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un
New User
Jul 31, 2012, 11:15 PM
Post #1 of 8
(4250 views)
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1999 tahoe 5.7, 148,000 mi. Driving long distance from MN to MT and the tahoe lost power and stalled, could start and go 1 to 2 mi before the same prob again, check eng. light came on (94 deg out). Mechanic checked next morning, fuel pressure OK, check eng. was both front O2 sensors, they changed fuel filter (was dirty)((also has a new fuel pump, less than 4 months old)). Drove about 300 mi and the same prob started again, no check eng. light (99 deg out). Myself and the mechanic tried new mass airflow sensor, catalytic convertors not clogged, fuel pressure good, cleaned distributor, still not running well. Next morning made a run for it and made it the 200 mi. home with no probs (never over 86 deg). I think it was vapor lock, but could it be the fuel pressure regulator, or something else? Would love to know what the F is going on, thanks for any info.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Aug 1, 2012, 2:02 AM
Post #2 of 8
(4211 views)
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These shouldn't suffer from vapor lock at all - a problem mostly from both ambient temp and engine heat boiling fuel in the lines. What these do suffer is fuel pressure problems and heat is a huge enemy of fuel pumps.
Replacements if not OE fail terribly.
What was the dirt in the fuel filter? Critical as if a magnet would pick up debris poured out of it you may have a seriously rusted gas tank. I know those temps you listed seem hot but to a vehicle that's nothing. Extremes bring out the weak links either way, hot or cold. It will have to be checked while it's happening for fuel pressure.
By about 58 PSI they will show symptoms and won't even run at about 55 PSI!
T
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Hammer Time
Ultimate Carjunky
/ Moderator
Aug 1, 2012, 3:15 AM
Post #3 of 8
(4205 views)
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Tom is on the right track here. You need to know the exact fuel pressure as the problem occurs. The spec is 60 to 66PSI and as tom pointed out, will not run under 55PSI
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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un
New User
Aug 2, 2012, 1:08 AM
Post #4 of 8
(4173 views)
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First time prob happened, key on...55psi, running...60psi. After new fuel filter installed, key on...60psi, running...65 psi. Second time prob happened, we checked fuel pressure when revving the engine while engine was missing (hesitating, gasping) and pressure was 65psi. Question, how do you know non-OE pumps fail... do you work on a lot of GMs? Also, fuel tank is plastic, or can that much rust come from fittings, attachment points, etc.?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Aug 2, 2012, 3:58 AM
Post #5 of 8
(4164 views)
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Hmmm? You saw 55 KOEO and this is intermittent as apparently it can go for hours/miles without trouble. I doubt fuel filter if clogging but not solidly blocked would mess with plain Key On Engine Off testing.
OE or aftermarket? Did battle with an intermittent one, history since new always caught it within correct pressures but had witnessed having to try twice ( a never with that vehicle) to start from cold but could go weeks with no more issues. That one finally caught with ~53 PSI not for long and condemned it. New whole OE unit and it's fine now going over two years.
Yes -the OE vs aftermarket has been reported here, elsewhere and with the shops I deal with that do many more by volume of vehicles AND parts stores (not grocery store parts stores) warnings of the high failure rates.
Dirt of what type in fuel still could be rust with plastic tanks from the source it was in before you bought it or items not rust resistant on the vehicle - even damn fuel filters rust so bad the pour out fuel!
Other is battery and operating voltage tossed in. Now if that's a factor you need to know it's voltage holding with plain KOEO and nice to know a voltage drop when cranking which would be a clue of its reserve to hold proper amps at proper voltages. Certainly if charging system is behaving it should behave while engine is running.
Stinks when a problem refuses to stay broken consistently but if you trust that 55 PSI reading that's a reason,
T
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un
New User
Aug 2, 2012, 4:35 PM
Post #6 of 8
(4149 views)
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Changed out fuel filter today and it was clean. When pump was changed out they had to put a new fuel pump retaining ring on (old one was rusted badly), I am guessing that is where the crap in the filter came from? Fuel pump is a NAPA "OEM equivalent" part... you think this part is no good?
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Hammer Time
Ultimate Carjunky
/ Moderator
Aug 2, 2012, 4:49 PM
Post #7 of 8
(4146 views)
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You have to look closer at it to see if there is a brand name or country of origin. I got a Napa pump the other day that was actually a Carter which I've had decent luck with.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Aug 2, 2012, 6:23 PM
Post #8 of 8
(4138 views)
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NAPA (plug for the outfit) has been my #1 most dependable source of parts since forever and historically held strong to quality products and rarely the low price. Back far enough they didn't cater to (but would) walk in customers but dealt more with the trade at least locally.
Competition is wild out there and it's sink or swim so more and more the packaging says NAPA but the part could be from anywhere and they will tell you up front if known or my folks do.
It gets worse. Have gone to new vehicle dealers and their parts can be outsourced as well then I'm ticked off after being willing to pony up the price.
Forget that for now. If it was the best known part it is still possible to have a problem with it. For this problem and vehicle it is known that they are very fussy about fuel pressure. Wish the dang things would just fail outright and take out the games but not always the way it happens. Codes TMK will not tell you of a momentary below spec pressure but if/when it can cause engine to run poorly and set a code noticing that.
It is still high on the list IMO newer or not and stinks,
Tom
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