Hard Start, Stumbling And Sometimes Stallling

[djkicks]

Hello, first post here. I have a 1996 GMC Yukon. I have had a hell of a time with getting this thing running correctly. A few months ago, the fuel pump went out and I had to replace it. Just a few weeks ago it died and would not start and I was able to deduce that the outlet line had come off of the new fuel pump. I dropped the tank and reattached and clamped the outlet line on so that fuel was again flowing.

 

It still wouldn't start. I started looking online and most folks seemed to indicate that maybe the pressure wasn't up to snuff. I got a pressure tester and the pump put out about 52 psi with the key on. It was supposed to be 65. It ran fine before but I got a new pump. New pump installed and now I got good key on pressure of 65 psi but it still wouldn't start. I also noticed that the pressure would quickly drop to 0 after I turned the key off. I had already replaced fuel filter too btw.

 

I replaced the FPR. Finally the truck would start but would sometimes take a while. When driving to get fuel, it died on me but I was able to restart it. Put fuel in the tank and it ran fine but still sometimes took several seconds or attempts to start. Pressure is 65 before starting and about 52 or so while running but still drops off quickly once the key is off and the pump is no longer energized. I don't get any black smoke and none of the plugs seemed fouled. When I changed the FPR I noticed a lot of varnish on the parts inside but didn't have a chance to clean it since I have to get this thing running asap to work. I am kind of at a loss to figure this out and now I don't trust my truck.

 

thanks,

 

DJ

[djkicks]

More info: When the the tank runs below 1/4 of a tank, it sputters and stall like it's out of gas. After limping to work and barely getting to the gas station after, I put about 3 1/2 gallons in and it ran fine but still took several seconds to start. It also seems like my already terrible gas mileage is even worse now but I can't absolutely confirm it.

[jro909]

fuel filter changed? is there any blockage or air in the fuel lines? injectors in good working order?

 

 

 

 

p.s

don't ever run a vehicle below a quarter of a tank, it kills fuel pumps over time

[djkicks]

The fuel filter is brand new. There does not appear to be any blockage in the lines that I can tell. I imagine there is air in the lines when I shut it off since the pressure drops but it pressurizes when the pump is on. I don't know the status of the fuel injectors but the truck had none of these issues before the line on the fuel pump came off. I know about the pumps dying if the tank runs too low but this one is brand new.

 

DJ

 

 

 

<br />fuel filter changed? is there any blockage or air in the fuel lines? injectors in good working order? <br /><br /><br /><br /><br />p.s<br /> don't ever run a vehicle below a quarter of a tank, it kills fuel pumps over time<br />

<br /><br /><br />

[[email protected]]

Fuel regulator? Oh, I see FPR. Could be a leaky injector that's pooling fuel in the intake when you shut it off, thus making it seem like it's flooded when you try to start it for the first few seconds.

[rodram]

... these 96-99 vortec engines with the SCPI injection system need to have 61 to 66 psi fuel pressure at all times of operation, starting and running ....

 

... not sure why your second new fuel pump will not sustain the 61 to 66 psi while running... either a faulty new fuel pump or faulty fuel pressure regulator ... on these engines, the fuel pump is usually the culprit...

 

... everything you describe points directly to low fuel pressure ... the little poppet valve at the tip of each injector needs to have the 61-66 psi behind it in order to operate properly to open and close cleanly to inject the fuel.... I've heard of some engines starting and running as low as 58 psi... but anything below that will not permit the poppet valves to operate when starting or running the engine

 

... ACDelco from a dealer or Delphi brand from a good parts house is the best investment for a fuel pump... the other brands are less reliable (they can useless right out of the box or die within a year), and there are lots of counterfeit pump units out there on the internet that are crap.

 

... I agree that you should not let the fuel tank drop below 1/4 tank ... just adding 3 1/2 gallons to an empty tank doesn't do it.... but as you said, the truck did run but was hard to start.... check the fuel pressure regulator again, and if it appears OK then you have to suspect the fuel pump

[djkicks]

I was wondering about the leaky fuel injector issue as well but wouldn't I get a big puff of black smoke when it started if I had fuel leaking from the injector? Also, would that cause the truck to seem like it's starving for fuel when there is approx 1/4 of a tank? How would I find out?

 

Thanks,

 

DJ

 

<br />Fuel regulator? Oh, I see FPR. Could be a leaky injector that's pooling fuel in the intake when you shut it off, thus making it seem like it's flooded when you try to start it for the first few seconds.<br />

<br /><br /><br />

[djkicks]

<br />... these 96-99 vortec engines with the SCPI injection system need to have 61 to 66 psi fuel pressure at all times of operation, starting and running .... <br /><br />... not sure why your second new fuel pump will not sustain the 61 to 66 psi while running... either a faulty new fuel pump or faulty fuel pressure regulator ... on these engines, the fuel pump is usually the culprit...<br /><br />... everything you describe points directly to low fuel pressure ... the little poppet valve at the tip of each injector needs to have the 61-66 psi behind it in order to operate properly to open and close cleanly to inject the fuel.... I've heard of some engines starting and running as low as 58 psi... but anything below that will not permit the poppet valves to operate when starting or running the engine<br /><br />... ACDelco from a dealer or Delphi brand from a good parts house is the best investment for a fuel pump... the other brands are less reliable (they can useless right out of the box or die within a year), and there are lots of counterfeit pump units out there on the internet that are crap.<br /><br />... I agree that you should not let the fuel tank drop below 1/4 tank ... just adding 3 1/2 gallons to an empty tank doesn't do it.... but as you said, the truck did run but was hard to start.... check the fuel pressure regulator again, and if it appears OK then you have to suspect the fuel pump<br /><br /><br />

