bigpimpinben

I am working on a new to me 1989 xj 4.0 aw4 231. I bought this xj yesterday. The symptoms are that it will sit there and crank and blows gas fumes out of the throttle body. the vacuum system seems to be working backwards. If you pull a plug it blows out hot air when it cranks. when I unplug the cps it doesn't blow gas out the throttle body. I have fuel and I have spark. Here is what I have done.....

All plugs, wires, cap and rotor are new
replaced cps
replaced idle air sensor
replaced all vacuum lines
inspected egr valve it is new
checked all plug connections and order multiple times
disconnected cat
tried disconnection every sensor individually
checked for fuel pressure

Me, dellstopjeep, and goblazers_6 are all stumped. any suggestions before I check the timing chain?

bigomudders

Have you checked your crank sensor on top of the trans on the left side of the engine?

dellstopjeep

yup, it was repalced with brand new one

jd4x426

try checking the injectors with a noid light it checks the pulsing of the injectors you can pick one up a kit at harbor freight for like 20 bucks

bigpimpinben

I am going to index the distributer. it was loose when I got it. I think it was tampered with..... like miley cyrus on prom night

BuckB91XJ

Based on your story and all the things you've already tried. The only other thing I can think of is that it's jumped time. Somebody over revved it or the timing chain just got loose and one of the gears has jumped a tooth or two.

bigpimpinben

Well I was able to get a couple hours in on it today... had eric's bachelor party all weekend. First I indexed the distributor. It fired up. now it is just running supper rough. Then i checked the compression in all cylinders, nothing amazing, but not bad enough to cause it to run like it is... this is what I got.
1-140
2-125
3-140
4-135
5-130
6-125
So we started experimenting with it idling. When I sprayed starting fluid in the throttle body, it would run better. Disconnecting the fuel injector cables did nothing. Unplugging spark plug wires one at a time did very little. I went through unplugging sensors. The throttle position sensor did nothing, the idle air sensor did nothing, but when i disconnected the brand new crank position sensor it died. I am going to buy a new tps tomorrow. Thinking about it I should have tried the map sensor also... any ways let me know if there is anything that you guys can think of that I am missing.

bigpimpinben

I replaced the tps with a brand new one, nothing happened. All the plugs, wires, cap and rotor are brand new. I went through unplugging fuel injectors no matter which ones I had unplugged it would run on 3 or more injectors, and it didn't really change between having 3 and 6 injectors plugged in. It won't rev up unless you sit there and feather the throttle and it will maybe rev up a little. It back fires. I rechecked the distributor indexing.

bigpimpinben

I am getting so sick of this........ Does anyone know where to read a timing light on the 4.0?

BuckB91XJ

You can't even check the timing on a 4.0 with a timing light. There is no scale and no timing marks.

bigpimpinben

There are timing markson the top of the crank pulley, and a notch in the pulley, it just isn't visible from the top or bottom of the motor.

bigpimpinben

I finally had time to dig into it. It stoped firing up all together once I got it home. I got the timing chain cover off. There is 1/2 inch of movement when you turn the slack between sides on the crank. That is right at the point of where it should be replaced.. but not enough to make it run how it was. I think that it must be something internal in the motor.