1990 4.2 Doesn't Have Enough Power to Move

[AngusMurphy]

YJ idles great and operates through rpm range perfectly at rest but has no power...none....as in it's tough to get it moving. Weber 38 tuned well, cleaned and less than 2000 miles on it. New plugs, wires ,hei, fuel pump, fuel filters, accelerator pump, fuel lines from carb to tank and fuel pickup. Checked for vacuum leaks everywhere and verified fuel pressure at carb. Starting to lose patience...any advice is GREATLY appreciated.

 

[Flyer58]

It sounds like a problem when the timing gets way off. I'm not familiar with setting the timing on a 4.2. On my 2.4 there's nothing to set, it's all computer controlled.

 

[AngusMurphy]

Thanks for the advice. I am leaning that way, too, but I'm not quite educated enough to figure it out. I've set the timing, but it's a new distributor (that was cheap) I installed while fixing some other issues. I'm not sure if it's not advancing or what.

 

[Flyer58]

Looks like the most common mistake is not removing the vacuum line from the distributor to the carb when checking the timing. Be sure you plug the vacuum line or the carb settings will be way off.

You can check to see if the timing changes with a strobe light by having someone punch the gas a few times with the engine running.

 

[Lineman85]

check timing, like stated make sure it is done with vaccume advance disconnected and that port plugged on the carb.. 2 get yourself a vaccum gauge off Amazon.. worth its weight in gold. 3. Make sure it doesn't sound like a clogged shop vac when you crack the throttle. This is a clogged catalytic converter. Engine will idle great but fall flat on its face under load.

 

[AngusMurphy]

Thanks everyone for the helpful words. The timing is good with the vac advanced plugged. The catalytic converter is a distant memory and I can't hear anything unusual anywhere. It's baffling. I'm beginning to wonder if this cheap distributor/HEI I bought is junk. Next time I open the hood, I'm going to pull the cap and see if anything at all happens inside when I put vacuum on it. I like the idea about the vacuum gauge. That's good advice I'll take you guys up on.

 

[flyfisher]

one important thing you should check is the mechanical advance,
with the distributor cap off you should be able to twist the rotor cap, not sure what the advance curve is but it will be easy to rotate in the direction of rotation, it may only move @10-15 degrees ( of the 360 degrees the rotor turns), remember that the rotor only turns 180 degrees per one crankshaft revolution. hence 1 degree of rotor rotation is 2 degrees crankshaft rotation.
It makes a really big difference preformance wise.
Also check vacuum advance, this will require a hand held vacuum pump, you should see the plate with the pickup coil move when vacuum is applied, which it should hold, not leak, but I have seen the plate stuck in place even though the diaphram holds vacuum.
A quick and easy way to somewhat check this is to have the engine running remove the ported vacuum source for the advance, place it onto a manifold vacuum source, you should see a noticeable increase in the engine idle speed, because you just advanced the base timing. Thats assuming the vacuum advance is working properly.
Hope this helps, I realize its a long post but I wanted to be as clear as possible.
Good luck.

 

[AngusMurphy]

one important thing you should check is the mechanical advance,
with the distributor cap off you should be able to twist the rotor cap, not sure what the advance curve is but it will be easy to rotate in the direction of rotation, it may only move @10-15 degrees ( of the 360 degrees the rotor turns), remember that the rotor only turns 180 degrees per one crankshaft revolution. hence 1 degree of rotor rotation is 2 degrees crankshaft rotation.
It makes a really big difference preformance wise.
Also check vacuum advance, this will require a hand held vacuum pump, you should see the plate with the pickup coil move when vacuum is applied, which it should hold, not leak, but I have seen the plate stuck in place even though the diaphram holds vacuum.
A quick and easy way to somewhat check this is to have the engine running remove the ported vacuum source for the advance, place it onto a manifold vacuum source, you should see a noticeable increase in the engine idle speed, because you just advanced the base timing. Thats assuming the vacuum advance is working properly.
Hope this helps, I realize its a long post but I wanted to be as clear as possible.
Good luck.

That's similar to where I was going next. I didn't think about moving that vacuum source though. I've moved the Jeep away from home so I'm not hands on with it everyday anymore. It was driving me crazy and I had to get away from it for a while. If all of this is due to that cheap distributor, I'm going to really be kicking myself!