<br /><br /><br />

 

Thanks for the added info. I'm wondering about the new fuel pump now too. God knows I'm so not in the mood to take the tank out yet AGAIN. lol. The 3 1/2 gallons I added was to about 4 or 5 gallons already in the tank. That's what was making me scratch my head, if the tank was actually empty or very close, I'd understand that it might sputter. However, experience with this truck has told me that when it's out of gas, it's really out of gas. It gives me about 5 seconds of warning before it's not going to run anymore. That was with both the fuel pump that came with it and the one I put in a few months ago. Now I'm on pump #3 (for me).

[rodram]

... also if you had a persistent leaky injector(s)... you would end up noticing that you are getting a lot of gasoline in your engine oil.. you might get this anyway with all the trouble you have had trying to start the engine ...

 

I don't know a lot about trouble shooting fuel pressure regulators...

 

.. but one thing I do know... is when you get this running again life will be a little more stress free

[djkicks]

<br />... also if you had a persistent leaky injector(s)... you would end up noticing that you are getting a lot of gasoline in your engine oil.. you might get this anyway with all the trouble you have had trying to start the engine ... <br /><br />I don't know a lot about trouble shooting fuel pressure regulators...<br /><br />.. but one thing I do know... is when you get this running again life will be a little more stress free <img src="style_emoticons/default/biggrin.gif" style="vertical-align:middle" emoid="" border="0" alt="biggrin.gif" /><br />

<br /><br /><br />

 

Oh, I didn't think about gasoline in the oil. I will check that. Amen to having less stress in my life. One of my jobs requires me to use my truck for hauling. Not only is this stuff costing me money that I really don't have (hence doing the work myself and not just having a shop fix it) but I'm losing money by not working.

 

Thanks,

 

DJ

[djkicks]

Ok, just spent a few minutes with the truck to get some more info.

 

Key on fuel pressure-60 psi Pressure while running-50 psi

Pressure comes up when key is in the 'on' position and then immediately drops to 0 after a few seconds (when pump stops)

Pressure is 50 while running and immediately drops to zero upon turning off car

 

Pressure checked while pinching return line-

Key on pressure 70 psi while running 60 psi

Pressure immediately drops to 0 when key is off or after a few seconds if key is turned to 'on' but truck is not started.

 

Truck started up faster with return line pinched but, to be fair, had been running for a few minutes beforehand.

Oil SEEMED to smell a bit like gasoline but wasn't overpowering and by now, freakin' everything seems to smell like gasoline. lol

[vettelovralexand]

Ok, just spent a few minutes with the truck to get some more info.

 

Key on fuel pressure-60 psi Pressure while running-50 psi

Pressure comes up when key is in the 'on' position and then immediately drops to 0 after a few seconds (when pump stops)

Pressure is 50 while running and immediately drops to zero upon turning off car

 

Pressure checked while pinching return line-

Key on pressure 70 psi while running 60 psi

Pressure immediately drops to 0 when key is off or after a few seconds if key is turned to 'on' but truck is not started.

 

Truck started up faster with return line pinched but, to be fair, had been running for a few minutes beforehand.

Oil SEEMED to smell a bit like gasoline but wasn't overpowering and by now, freakin' everything seems to smell like gasoline. lol

 

Trick that I learned a while ago. take a drop of oil and put it on a piece of paper. If there is fuel in it, you will see two distinct rings where the fuel more quickly absorbs into the paper than the thicker oil. Takes smell out of the equation.

[djkicks]

Ok, more info. I'm pretty sure that my 'new' fuel pump is a clunker. I went out and energized the pump and once again pressure went to 60 psi. I then clamped the output line of the fuel pump to see if the leakdown was at or after the pump. The pressure held fine. There doesn't seem to be anything leaking at or after the fuel rail. The pressure drop is due to a bad fuel pump. Curses.

 

DJ

[[email protected]]

Yep sometimes the relieve valve on the pump won't hold pressure like it should. Definitely return that one for a new one. I've noticed that aftermarket fuel pumps are usually inferior to their OEM counterpart. Just one more thing to keep in mind.

[djkicks]

<br />Yep sometimes the relieve valve on the pump won't hold pressure like it should. Definitely return that one for a new one. I've noticed that aftermarket fuel pumps are usually inferior to their OEM counterpart. Just one more thing to keep in mind.<br />

<br /><br /><br />

 

I called the place I got it from and they are going to give me a refund. And I didn't even have to get nasty. :-)

 

I'm not looking forward to installing another pump though. On the bright side, I'm getting pretty damn good at it. loll

 

DJ