Help.. Really weird problem: Began last winter, in florida, didn't like to start & often wouldn't start when cold. Once it warmed up it would start & run fine. All summer ran great-zero issue. Now this winter same thing. I discovered the fuel pump wasn't coming on so I added a jumper for manual fuel pump on, Still no start- discovered spark would go away too so tied jumper into fuel pump harness to back feed- still no start until temp reached 60 deg + +/-.. It runs great when the temp is warm! I changed computer, better but not great,, but progressively got worse. Now i'm back to no or hard start until temp gets above 65. I also noticed AGAIN the fuel pump doesn't always come right on, & once I hear it- it usually starts, but NOT easy. I'm at a total loss, i've had high heat cause issues, but not cold. I changed the coil too due to a crack- no better.. It starts & runs great when warm out. Ideas please?????? I've had this jeep for many yrs minimal problems- I like it, but this is on my last nerve

 

you might have a couple of issues at play. First, check the fuel pump relay and the wiring to the fuel pump; they can be sensitive to temperature changes. Also, look at the crankshaft position sensor, as it can affect spark timing when cold. Make sure all ground connections are secure, as cold weather can exacerbate electrical issues. Since it runs fine when warm, it’s likely an electrical or fuel delivery issue. Let me know if you want to dive deeper into any specific area!

 

Thanks for the reply. Just the other day, for ****s & giggles I ordered a crank sensor. Since you also suggest that, maybe i'm on to something. I'll let you know the result after I get it installed.

 

Hey, Still no luck, Crank sensor & intake air temp sensor both replaced this past week. If anything, it's deteriorating. So to recap: last winter- tried 2 fuel pumps & replaced coil i found cracked. After finding the Fuel pump wasn't coming on, I added a remote jumper- still no start, thats when i discovered no spark either, Plugged fp jumper, With additional ground also, back into harness to backfeed to hopefully turn on ignition- still no cold start. Drove it alll summer- no issue starting- it did cough a couple few times- kinda like if ign was turned off & on- but it never quit. This winter same same. Changed computer- better but deteriorated pretty rapidly. I can't trust it at all anymore. Even @ 60~65 deg = hard start. It'll turn & turn & it doesn't start to hit until I hear the pump come on, When it used to start right up after hearin pump- now it's still hard- crank & hit crank & hit crank & hit till it finally runs- even then it still takes 30 sec to a min b/4 it smoothes out- gotta pump it like a carb to keep it runnin, almost sounds & smells like a "flood" rough until it clears up
I did swap & change out the relay's last winter. Next i'm gonna start cleaning all the grounds I can find. Can Vacuums have anything to do w/ it? It is at the age where those small hvac vac's are breaking, i've plugged & replaced a few in the past, I've heard taking those dashes out is a bear to access the control vacs. I also emptied the cat 1/2 doz yrs ago after it plugged- stuck a straight pipe thru it/ welded it in. I think i replaced the front exhaust sensor yr or so ago..
I keep guessing it's "something" telling the computer to turn on or not??? There's not a whole lot left. Idea or suggestion?

 

You test the battery and alternator yet?

 

just for the hell of it..next cold morning.....pull the connector on coolant sensor at the thermostat housing.

 

Not w/ a meter, but they're both good. She cranks good & fast. I take that back, used my meter to ck fuses earlier- 12.68vdc. batts only couple yrs old.. swapped out FP & start relays again. I also changed another switch last yr, don't remember the name but it has a vacuum line & a 3pin plug on the firewall. I also noticed today a Resistor?? on the driver inner fender- its white ceramic rectangle w/ a single wire each end, has a small crack at the mounting bolt hole.
Got it started today again 65~70 deg. had a fuel psi guage attached, crank & crank nothing, tried leaving the key on to see how long it took to turn on the FP- it wouldnt come on until i kept trying to start off & on. When the pump started showin psi is when it started hitting, it wouldnt stay on constant for 30 sec ~ a min +/-. Still gotta keep playin the throttle once it does start to keep it runnin till it clears & stays on.
Thats where i'm at still. runs great once I get it going. I did remove & clean the ground right there next to the computer- no change

 

Look into that resistor. I've only got experience on 96 and later, but I've heard those resistors can cause a lot of problems. Look for cruiser54s tips on this site. He left a lot of knowledge about the older models.

 

Any idea what that is? I'm jus guessing resistor, diode maybe?? I' can't find it on the rock auto site. About 3" long rectangle- white ceramic looking- single wire/ spade ea end- single mount bolt in center

Nevermind, I found it. Ballast resistor.

 

Yup, many think it was mainly the RENIX years with this, but the infamous ballast resistor was standard on with the XJ through 1993. You can jumper it to bypass it, many have done that; it's safe to do so. Good luck!