renix now has low power

so i am still trying to get to the source of my low power issue.
everything works now as it should, i get a short high idle then it settles back down in just a few seconds.
new sensors are : o2 , block temp
other new parts in last 12 months : injector o rings, fuel pressure regulator
engine mounts,oil pan gasket, rear main, fuel filter, and ignition module

fuel pressure checks out, in spec.
before my harness problems, the power was there. ran like crap ola for near two months, and now low power.

Thinking back to when mine had low power issues it was most often a fuel issue. Checking fuel pressure at idle isn't the whole story, you have to check it at higher RPM's and even under load and various vacuum conditions. First thing to do is to jump the ballast resistor and see if the issue disappears.

Another possibility is the ignition isn't advancing properly. Mostly from a faulty TPS, TPS adjustment or TPS wiring. Though the MAP does have some input also. Be sure and check the MAP vacuum line, it can develop tiny cracks or rubs that are almost impossible to see. I usually feel the flaws in the vacuum line with my finger tips. The MAP vacuum line can get really brittle, be careful.

O2 sensor issues on mine usually showed up around 2000 RPM and then again at higher RPM above 3500. The O2 sensor isn't the whole story, the harness runs very close to the exhaust manifold in the front and can cook there. Really hard to see if it is cooking from the top of the power steering pump mount. I've had to disconnect the O2 sensor, the knock sensor and engine temp sensor and pull the harness up some in the front to inspect it closely. Cruiser has a write up on proper routing for this harness, it often gets rerouted wrong during a water pump replacement and gets too close to the exhaust manifold.

I've had low power issues in the beginning stages of CPS failure. A weak or intermittent CPS signal can cause low power.

Just some ideas.

hey thanks for the help. with my wiring problems, i did re route and inspected that part of the harness you mentioned. it was in good shape but was routed wrong. i ll start replacing sensors as i had planned on it anyways now that the wiring is at a state i can call good and not causing problems.

also, i have a leaking fuel tank. going to just get a new tank and pump assembly as well to rule that out as being a problem.

God list 8MUD, only addition I can make is to post up the shift point for acceleration under power. My old Renix files thread was partly about a working, calibrated (on the ECU side) TPS that was bad on the TCU side and had my AW4 tranny up shifting at 1200 rpm and I was in 4th gear at 20 mph already, never could get any power and took three minutes to go from 0-6- mph at WOT. A good test at the time had I known what I know now would have been to cut power (fuse?) to the TCU and shift manually.

i ll check it. thanks Mike for posting up, i appreciate your knowledge and Renix experience, very helpful. i ll post my rpm shift points friday night.

Gunter said:

also, i have a leaking fuel tank. going to just get a new tank and pump assembly as well to rule that out as being a problem.

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Careful on those new tanks that come with a pump. The pumps are not the best quality and senders will never read the tank accurately .
On the bright side aftermarket tank have extra capacity so you'll probably gain a gallon or two.

Gunter said:

i ll check it. thanks Mike for posting up, i appreciate your knowledge and Renix experience, very helpful. i ll post my rpm shift points friday night.

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Sounds good, in my very early days with my first Renix AW4-4.0 rig my mechanic buddy and I could not figure out for 2 years why the 87 Wagoneer had such low power. The stock answer was a worn out engine and torque converter, blah blah blah. The entire online jeep world had not discovered and posted what I found after 2 years of not accepting the stock answers. Being an entrepreneur design engineer I kept testing and once I finally found an OEM-Renix Multi-port manual that explained what all the sensors and control hardware where, did and when and how, I was finally able to run some non typical tests on a new, used and the still installed TPS and discovered that one side could be good and the other bad and thus cause such off spec shifting that looked like a low power engine because the shifting was too soft, and too low an RPM to feel the sifts. I wrote extensive details of that journey here in my thread in the OEM section called "The RenX Files" . There is test data there that is in no manual or any other posts on the internet!!!!

I must thank the Lundford (sp?) site for the first education I got on calibrating the Renix TPS.

