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'86 2.5L TBI MJ Won't start now (Get comfortable)

SilverMJ

NAXJA Forum User
Location
Fort Mill, SC
Okay, I did a search, and learned alot of new things, but not what I came here to learn.

On Friday, I drove the MJ to the store. When I came out and tried to start it, it nearly caught on about the 3rd rotation, but didn't. After which it took a good while of cranking (multiple attempts) before it started. Once it did, it ran...okay, it ran about as good as it usually did (don't get me started).

Then on Saturday, it did it again while I went to another store. Again took a while to start. This occurred twice again at a couple of stops I made. In between those, one time it cranked right up when I got in and turned the key.

After it not starting, then finally catching, it would rev like mad for a sec, I assumed as it burned up the gas that was in the TBI/manifold/cylinders?

I had a bottle of fuel injector cleaner I'd been meaning to put in this week, and decided to drop that in Sunday morning. I tried to start it and let it run for a bit, but it again nearly caught and then just cranked without starting. It's been that way ever since.

If I dump a couple tablespoons of fuel into the carb, it runs for the second or so until that fuel is gone.

So, we come to what I think is the logical conclusion that it's not getting fuel. Altho that doesn't explain why it revved outta control when it DID start.

But my question is, is there a way to find out whether it's the pump, filter, injector, or something else I haven't thought of without just throwing parts at it?

The Haynes manual says to connect a pressure gauge (which I don't have) to the TBI and let it run for 30-40 seconds.
:huh:
Kinda hard to do right now...

Any ideas, oh great masters of the best Jeeps of all? :viking:
 
First thing I woudl check is if the pump was priming. Key on dont start and listen for the wirrrrrrr sound.
 
Okay, gonna try those things when I get home. Now that you mention listening for the pump, I recall that I never HAVE heard the pump on this thing. How loud is it? Do I need to be up by the tank to hear it?

And after thinking about it, why would it just not start, but run somewhat well once it DID start? Wouldn't it need the same, if not more, amount of fuel/pressure as when starting?

Now I'm completely confused! :helpme:

Thanks for the help guys.
 
Well, do you start your XJ with every thing on like most people do? Turn it all off and key it on. If it is FI you should hear a faint wirrrrring sound. If you do nto hear it then start with fuses then check volts to the sending unit outside the tank. If you have volts there pull the unit and see if anything is loose. There is a hose that goes from the sending unit to the bottow of the tank. Last year at Tellico Fore Wheeler's Father-in-Law (I think that is who it was) had that happen. Good luck let us knkow if we can help!
 
Well...there's nothing to have on.:laugh:

A/C don't work, radio's gone. I don't use the CB unless I'm on the trails.

I'll listen for it tonight. The only noise I remember hearing when I turn the key is the momentary sound of the throttle position motor moving.

What fun! I love my MJ!!!:woohoo:
 
And after thinking about it, why would it just not start, but run somewhat well once it DID start? Wouldn't it need the same, if not more, amount of fuel/pressure as when starting?

If the fuel pump was not working at all it would never start or run, however if it just on the fringe of going bad it may miss every now and then. If you test the fuel pressure it should be low if the pupm is not working to its full potential.
 
Okay, I got down under the truck and put my ear to the tank. There is no noise coming from that area.

But I swear in all the years this thing has been handed back and forth between my dad and I I've never heard the fuel pump running. Then again if it's a quiet pump...
I've never gotten under the truck to listen before. Never had to, it ran.:laugh3:

I'll stop by one of the parts places on the way home tomorrow night and see what they've got to rent.

Oh hey, Ghost, any idea which fuse runs the pump? I see nothin' labelled as such and I never had an owner's manual for this thing. Maybe after my daughter goes to bed I'll head out there with a meter.
If I decide I'm gonna keep this ornery beast, I'll have to invest in a FSM for it The Haynes manual is a bit vague in the fuse ID department.(n)

Thanks again for the help guys. Y'all rock!
 
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Okay, so at the connector right before the tank... with it disconnected I get half a volt across the orange and black wires. I figure it takes more than .505 volts to run that pump!

The half-arsed circuit diagram in the Haynes manual shows a Fuel Pump Relay but the book doesn't tell me where it might be. In fact, the only relay I'm aware of that might be affiliated with this is the one sitting beside the battery in the engine compartment and I always assumed that was related to the starter, but now I dunno...
 
This is an '86 MJ.

I'm afraid there isn't any fuse panel cover or underhood relay center.

It's just got miscellaneous crap strewn all over the fender wells and firewall. :dunno:
I WISH it had such things. Methinks life would be so much easier....
 
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Okay, so I forgot about those little green Bosch cubes on the PS fender well. Swapped relay 2 and 3 and it started!

Unless this is a coincidence I'm gonna say that's the problem and buy a replacement tomorrow after work. (anyone know what the second relay was? :laugh: )

Thanks again for all the input. I know I can always count on the NAXJA guys to have the right answers.
 
SilverMJ said:
This is an '86 MJ.

I'm afraid there isn't any fuse panel cover or underhood relay center.

It's just got miscellaneous crap strewn all over the fender wells and firewall. :dunno:
I WISH it had such things. Methinks life would be so much easier....

Not sure if its the same...but on my 88 the Haynes book calls it a B+ Latch relay....I tore my hair out one day cause i kept not checking it, cause I never heard of a B+ Latch...if it goes badf, it makes my elec fan go freaky too...
 
Ya know, I'm tempted to go see if it IS the horn relay... But I think that might tick off the neighbors since the MJ's sitting right under their bedroom window!
:firedevil :D

But now after reading up more here in the forum, I'm wondering if it's a coincidence. When I metered at the tank, the key had been in the "run" position for a few seconds (long enough for me to crawl back down and look at the meter). I didn't think about it shutting off once it was pressured up. :doh:

Oh well. I'm gonna replace the relay tomorrow anyway. I hope that's all it was.
 
Yea guys this is the 86 which is the first year of FI in the XJ/MJ and I think its also the first year of the MJ. There is no such thing as a under hood power distrudution block. LOL! The three relays were AC compressor, Fuel Pump, and horn I think. But I coudl be wrong. I have some appointments in the morning but I'll see if the 87 FSM has the fuse diagram in it. I do not think it does. I'd bet that is was that relay going bad. but if it still does it I'd check the fuel pressure jsut to be sure.
 
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