nate5022

My 1990 Cherokee 4.0 started stumbling and hesititating about a week ago. I checked and saw that two of the hard plastic vaccum lines were cracked. I presumed that it was vaccum leak and replaced the front/back vacuum harness that comes from the valve cover. It's still stumbling under a load, backfiring when revved in park and dying after revved in park. I went through and pinched off every vaccum line one at a time and could not isolate a leak. Its stumbling under load and if in park and revved it will stumble and die. Occasionaly it seems ok. I have replaced many parts within the last year including all sensors, computer, injectors, distrubutor, coil and others. I am so frustrated with it and ready to send it to pick n' pull. Any suggestions would be appreciated.

RTorrez1

Have you tried to see if it's putting out any codes?

cruiser54

It's a Renix, Robert.

OP- do a fuel pressure test as your pump may be onn it's way out. Gotta elim inate that as a possibility first.

nate5022

Checked fuel pressure. The pump filter and regulator are all about 7 months old . I tried pinching various vacuum lines but seemed to have no affect. I don't have a vacuum line diagram so not sure I hit them all. I have a ton of new parts on it but getting frustrated with it. It is stumbling and backfiring in neutral also now. Could it be an egr valve malfunction? Thanks

cruiser54

Here's a diagram. Perhaps the eGR is hanging open?

nate5022

I thought it might be a clogged cat, so I unbolted it and it still does the same thing, just loud. I manual acutuated EGR vavle and it would die so I assume it is not stuck open. Not sure what else to check, the vaccum system seems like it shoudl be intact. Is there not vaccum resevior on a 1990?

cruiser54

What were the fuel pressure results?

codykrr

if you have access to a vacuum pressure gauge, take your brake booster vacuum line off at the manifold. at see if its holding good pressure. I cannot say what its supposed to run with these engines exactly but I know with SBC it should be around 15-25 at idle.

you need to find out what normal operating vacuum is for sure, check it and that will least least you know if you have a vacuum leak.

if it is leaking(wont hold manifold vacuum) take a can of brake clean, and start spraying it while idling around the manifold, throttle body(or carb) and see if it idles up.

you can sometimes pin point a leak easily this way. sometimes not so much depending on where the leak actually is.

also, could be a valve spring, out of adjustment valve lash, or worse a collapsed lifter.