilHorace** » Tue Jul 23, 2013 7:40 pm

All Imports that I've ever worked on require an RPM signal for a FP to operate and I was always told that that was a safety concern in the event of an accident. Apparently GM is different.

Anyway, I've done a little searching but your best bet is on a 'vette forum.

When it doesn't start, have you then tryed to spray starting fluid into an intake hose? If it then starts off that, you know it's fuel related.
Do you know the injectors pulse, tested with a device called a "noid"?

Any fault codes?

http://www.justanswer.com/chevy/68bgw-1 ... ssure.html

http://www.corvetteactioncenter.com/for ... rting.html

Executioner · Post by **Executioner** » Tue Jul 23, 2013 9:47 pm

EvilHorace wrote:All Imports that I've ever worked on require an RPM signal for a FP to operate and I was always told that that was a safety concern in the event of an accident. Apparently GM is different.

Anyway, I've done a little searching but your best bet is on a 'vette forum.

When it doesn't start, have you then tryed to spray starting fluid into an intake hose? If it then starts off that, you know it's fuel related.
Do you know the injectors pulse, tested with a device called a "noid"?

Any fault codes?

http://www.justanswer.com/chevy/68bgw-1 ... ssure.html

http://www.corvetteactioncenter.com/for ... rting.html

Thanks for the links! I have a code tester, but haven't tried that yet. I spoke to a mechanic that I trust, and he told me:

Your Fuel Pressure Should Hold At 41-47 psi.
As To Low Pressure, It Could Be Wiring, Voltage, Pump, Lines, Filter Ect.
A System Test Would Pinpoint The Malfunction.

So I'll be leaving the car with him. I simply don't have the time to deal with it now. We just had a layoff at work and I survived layoff #8. My wife goes into surgery next week on her colon, but I will be putting my code reader on this weekend to see if threw any codes.

Executioner · Post by **Executioner** » Sat Aug 10, 2013 1:20 am

Update: got it fixed. It was the fuel pump. As soon as I turn the key to on, I have 50 psi. If I start the car, it drops to 47 psi so I'm good to go. Also the strainer that is attached to the fuel pump was black and split open so it was not even filtering anything going into the fuel pump. Don't know if the color has anything to do with it. Thought it might have been like a cream color instead of black.

When I used a code tester, no codes were shown on the instrument. Also had the transmission serviced. Damn parts were expensive. Brake down:
Transmission Filter Kit: $40
Dexron-VI: $54
Fuel Pump Kit: $157
Fuel Filter: $14
Strainer Assembly: $50
Transmission Additive: $22

Total Parts: $336
Labor: $388

DaMaN · Post by **DaMaN** » Sat Aug 10, 2013 9:19 am

Glad you got it resolved.

EvilHorace · Post by **EvilHorace** » Sat Aug 10, 2013 10:32 am

That's not too costly IMO. I recently had to replace the fuel tank sending unit assy with pre-pump in my '94 Volvo 945T because the gauge wasn't working right. The part was $500 and that my discounted price. No labor cost but still....

DaMaN · Post by **DaMaN** » Sat Aug 10, 2013 11:00 am

My AC Delco fuel pump and sending unit was 225 from rockauto.com but i installed it myself.