NO High RPM power

[kolb]

I have a 2002 EB 4.0 SOHC AWD with the following mods - Mac intake (loud!), Cut fins from throttle body, new plugs, wires, fuel filters, cleaned the MAF meter.

When you go to passing gear the truck will down shift, the RPMs will go up to red line, but the tuck just feels like it isn't doing anything past about 3500-4000 rpm. It will RPM faster, but there isn't any more power to be had. It almost feels like it is starving for air or fuel. I checked the fuel presure and it sits steady at 67 psi at idle. There are no codes or CEL. Driving around town the tuck feels ok it just doesn't have much highway power. While it is winding out to the moon, you can feel it pull a little harder for a split second and then back to not much (almost like a spark miss). I'm pretty good at turning wrenches but this one has me stumped. Or, am i expecting too much from this V6 and they all do this? It is after all, the smallest engine we own. The fuel mileage is around 19-20 on the highway.

 

[ThePhoenix]

i would have guessed fuel filter....or wires, but you replaced them both. You should have enough power, so something is wrong...IMO

 

[askingxforxit]

I have a 2002 EB 4.0 SOHC AWD with the following mods - Mac intake (loud!), Cut fins from throttle body, new plugs, wires, fuel filters, cleaned the MAF meter.

When you go to passing gear the truck will down shift, the RPMs will go up to red line, but the tuck just feels like it isn't doing anything past about 3500-4000 rpm. It will RPM faster, but there isn't any more power to be had. It almost feels like it is starving for air or fuel. I checked the fuel presure and it sits steady at 67 psi at idle. There are no codes or CEL. Driving around town the tuck feels ok it just doesn't have much highway power. While it is winding out to the moon, you can feel it pull a little harder for a split second and then back to not much (almost like a spark miss). I'm pretty good at turning wrenches but this one has me stumped. Or, am i expecting too much from this V6 and they all do this? It is after all, the smallest engine we own. The fuel mileage is around 19-20 on the highway.

Throttle body, Throttle position sensor, Torque converter?? Maybe gear is slipping in the trans??

And BTW, what does cutting the little fins of the TB do?? I noticed those yesterday when I was cleaning it.

 

[manaen]

perform a vacuum test to make sure your exhaust is not plugged up, you could have a plugged up cat, which would cause problems.

Did you reset your computer after adding the mods?

are you used to driving a more powerful car? because these SOHC's run pretty good, but comparing this truck motor designed for torque against a car designed for high RPM HP will always make the SOHC feel tired.

 

[kolb]

TPS checks out OK with a volt/ohm gauge.

Computer was reset (disconnected bat for about 30 min). I ASSume that is enough to reset it.

The CAT converter issue is an interesting thought. Like I said, the truck pulls pretty good up to about 4K but then starts "wheezing" if floored. It's almost like how cars with TV cables worked if the cable was adjusted too tight (the engine is ready to shift but he trans is still wanting to wind up). It actually SEEMS to do better if I back out of the throttle a little from being floored. I can see how if the cat was plugged it could cause a similar situation. Any links or stickies on how to test the cat?

Other vehicles? - 360HP/ 650TQ 7.3 Powerstoke and a 5.0 V8 powered Miata. So, yeah, it's the weakest in the shop but it still feels adequate until it starts runing out of breath. I'm going to ASSume (again) that other 4.0s don't do this.

Thanks for the ideas. Keep 'em coming!

 

[kolb]

what does cutting the little fins of the TB do?? I noticed those yesterday when I was cleaning it.

It's supposed to help a little with power. I have also been considering cutting the EGR tube behind the throttle body out for better air flow. That is an old LS1 trick for a little more power for free.

 

[manaen]

The fins in the TB will effect 0 to 1/4 throttle mostly, so in this case I really don't think he will notcie a difference on the top end.


When running a vacuum test a normal reading at idle with a gradual drop to 0 or very near it as the engine is speeded up is caused by a choked muffler, clogged cat converter, or any stoppage of exhaust flow. So as you raise the RPM of the motor with the vacuum gauge connected initially the vacuum will drop however it should quickly settle back to the normal idle vacuum (around the 18 level). If it does not settle back to normal and continues to get lower and lower with more RPM then you may have a problem. I usually hold my engine at about 2000 to 2500 rpm and watch the needle to make sure it settles back around the normal idle mark.

I hope that makes sense its been a crazy morning and my mind is a little rampant right now

 

[kolb]

The fins in the TB will effect 0 to 1/4 throttle mostly, so in this case I really don't think he will notcie a difference on the top end.


When running a vacuum test a normal reading at idle with a gradual drop to 0 or very near it as the engine is speeded up is caused by a choked muffler, clogged cat converter, or any stoppage of exhaust flow. So as you raise the RPM of the motor with the vacuum gauge connected initially the vacuum will drop however it should quickly settle back to the normal idle vacuum (around the 18 level). If it does not settle back to normal and continues to get lower and lower with more RPM then you may have a problem. I usually hold my engine at about 2000 to 2500 rpm and watch the needle to make sure it settles back around the normal idle mark.

I hope that makes sense its been a crazy morning and my mind is a little rampant right now

Sorry, either that was confusing or I'm not very smart (both are possible lol). So, I hook up the vacuum tester, drive the tuck at WOT and the gauge SHOULD read zero (or near it) if the CATS are clear and NOT plugged. Will it read MORE vacuum if the CATS ARE plugged :scratch:

 

[manaen]

no no, I'm sorry I had a bad morning, found my water heater leaking all over my basement, I answered between research on new water heaters. Anyway....


1) pop the hood and hook up a vacuum gauge to the brake booster line
2) start the truck and let it warm up and go into closed loop idle
3) read the vacuum gauge at idle and note the number, should be somewhere around 18hg
4) Now have a friend, spouse, or trained pet bring the engine up to 2000 to 2500 rpm and just hold it there (in park not moving)
5) you will notice the gauge go down when the throttle first opens then it will finally settle after about 5 seconds (or at least it should)
6) read the number on the gauge and it should be real close to your idle reading
7) if you have a blockage in you exhaust your vacuum will be much lower at 2000-2500 rpm due to back pressure in the engine
8) note and odd bouncing of the gauge, it should be pretty steady at idle and when holding a constant rpm if it is bouncing then there could be other problems like valve issues or dead cylinder etc...


BTW my new water heater is in and I can think much clearer

 

[kolb]

I'll try that this weekend and post my results.

I bet it's nice to not have your stuff getting wet. Water heaters always seem to leak at the most inopportune times.

Thanks again for the help!

 

[Jason redden]

IM having the same exact problem with my 04 explorer did you ever come up with an answer?

 

[kolb]

Nope. Never did. Now the POS trans is bad. It's gonna go be beer cans somewhere else soon.