89 has spark and fuel..won't start
 

Hello all, new to the forum.. i've searched all over the place and am desperate for some kind of answer.. I have a 89 Cherokee 4.0 with Auto trans that was manufactured 5-89 and i believe it is a Renix. Anyway it was running great until one day it just wouldn't start. It cranks and cranks, nothing. I have replaced the coil, and even the distributor.. all new plugs, I am getting hot spark to the plugs and everywhere i test it. I am getting fuel to the engine with good pressure. I spray starting fluid and it just cranks and cranks and then eventually backfires.. it won't even run for a second.. I would think with starting fluid it would run for atleast a second or 2,but it won't... would this be a cps problem or maybe a computer problem?? thanks much!!

I'd start with the CPS and the MAP sensor. Yes it is a RENIX. There is also a spark thingy somewhere on or around your coil that may also cause this problem(I think?)

The PCM won't deliver fuel OR spark without a solid signal from the CPS. Normally before they die there are warning signs like dying spontaneously. Sounds like a timing issue to me, are the spark plug wires new and in the right spots? Dizzy cap good?

+1



How are you testing for spark?

There is no timing adjustment, and it's an ECU, not a PCM! Sheez. (try to raizm' right).


AC voltage CPS test; Small clips on the meter leads really helps.

Unplug the connector at the back of the manifold with two wires going down to the bell-housing/cps.
Probe the two wires to the cps with the meter set on AC volts. (a 200 scale on mine).
Crank the engine and note the voltage. (jump it if your battery is low). Sounds like yours is under .35 (ACV).
(I don't mean to "burn bridges", I may need Salad's help at anytime!).

Wathorne, you hit on a couple. (or three) , of the sharpest guys here tonight. Radi, no question, the other two....? The Electronic Control Unit waz replaced by the Power-Train Control Module in 91. (end of Renix). 91 on has the "nag light" Really to deal with a Renix you need a DVM. (digital volt meter).
You can't turn the distributor, timing is done by the computer, whatever they choose to call it.

Cruiser wrote a bunch of great stuff on your Jeep, in the link in my signature. I'd check the CPS first. We will see at 5:03 AM PST if Cruiser thinks you should clean your C-101 connector first or not.

If your CPS were bad you would not be getting good spark. Test if you like but if you've got good spark, it's not your CPS, ignition module (under the coil), coil, plugs, wires, distributor or anything else related to the ignition. The only thing it could be are mis-routed plug wires but that could only happen if you disconnected them and it seems like you would have mentioned that.

Tell us how you know you've got good fuel pressure at the rail? Can you hear the fuel pump priming? Have you checked your injectors to confirm they are pulsing? Have you checked the resistor ballast on the driver's side inner fender? This is where that DVM mentioned by DFlintstone comes in handy. I've got a funny feeling you're dealing with a fuel delivery issue here.

Wait....it's flooded. The Map line is busted?

There is a brittle little tube. It comes out of a rubber plug, low on the engine side of the throttle body. It runs back to the firewall, then up to your MAP sensor sort of high up there near center on the firewall. CRUCIAL!! The MAP will tell the ECU to dump fuel with less/no vacuum. Any crack or blockage and it will be pig-rich. (black smoke, fouled black plugs). You can pull the line off the MAP and feel for vacuum with your finger. If it runs!

Howdy Jeff, yea, agreed. It takes me a while to type anything! (still, on a renix it's a 3 minute CPS check, but, agreed)

Worth looking at. The fact that the dizzy was replaced leaves room for an improper installation masking other issues.......

Yes timing is non adjustable, unless the wires are messed up or distributor is 180 degrees out or something lol. Don't think I didn't see what you wrote pre-edit last night Flintstone :P

missed the part on dizzy replacement.

it's not fuel
 

Hey guys , i appreciate the help.. a few things to answer some questions..

I know its not the dizzy because it's doing the same exact thing it was before I replaced it. I took photos and I know it went back in right.. I have done that job many times on other vehicles.. and the plug wires were not touched prior to it not running. it literally ran one day and the next day nothing. I don;t know if each injector is spraying properly, but i did unhook the line where it goes to the rail and as it cranks it spews plenty of fuel out as it should. also, am i incorrect, but if it was a fuel problem, wouldn't spraying starter fluid atleast make it run temporarily?? This is where I am boggled.. I spray ether in and its just a explosion backfire and it's pretty ridiculous.. it should atleast try to run for a second or 2 shouldn't it? so, are there any sensors that would just not allow it to even start at all? In the world of mechanical things, it is making no sense at all, it has air fuel and spark. I am testing the spark at the coil and also at the end of every plug wire where you would pop it onto the plug and im getting a nice blue strong spark. Does anyone think the computer is dead? Not sure what my next step is after i check the cps and map sensors.... thanks again

hm... Have you refreshed your Grounds at all... Your Cps might not be getting a strong signal.... the Renix will not run with out a cps signal no matter what you do.... Refresh your Grounds... Click on the Cruiser link in my sig and enjoy the Renix trouble shoot... Renix is a great system just need a little time and love to get going ;)

All you need is compression, air, fuel and spark. It sounds like you have verified good spark. I would check the fuel pressure and injectors next. Also a compression check may be needed.

I do very much try to respect that. I correct spelling or add or remove commas..ect. If I change any actual content I mention it. (try to). If I add stuff later is is usually green.

That's why being flooded was mentioned. That is one situation where you can have that and a no go. Also, probably not your issue, but the books and online manuals are wrong. #1 is at 5:00 viewed from the side. (153624, clockwise). The serews for the cap point about an inch left of center of the front of the valve cover.

A while back I suggested to a guy he unplug the rear wire on his ballast resistor, (to eliminate the pump), and see what it does with just starting fluid.