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Renix=slow HO=fast!

M

maybe2fast

NAXJA Forum User
Location
COMMERCE, MI
So I recently bought a 1988 Renix and have been getting it running for the winter here. I replaced most of the sensors and have done Cruisers checks and mods. Overall I believe it runs pretty well. Shes not the fastest thing but does the job. Then I drove a 2000 XJ with the same 3in lift and 31s just like mine.

The HO felt like a racecar! So much more pep! WOW!

I understand the difference in throttlebody and exhaust and the RENIX HP rating. I have the 529 ECU (182hp from 177hp) and am pretty sure the RENIX is running properly. I have no stumbles, hesitations, bogging,misfires, ect

I have a slight hot high idle at 1100, but drops to 800 in gear. Cold it behaves well.

I verified by the tag that both 88 and 00 are 3.55 gears, AW4. The 88 has the 242 and the 00 has the 231, but both were driven and compared in 2WD.

I cant figure out if the RENIX is ok, or now based on what I consider is a huge difference that something is not right.

1988 has 149,000miles
2000 has 168,000miles
 
Never trust a butt dyno.
 
maybe2fast said:
it was night and day difference, too much to ignore. Maybe it was the biggger TB but it was significant
Click to expand...

I felt the same way on my motorcycle. Dyno'd a whole 1 lb*ft of torque (69 to 70) different. Cam'd it and had similar butt dyno results but this time it went up 10 more lb*ft. I never trust my butt dyno anymore and only rely on measurable results
 
On a Renix, unplugging the ping sensor can actually cause significant false ping detections and will severely retard the timing.
 
to be honest, I broke the knock sensor while rerouting the coolant temp to the t-stat housing. There was no noticeable difference before and after the breakage occurred. I will have a new knock sensor when the mail man brings it.
 
no cat...PO "unclogged it"

tail pipe seems to be flowing smoothly

Basically what you guys are saying is there shouldn't be a massive difference in feel.
 
maybe2fast said:
I understand the difference in throttlebody and exhaust and the RENIX HP rating. I have the 529 ECU (182hp from 177hp) and am pretty sure the RENIX is running properly. I have no stumbles, hesitations, bogging,misfires, ect
Click to expand...
Does the '88 have the "Power/Comfort" switch?

My '90 does, it changes the shift points. Later models eliminated this choice and defaulted to the "Power" shift points.
 
Yeah I have been through the grounds and cables, bypasses the C101 for the sensor ground among other things (ground refresh)

Like I said, it runs ok...until I drove a stock HO with same mods...massive difference. Something is not right.
 
Took me ages (years) of forensic analysis on my 87 Wagoneer to solve most of that problem. It turned out the FSM was clueless as to how to isolate the problem. My 89 has all the power and acceleration you could possibly want. The 87 had a good on the ECU side TPS, that was toast on the TCU side so at WOT it never got past 1200 rpm and was shifted into 4th gear by 20-25 MPH at WOT from a dead stop. Took 3 minutes to reach 55 mph LOL. The details are in my ancient "RenX Files thread in this forum.

I hope to solve the second low power issue with a rebuilt head soon. It has two spark plug oil fouler, worn valve stem cylinders. Also Cruiser says the 89-90 ECU's deliver more power than the 87-88 ECUs (or was it just TCUs?)

My 89, with about 224,000 miles runs like a bat out of hell.

maybe2fast said:
So I recently bought a 1988 Renix and have been getting it running for the winter here. I replaced most of the sensors and have done Cruisers checks and mods. Overall I believe it runs pretty well. Shes not the fastest thing but does the job. Then I drove a 2000 XJ with the same 3in lift and 31s just like mine.

The HO felt like a racecar! So much more pep! WOW!

I understand the difference in throttlebody and exhaust and the RENIX HP rating. I have the 529 ECU (182hp from 177hp) and am pretty sure the RENIX is running properly. I have no stumbles, hesitations, bogging,misfires, ect

I have a slight hot high idle at 1100, but drops to 800 in gear. Cold it behaves well.

I verified by the tag that both 88 and 00 are 3.55 gears, AW4. The 88 has the 242 and the 00 has the 231, but both were driven and compared in 2WD.

I cant figure out if the RENIX is ok, or now based on what I consider is a huge difference that something is not right.

1988 has 149,000miles
2000 has 168,000miles
Click to expand...
 
The HO eliminated the EGR valve, does yours still have the EGR on the 88? Is it working properly?
 
FWIW, my 89 Renix would probably do the 1/4 mile in half the time my 87 would. I think I am down to the running on mostly 4 cylinders with 2 having an oil fouled problem, head swap is on the round to it list.
 
maybe2fast said:
Yeah I have been through the grounds and cables, bypasses the C101 for the sensor ground among other things (ground refresh)

Like I said, it runs ok...until I drove a stock HO with same mods...massive difference. Something is not right.
Click to expand...

You drove a stock with some mods. You did not say what those mods were. Stock and mods really should not be used to describe the same XJ if they include the engine or drive train gearing. Do tell what those mods are so that the Renix guys could make an educated guess.
 
Been a while since I had my 88 so I don't remember too much. But also the 00 is rated at like 195 horse or so. Given the different manifold design, head port design and the coil on plug ignition the 00 is bound to have a different power delivery curve. My wife's 01 feels dramatically different from the two 98's I have. Not necessarily more powerful but different. That difference may translate to more power on the butt dyno. Just a theory.
 
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