Running like garbage
January 23rd, 2014, 9:18 PM
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Running like garbage
Hi everybody, this looks like a great place. I wonder if y'all could help me. I'm pulling my hair out.
I've got a 2004 flex fuel suburban 4x4, 5.3 engine, 130,000 miles. Pretty much use it just to haul the family around, no towing or offroading. I've had a misfire at idle for almost a month. Prior to that it was throwing a code, can't remember the P number, but it was the fuel vent purge valve on the intake manifold, replaced it and cleared the code and hasn't thrown one since. Shortly after that fix it began idling rough and misfiring. There's been no noticeable power loss above idle, but just leaving a stop light there's been a stumble from the miss. Last Sunday we ran around town, I noticed the miss seemed to be getting worse. Parked the burb in the garage and the next morning it wouldn't start. Just crank and crank, not even pop off at all. After cranking on the starter for a while, finding a spark from #2 and #4 plug wires to the exhaust manifold to be orange in color but jumping about 3/4 inch gap, checking for gas at the Schrader valve and getting a spary, shooting some ether in past the throttle plate, and still not getting the engine to even try to start, the SES light was on. Bought a code scanner and fuel pressure gage the next day. Found no codes (even though the SES light was still on) and pressure in the fuel system at the Schrader valve. Pressure when the key is switched to on jumps to 52 psi, then drops to 48 when the pump shuts off, then drops to 42, then up to 50, over about three minutes. Still no start. Battery was getting tired so stuck the charger on it and went to bed.
The next day after work - removed the charger, shot a bit of ether in the throttle body (forced open the throttle plate), and the thing started right off. Let it run, SES light went out, shut it off, restarted maybe four times. I thought it was the battery. Still checked the fuel pressure though, just for some data. Install the gage, turn key on, 48psi down to 42, back up to 50 just like before. Start the engine, the needle vibrates like crazy over a 4 to 10 psi range, but stays between 40 and 50. Then shut the engine down and turn key to off. Then switch to run (not start), psi hits 52 while the pump is on, drops to 50 and stays steady over 5 minutes. Start the engine and needle vibrates like crazy around mid 40's.
Next day at lunch, no start. I heard that Wide Open Throttle might send a signal to disregard low fuel pressure limit in some cars, so tried that and it started. Restarted a few times with just the key, not moving the accelerator.
Today after work, no start. WOT when trying to start again, and it starts. Restarted 4 times without touching the gas. Took it to part house to check battery, battery is good (12.9 V loaded). Still running rough, and stumbling off the line. Mashed the gas from about 15 mph and it pulls hard and smooth up to 5500 rpm.
I don't think its fuel filter but bought one anyway and will put it on tomorrow, but since it pulls hard to redline I don't suspect it will help. I'm thinking maybe fuel pressure regulator? Would I see >50 psi with a bad pump while its running?
I'm wondering what you guys think... Anyone want to throw in?
I've got a 2004 flex fuel suburban 4x4, 5.3 engine, 130,000 miles. Pretty much use it just to haul the family around, no towing or offroading. I've had a misfire at idle for almost a month. Prior to that it was throwing a code, can't remember the P number, but it was the fuel vent purge valve on the intake manifold, replaced it and cleared the code and hasn't thrown one since. Shortly after that fix it began idling rough and misfiring. There's been no noticeable power loss above idle, but just leaving a stop light there's been a stumble from the miss. Last Sunday we ran around town, I noticed the miss seemed to be getting worse. Parked the burb in the garage and the next morning it wouldn't start. Just crank and crank, not even pop off at all. After cranking on the starter for a while, finding a spark from #2 and #4 plug wires to the exhaust manifold to be orange in color but jumping about 3/4 inch gap, checking for gas at the Schrader valve and getting a spary, shooting some ether in past the throttle plate, and still not getting the engine to even try to start, the SES light was on. Bought a code scanner and fuel pressure gage the next day. Found no codes (even though the SES light was still on) and pressure in the fuel system at the Schrader valve. Pressure when the key is switched to on jumps to 52 psi, then drops to 48 when the pump shuts off, then drops to 42, then up to 50, over about three minutes. Still no start. Battery was getting tired so stuck the charger on it and went to bed.
The next day after work - removed the charger, shot a bit of ether in the throttle body (forced open the throttle plate), and the thing started right off. Let it run, SES light went out, shut it off, restarted maybe four times. I thought it was the battery. Still checked the fuel pressure though, just for some data. Install the gage, turn key on, 48psi down to 42, back up to 50 just like before. Start the engine, the needle vibrates like crazy over a 4 to 10 psi range, but stays between 40 and 50. Then shut the engine down and turn key to off. Then switch to run (not start), psi hits 52 while the pump is on, drops to 50 and stays steady over 5 minutes. Start the engine and needle vibrates like crazy around mid 40's.
Next day at lunch, no start. I heard that Wide Open Throttle might send a signal to disregard low fuel pressure limit in some cars, so tried that and it started. Restarted a few times with just the key, not moving the accelerator.
Today after work, no start. WOT when trying to start again, and it starts. Restarted 4 times without touching the gas. Took it to part house to check battery, battery is good (12.9 V loaded). Still running rough, and stumbling off the line. Mashed the gas from about 15 mph and it pulls hard and smooth up to 5500 rpm.
I don't think its fuel filter but bought one anyway and will put it on tomorrow, but since it pulls hard to redline I don't suspect it will help. I'm thinking maybe fuel pressure regulator? Would I see >50 psi with a bad pump while its running?
I'm wondering what you guys think... Anyone want to throw in?
February 2nd, 2014, 6:35 PM
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I went ahead and installed a new fuel pump. The misfire at stop signs seems to be gone, but there's still quite a bit of hesitation when you leave a stop. I installed a Delphi pump, and it's only been in the vehicle for about an hour. I just took a test drive and parked it. When I started it up at first, it did the same thing it was before - acted like it wanted to start and wouldn't go, then just crank and crank. As soon as I opened the throttle (wide open) it fired up. Would you expect this immediately after a fuel pump replacement?
February 2nd, 2014, 7:24 PM
#4
I went ahead and installed a new fuel pump. The misfire at stop signs seems to be gone, but there's still quite a bit of hesitation when you leave a stop. I installed a Delphi pump, and it's only been in the vehicle for about an hour. I just took a test drive and parked it. When I started it up at first, it did the same thing it was before - acted like it wanted to start and wouldn't go, then just crank and crank. As soon as I opened the throttle (wide open) it fired up. Would you expect this immediately after a fuel pump replacement?
I found this online which might help?
Troubleshooting - Engine
Your fpr?
February 3rd, 2014, 12:32 PM
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Over lunch I checked the pressure - key on pump running 52psi, pump shuts off 50 psi, running at idle 44 psi, engine off after running slow gain to 50psi and holds. This is a flex fuel vehicle, I've been told that 48 -54 psi is sufficient, but I don't necessarily trust that source. Could this be a bad pump? Regulator?
February 13th, 2014, 7:42 PM
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Well, just to fill everyone in so they might give it a try if needed. I think the problem is fixed. All it took was a can of BG 44K in a 1/2 tank of gas. Thing was running tons better in less than 15 minutes. At least I have a new fuel pump, ought to last a while now.
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