running very very rich

Ok, first let me appologize about the length. But a long time ago my zj quit at the same time that my xj (90 wagoneer) had leaky fuel injectors. So in order to get one running vehicle I swaped the fuel injectors form the 93 zj 4.0L into the xj. It was rainy and cold so I just put them in and called it good, no more leak and it ran fine, great in fact. My GF has been driving it daily for a few months now and was complaining about the mileage she was getting, and it not warming up very quickly. So I have been driving it for a week now to see whats up and I got about 8mpg on the last fill. She also just recently blew the exhaust system off of it. I think all the excess fuel plugged the cat and the pressure just blew it off. I now have a new exhaust system from the cat back. I had switched to the open cooling system a year or so ago.
Any way here is a run down of the symptoms. It runs really smooth, but idles a little low (between 500 and 600rpm when in gear but fine, like 800 when in nutral). There is a lot of moisture on the ground where the tailpipe ends, dosn't smell like gas though. It has a new TPS and IAC motor. I don't hear any vacuum leaks and I havn't been able to detect any with the propane test. I haven't been able to test fuel pressure because I don't have a guage. I am going to get one thursday though. I just put a new fuel pressure regulator on and it made no difference. Temperature wise it only gets to a little over the first line, probably only about 180deg. And it eats fuel. I don't have any check engine light. I figure I'll get a thermostat for it. It's pretty cheep and can't hurt. So any ideas what may be wrong.
Thanks,

Don't trust the check emissions light to tell you if there is something wrong. On the '90 it is strictly driven off a timer under the dash. When the timer sees 60K miles, IIRC, it turns on the light. This is your warning to replace the O2 sensor AND the timer. Yes, the timer is a one-shot and is consumed in use. Yours is probably unplugged, like mine was when I bought the car. I think most of them are so you don't have to look at the light and buy a timer to shut it off.

If you don't know when the last time the O2 sensor was replaced, it probably needs one. That can give you bad mileage, but I don't know if it can knock you down to 8 MPG. Before I replaced my O2 sensor, my mileage dropped from 19.5 to 15. A new O2 sensor fixed that.

You also need to get the temperature up to normal operating range. Untill it gets above 140 IIRC, the computer has the controls in open loop and running rich.

MoFo

Thanks MoFo, I think its above 140 but defenitly not 190. Yea open loop richens the mixture but not as rich as this thing is running. I figured the O2S would be suggested. I'll check that and replace it if I need to it only has about 40k on it though. Oh yea, Which fuel line is the return on the fuel rail? The one in the front of the engine or the one back by the fire wall.

The fuel line on the front of the rail is the return line.

Injector swap

The 93 and 90 have different fuel management systems. I believe the injectors have different specs. Can't tell you for sure, but the heads and ECU are diffferent.

180 or 190. Either is fine in my opinion. That temp gauge may or may not be accurate. I second the O2 sensor... it is one of the things the ECU uses to determine how lean or rich to run. 8 mpg is terrible! Something is horribly wrong. My 5.2L V8 gets 14!

Hmmm my 93 4.0L ZJ gets 12mpg. But I'm putting an O2S in the 90 this weekend. Is a Boshe ok or do I have to get an OE from the dealer. I know for some later years the aftermarket sensors have been known to cause some problems.