Have Spark, Have Gas, Cranks, No Start

[Powderhound]

Okay, I just had a buddy crank while I sprayed carb cleaner into the TB. It stumbled, but wouldn't start. This is actually great news, as this is the most action I've seen out of it thus far. I'm going to go pull and replace the fuel pump. Fingers crossed, I'll post later as to the status of the project! Thanks everyone, keep the ideas comin'!

 

[89xj]

Okay, I just had a buddy crank while I sprayed carb cleaner into the TB. It stumbled, but wouldn't start. This is actually great news, as this is the most action I've seen out of it thus far. I'm going to go pull and replace the fuel pump. Fingers crossed, I'll post later as to the status of the project! Thanks everyone, keep the ideas comin'!

a more accurate test for the fuel pump is with fuel pressure gauge

 

[Powderhound]

Wrong fuel pump from the stealership. I'll post the discrepancy in fuel pump #'s from Mopar for reference for others. The pump that Mopar says I should have is too short for the sending unit. Anyone else have this experience with a 1991, or any 20 gallon tank for that matter? Also, how does a guy be sure that the stopper is back in the groove of the gas tank? Thanks folks. Hopefully a new fuel pump nails it.

 

[Powderhound]

a more accurate test for the fuel pump is with fuel pressure gauge

For sure, it's just that I don't have access to a fuel pressure gauge.......

 

[Powderhound]

Re: Have spark, no fuel, cranks, but won't start

Had a similar problem, cold start trouble. Also changed the temperature sensor- didn't help. Took it to the dealer in frustration, he changed a diff sensor- fixed it. Can't remember which one- had done the CPS before, that was a different issue.

Could it have been the MAP sensor, or the cam position sensor?

Does anyone know what sensors can truly keep the XJ from running?
1. Crank shaft position sensor
2. ??
3. ??
4. ??

 

[imwally]

Mine would do what you are speaking of. I was messing with the relays under the hood and I pulled the one for the fuel pump and turned the key and it started right up. I have no idea but it did. so I put it back in and have not had an issue for the past 3 days now.

 

[McQue]

In theory, the Map sensor and camshaft position sensor can keep the XJ from running...
These sensors get 5volts from the PCM...all the sensors are tied together on the sensor ground side....if a sensor shorts it power source internally to ground it will hose over the other sensors that use that same power source......the map sensor and the camshaft position sensor use the same 5 volt source as the crankshaft position sensor...
That 5 volt source comes from the PCM..... There is a secondary 5 volt circuit for the oil pressure sensor and vehicle speed sensor... My thoughts are that if a sensor is "loading down the PCM" it can cause the PCM to not function...So, I think a good DMM voltage check at the PCM, ground checks at the sensors, etc. are worth the time to make...

 

[Powderhound]

Finally got the right fuel pump! Epic....

Did a '91 come from the factory with a sock filter on the inlet for the pump? Mine didn't come out of the tank with it, but I'm wondering if it's floating around in there.... (I do have a inlet filter for the new pump, but I'm curious if I need to fish for the old one) Thanks guys!

 

[Wildmatt]

I am unaware of ANY vehicle coming without a fuel pump sock. It is probably in there somewhere, or it was built on friday. Either way I wouldn't worry about it, just put the new one on.

 

[Powderhound]

I'm going to hunt for a cam angle sensor, and a camshaft position sensor.
I put the new pump in, and still, no start.
This is getting a bit frustrating, this thing has eaten $500 in the last 4 days, and it's the longest she's ever been down........

 

[Powderhound]

The jeep is now throwing code 24 = throttle position sensor.
I picked up a multimeter from wallmart, and it's fluctuating wildly just sittting in my kitchen. But, I've never used one before, so this may be normal? I assumed that I'd want to be testing DC volts, correct?

Could a bad throttle position sensor keep this thing from running? Thanks!

 

[RyanM]

IT should run but it will be shitty and missing. Ive started mine with it disconnected

 

[Powderhound]

Good news is, the jeep is up and running again. The bad news is I ran out of ideas, and had to take it to the stealership.

However, this has been a great learning experience for me, and I think the finish may surprise some folks.

My no start (cranking and never starting) was due to a bad O2 sensor. It had fried, and stayed on, dumping too much gas into the motor, flooding it. The whole time I thought it was a fuel issue, but I didn't think it was getting to the injectors, turned out to be too much fuel. So, we can add a bad O2 sensor to the list of sensors that *can* keep the '91 4.0L from running.

Those sensors are:
1. Crankshaft position sensor
2. Camshaft position sensor
3. O2 Sensor.

Here's a test for the O2 Sensor (and tells you if you've got too much fuel) Unhook the fuel pump from the line, and try to start the engine, if it starts, it just might be your O2 sensor.

*as a side note, the jeep would not start when putting the pedal to the floor, hence putting it in WOT start. This shuts off the injectors to clear fuel from the motor, however, this didn't work for me

The stealership took 360 bucks from me to "diagnose," change O2 Sensor, and change the oil. A bummer, because I could have changed the sensor and the oil in less than an hour, but, I'd been working on the jeep for a full week before I took it in, and I was out of ideas. This was the jeeps first visit to a mechanic in the 125,000 miles I've owned it. Not bad really. I love the XJ, and is an excellent resource for all of us owners. I definitely need to become a member to support this awesome association.

Feel free to shoot me any questions & thanks for everyone's ideas & help!