88 Cherokee Chief
4.0 5 Speed
Starts and idles great.
Put it in gear and start giving it fuel, it starts backfiring thru the intake but still has power. It also does this as the RPMs rise while sitting in nuetral. I'm at a loss as to the problem. Did a search but didn't find anything to help.
I'm putting a new pickup coil and crank sensor on it in the morning if the weather cooperates.
Any help is greatly appreciated.

 

A backfire many times is due to an imbalance in the fuel-air ratio. Backfiring through the intake is often "lean" and backfiring through the exhaust is often "rich".

I think the #1 thing I would do is to verify fuel pressure with a fuel pressure gauge. Many parts stores rent this tool; call around. On an 88, you should have 31 psi at idle. Then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Also be sure that the vacuum line to the regulator is pulling good vacuum and is not wet with fuel. If it has fuel in it, you have a ruptured diaphragm in that regulator and it must be replaced.

Also be sure you don't have any major exhaust or vacuum leaks.

This does not sound like a crank sensor problem. The cam sensor (pickup) inside of the distributor can be tested with a manual and a meter.

Good luck and let us know what you find!

 

Weather didn't cooperate today. I did find the pickup coil to be very rusty as was the piece on the distributor that it gets signal from. Was able to clean the one piece but not the pickup coil, rain won't stop and I can't get it inside the garage because it's full of antique tractors(not mine).

 

Turns out it was a tank of bad gas. Seems to be running better now. Haven't gotten to run it alot but it has smoothed out some.

 

I used my first can of Seafoam-- in my take and I probably got the most MPGs out of it on that one tank. Also threw a can of Techron in there 2 tanks later. Anytime you fill up and the car is acting weird its most probably the gas.-Toss a bunch of Seafoam in there and get some GOOD gas from a reliable station at the 1/2 way point if nothing else.