Topic: YJ wont start

[yjsandaddict]

I am having a hard time figuring out whats wrong with my jeep and was hoping i could get some help. I have a 91 YJ 2.5l and the other day i was driving it when it died. It revved high then dropped then up agian before it died. I turned the key and nothing happened. Then i turned it agian and it started up. I drove it a couple miles and it did the same thing except it hasnt started since. The fuses and relays are all good. I pulled the fuel pump and it shoots fuel, but sometimes theres pressure in the fuel rail and sometimes there isnt. I changed the filter and checked the hoses for leaks but they all look good. I pulled a plug and there wasnt any spark either and the fuel pump is weak. Could there be something wrong with the computer or maybe a safety shut off? I dont know why there would be suddenly no fuel or spark, the distrubutor cap looks good still. Should i just install some pedals or turn it into a flinstonemobile? I would really appreciate any help. Thanks.

[sharpxmen]

have a pressure gauge connected to the fuel rail and see what pressure it shows (31psi idle and 39psi when you floor it; it should also hold 39psi when the ignition is off). Also, check that you have power to the injectors (they have 1 wire at 12v when running, they are opened by ground on the other terminal). Check if you have 12v at the ignition coil, and of course if you get spark (not at the spark plugs, at the coil, and if you do then check if you get a spark at the plugs); also check and make sure your distributor is spinning when you crank the engine. based on these you might want to check relays, fuses and so on (if distributor is not spinning then you might have an issue with the timing chain for example). It could also be something more simple, but i'm not sure what the behaviour is when one of these fails completely: map sensor (check if you have 5v at it, if you don't then it is a fuse, relay or computer), tps or the most unlikely is the computer. You might want to look at the service manual as well (you can find them on this site). Let us know what your troubleshooting results are, this is interesting but hard to guess with little info.

[yjsandaddict]

Thanks for the help, ill play around with it more in the morning and see what i can find, im wondering if the 4ft. deep mud hole i drove through could have affected it, but it was about a month ago and ive been driving it since. Ill let u know what i find. Thanks

[sharpxmen]

3 things to worry if you went in a pond 4 feet deep (depending on your tire size and lift also) -  O2 sensor (but it would start even with it unplugged), cranckshaft position sensor (sealed so unlikely) and ECU (computer). For the latter it is also sealed in silicone, however due to age you might have  a crack or the connector seal might be dried out - take the connector out and see if you got water in there and you can also take the plastic cover off the ecu and see if you got any cracks in the silicone. Unlikely that after so long to have a problem with the ecu unless it is the connector and you got oxidation on the pins (again speculation, i don't think that would be the case).

[neale_rs]

Make sure the check engine light comes on for a while when you turn the key.  It gets turned on as a bulb check that does not depend on any sensors.  This means that if it does not turn on you either have a bad bulb or associated connections or the computer is going bad or either the power or ground to the computer is bad.  I went through this a couple of years ago, it is the first thing to rule out.

[Jeffy]

My guess is that it's the CPS.  If that sensor goes you it can leave you SOL.  It doesn't really explain the low pressure at the rail though.  No spark, yes.  Also, the CPS is low enough that it can get messed up in water or mud.

[yjsandaddict]

Well its been over a month and i still cant get the jeep running. I tried changing the cap and rotor but still no spark. There is no pulse at the injectors and i changed the cps and it still didnt start. I took it to a local shop and they sent it back to me, they said its the computer or the alarm system wiring. Then i took it to a dealership and they said the computer looked bad when they plugged into it. They also said it started pumping fuel when they plugged their scanner into it. They said all they could do is replace the computer and see if there is any further damage from there. Being as cheap as i am, i didnt want to pay the $1,100 they wanted for the computer, i told them ill just put a chevy 350 in it for that price. They acctually laughed at me until i showed up to tow it home. So now its still sitting im my garage and i still cant drive it. I didnt want to change the computer until i was certain that was the problem because im on a budget but im running out of options. I appreciate all the help and if you guys have any other advice id love to hear it. Thanks

[neale_rs]

You can get refurbished computers for a much more reasonable price and used computers often show up on ebay fairly cheap.

http://www.autocomputerexchange.com/Makes/Jeep/2   $250

[sharpxmen]

and probably around the same price from a wrecker.

[yjsandaddict]

Thanks thats a way better price, do you guys think that might fix it? Im leaving to the dunes Friday and was hoping to take it, but i need to do something soon because i start school in two weeks. I called the people from the link and they didnt say if they think that can fix the problem, i just didnt want to buy one and still have it not start. Thanks for the help

[sharpxmen]

Thanks thats a way better price, do you guys think that might fix it? Im leaving to the dunes Friday and was hoping to take it, but i need to do something soon because i start school in two weeks. I called the people from the link and they didnt say if they think that can fix the problem, i just didnt want to buy one and still have it not start. Thanks for the help

hard to tell (can be other things too). If i were you i would find one locally and ask them if you can bring it back if it is not solving the problem (would suck to spend that money and still no go)

[yjsandaddict]

I went ahead and ordered that computer. Theyre going to overnight it so i should know by thursday.

[sharpxmen]

good luck and let's hope that was it. keep us posted

[yjsandaddict]

Well i have good news and bad news. The good is i got the new computer thursday night and the jeep fired right up and i was able to take it to pismo friday . The bad is while i was there my drive shaft smashed into the transfer case and sent the shaft and my exhaust into the sand . Looks like i finally get to go SYE. Thanks for all the help.

[1994 green yj]

Glad you got it running!