I have a 90 4x4 w/3.9. Not only does it get terrible gas mileage (for a V-6), It is very weak, especially taking off on a hill or travelling up hills.
The engine only has 130K and has been very well maintained.
No codes, even had the tranny checked by 3 different shops, it also shows no codes. Recently replaced Fuel pump, filter, but no help.

I've read about swapping to a V-8, but I'll sell before I do all that. This is a very nice and well kept truck, how can I add some horses? I really don't want to sell it!
I's also starting to act like it wants to die on cold idle (in gear).

Any thought?

Thanks in advance.




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Reminds me of what happened when my uncles catalytic convertor on his S-10 went bad. We had a hill by our house, and the thing just barely made it up it. On the S-10, we just cut it off and welded in a straight pipe to the muffler (I mean... NO! We didn't!). Cat's can be had for under $100. You can visit your local auto parts store, order from Jegs (a DF sponsor). I couldn't tell you an actuall way to test it (without just cuttin' her off and see if that fixes it!). If you knock it with a mallet and it rattles, shes bad, but, it might not rattle and still be bad.

As far as mileage is concerned, what are you getting? You can see my post here. (Summary is, 11-14 city, 15-19 highway is normal, depending on how you drive). I bet the problem that is causing the no-power condition (which I believe could quite possibly be a clogged cat) could be effecting mileage.

Do a basic tune up if its about that time: spark plugs (do NOT get the multi-electrode plugs, such as Bosch+4, these have been used with negative results in most vehicles. The copper Champion are just fine for this engine, make sure you get the proper .035" gap), spark plug wires, distributor cap and rotor (or at least take a good look at them, but getting new ones are just a few bucks!), air filter, and PCV valve.

Post back with what you find out.

 

Good call dodgerules86!!!

Can get Coil, cap, button, wires and plugs all for less than $50. I got them all, but found the culprit during installation.
The previous own told me he put new plugs in and he did, so the plugs were literally the last thing I considered. But the number 4 plug was not gapped at all. I replaced all of the above mentioned and it made a big difference. It's not 100%, but much better.