03 Tahoe driveability

[biggsteve97]

I have an 03 Tahoe Z71 with the flex fuel 5.3L. Last week going down the highway engine at operating temp going about 65mph when I pushed throttle halfway down to pass someone the engine stalled and the whole vehicle shook violently. It happened fast and it was like someone turned the key off then back on quickly. It happened two more times over the next 15 minutes then nothing until last night. Engine was cold only about a min or so after startup. When I tried to leave the parking lot it happened again. Only this was barely pressing on the throttle. Its like someone turned the key off then back on again quickly. This happened several more times in the next 5 minutes roughly about the same spot in the throttle. So I floored it from a dead stop and it took off fine no problems full power shifted fine. So I held it in second gear manually at about 35 mph and slowly pressed down on the throttle. The engine suddenly died. Right before the tach dropped below 500 rpm I managed to lift off the accelerator and the engine roared back to life. I have an aftermarket exhaust system so its very easy to hear when the engine stalls out or starts acting weird.
I have no codes or a service engine light. I have checked to make sure all wires are ok. I checked the air box, the filter, the maf sensor, all the connections up to the throttle body, checked the fuel pressure regulator, checked fuel pressure, even checked for leaks at intake, throttle body, and the injectors and found everything to be good. I did a tune up about 3 months ago and there was nothing abnormal about the old stuff and I used ac delco plugs. Fuel filter was replaced earlier this year as well as the fuel pump but that was for a sensor failure not for a pump failure. Does anyone have an idea what this could be. I really thought I was gonna be stranded on the way home last night.

[67ChevyRedneck]

What fuel pump did you use? If it was a non GM pump (delco or delphi) the aftermarket ones are "known" for only lasting 6 months to a year.

How many miles on the tahoe? What was the fuel pressure? When you turn the key off the fuel pressure should hold, if not the check valve has gone bad and fuel is draining back to the pump and it's "about to go." Did you change the fuel filter? I didn't see that on your list above. Also, check your battery/cables. I had a battery that had the + terminal actually fall out of the battery. It was acting "weird", not starting, running rough at times, then one night while checking things I just barely touched the battery cable on the whole + terminal fell out. New battery fixed it.

Someone also mentioned something about the "drive by wire" sensor going bad causing weird stuff like you're describing in another thread, I'm not sure what year GM went to that... I think it was 03? I know my '00 5.3L actually has a cable.

[biggsteve97]

I replaced the fuel filter as well as the pump. I used an Oreilly's pump. The fuel pressure was 51psi. The spec was 48-53 psi for the flex fuel. I wish I had the non flex fuel motor. It seems to have more power than mine and less issues. It holds 48 psi for about 20 mins or so with engine off/key off. It does the same thing as my 02 Silverado with the 4.8L and it runs perfect. Ill check the battery cables but I think they were fine. Gm went to that drive by wire in 03 and I hate it. I would rather have the cable.
I thought I read something about that somewhere as well but I couldnt find it earlier so I started this thread. I was thinking it could be the pedal sensor but wasnt certain. Ive had plenty of throttle position sensors on the 87-95 engines do something like this but I dont want to just throw a pedal sensor at it without be 100% certain. those things are usually expensive.
Oh and it has roughly 183,000 miles.
Oh how I wish I had a tech 2 scanner

[biggsteve97]

Update: Check engine light came on last night. Pulled codes earlier and the only code was a cylinder 8 misfire. The engine runs great, no stumble or miss. Im at a loss. In the morning im gonna move the plug and wire to another cylinder and see if the code comes back.
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[67ChevyRedneck]

Bad coil pack? I guess if there's no change when you move the plug/wire that's what it could be?

[biggsteve97]

Well if it comes to that I will move the coil pack as well. If that doesnt do it. I know i can swap injectors
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[biggsteve97]

Ok. Well I dont see this being the whole issue but I can def see it being the cause of the cylinder 8 misfire....the spark plug was loose by about one full turn. I just tightened the plug and cleared the codes. So far it has not stalled and no ses light yet. Also has more power and better mpgs well according to the dash display for instant mpgs. Ill keep drivng and see what happens
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[67ChevyRedneck]

Dang! I'd check all 8 of 'em as well... you never know, they could be loose too. Crazy.

[biggsteve97]

I did check the rest and found no more loose plugs. I think it was because with the headers there really isnt room for the ratchet. I had to put the socket on first then kinda wedge the ratchet in against the header pipe just enought to get a bite on the socket. I tried a short extension but I was hitting the shield that protects the rear ac lines. So far so good. so I hope that was the only thing. I have never had one single plug ever cause this much trouble on any engine ever.