No engine lights appear and no codes show up. At a speed of 70-74 mph my Tahoe 4WD LT misses badly. If I let off the gas it runs fine and if I floor it the engine performs normal.

If I am on a ramp getting onto the highway and floor it to 95 mph, I have no problem. Only problem is when I creep up to the 70 mph mark.

Vehicle has 135K miles with a rebuilt transmission at 10K miles, fuel pump replaced at 89K miles, platinum AC Delco plugs at 50K miles. Still have original wires cap and rotor. Is this an electrical problem? I replaced the fuel filter a few days ago and ran some injector cleaner thru the tank. problem is very consistent. i turned off the performace chip and the same thing occurs. The analyzer shows no code detected in engine.

I have a 99 with the exact same issue. I have chased this problem for a year. The only thing I've found that made my truck quit acting up at 70mph was Seafoam. I ran two cans through my truck with a tank of premium. I've been running premium gas since then and I haven't had the condition return. By the way, I changed plugs, plug wires, Distributer cap, rotor, EGR, trans flush, U-joints, fuel pump, and, when it first started, I put a set of shocks on it because it shook so bad. I have read every post on this issue for the past six months. I think the most likely root cause of this condition is the carbon build up in the 5.7 vortec engines. Everyone says it's a characteristic of this design. Let me know what you find out on your truck. I hear the Seafoam fix is only temporary. I have also read that a cam position sensor may be a factor, but I never changed mine. It has something to do with the timing. Some also blame it on worn distributer gears. I haven't changed that yet either.

Very interesting! Did you pour a can of SeaFoam right into the tank along with premium fuel or did you pour directly into the throttle body right into the injectors? Last night the Tahoe shook worse then ever at 72mph and so bad that my anti-lock brake light came on and I tried re-setting and getting a code reading directly from the computer using my analyzer and the computer shows no error codes. Everything you say about the distributor gears and cam sensor makes a lot of sense. I need to change my wires and cap/rotor as they are still original. Any chance that this might be a transmission issue while it is under load?? I dont think this is electrical, but mechanical and it is either the transmission, the timing and mix in the carbon build-up issue and we have a real head scratcher going. Have you had the dealer take a look and do you think it is something I should just let them handle?? I am sure they have seen this problem before. Thanks a lot for any comments you have and I will keep you informed.

Get it put on a good engine/transmission capable scanner.
Ther problem should show up and codes should be stored in history or present.
Post back any codes.
MT

I have had this on my 98 C1500 for a few years now. Thought I had it fixed a few times. Mine is sticking valve guides. Still runs too good to mess with. Shaking is annoying but I just adjust my foot on the accel to get through the moment. I have 110K on my engine. On a recent hwy trip I got 18.7 MPG running at 75 mph. I put 2 cans of Rislone and 3 cans of Mobile Syn oil in last oil change. After 2000 miles it may be just a bit better. My idea is to get a bit of blow-by into the cyl so the intake or exhaust valve stem gets a bit more lube than normal. I have replaced all the ignition system, cam sensor, checked the gear, etc. Chevy dealer confirms the diagnosis but agrees not bad enough to pull the heads. Compression is 185-192 over the 8 cyl. No codes posted on my truck.
Best of luck and Happy New Year,
Steve

i have also seen this when the TCC starts slipping. Mmmoss10 did a tranny flush along with that long list, and that may have been his problem. check your trans fluid for water, or other contaminants and so on. good luck

I'm not sure what Hippy is referring to when he says the "TCC" starts slipping. My truck still had the shudder at 70mph even after the trans flush was done (at the dealer). I put two cans of Seafoam in one tank of premium gas and ran it until it was almost empty. That made the condition go away. One more thing my truck was doing was pinging awful bad. I'm still thinking it is the carbon build up.

My friends. Aprreciate all of the comments and it appears there are at least 10 different scenarios for this stalling/missing at 72 mph.

If I can make the condition go away with 2 cans of Sea Foam in the tank I will run over to Pep Boys in the morning and do that. I will also change the plugs and maybe even the rotor and cap as they are all originals. I do have platinum plugs with about 75k miles on them. May check their condition as well. I might dump a can into a 1/4 tank of 89 octane fuel and let the magic begin. I am running a Hypertech performance chip on my Tahoe. Have heard the extra boost can put a strain on misc powertrain components. Any comments. I have run Mobil 1 in engine since new and have run Mobil 1 SHC ATF in Trans after the warranty went out and Mobilube SHC 75W-90 in front and rear diffs.

Still am getting no codes on my analyzer and it is the same as the dealer uses. I think that if my changes don't clear things up, I will have the Chevy dealer give it a shot. If carbon was the issue, why is the performace being affected only at 72 mph.?? I would think that it would run spotty at 90 mph and even idle roughly.???

