Help me out here. I bought a little '91 YJ with a 4.0 for lite trail use and camping when I don't want to drag the big one out. So far, it's been running fine for a couple of months until the other day. I pulled up to the mailbox to get the mail, took the key out of the ignition (it still runs without the key in) since it had my mailbox key on it, walked about 10 steps away and it died out and didn't crank anymore.

Up until this point, for maybe a couple weeks previous, it was taking a little longer to crank after it had sat for a while (think first crank in the morning). After it had been cranked, each sequential crank was normal and easy. Also, by "little longer" I mean it was holding the key forward about 3-4 seconds until fire.

I am getting low on ideas at this point...

I have replaced:

fuel pump
fuel filter
crank position sensor


I am getting no pressure at all on the fuel rail. Lower the tank back down and get no fuel flowing out of the tank. I get ~12.5V at the fuel pump for about 1/2 a second, just enough time to read the multimeter. I've got spark, so that side it good. I took the time to read a bit about the SEBII going out (capacitors for example), but it seemed that the check engine light, and the other ones above the steering column, seem to not work when the SEBII is bad. Checked the ground for the fuel pump again up on the fire wall and even hooked it directly to the battery with no difference.

Other things I did, is swap the relays around up in the power distribution block since all 3 I have in there are the same, no change. I also did the same for the fuses in there too with no change either. So right now, as it sits, I turn the key, the engine turns over, but no fire because the fuel isn't making it out of the tank... all this while the fuel pump only gets 12V for a fraction of a second.

Anyone have any ideas? Was wondering about the ignition cylinder but thought that might be a long shot. Crossed my mind since the key is able to come out and still have it run. Still diagnosing, just figured I would see if anyone had some fresh ideas.

You can now add oil pressure switch to the list of parts changed.

You've done your own diagnosis, Dan. :D I think you should have voltage to the fuel pump for 2-3 seconds, cause if you can read it on the meter, it is longer than .5 sec, I suspect. (anyway, you are supposed to get it for 2-3 secs)

Sounds like wrong or bad pump IF in tank fuel line also checks out ok... I had one kink on me a few months ago when I replaced the pump and had the same symptoms. I am gonna guess that the pump relay under the hood is ok since you do get voltage to the pump.

Test your coil. Similar symptoms on mine. It ended up being a bad coil. You can test it using a multimeter. I will update with the numbers.

Edit: here you go:
http://www.pirate4x4.com/forum/showthread.php?t=717149&highlight=jeep+start

You've done your own diagnosis, Dan. :D I think you should have voltage to the fuel pump for 2-3 seconds, cause if you can read it on the meter, it is longer than .5 sec, I suspect. (anyway, you are supposed to get it for 2-3 secs)

Sounds like wrong or bad pump IF in tank fuel line also checks out ok... I had one kink on me a few months ago when I replaced the pump and had the same symptoms. I am gonna guess that the pump relay under the hood is ok since you do get voltage to the pump.

Definitely not getting 2-3 secs. In fact, I don't even hear the pump kick on. When I say I have just enough time to read the multimeter, I mean I can make out 12 and nothing following.

I was wondering about a bad pump, even though it new and picked it up at NAPA. The only thing that makes me think it's not that is due to the short presence of voltage at the actual pump. You very well could be right though. Same with the relays, I swapped all three around since they're the same and nothing changed.

Test your coil. Similar symptoms on mine. It ended up being a bad coil. You can test it using a multimeter. I will update with the numbers.

Edit: here you go:
http://www.pirate4x4.com/forum/showthread.php?t=717149&highlight=jeep+start

I haven't tested the coil, but I'll give it a shot. I am getting it to turn over though when I dump a little gas down the throttle body. Based on that, and no fuel being delivered up to the fuel rail, I hadn't made it up that far trouble shooting the coil, distributor, wires, etc.

I'll do a little more reading and see if anything up there spark related could retard the voltage heading back to the pump. My other YJ is a '94, nothing really original left, but this '91 appears to do things a little differently form what I remember on the '94. I'm almost ready to drop the LT1 in the little Jeep and LS1 the crawler. :flipoff2:

Keep the ideas coming if you have them. I'm really not that knowledgeable when it comes to the Jeep engines and their intricacies.

BTW... codes flashed:


12* Direct battery input to PCM was disconnected within the last 50 key-on cycles.
33* An open or shorted condition detected in the A/C clutch relay circuit. (no A/C installed though)
22** Engine coolant temperature sensor input above maximum acceptable voltage.
or
Engine coolant temperature sensor input below minimum acceptable voltage.
17* Engine coolant temperature remains below normal operating temperatures during vehicle travel (thermostat).
55* Completion of diagnostic trouble code display on the malfunction indicator lamp (check engine lamp).



Ironically, only thing that I've changed since I got it was the thermostat. Cleared codes and they are still there.

I was really puzzled for awhile when I did the pump swap, the bad pump even came on when direct power applied to it, but not enough power to pump the fuel.

I ended up having the tank on a stand just low enough to check the pump and wiring direct from the Jeep, having it all hooked up and testing grounds, volume of fuel, etc. right at the tank. Then I had good flow with a different pump and put it all together with a kink in the rubber line in tank.....:homer:!! Took it out AGAIN, found the issue and been running sweet happily ever after....:shaking:

edit: unfortunately, all I see for codes is some unrelated issues...I really doubt any of those is gonna help ya other than maybe a bad temp sensor...:)

For anyone using the search...

Went through everything again, checked all the voltages and everything checked out. Only thing that made sense, although it seemed highly unlikely, was the new NAPA fuel pump was bad right out of the box as was mentioned above. Took the pump back, exchanged it, and bam, fuel was flowing.

Did you get a new temp sensor while you were at it? lol
:D