Why is my 1999 V6 so weak?

Are you leaking out the head gasket? My last 2000 3.4 runner was, and I just bought another that feels like it has more pep and it has less miles with no leak.

 

The MPG on this past trip was about 15. That's highway but up and down hills. My Prerunner would get around 20 in the same terrain.
I can see why the tires would make a difference. But I don't want to spend $1000 on new tires if its really a compression issue. So I might just have that checked first.

 

Believe tires make a huge impact!!!! How do I know, I got lt 265 75 16 and my truck feels sluggish, when I had P265 70 16 it was a different story it felt like it had balls. Love my BFG 265 75 16 it's a truck not a sports car.

 

i just took it over to a shop and had them scan it for any codes. he said it was clean and didn't think they would find a compression issue. he thinks the tires are probably the culprit. If that's the case, I'm not sure if I'll change them out. If I do I'll report back here and let you guys know how much it improves. But I'm with you on that it's a truck, not a sports car. I was more concerned there is something seriously wrong with the engine. Thanks!!

 

Like I said before, my truck lost bunch of power after getting bigger tires.

 

Could also look into regearing, dunno anything about what's worth it with tire size vs gearing for first gens though.

 

An increase in tire size alone without re gearing will kill your power. Not just the extra weight, but the extra diameter effectively changes your gearing, and kills acceleration, which is why you must now downshift.
Also, 4wd adds a bunch of weight, and a lot more parts to spin going down the road.

 

Just updating. Enough of you convinced me its the tires, but I did these other things just the same, since they needed to be done.

I put in new plugs, new fuel filter, and drained and filled the fluids. It feels a little better, but is still much weaker than my old Prerunner.

The tires are next, but I'm not sure when I'll get to them. Its kinda lame too, because they have a lot of tread left on them and I'm on the road and don't have anywhere to store them.

Anyway, I'll update when I swap them out.

 

OP,

You should take a look at your automatic tranny. I have an 5.8L Bronco that started getting really really weak pulling up hills. 2 months after it started doing that, the transmission blew.

 

Yeah good point. Do a flush and swap with Synthetic ATF. Great DIY thread by mountain lion. I've done it on both my yotas.

 

I have 31x10.5s r15 on my truck and can bomb up the mountain passes in 4th gear if I want to. It doesn't lack any balls whatsoever.

And our tires are pretty comparable in size.

 

Madjik_Man, is yours a 4x4? Any mods?

Moco, did you have any other symptoms besides weakness going up the passes? I just drove from Tahoe to Barstow, through the Sierra Nevadas and the trans felt fine and shifted well. Using ECT helped a lot.

 

I didn't really notice any other major symptoms. The Bronco wasn't my daily driver at the time, so it took me a while to even notice the issue with the hills. One day, I was going up a relatively steep hill, the tranny was slipping and the truck wouldn't go faster than 15 mph, I knew something was wrong. I didn't get a chance to check it out until a few weeks later, I was driving up a long hill and just as she got to the top, I lost every gear but reverse. That was it.

 

4x4 TRD, V6, 5-speed, bone stock

 

There are a lot of things that can cause one truck to have more power than another. Weight, transmission gear ratio differences, diff ratio differences, tire size. Even though the HP rating is the same, I believe that the 2004 had a higher torque, which can make a difference as well. Though I could be wrong on the torque difference.

 

A higher torque on the '04 would explain things. Does anyone know if that's true?

On another note, I had a drain and fill of the trans done. He said he put in the same amount that he let out. But after many subsequent checks of the level, it was clear it was low. It needed an extra quart.

If the mechanic was telling the truth, then the prior owner of the truck was running it a quart low. Since adding the correct amount, the truck feels better and closer to my '04. Still weaker on hills or inclines though.

I'll give it a few more days and see if it irons out. I hope the trans wasn't damaged from running it like that.

It's getting there.

 

Also, just plain age will make some difference. No engine makes the same power after a few years that it from the factory, and your 99 is 5 years older.

 

Being a 4wd, you are going to have more parasitic loss due to the power having to go through the trans. and transfer case. I have personally never drove a v6 prerunner but we have 2 chevy fullsizes, one being a 2wd with 2:42 gears and the other being a 4wd with 3:73 gears. Same motor and transmission but the 2wd will skull drag the 4wd all day long. I would still check everything like plugs, wires and fuel filter but I think that it might be fine.

 

In another person's post, you said you could haul ass up a mountain pass no problem. What kind of grade, speed, and gear, are you talking?

You have a manual, no?

I'm still trying to figure out my truck's issue. When it's loaded with gear, it maxes out on a 7% grade at 60 mph on the speedometer. It has 32's, so there's maybe 5mph more than that in actual speed. I have an automatic. It holds at 60mph in third at about 3000 rpm. I don't have it floored, but if I did, it wouldn't push it fast enough to let 4th take over and actually hold the speed, so that seems to be its best.

On flat ground it's fine. I can take it up to 90 or so.

But it's slow to accelerate, generally. 2nd gear seems to be the weakest.

 

Colorado mountain passes, eg Eisenhower Tunnel, Vail Pass, etc... Most are typically 7% grade.

Typically in 4th gear for most the way up (assuming no traffic). Might have to drop it into 3rd, but rarely.

Yes, a 5-speed manual.