My friend and I are officially at wit's end with this thing.... Last week, out of NOWHERE, my 91 4.0 Laredo didn't wanna start for anything... First things I did was spray starting fluid into the throttle body and check for computer codes. Nothing. Tested spark and it was weak. Towed it home and replaced crank position sensor, nothing. Replaced ignition coil, no good either. Eliminated ballast resistor as being the problem and replaced distributor and battery, still won't start. Tested spark again, getting better spark now. Tested timing, timing is perfect, my friend put the distributor in exactly the way the old one sat. Tested coolant temperature sensor by bypassing it and putting a jumper wire on it, still no good... We have literally tried everything on this thing. He's been working on cars his entire life and this is completely beyond him. Recently, I have replaced the thermostat and belt before I started having issues. Last winter I replaced the throttle position sensor. I have kept up with the tune ups as well. The only thing I can think of now is to kick the crap out of my truck! Any help would be greatly appreciated.

 

try putting the key in the driver side door lock it and un lock it then turn the ignition on see what happens.

 

Check fuel pressure at the rail. Fuel pump may have died. Do you hear it prime when you turn the key to "RUN" (not start). If you don't, it may not be running. If you have spark, the coil is probably ok and the plugs too so the next to try is fuel related stuff.

 

What exactly is that going to do? Is that a common problem with these trucks? Doesn't make sense to me how the door lock would affect the engine starting

 

Fuel pump turns on when I turn the key and I smell gas like no tomorrow when trying to start this thing... Also, we're spraying starting fluid directly into the throttle body so if it wasn't getting fuel that alone would start it right up considering you're directly feeding it fuel, right?

 

the stupid jeep security system will cut off ignition source

 

This is flooding it most likely .

 

Hmm alright so should I just let it sit for a few days then and see what happens considering we put a LOT of starting fluid in today? The distributor was just put in today also and putting that in did give me a much better spark than what I was getting

 

Ah ok... Well I have locked the truck up and unlocked it again the next day when I've been letting it sit overnight after I got done trying to get it run almost every day this week so I doubt that will be the issue but I'll try it anyway thanks!

 

Repeatedly trying to start will deff flood it out. Every time keys turned motor gets fuel. Try keeping key in start position longer see if it fires that way. Starting fluid just needs a squirt if no fuel is confirmed going in.

 

The fuel rail is pressurized by the fuel pump, the ECU controls the injectors. A bad CPS will not allow the ECU to fire the injectors so if you have fuel pressure and are flooding it, you would be lead to believe that the CPS and ECU are both good.


Try putting the gas pedal to the floor while cranking. At Wide Open Throttle (WOT), the ECU won't allow the injectors to fire so it should clear the fuel from the system. A good amount of cranking time is required with the pedal to the floor.


I'd check for engine grounds around the distributor side. Is the battery negative cable going to a good ground on the engine block? Take that off, clean with wire brush to make sure everything is good.


1991 is OBD1 I think. Most of the codes won't be too helpful anyway for this kind of thing. You probably have something basic wrong. You're sure that you checked Top Dead Center on #1 when you had the distributor out so that the spark is correct? You've checked Firing Order?


I've only worked on the Renix Jeeps ('87 - '90) so I'm not sure if all this is applicable to yours.

 

Putting the gas pedal to the floor? OK awesome I'm definitely going to do that along with replacing the plugs, as should be done anyway with the new distributor in. Last time I checked the negative ground a few months ago it looked fine to me, I will definitely double check it again. The wires are just where they need to be in the correct firing order positions and we checked the timing last night, the timing was perfect and the rotor was exactly where it needed to be when the #1 piston was at top dead center. I work at AutoZone and one of my customers told me today something about a Body Control Module that goes bad on these trucks that's mounted on the firewall on the passenger side, does anyone know anything about this? He said the soldering inside of them tends to let go and most wind up fixing the unit themselves by opening it up, using a continuity tester, and resoldering as necessary. It also should be noted here that the neutral safety switch is definitely not an issue here, for my friend and I bypassed that with a starter button a few years back.

 

I think he may be talking about the C101 connector-it was eliminated in later years. It's on the driver's side though. You can take it a part and clean it and poke around the pins to make sure there is a better contact. Take a picture of the engine compartment so we can see what it looks like.


http://www.lunghd.com/Tech_Articles/...und_straps.htm

 

Your customer meant the PCM Board I think. That is actually the computer brains of the operation.

 

What's the fuel pressure in psi? Try a factory Crankshaft Position Sensor yet?