What is TCC ??

Torque Converter Clutch. In 3rd and 4th gear, the PCM will lock up the converter if the throttle position is constant and the speed is the correct range.

//2000CAYukon

My friends. Aprreciate all of the comments and it appears there are at least 10 different scenarios for this stalling/missing at 72 mph.

If I can make the condition go away with 2 cans of Sea Foam in the tank I will run over to Pep Boys in the morning and do that. I will also change the plugs and maybe even the rotor and cap as they are all originals. I do have platinum plugs with about 75k miles on them. May check their condition as well. I might dump a can into a 1/4 tank of 89 octane fuel and let the magic begin. I am running a Hypertech performance chip on my Tahoe. Have heard the extra boost can put a strain on misc powertrain components. Any comments. I have run Mobil 1 in engine since new and have run Mobil 1 SHC ATF in Trans after the warranty went out and Mobilube SHC 75W-90 in front and rear diffs.

Still am getting no codes on my analyzer and it is the same as the dealer uses. I think that if my changes don't clear things up, I will have the Chevy dealer give it a shot. If carbon was the issue, why is the performace being affected only at 72 mph.?? I would think that it would run spotty at 90 mph and even idle roughly.???
My truck started out only doing this at highway speed under a slight load or incline. The condition will get worse if it is indeed the sticking valve guides.
My perf is great as noted, 18.7 MPG HWY...
Seafoam used to help but does not help me anymore....
Best of luck.

Greetings...this afternoon took my tahoe into a reputable AAMCO/Cottman tranny shop and this technician jumped on board along with his scanner and test drove the Tahoe as the scanner did its magic. Finall result is that the rpms going into the torque converter from the engine and the output into the transmission is as normal as can be. I was assured that my Tahoe's Transmission is running fine. The TCC is NOT slipping!! I stopped off and picked up platinum plugs, Silicon wires, rotor and cap (ALL AC-DELCO) and if that does not solve the issue I will take it into a dealer. I dumped a can of Sea Foam into the tank with about 5-gallons in it and drove 12 miles to put 10 gallons of premium along with a second can of Sea Spray to see if any carbonization on the injectors gets cleaned up in the mean time.

There is "no pour in the tank" long term fix if the valve guides/carbon is the problem, the guides must be reamed another .0015 to gain the proper valve stem to guide clearances.

Glad to hear that the tranny is O.K. I think you will see an improvement with the Seafoam. It's freakin' MAGIC.:grinyes: Good luck. If you do decide to take it to the dealer, please post the results! Might save us a buck or 500!

Mr Moss - I will definitely post any and all actions that I take on getting this issue fixed. Tonight I was able to change 8 plugs (kept the original wires, rotor and cap and took the truck out for a spin. The Platinum Bosch plugs were fowled pretty bad and their gap was 0.050 mm. I installed 8 AC Delco Platinum and gapped them to the recommended 0.060 mm.

Still has that severe miss in the mid 60s mph. Tomorrow I will change the Wires, cap and rotor and test drive it again just to see if there is any difference and to see if the Sea Foam has done anything. I cant imagine the valve guides are sticking. I must be living in denial because I just can't see that happening, but there are a couple of guys that swear that is what their issue was. That would be a huge job!! I hope that is not my problem. Will keep you updated!!

I wish you the best of luck, all thoses parts are not cheap, I know. If you plan on keeping the truck, go ahead, good maint. If you may sell due to the sticking valves, leave it alone and trade it now. My $$$$ long term is on the sticking valve guide problem...

Yesterday the tahoe would barely run after running decently in the morning. This morning I (barely) made it to the dealer and they confirmed that the miss and the stalling/back-fire of the engine was a bad fuel pump. The Crankshaft sensor went out, they will de-carbonize the injector system and I should be good to go!!

Yesterday the tahoe would barely run after running decently in the morning. This morning I (barely) made it to the dealer and they confirmed that the miss and the stalling/back-fire of the engine was a bad fuel pump. The Crankshaft sensor went out, they will de-carbonize the injector system and I should be good to go!!
you have stated at 89k mi fuel pump replaced. what name of pump is it as this failure is premature. i hope they guarrantee that what they replace will fix this problem in writing........good luck!

I installed new Die-hard battery (last silver model lasted 7+ years!!!), new AC Delco plugs, wires, cap, rotor and fuel filter ($335) and now the dealer hit me for $1450 for the injector system maintenance, replace crankshaft sensor, drop the tank and replace the fuel pump!:banghead: Last fuel pump lasted 47K miles and the original lasted 89K. Oh well. the truck is solid and worth a lot more to me then the actual value and it has been extremely well maintenained with a ton of extras like 20 inch rims, brush guard, KC hi-lites fog lamps, borla exhaust, Hypertech chip, Cold-Air K&N intake, etc.,. i can't afford to part with this awesome truck. Chevy trucks are the BEST!!!

