Hi,
My 87 Cherokee (4.0l) has gone and died on me. Two days ago I had some trouble starting it - it turned over and fired, but ran very very rough with a bit of light blue smoke. Eventually it smoothed out and ran just fine.

Later that day I was driving along and when I tried to accelerate from idle at an intersection, it again ran very rough, barely keeping going until I floored it which again got it running smoothly. Since then it has been running fine so I chalked it up to a temporary glitch and crossed my fingers.

Today it would not start at all: it is turning over normally, but not firing. I had a similar problem (turning over, not firing) a few months ago, but replacing the oil pressure sender seemed to have fixed it. Now I'm not sure...

At first I was thinking it was perhaps a timing issue, but it would make no sense to me for that to appear and then go away. Now I am thinking either electrical or fuel. The fuel filter was last replaced a couple of years ago, but I suspect that if it is fuel, it would be a pump/pressure problem. Am I heading in the right direction there?

Any suggestions?

Many thanks

 

checking fuel pressure would be a start. May be a fuel pump going bad.

Picking up a tool to check spark is cheap and a good idea. If possible get the one with an adjustable gap as the one with a strobe can indicate a false spark (might not be strong enough to fire a plug but enough to light the lamp)

 

Harbor Freight sells a cheap fuel injection tester gauge,, you can turn your key on with the gauge on the rail and check to see if you have fuel, your TPS, or throttle position sensor may be bad also,, and just because a fuel filter is 2 years old is meaningless, how many miles on it,, how much crappy fuel has gone into the tank, , I change yearly, they are cheap enough, and I also run STP super concentrated fuel injector cleaner every now and then, I usually only Run Chevron or Shell gas too,, might cost a buck more a tankful but it is better than the swill those nameless brand stations sell

 

I would check fuel and spark. Since your at it I would do a dry and wet comp. test. Do the dry first.

 

1st should be fuel pressure at the rail, i forget what it should be but somewhere around 39 psi

2nd pull a plug wire and check for spark with a screw driver near something metal. No spark means a sensor is out and renix systems are a pain to figure out.

 

fast easy test to see if its fuel or spark. try it with starting fluid and if it fires then you know it is a fuel issue. if it doesnt then you know its no spark issue.

 

Spark was good, and there was good pressure in the rail. So I figured maybe it was the crankshaft position sensor. Jiggled a couple of wires and cleaned a connection, and it's working fine now.