With any luck maybe yours is as simple as a poor ground on the back side of the TPS, (the Renix TPS has two independent wires going to ground, one can be bad and the other good!!!), or a bad TPS on the TCU transmission computer side only? The Factory manual test and calibration does not test both sides, a critical factory manual error!!!!! Because both sides are 100% independent variable resistors on a common shaft with independent power supplies from different computers feeding each side, and independent ground wires, they must treated and tested as such. I calibrate one side then test the calibration on the other!!!! I also test both sides for noisy operation another oversight by the factory manual

so an update.
i had close to full function.
the only thing left for me to try, is the CPU.
i had lower idle, but nothing like stock.
using fluke. all my grounds work.
all my wiring repairs are working
everything on this jeep works except idle and fuel delivery and spark advance.
no vac leaks.
all vac lines are new.
EGR is still bypassed and plugged the vac lines for it.
new TPS and cant get voltage in range to bring idle back down.
have a new cps.
throttle body is clean.
IAC was cleaned out and is working
my relay by the battery recently was replaced and last week developed a grounding issue, i have it working and will make a ground wire for it.
my fuel pressure is right. i have also replaced fuel pump and sender, and fuel tank.the problem is not fuel pump/pressure/delivery/filter related.


if a CPU doesnt bring it back, i am sitting on it and start collecting everything to LS swap it. like a d35, i will never waste one cent on a renix era Jeep again.

what is your input voltage on the tps wires? also what year is it? if its and 87-88 you may want to check the c101 connector. if its an 89-90 you shouldn't have this connector.

Gunter said:

so an update.
i had close to full function.
the only thing left for me to try, is the CPU.
i had lower idle, but nothing like stock.
using fluke. all my grounds work.
all my wiring repairs are working
everything on this jeep works except idle and fuel delivery and spark advance.
no vac leaks.
all vac lines are new.
EGR is still bypassed and plugged the vac lines for it.
new TPS and cant get voltage in range to bring idle back down.
have a new cps.
throttle body is clean.
IAC was cleaned out and is working
my relay by the battery recently was replaced and last week developed a grounding issue, i have it working and will make a ground wire for it.
my fuel pressure is right. i have also replaced fuel pump and sender, and fuel tank.the problem is not fuel pump/pressure/delivery/filter related.


if a CPU doesnt bring it back, i am sitting on it and start collecting everything to LS swap it. like a d35, i will never waste one cent on a renix era Jeep again.

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Have you done a vacuum test?

Cruiser’s Vacuum Test for Exhaust Restriction

Your vacuum gauge should come with an instruction booklet outlining this procedure.

Hook the vacuum gauge up to a source on the intake manifold.
Start the engine and note the vacuum reading.
It’s usually 17 to 21 inches of vacuum.

Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle.

Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading.

If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.

Realize those numbers are for sea level. They will be about 3" lower in Colorado.

old_man said:

Realize those numbers are for sea level. They will be about 3" lower in Colorado.

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Yes. as much as 1 inch of vacuum for each 1000 feet above sealevel.

the high idle on start and then going back to normal is from a miss-adjusted or bad tps. i can confirm this because mine is doing that and it is bad.

90xj06 said:

the high idle on start and then going back to normal is from a miss-adjusted or bad tps. i can confirm this because mine is doing that and it is bad.

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That and/or bad grounds to the TPS, IAC, MAP, CTS etc.

90xj06 said:

the high idle on start and then going back to normal is from a miss-adjusted or bad tps. i can confirm this because mine is doing that and it is bad.

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Many other things can cause a high idle at start up. Usually not the TPS, if the idle drops back to normal seconds later.

UPDATE
well all my other repairs were good and worked. and I checked 3 times at least for this.......i changed out the intake exhaust gasket. all the lower bolts were 3 to 4 turns out. if you ever have HIGH IDLE you cant fix, replace this gasket!!
AND remove the fuel rail and the metal shield , you need to be able to see the nuts on the lowers. now to get my TPS set and wee what i have.
my electrical repairs were all good.
my ground connections that were cleaned were all good.
my fuel system was all good from the tank to the fuel injectors
my cat was not clogged.
cps good.
iac good.
tps good
battery good.

to everyone, thank you for your suggestions.

Congrats, Git-r-Done!!!!!!!!!!!!!

Gunter said:

UPDATE
well all my other repairs were good and worked. and I checked 3 times at least for this.......i changed out the intake exhaust gasket. all the lower bolts were 3 to 4 turns out. if you ever have HIGH IDLE you cant fix, replace this gasket!!
AND remove the fuel rail and the metal shield , you need to be able to see the nuts on the lowers. now to get my TPS set and wee what i have.
my electrical repairs were all good.
my ground connections that were cleaned were all good.
my fuel system was all good from the tank to the fuel injectors
my cat was not clogged.
cps good.
iac good.
tps good
battery good.

to everyone, thank you for your suggestions.

Click to expand...

thanks for the update and success story