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'98 running poorly

Jeff 98XJ WI

NAXJA Forum User
Location
Butternut, WI
First, I did do some searching, but didn't find anything leading me to the cause of my problem so far, so here is my story:

Hey guys, I am looking for advice as to why my '98 is running poorly.
First some background:

'98 4.0HO, auto, air, 100000+ miles

It will start ok, idle ok usually, and run ok at part throttle. I can
get it to rev to redline if the throttle is operated slowly. However,
if the throttle is snapped open and or if there is a load like while
driving down the road, it will blubber, sputter, and cough usually above
3000rpm.

First, I cleaned the air cleaner. Then I checked for a fuel filter only
to find that it is in the tank. I suspected the fuel pump or regulator
originally, so I did some tests. Fuel pressure is fine. Leak down is
fine, volume is fine. I changed cap and rotor this morning and pulled
one plug. It was a Bosch Platinum +4 and looked to be in really clean,
good condition. They must have been installed by the previous owner. I
checked the Throttle Position sensor with an ohm meter and it seemed to
be fine and not have any rough spots or anything. I can't find any
vacuum leaks or anything obvious under the hood. The catalytic convertor probably has over 200,000mi on it since I took it off my '92 and put it on this '98 along with the rest of the exhaust including a Borla header and cat back about a year ago. However, I am not getting a check engine light indicating that the Cat. is not doing it's job. That's about where I am at now.

I tried getting any codes in the computer by cycling the key, but it
doesn't seem to work in the '98. The manual just talks about using a
DRB II tool. Oh yeah, I have NOT gotten a Check Engine light...until
this evening when I unplugged the sensors connected to the throttle
body with the engine running. Is there a way to check the O2 sensors with a volt meter? Could they be causing this problem? Also, when revving the engine while under the hood doing a visual and having the engine run poorly, I did notice that the Borla header actually glowed cherry red! I'm not sure that is normal or not, but it made me think of a rich fuel mixture. I did get it to run ok while revving for a bit and the exhaust manifold got red then too. Also, the check engine light did go out this morning after a number of restarts. Thanks for any inf. Jeff
 
strange that you're not getting codes. my 98 does codes when something's wrong. maybe it's the computer...
 
Update! I replaced the CAT with a Catco direct fit unit for a '92 (because the exhaust is a '92 from the Borla header all the way back) and welded on an O2 bung in the rear of the cat for the '98s second O2 sensor and the thing runs great! Jeff
 
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