AS Burned said, you really need a live data scanner. I can't believe how much cash you through at this thing already and your issues isn't resolved.

STFT running double digit negative indicates it's running super rich. Too much fuel being sent to the motor. This can mean a few things.

STFT running positive double digits means its running lean, not enough fuel. This can also be caused by multiple things. Invest a few bucks into a cheapy scanner that does LIVE DATA and post those results for the STFT a long with engine operating temperature, any pending or stored codes, etc.

 

Anybody come up with a answer to this problem yet ? I really hate to bring it to a shop

 

There is 6 pages of answers yet. Well help anyway.

 

I have been traveling a lot for work still, so I haven't had much time to spend on this problem with my truck. (low power upon acceleration when truck is warmed up)

I have been talking with a friend of mine that is pretty mechanically inclined and knows about cars.

This is what he explained is possibly happening:

The engine/transmission isn't properly cooling down enough.
The Engine/Transmission fluid reaches past a certain temperature and as the oils heat up, they loose the ability to properly keep friction and actually become more "liquidy or thin", keeping the transmission from functioning properly. Thus, we hear the fan blowing hard under the hood trying to cool down the oils.

When the engine reaches a certain temperature, the coolant is suppose to kick in and do its thing. "cycle through the system cooling down the engine/transmission fluids, etc".

I definitely did not explain this as well as he had explained to me, but my friend did say "If you fix your coolant issue, you'll fix your acceleration when warmed up issue"

He mentioned a few things for me to check when I get home. They are as follows:

1. The truck may need a "low temp thermostat". - I guess they come in a few different temperature ratings. (I will double check mine when I get home and make sure its the proper thermostat)

2. Check the Transmission fluid - Smell it. If it smells burnt, this verifies its a coolant issue.

3. Do a Hillbilly Radiator Flush - (no offense to anyone) This would require draining the radiator fluid completely and adding water and "Dawn dishwashing soap" to the cooling system to do several flushes. Apparently this is suppose to do wonders to removing crud stuck in there and is supposedly works better than what shops can do. (I personally will be researching the Pro's & Con's of this method to determine if this is something I will do to my engine. I would advise anyone else to proceed with caution)

 

Ya I'm pretty convinced it has to do with the cooling issue, My problem is I bought the truck with a bad motor so I don't know the history of it. I'm thinking this was a issue before I rebuilt the motor. Truck starts and runs great until temp goes up. Looks like P/O put a new waterpump and radiator in before I got it so I'm kinda stummed on this one. I read alot of posts on this issue and checked alot of stuff. fuel pressure at filter is 86 and holds at 83 for atleast a hour, but it drops 15 lbs. at the injectors in 10 min. so I'm sure I need a spyder unit, but really want to solve temp issue first. I'm kinda old school and like to fix something rather than guess a throw parts an money at it. But I'm starting to wish I just gave my son the 500.00 for his birthday and didn't buy this project. To bad it's a nice truck with a fresh motor that only runs for 10 min. at a time Ha Ha Thanks for the help

 

First time I've ever heard of putting dish soap in the coolant system. Sure your buddy really knows vehicles?

Guess I must have missed the part of overheating where ever you posted it. Coolant systems are pretty simple. I'd recommend using running a coolant cleaner through the system per the manufacture's instructions before throwing some dish soap in there, if overheating is the problem your have been having. And rather than throwing a lower temp t-stat in there, try throwing the proper temp t-stat in there first. You also might want to look to see if there is anything clogging up the fins of the a/c condenser and/or the radiator.

No experience with this one but I've heard of folks put in the wrong water pumps, as in the wrong flow. As in, the engine requires a clockwise turning water pump and a counter-clockwise pump was installed.

I'd start with running a cleaner through the system. Then one heck of a flush of the entire coolant system with the t-stat removed. Then install the correct t-stat with your choice of coolant and see what happens.

Again, this is providing you do have an overheating situation. Leave the Dawn to the dishes.

 

I'm not sure if I read this tip on here or on a different thread, but as I was tinkering on my Blazer the other day, I remembered a post about trying to drive it with the MAF unplugged. I thought I'd give it a shot.



Holy cow did it make a difference! It feels like a new truck! Plenty of power, no dead zones while accelerating, and sounds much healthier. The only other difference besides the CEL being on, is the thing now seems to shift at a higher RPM and the shift also seems much more stiff/abrupt. I'm not sure I am or should be worried about this, as it seems to snap off up-shifts like a much newer vehicle does. Any reason I should NOT keep running it like this? Could I do permanent damage to something? I want to make sure before I start driving it 50miles round trip to work again.

 

I have a 98 GMC Jimmy that i have been having the same issues with...bought it about a month ago and it drove super then i started having issues with it "not wanting to go" when it's warmed up...once it shifts from first to second it seems to run fine...im gonna give it a shot with tryin to unplug the MAF sensor first...these threads seem to be telling about a myriad of things that could be wrong with it but from the last posting, the guy that unplugged his seems to be running ok without it plugged in; but my question is the same as his...if this MAF sensor is unplugged for very long will it cause any damage to my vehicle till i can come up with the money to buy a new one, IF that is what the problem is lol

 

ok i just had the same problem. Driving down the highway and all the sudden i had a loss of power and a loud air leak under the truck in my 4.3 blazer 02. After spending a bunch of time on here and reading all kinds of forums and no one comes back with a clear answer because no one understands mechanics apparently. Im a little distrurbed with all the people who say oh yeah just unplug this or change this sensor. I understand when you have to hoodbilly something to get it home, like i did from cleveland to columbus. After reading forums i first started with the cat and cut a the pipe open before it but let it breathe into tail so the sensor would still warm up and no change. then like an idiot i put a new fuel pump in and no change (i have an access panel so it took 30 minutes but cost 250). So at this point im reading and reading and people are talikng about transmissions and coolant now im about to burn it. But before let me cut a hole in front of the pre cat and boom its loud but drove it all the way home and ran like normal.

 

Ok before you throw parts at it this is what happens, the exhaust gets clogged and sends a signal to the computer from the 02 sensor that its not getting a good reading (which is what its supposed to do) then that tells the maf to back off on the air because there is no airflow because its clogged and then the fuel is leaned out to make up for the air. So when you scan it and it gives you codes that means that whatever happens before that sensor is where your problem is. If you get a b ad 02 reading that means (most of the time) that its working and its telling you something is making it change its settings. Same goes for the maf and other sensors, they are working dont change them. In this case my pre cat would and did clog up before the cat did. Which comes first is the question you need to ask. Hopefully someone will read this and understand before they listen to the rest of the idiots who think they know everything but really have no good input to give. Sorry if i hurt your feelings but your feelings are worth less than the cash in my pocket.