All,
I just purchased a 1988 dodge W100 automatic with 318 and am having just a few problems.
First the 4 wd is not engaging properly i am assuming it is a auto locking hub on this truck that may need rebuilt/ cleaned up. secondly the engine runs great at power and at idle but runs pretty rough once warmed up in gear at idle like slowing to a stop after driving a while. and finally the check engine light is on. it goes off when brake is applied and the on off sequence with the key is not making it flash me the code. any and all thoughts are appreciated. thanks again.

 

OK so I did some research and found some information on the 4wd system. Following some diagnostic information I found I know that the 4wd is engaging at the transfer case as the front drive shaft engages and disengages. I then checked for vacuum at the CAD system and there was none on either tube. I trailed the line back to the transfer case and all looked good. I then checked to see if there was vacuum at the vacuum ball and there was none. what I am not sure of is how does vacuum get to the ball is it one of the two lines in the picture bellow. It looks like both these lines go back to the transfer case. Also where is this line suppose to go? It does have a vacuum pulling on it?
Any help tracing this down would be greatly appreciated.

 

CAD HOSES

 

Vacuum ball and hoses

 

Unknown hose. It was drapping down behind motor

 

If the lines to your CAD are all in good shape, my guess is that the vacuum switch in the transfer case has pooched. It's a semi-common part to fail, and if memory serves they're less than $20 at most of the local parts stores.

 

I have seen that quite a bit but how does the switch get vacuum. I thought it came from the vacuum ball some way but don't have vacuum there either.

 

Not sure about an 88 but you should have a vac canister somewhere. Look at all the vac lines you should have one running to the intake/carb for a supply line. There also should be check valve on it also.

 

I have looked and still can't find the line going to the intake but i did go ahead and buy the 16 dollar vac switch to try just in case.

 

The 88 318 should be F.I.,unless it was a late 87, early 88,360 or someone changed things.
Sounds like a vacuum leak for the running issue and maybe the 4wd issue.
Does that have a disconnect front axle?if so do yourself a favor and through the vacuum portion away and get the mechanical operated kit.