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Runs rich, replaced everything.

88XJSport

NAXJA Forum User
Location
Michigan
My 88 RENIX runs slightly rich at cold and hot engine temp. Temp runs at 195-200 consistantly. The O2, CTS, and MAP are about 25,000 miles old, I have a new TPS adjusted correctetly, newer IAC, and a benched clean throttle body. I have a disconnected and plugged EGR, and I just noticed, while WOT during the night, I can see a gray haze on the cars headlights behind me, coming from my exhaust. But this isnt noticeable in the daytime. Ever since I got my new exhaust system, I had a sooty exhaust at the end of the pipe. Like I said, I replaced everything computer related, so Im stumped. Oh and my gas mileage SUCKS. (10mpg) Thanks for any help.
 
Are you running an OEM tstat? 195-200 is a tad low for the 4.0 (should be 210)
 
low engine vacuum? a low signal to the MAP will richen the mixture. I'd also verify solid ground connections and that the CTS and ACT are reading within specs. If it's been running rich for a while, the "relatively new" O2 sensor could also be covered in soot and responding to mixture changes slowly which will increase fuel consumption as well.

--Shorty
 
you wouldn't necessarily need to "strengthen" the vacuum, but verify the vacuum being pulled at the throttle body is same as full engine vacuum (no plugged hose or T.B. port) Also, as an engine wears vacuum decreases with looser clearances. Hook up a vacuum gauge and verify valves are not leaking and the engine pulls at least 17 inches of vacuum. I'm not sure what the exact spec. is for a 4.0l, but I know that things get screwy when you get much below 17 inches.

--Shorty
 
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