renix engine and computer

i put a new 4.2 engine with my renix computer to replace the renix 4.0 in my 88 cherokee, now i have a problem with it running lean. so i put an adj. map sensor on it and now it runs rich and still has a stumble. i was told that the renix computers could not learn so i figure the jeep still thinks the 4.0 is in it. i was wondering if you could swap computers so it will run better so the engine could teach the computer a thing or two. lol. thanks for any input.

since 4.2's never had fuel injection to my knowledge, i would think that wouldn't work to switch computers...the 4.2 wouldn't have one.

The Renix computer doesn't "learn" anything, but it does constantly adjust the fuel-air mix according to feedback from the O2 sensor and a couple of others. It it is running lean, the injectors are either clogged or too small. If the injectors can't deliver enough fuel, a different computer isn't going to help.

I would suggest going back to the original MAP sensor and installing slightly larger injectors. The Renix injectors are rated at 19.6 pounds/hour, I believe. I think early HO injectors are 22 pounds, so that might be worth a shot.

rehab said:

i put a new 4.2 engine with my renix computer to replace the renix 4.0 in my 88 cherokee,

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Do you mean a stroker when you say 4.2 engine? If so, 24 lb/hr injectors are recommended.

On my '88 I just installed the 19 lb/hr injectors I bought from Bruce at Five-O Motorsports, a great guy to work with by the way. It really made a difference! I had 180,000 on the stock injectors and they were due for replacement, My Jeep wouldn't rev much past 3 grand, now it accelerates easily past 4,000 RPMS. The consences on the RENIX motors seems to be 19 lb/hr injectors on stock to lightly modified (eg; air tube, exhaust upgrades) and 24 lb/hr on strokers. Next, I planning to install a MAP modifier I bought from XJ-Armor. With the MAP modifier, I figure I should be able to fine tune the A/F ratio to tailor it to my Jeep. Now, I want a wideband A/F meter to see where I'm at. Armed with a good (wideband) A/F meter and a pyrometer (exhaust temp gauge) I think a guy could really dial in a rig.

Five-O motor sports: http://www.fiveomotorsport.com/Injector_SetsJEEP.asp

Good Luck

Woody

the engine is a 4.2 block with a 95 HO head and an 88 intake and exhaust. before i put the adj. map sensor on i replaced the injectors with some 95 HO injectors which are 22 or 24 lb/hr and it showed no improvement to the hesitation and stumble that occured at 1500 rpm. now with the map sensor getting 7.2 volts it is running rich but the engine does not hessitate as much, when i turn the voltage down however, it runs like crap sputtering and barely accelerating. if i stomp on the gas it pulls really hard and seems like it has a lot of power, which would be fine for drag racing but it runs like total crap at low rpm. i replaced the O2 sensor and it didnt help any so i took it back out and put the old one back in. i have been stumped on what to do next, the jeep is getting 11 mpg and it is really annoying to drive off road since the engine normally stumbles at low rpm. it is also running a little bit on the cool side like around 150 degrees, i think im gonna try replacing the thermostat and going back to the stock map sensor and the 24 lb/hr injectors. thanks

The 88 manifold doesn't match up to the HO ports. Did you enlarge the alignment holes to try to match the ports? If not you probably have a vacumn leak which could be your problem. I would use the 91 - 95 manifold, throttle cable, and fuel rail to solve the problem.

but what would i need to change because my 88 has alot of different stuff then the 95 did. with different style sensors. would i have to change the computer?

The 95 MAP sensor, CTS, etc are all the same. The T-stat housing bolts on, The only sensor is the TPS (throttle Position Sensor) which needs to be adapted to the HO T-body. Several write-ups are available on this change.
Also the fuel line needs (??) to be adapted to the 95 type fuel rail both in and out at front instead of fuel in at back on the 88. There is no need to change the computer.

rehab said:

...now with the map sensor getting 7.2 volts...

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How is the map getting 7.2 volts?? It should only have a reference voltage of 5 volts. How did you modify the wiring?

have you tried like, say, 6 volts? you really need a a/f guage to set it right, but the adjustment should be fine enough to get it right.