Turn key to run and cuts off (kinda long)

[Cottontail]

1990 XJ, automatic, 4.0L

Here is what is it doing:
Turn key, and it will start most of the time. It will run for a few seconds and then when the key leaves "start" and goes to "run" it will die. After a few tries of that sometimes it just cranks and won't turn over. Let it sit 30 seconds and I can usually get it to turn over again the next time. Sometimes it will run until I open the throttle and then "chokes out." When it does run, sometimes for up to 15 seconds, it runs terribly rough.

Here is what I have done:
New plugs and wires
New battery
New positive and negative battery cables
New ballast resistor
New fuel filter
New fuel pump
Unplugged the CPS a couple of times
Swapped around the relays in the relay box to rule out those as the culprit
Checked the wires below the coolant tank for possible shorts (heard about that from a search)

Here is what I (think I) know:
1. It is getting spark...due to the fact that I can get it to run
2. It is getting fuel...due to the fact that I can get it to run. The new fuel pump made a difference. It runs much stronger, and I can get it to turn over much easier.
3. The starter is fine, as it starts the truck right up when it starts, and I did grind it once, so I know that it is turning

Here is what I suspect:
It isn't getting enough air. As we all know it takes air, fuel, and fire to make and engine run. The only thing I can't seem to verify is the amount of air getting in. I don't suspect the Ignition Module because it will start, just not stay running.

I know from doing the forum search that it could still be a faulty CPS, or a bad Ignition Module. Throw a brother a rope and help me out!

Shot in the dark: Could it be possible that the cat is clogged and it won't stay running because the exhaust is backing up into the engine?

 

[XJXJ]

1990 XJ, automatic, 4.0L

Here is what is it doing:
Turn key, and it will start most of the time. It will run for a few seconds and then when the key leaves "start" and goes to "run" it will die. After a few tries of that sometimes it just cranks and won't turn over. Let it sit 30 seconds and I can usually get it to turn over again the next time. Sometimes it will run until I open the throttle and then "chokes out." When it does run, sometimes for up to 15 seconds, it runs terribly rough.

Here is what I have done:
New plugs and wires
New battery
New positive and negative battery cables
New ballast resistor
New fuel filter
New fuel pump
Unplugged the CPS a couple of times
Swapped around the relays in the relay box to rule out those as the culprit
Checked the wires below the coolant tank for possible shorts (heard about that from a search)

Here is what I (think I) know:
1. It is getting spark...due to the fact that I can get it to run
2. It is getting fuel...due to the fact that I can get it to run. The new fuel pump made a difference. It runs much stronger, and I can get it to turn over much easier.
3. The starter is fine, as it starts the truck right up when it starts, and I did grind it once, so I know that it is turning

Here is what I suspect:
It isn't getting enough air. As we all know it takes air, fuel, and fire to make and engine run. The only thing I can't seem to verify is the amount of air getting in. I don't suspect the Ignition Module because it will start, just not stay running.

I know from doing the forum search that it could still be a faulty CPS, or a bad Ignition Module. Throw a brother a rope and help me out!

Shot in the dark: Could it be possible that the cat is clogged and it won't stay running because the exhaust is backing up into the engine?

"...when the key leaves "start" and goes to "run" it will die. "

It sure sounds like something do with the ballast circuit. I see you changed the resistor but I would dig deeper into that circuit and verify it's doing what it's supposed to do.

The Synch Signal Generator (distributor) can be funky since the ECU will basically guess about #1 cylinder. But there wouldn't be any relationship to the ignition key that I can see. It can run like crap though with no synch input.

I seriously doubt you have something clogging the intake/exhaust enough to cause this trouble. rarely do these engine lose cam timing but it is a chain so make sure everything (crank, cam, distributor) is timed like it should be.

 

[langer1]

. Did you check your fuel pressure, it should be 31#. Don't forget, to get air in you need to get exhaust out. Sounds like you have a Potato in your tail pipe.

 

[Eagle]

Have you verified that at least some of the time you cam keep it running (albeit badly) with the key in the RUN position?

I ask because the START position bypasses the ballast resistor for the fuel pump. If the ballast resistor (or that circuit) is bad, the engine will start with the key in the START position due to the bypass, but when the key is released to the RUN position, the fuel pump shuts down and the engine runs only as long as it takes to use up the fuel in the fuel rail.

 

[langer1]

Have you verified that at least some of the time you cam keep it running (albeit badly) with the key in the RUN position?

I ask because the START position bypasses the ballast resistor for the fuel pump. If the ballast resistor (or that circuit) is bad, the engine will start with the key in the START position due to the bypass, but when the key is released to the RUN position, the fuel pump shuts down and the engine runs only as long as it takes to use up the fuel in the fuel rail.

None of my FSM's show that, what mine show is the start position bypasses the ECU fuel pump output, but not the ballast resistor. Anyway when in doubt jump it out.

 

[Cottontail]

Update...

I went out and tried again, and it fired right up, smoked like a chimney and idled (rough) for about 2 minutes.

I got in and backed it out of the garage, and halfway out of the garage it died, and wouldn't start back up.


But it did start and idle! Yah!

I did forget to mention last post that the fuel in it was about a year old. I did drain all the old fuel from the tank and then refilled it with fresh fuel.

 

[langer1]

Update...

I went out and tried again, and it fired right up, smoked like a chimney and idled (rough) for about 2 minutes.

I got in and backed it out of the garage, and halfway out of the garage it died, and wouldn't start back up.


But it did start and idle! Yah!

I did forget to mention last post that the fuel in it was about a year old. I did drain all the old fuel from the tank and then refilled it with fresh fuel.

Really sounds like a plugged Cat.

 

[Cottontail]

On that ballast resistor, would it be a waste of time or a good idea to take the "end caps" off the wires that attach to the ballast resistor, and solder the wires to the prongs on the ballast resistor.

That would pretty much guarantee that there isn't a bad connection to the ballast resistor right?

Anyone else want to second the clogged catalytic convertor??