NO low end on 4.0

[DFracing]

hey guys, a while back i did my timing chains on my sohc, and had the heads rebuilt, at the same time i Put a camburg kit and 33's on it vs the stock 29's. Ever since then the truck has had about 1/2 the low end power it used to. I had just been assuming that it was because of the larger tires but, now im not so sure, the weird thing is, at about 3800k the truck wakes up and shoots off like a rocket, almost like vtec. Seriously, i would almost define it as turbo lag if i had a turbo. previously i could do 75 up a 6% grade loaded down with a 450 quad and a weekends worth of gear at the desert, for two people, in overdrive at 2400 rpms. (3.55 gears) now the damn thing bogs down, and has to down shift if it even looks at a hill doing 65 on the freeway. Is this because the taller and wider tires, or could there be an issue with my timing...........

air filter is clean, and there are no check engine lights, ive scanned the motor multiple times for a trouble code and have found nothing.

thanks in advance

 

[alwaysFlOoReD]

I used the calculator in the gear section
http://www.therangerstation.com/tech_library/Gear_Tire_RatioChange.html
And it says that your gear ratio is now a 3.12 equivalent. You would need to get 4.10's to get your stock ratio back. With the bigger circumference there is more inertia to overcome as well. I think it's gearing.

Richard

 

[SeanWilson]

^ i agree, our motors make the bulk of there horse power at the top end while were torqy down low.
i had the issue with mine when i ran 3.73’s and 33’’ tires, i jumped to 4.56’s (with intent on 35’s soon) and now im a rocket

 

[DFracing]

hmm maybe, just weird to me that the power comes on so strong at such a high rpm. but let me say this, it has plenty of power until the oil comes to temp, once oil and water are up to temp it starts acting like that.

 

[alwaysFlOoReD]

So it's running fine in closed [open?] loop? That means the computer is running off of predetermined air/fuel ratios. And once the o2 sensor and other sensors start speaking to the computer, it all goes wonky? That means to me that there is a bad sensor or bad connections to the sensors. Double check all connections. I had a no start condition once because I taped a connection believing it was good and then never checked again for a few months. It ended up that the o-ring inside the connector was dry and not letting it seat together properly. A little wd-40 fixed that.
Did you change the cam? If you went to a higher out-put cam the low end would suffer.

Richard

 

[DFracing]

So it's running fine in closed [open?] loop? That means the computer is running off of predetermined air/fuel ratios. And once the o2 sensor and other sensors start speaking to the computer, it all goes wonky? That means to me that there is a bad sensor or bad connections to the sensors. Double check all connections. I had a no start condition once because I taped a connection believing it was good and then never checked again for a few months. It ended up that the o-ring inside the connector was dry and not letting it seat together properly. A little wd-40 fixed that.
Did you change the cam? If you went to a higher out-put cam the low end would suffer.

Richard

ill see what i can find on connections, i may have missed a ground when i put the motor back in. All oem components went back into the motor.

 

[6.2]

3.55 gears and 33's?

Uh. Yeah of course it has no low end power.

 

[DFracing]

3.55 gears and 33's?

Uh. Yeah of course it has no low end power.

its not so simple as that, yes its lacking on low end torque, but i am almost wiling to guarantee if i put stock sized tires back on it would behave the same, my 3.0 didnt have this much of a power change from 27's to 31's in basically the same sized truck w/ equivalent gearing. plus it wouldn't be losing power as the engine comes into temperature.

 

[alwaysFlOoReD]

Do you have another set of tires? That would be a good test.... but you probably already thought of it.

Richard

 

[DFracing]

Do you have another set of tires? That would be a good test.... but you probably already thought of it.

Richard

I've thought about it but i don't have any.

what i don't understand is why it would do this and not throw a code.

 

[DFracing]

found a ground that was hanging out but same results, just may go have a diagnostic run on it. i dont have time or money to be replacing everything 1 part at a time

 

[naford]

Did you disconnect the battery while doing the timing chain? If not maybe you should to let the computer relearn everything. It's cheap to try.

 

[DFracing]

double post

 

[DFracing]

Did you disconnect the battery while doing the timing chain? If not maybe you should to let the computer relearn everything. It's cheap to try.

the motor came out of the truck and the entire wiring harness was disco'ed. I've unplugged the battery more than a few times since the timing chains were replaced. i've tried that, i even have a scanner that i've looked for codes with, but i don't know enough about engine management to trouble shoot something like that