How did they diagnose the crank shaft sensor?

Yes, I agree that the fuel pump prematurely failed at 47K miles, but it was replaced by a non-dealer garage and I am sure those electrical pumps have a warranty that is much less then what life I got out of it. Also, the dealer wont guarantee anything verbally nor in writing but my Tahoe felt from the first time it started missing that the fuel was not getting to where it needed to be. It got progressivley worse and the dealer confirmed that this was a fuel pump. All along I felt like it was some sort of fuel line issue, but I still dont think my issue was valve guides. Last night when i barely got to my garage, I re-turned the computer programming to the original factory settings, i personally received the P0339 crankshaft sensor code on my analyzer. The technician also saw it after I cleared the problem and I was told it was an electrical item that goes out often and there was no further comments from the guy! This truck died on me 9 times yesterday under full load and 3 times this morning going to the dealer. The engine idles perfectly, but when put under load, the pump cant get the fuel to the intake. This is a fuel issue and not a valve guide issue! I am a mechanical engineer and I have known to be wrong at times, but this is a classic case of a fuel system issue. Valve guides?? Still trying to figure that one out. I am scratching my head.

$1450 sounds like $1100 labor! That's a little steep! Might be worth getting your soft, clean, engineer hands dirty!:grinyes: Thanks for keeping us updated. I can't wait to see if this fixes your truck. I replaced my pump assembly with a new AC pump that I bought from the dealer. I still had the miss, so the next morning I used the Seafoam. Maybe it took that long for my computer to adjust to the new pump? Maybe the pump did solve my problem. Oh no, that means my precious Seafoam is not Magic!!!!!!!:eek7:

Thanks for your comments.... :rofl: I really don't have a garage set up to drop the tank and change the pump although i could do it. Time is of concern as well, as I leave this week for the Dominican Republic and there are some jobs that I just wont do!! Changing the fuel pump and a system injection flush is something for the dealers....Yea, there is 80% or better of the charge that is labor, but that is life now-a-days. I did everything that I could do for the unit. After using the Sea Foam, my problem worsened. Sure it was coincidence, but I saw no benefit from it. I am sure the work the dealer will do will be acceptable and the problem should go away. Are you still thinking valve guides?? :grinyes: Actually, if you take into account my labor rate, the dealer is cheap....

Nice one on the labor rate.:sunglasse You win. I'm glad you got the joke.:evillol: That proves to me that you really are an engineer!:biggrin: I think you're on the right track. I really don't know if the "valve guide" issue is valid. I do find it interesting that about the crank sensor. I might look deeper into that for my having to run the higher octaine gas. I've never seen that code on my scanner, but it's not a fancy one. I still think that labor rate is outrageous, but if it fixes the problem, it will probably be cheaper than the route I took to fix mine. Let us know if it fixes it. Good luck and have a safe trip!

Thanks MMoss....I knew where you were coming from. :loser: You must have sense of humor when dealing with automotive issues!! Thanks for staying on top of my issue and your advice. :biggrin: I will pick the Tahoe up next Friday night when i get back into the US! I just researched the crankshaft sensor and I understand that this has nothing to do with the missing fuel to the engine intake issue. Possibly the tremendous amount of shaking, kicking and backfiring caused this electic sensor to go on me or it was a coincidence. It did show up last night for the first time. Also, the AC-Delco fuel pumps have a warranty of 12K miles and/or 12 months and I had my original changed out in April of 2003 for $678 in Missouri by a small garage and at that time I had the wires and plugs changed and injectors flushed! This guy towed my Tahoe in as the pump just quit on me one evening. Been 4 and a half years and prices do go up. At that time the pump was $225. Huge on the labor rate as GM engineers really crucified this design on having the pump in the tank. They have their reasons, but the good ole days were easier on us hands-on guys. I have not seen the dealer breakdown, but when i get the bill they know they have seriously inflated prices and I might be able to get a couple hundred bucks knocked off. These guys are criminals in the charge for service department at the dealers. Amazing he wanted $89 for a fuel filter install. I bought my luberfiner at Autozone for $7.99. Unbelievable!!!!!:screwy: took me 15 minutes to change out!! :evillol:

98 tahoe same thing but i just put new bridgestone tires on and thats when this chatter started so far after one week in the shop we found the tires have gone out of bal three times twice where i bought them and at repair shop good after bal two- three days tires out again did all cap rotor plugs wires pcv fuel filter air filter check and replaced u joint rear shaft checked ft.slip yoke trans check for lockup all good ,tires must be difected