worst no start ive ever had...

[jeep.kevin]

ok...

ill try to make sense of this. ive been reading a tons of threads and trying there fixes. but none of the threads list their fixes.

right now the only way my jeep will run is if i jumper the 4th and 3rd relay from the firewall. also, when i turn the key to "RUN" i dont get the 2-3 second fuel pump prime.

1. tried to jumper the white fuel pump ballast.

2. checked and re checked the CPS

3. ran the entire wiring harness from the relays back to the ecu to check for breaks (love the ghetto factory splices i found)

4. bought 4 new relays and put em all in and same problem

having done all these checks makes me think it is the ECU. like its not giving out the signals to initiate the relays and start the whole starting sequence.

does the factory dash clock not being installed have anything to do with this?

last, i am electrically challenged and had recently wired in 4 new hella lights, and also did some welding on the chassis without knowing it could mess up anything.

please help, i'm at wits end here. :wow:

 

[Begster]

It sounds more like the ignition is messed up, have you checked into that?

 

[kastein]

Check all the fuses? What year XJ? I can tell it's a 93 or earlier, approx, from the ballast resistor, but need a bit more detail.

Start sequence is really simple, power wise. Turning to START energizes the starter, ECU, and a few other things. Letting it turn back to RUN then turns off the starter and a few of the other things but not all of them. In fact you can get an XJ to start by putting it in RUN and then jumping the two terminals on the starter with a wrench from under the vehicle with it in park. I know because I had to do that to get the darn thing home once when my ignition switch broke.

The fact that it runs when you jump some relays indicates to me that it's one of a few things -
* did you check all fuses and fusible links?
* have you tried starting in neutral instead of park, if it's an auto?
* have you tried jumping the P/N terminals of the NSS harness and starting it?
* have you checked for ECU output on the wires that drive the ASD, fuel pump, and starter relays? I'm not entirely sure which relays you're referencing, or what year XJ you have, but it sounds almost like some of the wiring for the ASD/B+ relay or fuel pump relay is bad.
* does it crank but not start? or not crank at all?

And yeah, those ghetto factory splices with chrysler duct tape on them crack me up every time I see them.

 

[jeep.kevin]

its and 89 XJ auto. i did try starting it in neutral as well.

if i dont jumper the wires the engine just cranks and cranks.

ive traced all the wires from the relays (fuel pump, b+, ASD) to the ECU and cant find any breaks either.

all the fuses on the block in the cab are good.

the relays im jumping are the 3rd and 4th ones from the firewall out on the passenger inner fender.

ive got my whole dash out now so i can see/access all the wires on my jeep. any more ideas? all this seems to point at the ECU to me?

everything was fine until i wired those 4 hella lights i drilled two holes in the blank square under the dash clock to mount the switches for the lights, does the circuit board inside there interface at all with anything like the ECU?

oh, ive also replaced the motorcraft style ignition switch next to my battery as well.

 

[kastein]

Sounds like wiring from the relays to the ECU to me, but could be the ECU... it's rare though.

Since yours is a RENIX you only have a B+ relay - there is no ASD relay. I think there is a separate fuel pump relay still though.

Any chance you could try only jumping the fuel pump relay and attempt to start it again? If that doesn't work, only jump the B+ relay and test it. I'm curious which relay (or wiring, or relay driver in the ECU) is actually at fault here.

 

[jeep.kevin]

i tried to jump the fuel relay on its own and start - no start

then tried the b+ relay on its own - no start

before i wired my lights up i was looking for a key on 12v source for the lights with a multimeter (that i dont know how to use btw) and i got a few arks and im wondering if maybe miss using that multimeter shorted the ECU?

like i said im electrically stupid and i was touching the multimeter leads all over the place. i cant figure this out.

P.S. i had the key on to "run" while i was using the multimeter (probably the dumbest idea ive had for a while)

 

[kastein]

that sounds like it probably burned out a fuse or something. Did you bridge some contacts with the meter probe? Have it set to voltage or current?

 

[jeep.kevin]

when i was using the multimeter (that i dont know how to use) i was touching the black lead to the batt negative and the other to the places i thought might have 12v applied to them.

none of the fuses are blown tho, and all the fusable links are intact as well.

i was turning the dial on the multimeter to various settings while i was snooping around (to be honest i dont know what the symbols on the dial meant) and it would spark sometimes.

 

[kastein]

You should never use the settings listed in A, mA, or uA when probing for voltage, you'll either damage what you're probing or the meter itself. Always use the V settings - on an auto, the 20V setting is usually best.

I'll have to think about what this could have damaged.. not too sure.

 

[jeep.kevin]

yeah, my friend is an electrical specialist for the jets i work on (he knows how a multimeter works) and from now in im just gonna leave the probing to the professionals.

im still thinkin ECU considering it was on and active (it primed the fuel pump like it always does) while i was probing. then i stopped probing turned the key off and wired the lights then when i was all done (a couple hours, and beers later) i went to start it and the fuel pump did not prime and all it did was crank and not start. booo!

 

[jeep.kevin]

changed the ignition switch and got another ECU and now the engine starts... but, when i let off of the key it dies right away. this sux, any more ideas guys?

 

[Ecomike]

I would go back to what you said here in your first post:

"right now the only way my jeep will run is if i jumper the 4th and 3rd relay from the firewall."

A bad ECU would not have started and run at all.

Get an FSM wiring diagram, go buy some beer and call your E-wize buddy!

 

[Ecomike]

Also we have no idea what 3rd and 4th relay you mean, front to back or back to front on the count, from the front of the jeep?

And just which pins did you jump? There are 4 to 5 pins on each, LOL!! Starting from the front of the jeep, numer uno is the O2 heater power relay, #2 is the fuel pump relay, which is probably where you real problem is!!!
Renix computers are nearly impossible to damage.

 

[cruiser54]

changed the ignition switch and got another ECU and now the engine starts... but, when i let off of the key it dies right away. this sux, any more ideas guys?

Ballast resistor for the fuel pump located on the driver's inner fender?