Tahoe going insane? Weird intermittent issue.

[BDKesling]

Just made a trip from eastern NC to north central WV for my brother's wedding. Was pulling a 5x10 utility trailer with two dirt bikes (all WV weddings require dirt bikes, lol). We got caught in some construction traffic right before the NC Virginia border, barely creeping along for about 45 minutes. Construction ends and I hit the gas to get back up to speed. Kaput kaput bang kaput, tahoe sputters and acts like it's dying, but keeps running. We're trying to go downhill at this point, pedal on the floor, engine is at 4,000 rpms, no acceleration going downhill. I pull into the VA welcome center and creep to the side of the parking lot. Temps are good, oil is fine, transmission has fluid. I watched two videos on replacing the fuel pump thinking that might be what I'm about to do. Put the nearest Autozone in the gps and figured I would limp down the shoulder and get my codes read. Started the truck, went light on the gas, and got it up to 65. At that point, I told my wife we weren't stopping unless it fell apart. Made it to the Flying J truckstop in Wytheville, filled up with 92 octane and Lucas injector cleaner. Truck ran like new the rest of the way in (10 mpg when it was struggling, 16.6 mpg the rest of the way in). This was Friday evening.

Saturday morning I got up and unhooked the trailer. Took the tahoe for a drive around town and it was running like new. Good acceleration, no hesitation, no issues.

Sunday we hooked up to come home. Filled up an hour into the trip (high octane, and another bottle of injector cleaner), 20 minutes later the tahoe has no power and we're pulling 4,000 rpms to go 60 mph. Found an autozone and had them pull codes.

PO301 (cylinder misfire)
PO131 HO2S-11 (Bank 1 sensor 1) Circuit Low Input
PO151 HO2S-21 (Bank 2 Sensor 1) Circuit Low Input
PO446 EVAP Vent system performance
PO131 HO2S-11 (Bank 1 sensor 1) Circuit Low Input
PO151 HO2S-21 (Bank 2 Sensor 1) Circuit Low Input
P1133 HO2S-11 (Bank 1 Sensor 1) Insufficient Switching
P1153 HO2S-21 (Bank 2 Sensor 1) Insufficient Switching

Not worried about the EVAP code, but the others look expensive (but not fatal). I figured I'd force it home or break down near a dealership and trade. Limped back out to the road, no power on take off, dangerously slow acceleration, and NEW PROBLEM, the break pedal now goes all the way to the floor coming down the mountains. It still stops, but way more travel in the brake pedal (fluid was fine). Got to Wytheville and refilled at the Flying J with another bottle of Lucas. I shit you not, the truck ran like new all the way home. Started up fine this morning and runs like a champ, brake pedal was back to normal with the fill up in Wytheville.


Looking for advice on where to start. Not interested in taking it to a mechanic who will replace a valve spring and O2 sensors then tell me it's all better. I think the codes are symptoms of whatever is going on, but not the cause. Something electrical? My mind is boggled, and I can't drive 3.5 hours to Wytheville every time I need gas. Overheated tranny needing flushed, causing a bunch of other issues?

Thanks,
Brian

 

[Doubeleive]

honestly I think a lot of that could be the result of a bad maf sensor, if you have a junk yard around it's worth a shot to pick up a used one cheap and try swapping it out
and I agree this is all most likely the result of a different problem not really sure what beside the MAF, I could guess maybe a cam position sensor? but before digging in that deep I would make sure you have good fuel pressure that's a pretty simple test. seems a little troubleshooting is in order.

 

[BDKesling]

Thanks for the suggestions. I hear a whining toward the rear when parked and idling and I'm guessing it's the fuel pump. I've had it for about 6 years now it's sitting at 226k miles, probably due for a fuel pump and maf sensor. Not being able to recreate the problem until I'm in a bind on a road trip is going to drive me nuts.

 

[iamdub]

I'm leaning toward fuel pump getting weak with temperature. High RPM with strong vacuum could be cause for change in brake pedal. Get the fuel pressure checked when it's running normal and again when it's acting up.

Those oxygen sensor codes are kinda throwing me off, but could in fact be an anomaly. I doubt the sensors are faulty, as the chances that both upstream sensors are experiencing the same failure at the same time are slim.

