No power at high RPM under load

[ronclark]

I am still new to a 4.0l I know every one says thy don't have high RPM power, I am pretty sure this is not right.
I am thinking its a MAF. Here's the problem
no codes,new fuel filter, O2's,plugs,wires,PCV, about 32 psi fuel pressure at idle. its a 100% driveable.

I notest the problem towing and going up hills. I have more power being light on the skinny peddle. If I floor it it and hit about 3000k it just acts like it sucking air, and no fuel. But only happens under a load.

 

[4.0B2]

have you checked your fuel pressure at all RPM's? may be starving... or TPS.

 

[ronclark]

I did check the TPS no flat spots. it toped out around 5v I think. I'll double check.
I did not check the fuel pressure at all RPMs.
Just a though, can the regulator get stuck?

 

[--weezl--]

Yes it can get stuck, I don't know a whole lot about TE ranger motors, but 32psi seems high to me... I think my stang was 15@idle and 30@wot...

Check your airfilter, it might be plugged... The other that could do it is a plugged cat, or a f-Ed fuel reg...

Typically you would notice an issue with the fuel reg dependent on throttle position, not on rpm range...

 

[ronclark]

Yes it can get stuck, I don't know a whole lot about TE ranger motors, but 32psi seems high to me... I think my stang was 15@idle and 30@wot...

Check your airfilter, it might be plugged... The other that could do it is a plugged cat, or a f-Ed fuel reg...

Typically you would notice an issue with the fuel reg dependent on throttle position, not on rpm range...

The air fliter is clean installed about 1000 miles ago when I did the swap.
I looked at the cats when I installed them with the swap. I could shine a light in them and looked good.

Tech lib says 39 - 40 PSI (30 PSI@ idle) (OHV Engines) for fuel.

I think its more load based since that is when it seems to get starved at that RPM. On flat freeway you can't really tell.

I can live with it but its anoying when I deside to pass up hill or tow.

 

[ronclark]

It might help with a example

1
I was towing a truck on a dolly both loaded, I had no trouble keeping 60 in 5th as long as I used every little throttle I say less than 1/4 or so but no more than 1/2

2
Yesterday I was going up a 7% hill and I wanted to pass in 4th around 50 mph. if I floored it it was as if it was not getting gas, I started to slow down. I had to keep it under 1/2 or less to speed up. That made for a slow pass. But if I leave it in 5th and keep don't put my foot in it it does just fine climing hills and doing freeway speeds.

Its really crazy.

I really wish it was a OBDII, plug in a scanner and drive around and see what's going on. This trouble shooting with out a scanner gets old.

If it would just give a code I would have a place to start.
Sorry, I just had to rant about dumb ecu systems.

 

[Big Jim M]

Yep!

It might help with a example

1
I was towing a truck on a dolly both loaded, I had no trouble keeping 60 in 5th as long as I used every little throttle I say less than 1/4 or so but no more than 1/2

2
Yesterday I was going up a 7% hill and I wanted to pass in 4th around 50 mph. if I floored it it was as if it was not getting gas, I started to slow down. I had to keep it under 1/2 or less to speed up. That made for a slow pass. But if I leave it in 5th and keep don't put my foot in it it does just fine climing hills and doing freeway speeds.

Its really crazy.

I really wish it was a OBDII, plug in a scanner and drive around and see what's going on. This trouble shooting with out a scanner gets old.

If it would just give a code I would have a place to start.
Sorry, I just had to rant about dumb ecu systems.

That sounds to me like a plugged exhaust system. Only so much exhaust can pass and changing to a lower gear makes more exhaust. It doesn't miss or spitter and sput... So it makes sense to be the exhaust.
Big JIm

 

[ronclark]

That sounds to me like a plugged exhaust system. Only so much exhaust can pass and changing to a lower gear makes more exhaust. It doesn't miss or spitter and sput... So it makes sense to be the exhaust.
Big JIm

How did you test for that or is it time to stop at a shop?

 

[Earl43P]

Depending upon your tire size and gear ratio, I'd call that normal.

I'd have figured 3rd gear, taching in the 3500+ range to do that 50 mph uphill.

I towed many a car and a 99 explorer 200+ miles with my 3.0 4wd (2000).
The ONLY time I got into 5th was coasting or downhill.

I know the 4.0 has more HP, which goes back to your tire size and ratio. Mine were smaller than stock tires (235/75-15) and 4.10.

I don't think your truck has a problem unless your scenario 2 was not towing a load.

Test the FPR and goose the gas hard, pressure should rise with the drop in vacuum.
http://fordfuelinjection.com/?p=41

 

[ronclark]

Depending upon your tire size and gear ratio, I'd call that normal.

I'd have figured 3rd gear, taching in the 3500+ range to do that 50 mph uphill.

I towed many a car and a 99 explorer 200+ miles with my 3.0 4wd (2000).
The ONLY time I got into 5th was coasting or downhill.

I know the 4.0 has more HP, which goes back to your tire size and ratio. Mine were smaller than stock tires (235/75-15) and 4.10.

I don't think your truck has a problem unless your scenario 2 was not towing a load.

Test the FPR and goose the gas hard, pressure should rise with the drop in vacuum.
http://fordfuelinjection.com/?p=41

Scenario 2 was just passangers and nothing in the bed.

I am not sure how to explain in scenario 2, when it was floored it lost all pull.
it like there is more air entering the engine and there not enought gas. If I lefted it floored I would proable slows to 30 mph or so.

I know from working on carb engines, when thy get pluged you you open to wot. It would rev to a point and that's it unless you choke it.

Its pretty much like that but in this case I can't get it to do in the drive way.

 

[srteach]

The exhaust is partially plugged (most likely). Back pressure building up stops fuel from getting into the cylinders.
If you can, unbolt the exhaust to bypass most of the pipe and retest the truck under load. Headers can be unbolted, but spray with pblaster for a few days before trying to take the bolts out. Hang the exhaust system with a wire so it doesn't drag on the ground.
If you have an O2 sensor, you can remove it instead. Really, any opening that will relieve backpressure in the exhaust system will allow testing for plugged pipes / cat / muffler.

 

[--weezl--]

i would not recommend removing the exhause manifold (header) your exhaust coming out directly into the engine bay like that can cause some major damage...

however, you can remove the back half of the exhaust with 2 bolts, then dealing with hangars... it's under the passenger seat roughly

 

[ronclark]

Thanks for the help,if i figure out whats going on I'll let you guys know.
at least i have a place to start.

 

[holyford86]

When I did my swap I had the same problem. I'm assuming since you swapped this into an 87 you kept the dual pumps? If so, make absolutely sure that the in tank pump is working. It will still run without it but it's hard on the high pressure pump to do so and it starves a bit at higher rpm. Also check your fuel filter if you haven't already. I tend to think that the problem is not a restricted exhaust because it would be accompanied by other symptoms than lack of power.

 

[ronclark]

I was at the pick in pull yard and got a MAf while i was there. it that seemed to help alot.
I am thinking about that one of my fuel is dieing, i am starting to hear the in tank pump making loud noises and it sounds like its bobbling in the tank.
I guess aftermarket pumps dont last long, i replaced it about 3 years ago.