no-start jeep, replaced CPS, Ign Switch, bypassed ballast resistor

1990 XJ 4.0

So I haven’t been able to drive jeep for 3 months now, and its really putting a dent in my life.

Sometimes it starts, I can drive it around. Others, it starts up, runs strong, while key is in crank position, and then dies when I let it go to the on position.

I have replaced:
Ignition Switch
CPS
Fuel injectors/orings
Fuel filter
Spark Plugs

I have thoroughly cleaned TB and related sensors.
I have bypassed the fuel pump ballast resistor with a section of wire.

I’m running out of options, and I don’t know where to look next- every bit of advice I've scoured from JU or leads me to the things I have replaced.

Please, any other advice is greatly appreciated. As a side note, it doesn’t seem to be electrical, the Optima red top maintaining voltage supplying power start after start, alternator is less than a year old, and works fine when jeep actually cranks, and the starter is definitely doing its job.

Thanks,

Paul

p.s. Last night, after hooking up ignition switch, started her, she ran- drove her across parking lot, turned off, started , fine- I repeated this action- start, drive, stop 3 or 4 times--- This morning, went out to start, cranked, let go of key, and she died

Did you try bypassing the ignition switch??

The switch is brand new- and worked last night- why should I try bypassing it?

Through every piece of equipment I have replaced or modified in this search for the problem, the symptoms have reamned exactly the same, sometimes starts, sometimes doesnt- I dont understand how bypassing ignition switch would do anything.

Since you replaced almost everything there and it's still not working, I'd eliminate as much out of the loop as possible: it might be an issue of bad wire, bad connection and so on. Once you get down to the point where it's behaving as expected, then it might be easier to see what's not workin.

Okay, well, admitting naiveity, how should i go about bypassing ignition switch?

PJKonNAXJA said:

Okay, well, admitting naiveity, how should i go about bypassing ignition switch?

Click to expand...

Do you have an FSM? It'd be good to trace the circuitry. ANother thing that just came to my mind is that if you have an auto the culprit might be the NSS (Neutral Safety Switch). Now owning an automatic I don't know how it'd behave it it was cutting out while engine is running, but IIRC it might prevent you from starting if it goes bad.

Cleaned NSS less than 6 months ago, and it gives me same symptoms in neutral as well, and the reverse lights work, so its not the NSS

No FSM tho

Try replacing the Fuel pump relay. On Renix (87-90) XJs the fuel pump relay sends full voltage to the fuel pump to start but then switches to another position to allow the balast resister on the fender to be used.

I do not recall where the relay for the fuel pump is located under the hood but I can check when I get home of you like.

I'd pop out the relay and replace it, that should fix your problem. I checked on www.oreillyauto.com and found they sell the relay for $7.89, BORG-WARNER p/n R3074 so looks like less than $10 for a replacement.

Try the relays as Martin suggested, I regularly play musical relays as a common troubleshooting methode. If that doesn´t do it and I remeber right, the large yellow wire at the coil, is hooked up directly to the ignition switch (through a couple of connectors), the same wire at a splice goes to the ign. input for the ECU (computer). If the yellow wire is getting juice with the ignition in the run position. This eliminates the ignition switch as the culprit. I would't touch a thing the next time the motor stops, when the key is returned to the run position, take something sharp to prick the large yellow wire at the ignition coil and test with a voltmeter or trouble light.
If it´s getting juice and the motor isn´t running, it eliminates many things as probable. You can begin troubleshooting down stream fromt the coil, imput. Then maybe later some of the imputs to the ECU and try and figure out why the igntion coil isn´t triggering.
Could be as simple, as a loose connector, a short or open high voltage wire, coil to distributor. Weak spark or other common problems.

How about the starter relay. This crapped out on me a few years ago, did everything you did but it still wouldn't start. Also when it starts how is the idle low or high. C101 connection might be your problem. Juice

Same thing happend to me, and all boiled down to the ignition control module under the coil, it was no good, went to junk yard got new coil and module and all is fine now.You have to watch though I had my coil tested at NAPA and it tested fine so I ruled that out for a while, then it was suggested to try the module and that was what it was.
just my 2 cents
Jim

it idles normal, 800-1000, and when its in the crank position it responds to the throttle

p.s. the outflow of help here is incredible

Just ran out and checked, power to yellow wire running out of ignition switch with key in on position, so the problem is not on the switch side.

