My Jeep somtimes won't start????????

[Jeep CB]

This morning my wifes xj wouldn't start it's been doing this every once in a while. like once a month. I has now been wanting to quite when I start it really low idle and somtimes if I don't hit the gas it will stop. It seems to be getting gas to the injectors, I don't know if it is the coil some of the readings are different then a new one, but I'v heard that with coils they useally work or they don't. The other tought is a vacum leak??

Please help it's starting to get really annoying!!!!

[Chris S]

Not an easy one to diagnose.

A vacumme leak could cause the problem, especially if it is the line to the MAP sensor, but they will also usualy casue a bunch of other funny symptoms like no cruise control and your 4wd light not working or not going out.

What year is your XJ? 91-97 XJs will give you the computer error codes so you can see if the computer is causing the problem.

http://members.home.net/mudpup/FAQ/codes.htm

Once you have tried reading the error codes then disconnect your battery, clean the terminals and posts, let it sit five minutes, and hook it back up. This will clear the error codes and force your computer to re-check for problems. If your rig now runs fine for a short time then goes back to the problem then you probably have a bad sensor. Oxygen sensors gone bad will produce all the symptoms you described.

Once your have confirmed that there are no error codes and you have done the above, then the next step is a fuel presure test.

if the fuel pressure is good then the next step is to convince a buddy to let you swap coils and see if your jeep runs better. :D

I assume you have already eliminated things like a cracked cap, worn rotor, fouled plugs, and all those little "tune-up" details.

[Jeep CB]

My cruise has been out for a little while. I have checked the routine stuff, I did a tune up last summer. My check engine light has not come on (other then when starting) will it still have the codes. My XJ is a 90'

Thanks for your help!

[Chris S]

If it is a 90 you probably have the older AMC computer. It still holds error codes, but it takes a major song and dance to retrieve them. I'd just skip that step and move on to removing and cleaning the battery terminals. If that helps but only for a few starts then get a mechanic to pull the codes for you.

[Jeep CB]

How do I check for vacuum leaks, I'm putting a 97 350 in my YJ and its less cramped than the XJ!

[Chris S]

Start with the obvious. Trace every rubber line off the manifold and make sure it is actually connected to something. Then take the passenger side end cap off the bumper and remove the vacuume canister from inside the bumper. cover the holes with your fingers and hold the canister under water to make sure it hasn't cracked or anything.

If there is an area you suspect but aren't sure about you can spray the area with something like carb cleaner that will make the engine stumble if it gets sucked in.

[Jeep CB]

It sounds like you may have done this before! I will try those suggestions!

[Chris S]

Unfortunately, yes. My problem was finally traced to a short in the wire from the TPS to the tranny computer.

[Jeep CB]

I was just visiting your site. I see that your hatch had the same problem as mine has. Just one more thing to fix!!! My wife and I were pretty close to trading in the Jeep for a newer on the other day, but figured it was more cost effective to keep fixing it :( wouldn't mind a newer on though.

Chris

[satan]

Not sure if you're "fixed" yet -- it's been awhile...

The Renix II ECU used on your '90 has a unique issue which may be what you're seeing.

Each time you switch the engine "off", the ECU writes codes to memory and "opens-up" (retracts) the ICS. Opening the ICS "sets" the "high-idle" for the next time you start your vehicle. If the ICS isn't opened, there is no way for air to enter the intake manifold while you're cranking the engine, unless you step on the gas -- BUT if you step on the gas, the vehicle no-longer sees a high-vacuum signal and the TPS is no longer at idle (which is why they make the ICS open anyway).

The tricky part of the design was trying to supply power to the ECU after you shut-off the engine...

The Renault & Bendix (Renix) guys came-up with a real rig... They have the ECU hold-on it's own power using one of those relays under that "magic" cover on the passenger's fenderwell.

In normal operation, every time you shut off the keyswitch, you'll hear one of those relays "letting go" about 1 or 2 seconds after turning off the key (during that time the ECU is trying to open the ICS).

So, anyway, the ECU drives that relay directly and the drive signal is on pins #3 & #5 of the larger diagnostic connector. Watching those pins will neither check the operation of the relay, nor the ICS, so they're really not that important.

I'm not in a position to go out and check which relay it is, but you should be able to hear it open-up after the time delay... If you don't hear it, try "mixing-up" the relays (I usually tak the rear-most one out, shift all of em backwards, then plug the removed one into the empty front hole) and listen again. If you still don't hear the relay letting go, thry to probe those qty=2 pins just to see if there's any signal out of the ECU.

As I was saying this is mostly relaterd to the ICS moving to open the idle passage - you could have a weak/bad/filthy ICS as well - it'd be worth looking at and/or cleaning (if you were really motivated you could remove the ICS, breifly start the car ***CAUTION RUN-AWAY IDLE ***, shut the car off and see if the ICS moves.

A perhaps less exciting "test" is try to add your own idle air the next time that her XJ is hard to start. After discovering the "hard start", open-up one of the vacuum connections (power brakes, PCV, ??? - try to avoid the MAP and Fuel Reg). If the ICS start-mode isn't set-up properly, your vehicle should start with the air you're letting in.


Just a few thoughts...

... any help?

[Jeep CB]

I'll try that one. I don't have to much time right now since I have finals this week.