The problem could even be the battery or alternator getting weak when hot, causing a low voltage condition which starves the fuel pump of power and makes the PCM go ******* because it's not getting the voltage it needs. Having said that, watch that voltage gauge when it acts up.

 

[Doubeleive]

Thanks for the suggestions. I hear a whining toward the rear when parked and idling and I'm guessing it's the fuel pump. I've had it for about 6 years now it's sitting at 226k miles, probably due for a fuel pump and maf sensor. Not being able to recreate the problem until I'm in a bind on a road trip is going to drive me nuts.

Ya the fuel pumps are known to whine on the NBS and there basically designed for 100k, if it's the original it's def way beyond it's life expectancy and if it is a second one it could also be at it's life expectancy, but the whine noise isn't really a determining factor some are just noisy after a while and some do it intermittently.

 

[Reidracer]

Looking for advice on where to start. Not interested in taking it to a mechanic who will replace a valve spring and O2 sensors then tell me it's all better.
Brian

Better I guess to throw random parts at the truck until either your wallet or your patience runs out.

There's a reason those Diagnostic Codes and the proper diagnostic equipment exist; it's the most efficient way to resolve issues with a complex system like the engine controls for your vehicle.

BUT if you insist on a recommendation on what to replace, removing the radiator cap and replacing everything between it and the back bumper will be 100% effective and you won't have to pay any silly diagnostic fee to a mechanic.

 

[BDKesling]

Better I guess to throw random parts at the truck until either your wallet or your patience runs out.

There's a reason those Diagnostic Codes and the proper diagnostic equipment exist; it's the most efficient way to resolve issues with a complex system like the engine controls for your vehicle.

BUT if you insist on a recommendation on what to replace, removing the radiator cap and replacing everything between it and the back bumper will be 100% effective and you won't have to pay any silly diagnostic fee to a mechanic.

Sorry, I didn't realize there was a contest to see who could be the most unhelpful *****! You win!! Since you were unable to comprehend the original post, let me review it for you. The codes are a symptom and not the actual problem. Also, the problem only manifests on long trips and everything is fine (i.e. no codes to diagnose) when driving around town. My option is to diagnose and fix the problem on my own, or wait until I'm in a serious bind in the middle of a trip and then delay my trip so a mechanic I'm completely unfamiliar with can try to diagnose the problem. Neither of those is acceptable, so I thought I would start on the forum where people are familiar with the issues. Now you are free to go suck the fun out of someone else's day!

 

[dmad1]

Might start with a gas cap. Could be running our of air instead of fuel...

 

[jbyler]

I have a 2003 Denali and it drove fine over a high/low winding highway...then on the way home, it would barely limp uphill and then I could coast going downhill. I replaced all spark plugs twice with different respected brands, replaced the ignition coils, replaced the ECU (sent it to this place-I think AES) in Florida and they said it went bad and wasn't repairable, so sold me a refurb for $100 more (total $400). Installed that, had a locksmith guy come to the house to reset the alarm so the engine would start and hold, etc. Still wouldn't operate correctly. Drove a few miles to the auto machine shop who did a number of things over a couple of weeks and found that the manifold was warped ever so slightly on each side and which is why it didn't have a good seal. Problem solved, $3500. Better than having to buy a new car... Transmission is next (truck has 250,000 miles on it and I've babied it the whole time, and towed my camping trailer with it...). I don't want to be towing and the transmission go out... it's taking a bit of time to get into 2nd. The other gears are fine. Hope you get your issue solved.

 

[iamdub]

Sorry, I didn't realize there was a contest to see who could be the most unhelpful *****! You win!! Since you were unable to comprehend the original post, let me review it for you. The codes are a symptom and not the actual problem. Also, the problem only manifests on long trips and everything is fine (i.e. no codes to diagnose) when driving around town. My option is to diagnose and fix the problem on my own, or wait until I'm in a serious bind in the middle of a trip and then delay my trip so a mechanic I'm completely unfamiliar with can try to diagnose the problem. Neither of those is acceptable, so I thought I would start on the forum where people are familiar with the issues. Now you are free to go suck the fun out of someone else's day!

Have you checked anything since your last reply? Fuel pressure? Alternator and/or battery?