I have 4 relays under plastic cover on passenger's side behind battery- anyone know which is which?

I just looked in my 88 XJ electrical trouble shooting manual. They show the Fuel Pump Relay on the passenger's side under that cover you removed. You will see 3 relay sockets who's wire go back toward the diagnostic connectors just aft of the relays.

They show the relay sockets from front to back as:
C215 - Power Latch Relay
C216 - Fuel Pump Relay
C228 - Oxygen Sensor Relay

I looked the schematic and the fuel pump gets power from the start relay when the ignition switch is in the start position. The fuel pump then gets power from then fuel pump relay when the switch is in the run position.

The C215 relay also has to be in the right position to get fuel. It looks like the same relay from the schematic. You may want to pick up two of that fuel pump relays at the store and change both. Cheap insurance, but if i had to lay money I'd say it the relay in C216

This is another relay located by the 3 i listed above. It is the AC clutch relay, you will find it's wiring going forward toward the radiator. You may want to experiment with the AC system, make sure it runs then turn it off, pull the relay, turn it back on to see if the clutch engages. If it does not then you know that NOT the socket for the fuel pump

Hope that helps.


I just was out at my XJ after picking up 2 new relays at the parts store. I decided to replace the latch and fuel pump relays to avoid your problem.

I pulled the forward most relay, started it and tried the AC and the clutch engaged. My guess is this is the Oxygen sensor heater relay since the engine did run.

I then pulled the rear most relay and that time the AC did not run. So that the AC relay

My guess is the fuel pump and the latch relay are the center two positions. Since you need both to make the engine run I stuck my two new relays in those locations. All the relays had the same OEM part number on them so switching them around is not a problem.

If it was me I'd pull the rear most relay- the AC relay - then begin to experiment. I take it you have AC and won't need to do this test. I'd replace the #2 position relay with the one fron the AC socket and see if your XJ runs. If it does you know which one is bad. If not then move to the #3 postion and do again, repeat at the #1 positon or until you fix your engine running problem.

Or you can buy 3 new relays and replace the 1, 2 and 3 position relays with new ones and renew all the engine fuel control relays.

On a crank but no start you need to first check for the three basics of course -- air, gas at the fuel rail and spark at the plugs. Typically on the pre 91s a crank but no start, rough running or engine dieing situation is often cps related. Even a new cps often wont fix the problem when it is a cps issue due to a bad connector on the engine side of the cps wire harness connector. Here is a post I have posted a number of times in the past.

"Here is some info I have posted in the past.

If on a crank but no start the unplug and replug of the cps wire harness connector gets you going you may just have a wire harness connector going bad and may not need to replace the cps sensor. Here is how to test: hook volt meter to both wires from cps sensor w. harness unplugged. Set the range on meter to less than one volt. Crank engine and if cps generates .5 to .8 or more volts it is ok and your connectors need tightening or replacing. I got my parts for a couple of $ at Pepboy but advanceauto.com also has them. They were made by Dorman under the Motormite Conductite tech grad name # 85303, 85304 and 85305. There are about 5 pieces in each box. You can also get a small tool set that helps on the install number 85360. I fixed my 89 this way a couple of months ago when I got tired of unplugging and re-plugging the connector every few weeks. My cps was only 1 yr old so the engine side harness connector part was worn out. I replaced both the female and male side internals of the connectors and it not only starts every time but the idle was also improved. Greg "

P.S. it has now been over 1 yr since the rebuild of the cps and it has never run better. Greg

I can put money on it being the fuel pump relay, my 90 xj did the same exact thing and when I changed the fuel pump relay ($5) it stayed started everytime. make you you get yourself a wire brush and electrical cleaner and clean out the connections where that relay goes. top and bottom. and it should work great.

Hallo. Your advice is coming a little bit too late .
But useful for the future. LOL .:roflmao:

'92 XJ

I was just about to say that this was an older thread... But I do wonder what ever ended up being the fix!!! That would be nice to know for future needs!!!