Over head not working is yet another clue...

You might help us a LOT if you did a comprehensive post with the entire history ,,,in chronological order, listing each and every known fault and condition

Notice..... a lot of us are sticking with you on this one... Of course the curiosity factor is very high and there are some of us that like puzzels...

 

How about you keep all your posting on this one vehicle in one post please

OH yes take my advice above you are starting to tick off a few of us by forcing us to follow many threads to help you

Art
can you consolidate all of 900rrs posts into one thread please?

 

You may want to try a new mass air flow sensor, or borrow one from a known good
vehicle. Cleaning them does not always work and they can be difficuilt to diagnose
because scan tool data is difficult to read and they usually won't throw a code unless
they are really bad.( And when they really go bad you will get lean codes on both banks). Hope this helps! Keep us updated.

 

cleaned every thing waiting for codes and info from my mechanic and it may be a while until i tow again because there is no snow in new york to snowmobiling yet

 

Starting to think he may have confused himself as much as he has confused me. Asking questions on different posts will not make the mileage improve or fix the problems any quicker.

 

Sounds fuel-starved under load. But...Watson what do you make of the poor gas mileage?

OK, this may sound off the wall but, I kid you not, I solved an intermittent like this once. Working on girlfriends Ford for days after work. Thought I had thought of everything. One night I lost my light for a few minutes and I was too tired to go fix the light right away while the engine was running I could SEE the corona glow off of the ignition system. Rerouted/replaced the wiring and POOF never a problem again.

Just a thought...

 

I`ve been peakin in on this for a few days now. My 2002 with 3.73 gears is still kinda lame. Mine is a CC 4x4 and I`ve been comparing it to our work truck. 1999 sc 2wd 4.10 gear. I know these 2 are not the same but the work truck with 2000# in the bed driving 65mph gets 16 mpg. Mine empty gets about 10mpg. Even though the trucks are different there shouldn`t be that kind of difference in mileage. Power wise the work truck will litterly smoke the right rear tire in first gear (285 tires on it too), mine just a little squeal (265 tires). Fuel filter was changed on mine about 500 miles ago and that seemed to help the performance at first but kinda tamed out now. Towing a loaded trailer (4000#) at 65-75 mph range on fairly flat land, minimal wind I get 7-8 mpg. I have put headers on but still have stock exhaust and cat.
What is wierd while towing in 3rd gear engine at 1300 rpms or so it has great torque and will pull hard. Get up to 65 mph in 4th (o.d.) and it falls flat on its face. In 4th it can be hard to maintain 65-70 mph but take it out of O.D. and it`s hard to keep it down to 65-70.

 

FTFG,
the 2trucks your comparing are apples and oranges weight wise(4x4 CC) and the gear has alot to do with it.

Rich

 

Like Rich said, but 10MPG?

4.10's vs. 3.73's are just under 10% difference ...

That's the difference between just barely slowing down in O/D going up a hill, and just barely speeding up - or more than barely - which is so much more thrilling than slowing down Or the difference between barely spinning the tire and smoking it.

Reset the computer. And I mean really reset it. Disconnect the battery, turn on the headlights and leave it overnight.

And, start your own thread! Give complete details of the truck, compare it to another truck (which you just did) even if it's apples/oranges because at least we get some idea of your impressions, tell us what you've already changed or cleaned or lubed, and any (MOST important!) other signs of something wrong ...

 

I posted on this thread only because I may have a similar problem that 900rr has and maybe my explanation and comparison could shed some light on a possible problem.

 

Actually, it just leads to an even longer thread that has already outlived it's usefullness

But no matter.

 

My apologies if this is too simple. I have the same truck configuration that 900rr is describing and had the same problem shortly after I bought the truck new. It ran fine empty, but was terrible for towing and got poor milage. Luckily, when I took it to a local dealer, the mechanic saw that I had put 285 size tires on it the day I bought it and checked to see that the door sticker called for 235's on the truck ( i had ordered the cheapest I could and replaced with larger AT's). He said that this slight difference was likely the problem as the computer on the 1999 and 2000 has a setting for the revolutions per mile for the factory tire size ordered on the truck. I didn't believe him untill he calibrated my computer for the 285 tires (I think it was 615 revs per mile for mine). It was a night and day difference for my truck. We tested it with my trailer in tow. It pulled remarkably better and the milage went to 10 mpg pullling, 12 around town and 15-16 on the highway empty.

This may not be the case with your truck, but check the door sticker and see what the factory tire was. If it was 235's, ask them to check your revs per mile setting in the computer and make sure they are set for 265's that you said you are running (your tire dealer will know what the rev per mile is for your tire).

 

Keith, excellent post...

I think the original poster's tires are 265's. Which are the same diameter as the 235's - I had 235's and went to 265's, no difference in speed with a GPS.

Anyone care to calculate the amount of "torque to the ground" vs. tire pressure?

 

This may sound crazy but I had a grand am way back in the days of high school with a quad 4. Damn thing started runnin like crap and would just billow black smoke when you stood on the go pedal. Mileage was horible but fuel pressure was correct. After throwin parts at it for weeks we finally put a new regulator on it and low and behold the problem was gone. My mileage was terrible, but some how the fuel pressure was correct as we checked it three times thinking it had to be in the fuel system, in the end it was.

My dad also had a similar problem with a fuel pump on grand prix. the dang thing would run fine for hours on end, that is untill you shut it off. once you shut it off it wouldn't restart untill it sat for an hour or two. check fuel pressure and other misc. things and everything check out. finally once day I took it and when I returned home it wouldn't start, so ran in the garage grabbed a spray bottel and filled it with fuel. I open up the air intake and had the nieghbor crank it over while I spray fuel into the butterfly, it started up and would run as long as I kept spraying fuel. ended up being a bad fuel pump. For some odd reason it would runn fine untill it was hot and even then it would work fine untill you shut it off. then cablam, no go!

It sure sounds fuel related to me and between the regulator and the pump I've seen things that you'd never guess to be the cause. My Cutlass Supreme also had a similar problem where it would run good untill it got warmed up and then it would start running poorly; that also ended up being the fuel pump.

I personaly would check that cat first, but when those things plug 80mph is pretty tough to get to. heck I couldn't get past 40 in thrid (5 speed) in my cutlass when that happened. I would then head to your fuel system and start with checking pressures but even if those are correct don't rule them out, I have first hand experience three times that the pressure didn't mean squat! Keep us posted

 

SLE, usually a bad regulator shows up when you test fuel pressure under load - as in, on the highway, doing the same thing that causes the problem...

The fuel regulator is controlled by vacuum - less vacuum (more load), higher pressure. If you don't see the pressure changing as you apply your foot... it ain't working...

Better yet - put a hand vacuum pump on the regulator, with a pressure gauge hooked up, and check if the pressure goes up as you apply vacuum.

From the 2001 service manual CD for F-series:

Fuel Pressure

5.4L and 6.8L Gasoline Engine Running kPa (psi) - 193-310 (28-45)

5.4L and 6.8L Gasoline Engine w/Key On Engine Off kPa (psi) - 240-310 (35-45)

Notice the difference between the minimum pressures with the engine-off and engine running? That's the difference the regulator makes with and without vacuum. It's a good working approximation of the range of the regulator.

Maybe we should all suggest "check fuel pressure AND regulator operation under load" instead of just "check the fuel pressure under load"

If the regulator isn't adjusting up when you floor it, that just might be it!

Great point, SLE!