Hi I have a 1990 cherokee with a straight 6 4L engine and it won't start. I have replaced the fuel pump and fuel filter, replaced the alternator, spark plugs, wires, distributor cap, rotor, and crank shaft position sensor but I still won't start. It cranks but that's it. If anyone can give me some advise it would be greatly appreciated.

 

Just keep throwing parts at it, you'll nail it pretty soon.

 

clay you need to narrow it down to fuel spark or air...

keep some money and test for spark, fuel pressure to see where you need to go from there. as for the air do a compression test.. see where it takes ya

 

Thanks I'll start doing some tests tomorrow. How do I do a compression test?

 

rent or buy a compression tester, remove spark plugs insert tester into spark plug holes and turn the motor over a couple of times.

typically you would want to pull the coil wire off or pull the ignition fuse to disable before doing that.

 

Alright thank you I will try that and go from there.

 

I would recommend testing for spark first. A lack of compression is the least likely source of your no-fire. Spark and fuel are the most likely. You can pull a spark plug, re-connect it to the spark plug wire and touch the base of the spark plug to a ground (like an engine bolt or a clean spot on the block or head). Now have someone crank the engine, there should be a bright blue, snapping spark at the electrode. You've got a Renix so it won't spark immediately, the crank/flywheel will have to rotate ~5 full revolutions before the ECU will trigger the ignition control module (ICM) to begin firing current to the plugs.

 

Did you test the battery?Just because it cranks it might not have enough power to spin it fast enough.If the battery is fine test to see if you have spark at each plug.

 

The battery is good I even tried to jump start it still nothing. I'll test the spark plugs after work today and let you know what happens

 

Ok so I tried checking for spark from the spark plugs and I couldn't see anything. However now I don't think I'm getting fuel to the engine. After trying to start it a few times I checked the fuel pressure release and no fuel came out. Is there an easy and cheap fix to this?

 

Not to discredit anyone else, but F1 gave you great info.

You need a digital volt meter to do much with your Renix Jeep. Hands down, you just can't do much without one. Even the $4 Harbor Frieght one works! (at least for a while).

First be sure you have both no fuel and no spark. You should hear the pump run a few seconds when you first turn on the Key. THEN, if you depress the schrader valve on the fuel rail there it should shoot fuel into the rag you are holding there. You have a ceramic ballast resistor on the inner fender near your air-box with orange wires. The front gets system voltage, and the rear goes straight to the fuel pump. That resistor, and it's connections are well known to fail. It's OK to bypass that and put full voltage to the pump. (it's just there to quiet the pump some).

No spark? Then why not insert a nail or small screwdriver in the coll out-put, and crank it while you hold it. Seriously, that is what I do with "no spark".

Until Cruiser comes along....I might swap the 2'nd and 4th'relays, (pic in my signature) On our older Jeeps a bunch of functions depend on that #2 fuel pump relay. (WE have no ASD relay). Swapping that with the AC clutch is a supper easy test. See Cruisers stuff, sensor ground test and CPS test. Link in my signature. The Cps will not prevent the pump from running, but testing it literally only takes a couple minutes for us Renix owners.

 

Really appreciate the advise I'll be doing those tests that you've suggested tomorrow and will let you know what happens

 

Like F1 and Andrew said, it needs to go past 300 RPM's for at least a couple revs before the ECU will fire the spark or injectors...But the pump should run.


Cruiser has way more experience with these than about any of us. The sensors are "blind deaf and dumb", if the grounds are not good. You can chase your tail all day if those grounds are not less than 1 ohm.
Welcome! and good luck....

 

I just checked for spark today and I do have spark coming from the coil and from the distributor cap. I also checked the fuel rail like suggested and I have fuel spurting out but it still won't start

 

Time to test the CPS.