Highway passing power

[Massfloefi]

Hey fellas,

Driving cross country and I noticed that if I need passing power from around the 70-80 mph the truck rpm’s will only jump to 3200-3400rpm and not pull further. This happens whether I give it half throttle or full throttle. Limitation of the 4 speed? Was thinking tps sensor but no codes and shifts fine when taking off from a stop and when I floor it at around 60.

 

[Doubeleive]

maybe, does it do the same thing if you put it in 3rd gear first?

 

[iamdub]

Sounds like weak fuel supply or clogged cat.

 

[Onebad1983]

Mine winds all the way up to redline from the 4k that it downshifts to. So it is definitely not a limitation of the 4 speed

 

[Rocket Man]

Have you tried manually it down into 3rd? Might not be shifting from 4th.

 

[Massfloefi]

Have you tried manually it down into 3rd? Might not be shifting from 4th.

Yes I have the same issue. Thinking the Evap canister charcoal might be clogging the lines. When fueling up often the pumps will shut of if left alone. I’ll have the evap, solenoid and purge changed out. Plus have the lines pressurized and blown out. I’d do it myself but I’m not sure how I would pressurize them.

 

[Massfloefi]

Mine winds all the way up to redline from the 4k that it downshifts to. So it is definitely not a limitation of the 4 speed

Thanks onebad1983. I was thinking it was abnormal.

 

[Massfloefi]

Sounds like weak fuel supply or clogged cat.

Yeah I’m thinking fuel.

 

[Massfloefi]

maybe, does it do the same thing if you put it in 3rd gear first?

If I start out in 3rd get to that speed and floor it? Yeah pretty sure but I’ll check again.

 

[Doubeleive]

If I start out in 3rd get to that speed and floor it? Yeah pretty sure but I’ll check again.

I mean if you are already in drive at cruising speed and then you manually shift it down to 3rd and then punch it.
at any rate if it seems kind of boggy it could be the maf, could be clogged fuel filter, dirty air filter. when was the last time it had a tune up?
I would check the obvious things first before jumping to clogged cat's or something critical, generally if the cat's are inefficient you would start getting check engine lights, poor fuel mileage etc.

 

[adventurenali92]

It could also be the trucks stock tune. When Just with blackbear performance tunes my truck he eliminated the rev limiter. Before that it rarely go up over like 3200 or 3300 rpms even when I gave it over half throttle. But not after the tune.

 

[Massfloefi]

I mean if you are already in drive at cruising speed and then you manually shift it down to 3rd and then punch it.
at any rate if it seems kind of boggy it could be the maf, could be clogged fuel filter, dirty air filter. when was the last time it had a tune up?
I would check the obvious things first before jumping to clogged cat's or something critical, generally if the cat's are inefficient you would start getting check engine lights, poor fuel mileage etc.

Yeah same problem even in 3rd. Yeah maf has been cleaned and tune up done less than 5k.

 

[Massfloefi]

It could also be the trucks stock tune. When Just with blackbear performance tunes my truck he eliminated the rev limiter. Before that it rarely go up over like 3200 or 3300 rpms even when I gave it over half throttle. But not after the tune.

I do have a blackbear tune. Thanks for the input.

 

[Doubeleive]

Well you might want to send some logs to bb and see what they say they can probably figure it out

 

[Massfloefi]

Well you might want to send some logs to bb and see what they say they can probably figure it out

Yeah I will this week. Thanks

 

[iamdub]

You're 100% sure it shifts from 4th (OD) to 3rd when you hold the throttle steady and manually shift it? When in OD ("D" on indicator) and you you give it more throttle, it may just be the torque converter clutch unlocking and allowing the RPM to jump but it's not actually downshifting. It should still accelerate, slowly, but still.

EVAP stuff being clogged wouldn't affect the fuel supply unless the tank vent was clogged and the resulting siphoning effect was holding back the fuel. You'd have a rushing air sound when you unscrewed the gas cap, though. Also, leaving the cap loose would fix this if a clogged vent was the actual problem. Your poor fuel pump, though!

You could borrow a fuel pressure gauge from Autozone for free and test that at least. On an S10 I was working on, I pinned the gauge to the windshield with the wiper and ran the hose betwen the hood and cowl to the fuel line so I could watch the pressure as I drove.

 

[Massfloefi]

You're 100% sure it shifts from 4th (OD) to 3rd when you hold the throttle steady and manually shift it? When in OD ("D" on indicator) and you you give it more throttle, it may just be the torque converter clutch unlocking and allowing the RPM to jump but it's not actually downshifting. It should still accelerate, slowly, but still.

EVAP stuff being clogged wouldn't affect the fuel supply unless the tank vent was clogged and the resulting siphoning effect was holding back the fuel. You'd have a rushing air sound when you unscrewed the gas cap, though. Also, leaving the cap loose would fix this if a clogged vent was the actual problem. Your poor fuel pump, though!

You could borrow a fuel pressure gauge from Autozone for free and test that at least. On an S10 I was working on, I pinned the gauge to the windshield with the wiper and ran the hose betwen the hood and cowl to the fuel line so I could watch the pressure as I drove.

Interesting, I will have to check about the shifting. What’s to be done if that is the issue?

 

[iamdub]

Interesting, I will have to check about the shifting. What’s to be done if that is the issue?

What's to be done if it's not downshifting when flooring it? Or if it IS downshifting but not accelerating?

The former could be a much cheaper fix than the possible causes of the latter.

 

[swathdiver]

With the AutoCal you can take a log and then play it back on your computer Ron with EFI Live. Watch your fuel pressure, trims, etc.

 

[Bigworm81]

My truck does the same thing did you ever figure it out?