new to jeeps, need some help with this thing.

[towmyvws]

bought a 90 xj and love it. couple issues with it though. the p.o. was all about shady mechanics and butchered a couple things up. 193k auto. starts every time, no problems out of it yet. i wish it wasn't renix so i could pull some codes and do this the easy way.

horrible gas mileage. this thing is stock and gets 7-8mpg (using trip meter to compute). it's killing me, im broke as it is.

1. it has an exhaust leak, but not bad. at the head. you can hear it, but it's not very loud i guess.

2. not sure if the vacuum lines are hooked up right. all the lines under the hood are going somewhere, but i dont know if they're the right places. the line for valve cover is cracked and leaks, i know that for sure.

3. it runs rich as hell, my shirt smells like fuel if i have the windows down.

are either of these two problems related to the gas mileage im getting? im broke as hell and don't want to replace any of this stuff if it won't help my gas mileage. very recent thermostat, plugs, cap/rotor, wires, air filter, fuel filter, and cleaning of throttlebody/iac sensor.

pulled the plugs, and they're super black and have crap caked on them.

any help would be appreciated.

 

[xjwisconsin]

almost all of the vac lines can be gotten at napa for a few dollars. this is a very good investment. it will help with some of your richness, that is my guess on the black sediment. also be sure to check for any oil leaks. most of them on the xj can be fixed by the home mech. with little stress
edit: check your fuel system for any leakage. check where the fuel injectors meet the fuel rail, and look for any wetness around where the two part injector is put together. our era fuel injectors are prone to leaking. also the exhaust leak on the manif. is not helping anything

 

[cygnus58]

I never changed mine but hear a bad O2 sensor will cause rich running when bad and that if it's not working, unplugging it will make no difference.
It keeps your Renix in open loop, bad.
Also Coolant temp sensor, Manifold air temp sensor, Throttle positon sensor and yes (least likely) even Crank Position sensor will cause trouble with open loop.

 

[cygnus58]

And if you want to check for vacuum leaks, spray carb cleaner at the suspected fittings while idling, a bad vacuum connection will cause a change in idle.

 

[h2opete987]

the exahust leak at the head is most likely why its running rich. the o2 sensor, as its name implies, measures the amount of oxygen in the exhaust, and the computer uses that to figure out how rich to run the mixture. if you have a leak at the head, more oxygen can get in, and that will throw off the sensors radings to the lean side, and you will run rich.

 

[Fred]

Except I would guess that the exhaust leak at the head is just a cracked exhaust manifold. I had one, never caused it to run rich.

One thing to check is that the fuel pressure regulator at the end of the fuel rail nearer the radiator has a vacuum line attaced to it and to the manifold at the tree at the front of the manifold. If there is no vacuum to the regulator it will increase the pressure to the fuel injectors.


Fred

 

[jeepman121]

If I'm not mistaken the 90 doesnt have EFI..so if i am not wrong then your carb may need serviced.

 

[mattbred]

If I'm not mistaken the 90 doesnt have EFI..so if i am not wrong then your carb may need serviced.

You are clearly mistaken.

87+ had the EFI 4.0L Inline Six.

 

[mcnamaag]

Vacuum hose routing for the Renix.

 

[mcnamaag]

Sorry about the pics being so big. Just wanted to make sure you could see everything clearly.

 

[Matthew Currie]

Sorry about the pics being so big. Just wanted to make sure you could see everything clearly.

You're just showing off that clean engine! You must be scrubbing it with a toothbrush.:jester:

 

[avnsteve]

You're just showing off that clean engine! You must be scrubbing it with a toothbrush.:jester:

not necessarily, a pressure washer and an obsessive/compulsive personality will do the same thing, ask me how i know :looney:

 

[mcnamaag]

X2 Ya got me.

 

[towmyvws]

thanks a lot guys, especially those pics.

 

[mcnamaag]

thanks a lot guys, especially those pics.

No worries. Good luck!!

 

[towmyvws]

the vacuum line to the map sensor was broken in one place and "repaired" in 3 places. essentially i was driving around with no map sensor i guess.

jeep idles MUCH better now, much more solid, drives better. dunno if it's fixed, but it feels better so far.

 

[cygnus58]

sounds like you got it.
Kudos.

 

[avnsteve]

if you get MPG problems again, or still, check that your not dragging brakes, they could catch fire and then you're really farkled!

 

[towmyvws]

apparently the leak was the issue. compared to before, it seems like my gas guage doesnt even move, the mileage is probably doubled.