BW5.7

I read a bunch of old threads but none exactly fit my symptoms. 99 Tahoe K1500


I have a loss of power and stumbling under moderate to heavy acceleration as soon as I tip in the throttle. In light acceleration, there is not a problem. It is fairly inconsistent and 10% of the time, during these stumbling episodes under acceleration, it will abruptly snap out of it and pull normally for a couple of seconds at a time and then revert back to stumbling. At WOT at 50 mph, it will barely gain any speed until you back off the throttle.


Based on reading other posts, I checked fuel pressure while driving. I actually put the gage under my windshield wiper. I found the following:
At Idle -> 50 - 54 psi
Coasting with foot off the pedal -> 50 - 52
Light Acceleration -> 55 - 57
WOT at 50 mph -> Usually 50 - 55 psi (Stumbling) / But Intermittently 60-61 with great power before reverting back to 52!


I would say it's the pump but the occasional blips of 60 psi with power make me think it's not the pump. Maybe the FPR? Has any one seen this behavior? What was the culprit?


Also, I pinched off the return line and started it in park and got 57 psi dropping to 54 when I touched the throttle a couple of times.


Thanks for any advice!

BW5.7

I also wanted to mention that I don't have any codes and not too many miles ago replaced the entire ignition including distributor to fix a misfire. Also the truck has 215k miles and replaced the fuel pump at about 110.

bobpur

I, too, have performance issues with my Suburban.
My fuel pump was tested at 63p.s.i. The normal range is between 60-66 p.s.I.
When was the last time you checked your fuel filter or pump?
This new gas isn't the best thing to be putting in your tank. You might want to try some high test and see what that does. Get gas that is all gas not the corn juice blend.
Good luck.

Hazcatman

Hi. I have been chasing a weird problem with his truck. Starts and runs smooth as silk stopped or on any speed on flat ground. Every time I accelerate up a steep hill, at exactly the same spot, it begins to hesitate, shudder and loose power. Once I clear the hill it will recover and drive ok. I ran it up this hill with a fuel pressure tester attached. I believe the spec on this one is 61-66 psi. At the time of hesitation the fuel pressure goes to about 57 and oscillates. Am I looking at a problem with the pump or somewhere else? fuel filter replaced, It had an O2 sensor left bank code, I replaced both O2 sensors. It had a cat code that went away after the O2 sensors were replaced. Thought maybe it was a coil breaking down possibly so that was changed. Full tune-up including cap, roto, wires, plugs. MAF sensor is clean.

I can duplicate this condition without fail on hills. I must say that I don't feel the acceleration on the flat ground is as good as it should be. Steady without hesitation, just not strong without downshifting.

Any ideas? Ted

OBS Kye

Did you find out what the issue was??? I'm having the exact same issue with loss of power, shuddering on the exact same hills and can replicate it with ease. I get P0300, P0303 and P0304 codes and a flashing engine light when it happens. Replaced everything I could think of fuel and ignition wise but I havnt done the crank pos sensor or throttle pos sensor yet.... or replaced the entire ECM haha.

MitchM

i am having the same weird problem. see my threads the last couple days on chevy express van p0300 random misfires in the van forum.i have only 52,000 miles on my 07 3500 express . regular oil changes w oil topped up, i use mobil 1 per the specs, do the change every 3000-4000 miles , LONG before the oil change lite comes on.

i did all the maintenance hazcatman suggested. fuel pressures test fine. no EGR codes. new MAF. injectors got professionally cleaned not just seafoamed. AND replaced the crankshaft position sensor w ac delco and relearned it TWICE. also cleaned up my ECU ground . i was getting a steady yellow MIL w a dtc of p0300 random misfire before and after all that work.

after the cCkPos replacement and 2 nd relearn i got worse codes: the steady MIL it threw at more than 2000 rpms only when pulling up a hill at speeds over 65 changed to a briefly flashing MIL , then back to a steady MIL . then when i leave up on the gas pedal at top of hill, and coast down the hill the MIL completely goes out. i get no p0300 and no MIL whatsoever if i drive at low rpms say less than 40 mph. up hills or not at slow speed does not throw a code. i never have knocking sound weird engine noise rough running or loss of power .

i found a few threads suggesting the newer timing chains are poorly designed and stretch out on the 'hi powered' v6 engines , mine is a high powered vortec. a timing chain that 's slipping due to lousy design could cause the random misfire . it's an expensive 12 hour repair.$500 just or the chains.

i sure wish a gm tech could explain what's going on. i hear the gm chevy dealers have very fancy computer diagnostic modules far better than the best obd the independent guys can get. so i guess i'll get myself there to my dealer next and apply for the bank loan to fix it...

BW5.7

I think I started this link years ago. Sorry for not replying with what fixed my problem. My 99 tahoe came with the original poppet valve operated fuel injection assembly which operates by pressure piloted fuel injector valves. These get fouled up over time and dump fuel into the intake causing all kinds of problems during acceleration especially. You can read my original post. I replaced this with an updated Multi-port fuel injection retrofit by GM/AC Delco - purchased off of Amazon: Description copied from my email below:

ACDelco 217-3029 GM Original Equipment Fuel Injector Kit with Bracket

This completely fixed my problems. I still have the truck and it runs like a sewing machine at all throttle positions and engine speeds with 241k miles. Before this I replaced the fuel pump and filter which did not fix the problem.

robbell87

My 08 LT does the same thing but only when I get low on fuel about 130 km to empty if i gas to hard.. u explained it to a T except it only happens when low fuel

Paulhomer11

It will be your FPR and then clean bank 2 (O2) sensor, run some sea foam in it and itll be ok! Viscosity of engine oil has to be good so camshaft sensors get a good reading and it will time itself.

MitchM

I had the exact symptoms in my 07 3500 w vortec engine for more than 2 years. p 300 random misfires, especially when pulling up a hill under load in hot weather. after 3 shops firing the parts cannon at it for 2 years (did do: 3 crank position sensors w re learns, 2 MAF s , coil pack, wires tuneups, new cam position sensor. I rejected suggestions to replace e c u and the timing chain . ) ,

in July 2022 I took it to a a 4th independent mechanic, I had a steady p 0300 and it was starting to throw intermittent P 0336 and occasional p0339 DTC s. with a good scan tool, he figured out there was fine fuel pump pressure but saw bad and variable signal voltage in the fuel tank pressure sensor . (the DTC s I had recorded over past 2 months showed were p 0300, one or 2 p 0336, and one p0339 . ) there was NO code specific to the failing f t p s. ) he realized that f t p s might be intermittently failing from his electric signal voltage readings on the f t p s , (without dropping the fuel tank. ) a bad f t p s can cause erratic signal to the p c m which then sends wrong fuel - air ratios to the injectors resulting in the p 0300 random cylinder misfire. he also noted a P 336 intermittent DTC and intermittent 339 suspect erratic solenoid operation. though the solenoid functioned fine to open and shut when he tested it. he suggested : replace both f t p s and solenoid, since they have to drop the tank for f t p s install . (has shop didn't t have a heavy duty lift for my 8000 # roadtrek rv modification on the 3500 chassis. ) the chitons and Haynes manuals have explanations of how a faulty f t p s and solenoid can cause bad signals to p c m of how much fuel to send to the injectors, too lengthy to go in to here. )

with his data I took it to my chevy dealer and insisted they replace the f t p s and solenoid . they did n't want to do it " because it isn't coding p0300 336 or 339 now and we don't accept customer OBD -II readings. . " I insisted and that work was completed fall 2022.

I have had no p 300s AND no symptoms AND no codes for the last 3 months. it runs fine up hills , just like the olden days of its golden 2007 youth.