I had a 98 ext cab dak with the 5.2 but with 4WD, and I felt the same way about the power. I was really surprised as well, because I thought the 5.9 would have more grunt, but I guess the added weight really makes a difference. The 98 had the 3.55 gears, and this one has the 3.92's.

 

That's good to know. At least I'm not imagining things. Maybe I can make up the difference with a few mods. How much of a difference did your exhaust/intake/etc mods make?

 

for me, with superchips, larger tb, exhaust and intake mind you the 4.7L only 180 to the tire

 

I'm having the same situation. I had the 3.9L in high school and it would roast the tires, and now I have the 4.7L and it has serious trouble with torque.

 

3.9L to 4.7L should be no competition.

OP, is there anything funny going on? Like can you tell if anythings a little screwy? Does the tranny shift fine, do the RPMS surge?

It may just be the extra weight, but I don't like that idea.

 

Not that I've noticed. It doesn't hesitate or surge, and idles nice and smooth. The transmission seems to downshift at the drop of a hat, but I attribute that to compensating for the lack of torque.

The only engine-related issues are what I noted in the OP. An exhaust leak on the left-hand header (I'm pretty sure now), some valvetrain rattle, and a possible elusive vacuum leak.

The only other thing I can think to do is compression check or leakdown check the cylinders. I seem to remember that low compression generally causes problems idling, though, which I don't have.

 

check you intake and runners for air leaks using a spray of dish soap and water in a spray bottle while truck is running . even a small leak will affect air to fuel ratio . modern computers are made to self adjust but they do so at the expense of performance . this is easily over looked by most shops in a tune up s. spray while engine is running listen for rpm increase or drop if either happen while it is wet then you have air leak solving the leak could be asimple as tightening a few house clamps . also when doing tune you can have the shop advance your timing a noch or two in the advance side this will increase performance as well but at expense of fuel enconomy.

 

Checked all vac hoses, intake plenum, TB area, both valve covers and fittings, oil cap, brake booster hoses, and every joint that I could find that might possibly leak - nothing.

I was using starter fluid spray, and checked that the truck would respond by spraying a little bit directly into the intake past the air filter. Sure enough, the idle dropped noticeably about 1/2 second after the spray and then recovered. But during the actual test, no changes in idle at all.

Also used the "heater hose stethescope" method and was unable to find any hissing near any of the hoses.

This makes me think that either I'm mistaking an exhaust leak (which I can hear pulsing at idle from below the left-hand header) for a vac leak under load (steady sucking sound), or there really is a vac leak, but it's located in such a way that it only opens up when the engine is loaded.

I'm starting to think that this might just be the way the truck is. It's possible my old truck had 3.92 gearing, plus being 2WD, having an aftermarket exhaust, and possibly more that I didn't know about. I sure do miss its torque though.

I'm going to try to dig up my old compression tester and give that a run to make sure the engine is as healthy as it appears (minus the power). If it passes that, I'm out of ideas.

On that note: what range of compression should I be looking for from this engine? And is there a quick and easy way to disable the fuel pump prior to the test so that it cannot possibly start? On my project car, I can reach under the trunk floor and unplug the fuel pump directly. Is that worth trying on my Dak or is there a better way?

 

When I added the air cleaner, and headers, I noticed a big difference on the top end, and for me, the efan only made a difference when first starting down the road. I have other things that I would like to do eventually, but I need to wait for the cash flow to step up a couple notches.

 

Bob , maybe the tell tale sign you had when you test drove the truck could have saved you a lot of money and aggravation . Chances are ,the truck was over driven and or poorly driven in simple terms,Beat !.If I test drive a vehicle ,I always loo for the power, if the vehicle feels sluggish or non-responisve , I look else where. In my early years,I made the same mistake, one that will ever be duplicated ! Since you need to correct this issue,you should open you exhaust , modified TB , cold air intake , and then a Tuner , from almost everyone on the forum , they go with a Superchip Tuner . With that being done,you should get some added power , quikethrottle response and better gas mileage !