I have tried other forums for help on this, maybe someone here can help.

I have a 1990 Ford F-150 that shakes when the engine is running between 1000 and 1500 rpm. It does this whether it is in drive or not. I have replaced the plugs, wires, rotar, cap, fuel filter, and coil and the problem been reduced, but has not gone away. The shaking is pretty intense when in this range, but is gone when at highway speeds (200rpm). Is this a vacuum issue, compression loss issue, air leak, etc.? I've asked around and so far have not had much luck.

Any info is greatly appreciated!

 

Automatic or standard transmission, also check your harmonic balanecer.

 

It is an automatic, but I don't think that it is transmission related due to the fact that it shakes in park, neutral, 1, drive, and over drive.

I have pulled the belt off and checked all the pulleys and the fan, but they all seem fine. I even started it briefly with the belt off and it shook in the same rpm range.

How would I check the harmonic balancer besides pulling the belt off to see if it is loose?

 

Hummm, that is odd , most balancers are 2 piece with a rubber sleeve between the 2 , Look at it with a good brite lit , An see if its starting to seperate, I have found them with the outer hub cocked an half way off the hub. ( not cool ) , Check the big bolt in the center an see it its tight ., An really the best way is to pull it off so you can get a good look at it . You can get a cheap puller for like $10.00 bucks most parts store , Also you should not be able to turn the outer part of the damper, I've had a few that on the Truck after you pull off the belt , grab the outer ring an try to turn it one way or the other it shouldnt move seperate of the inner hub .

 

I'll check the harmonic balancer when I get home.

Is it possible that this could be caused by a bad fuel injector?

 

Well , just One Injector would not cause it to be --INTENSE-- as you said, plus the fact that it smooths out at higher speeds/ rpm,, If it was a whole bank of Injectors it would be real doggie to get rolling an have no power for like passing an such,, Also if the EGR valve is stuck partly open it would cause this as well , but you should be getting a code for that ! Also any vacuum leaks like PCV valve sticking open would cause it , or a vacuum line off, broke , or one capped off an the cap has developed a break in it , , Let Us Know what You Find , Oh an yea those other sites you said you visted---- WELCOME To The Best !!!!! , The folks are very helpful here an I would be afraid to try an guess the total number of years of Techinal Knowledge on This Board, You got guys here that work at various Ford dealerships , Independent Shop Owners/ Tech, , Or work For Various Aftermarket Garages An a good mix of Weekend Do it Yourself ppl.

 

The engine doesn't seem to be lacking power or missing. It actually seems to run well except for the shaking issue. I did talk with a service man who I was told was a big Ford guy and he said that it may be the upper plenum (I hope I spelled that close enough) and told me to spray carb cleaner in the intake area. If that was leaking it would suck in the cleaner and rev-up the engine. I did this, and there was no difference in the idle speed. He also said after that he would check each plug's spark and then after that he would check compression. I have a hard time thinking that it is spark now that I have replaced the coil, cap, rotor, wires, and plugs. That would leave compression, but it doesn't seem to be lacking power or running poorly - just shaking - so I have a hard time thinking that it is compression, either.

By the way, so far I'd say that this is by far the best forum! It's nice to get replies, guesses, and even advice on what could be wrong rather than just people viewing what I wrote and not replying at all!

 

With all I read my guess it the balancer as will, but Truckpuller had good point about the torque convertor it turns with engine and if its off balance it may cause same problem. But I'd check harmonic balancer first.

 

I forgot to mention that I also pulled the flywheel inspection cover off and took a look in there. It seems that all the bolts are tight and I didn't see anything unusual in there.

 

Good deal, its time to inspect the balancer, should mention that to remove it may require radiator removal [:'(]