renix won't rev

[8Mud]

The last time I had low idle it was the TPS ground. The ground always seemed to test out OK, but my ground was just bare wire lying inside of a crimp somebody forgot to crimp shut. Many people jump the TPS ground directly to the chassis, I just fixed what I had and made sure it worked right. As a side note my TPS ground ECU side was in the tranny connector, and the TPS tranny side ground was in the ECU side connector, somebody assembled it bassackwards.

IAC make sure the seat in the TB is clean, spray the piston/plunger with spray oil, let a little oil run behind the piston. Don't try to move the piston with your fingers or compress it. Clean the connector. Make sure your battery voltage is OK and your system is charging properly. The IAC needs all the volts it can get to work properly and is often one of the first things to act up when something is off in the charging system.

 

[Ecomike]

no floor mats and it's not a high idle it's an extremely low idle. may try another iac....i have 2 or 3 laying aorund

I was thinking you might have calibrated the TPS with the floor mat holding the throttle plate and TPS open (or something doing holding it open), then floor mat moves, and the idle drops.

 

[Ecomike]

As a side note my TPS ground ECU side was in the tranny connector, and the TPS tranny side ground was in the ECU side connector, somebody assembled it bassackwards.

Very interesting!

 

[shawnxj]

my tps ecu ground is showing .05 ohms to the battery. should i jumper the 2 together? i never checked the tcu ground

 

[Ecomike]

my tps ecu ground is showing .05 ohms to the battery. should i jumper the 2 together? i never checked the tcu ground

All the sensor grounds, are crimped to a master wire buried in the harness, loose crimp and they get high and change when the harness moves. You check them all, while wiggling the harness, and fix any that are not solid, including the TCU-TPS ground and the MAP sensor ground!!!

And I probably need to check my temp sensor grounds now that I think about it.

 

[shawnxj]

yup fixed those already. i followed all the grounding mods in cruiser's link and verified ohm's in multiple places before i sealed everything up. highest resistance was .2 ohms when i was done. lowest was .05

 

[sandsgg]

I Would Definitely Try The Oac, I Had A Similay Crazy Idle Problem From A Wonky Iac On My 90. I Want To Say That Was Also The Same Problem I Had On The 88 Mj Right Before The Coil/Ignition Module Took A dump... Just A Thought.

 

[8Mud]

yup fixed those already. i followed all the grounding mods in cruiser's link and verified ohm's in multiple places before i sealed everything up. highest resistance was .2 ohms when i was done. lowest was .05

A simple test that may help, is to put your meter on a low voltage setting and check the voltage from the ground at the sensor to the battery ground post. This will give you a standing voltage reading and lets you know just how constipated that particular ground is.

The TPS tranny half grounds through the TCU and typically has a little resistance built in. The TPS ECU side ground should be as close to zero as you can get.

The TPS is going to advance the timing as the throttle opens, with input from the MAP. The MAP is going to adjust as the manifold vacuum changes.

Most times I've seen the MAP crap out the motor runs really rich. my guess is default is full rich.

Most times I've seen an O2 sensor go bad it starves the engine of fuel around 2200 RPM (it my pop and buck around 2200-2500 RPM). Then leans out the motor again above 3500 (or there about) and lowers top end significantly.

Have you tried moving the arm behind the TPS with a screwdriver tip, while at idle, yet?

 

[Ecomike]

Interesting O2 story. Pull the O2 sensor and see if the rev limit disappears?

 

[shawnxj]

went to go play with the tps arm like 8mud suggested and got a new symptom. doesn't like to start when it's hot... so that's a cps issue correct?

 

[cruiser54]

went to go play with the tps arm like 8mud suggested and got a new symptom. doesn't like to start when it's hot... so that's a cps issue correct?

Easy enough to test the CPS.



Renix CPS Testing and Adjusting
　
　
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out the upper mounting hole to 3/8" from the stock 5/16", or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.

　
　
Revised 01-26-2013

 

[Ecomike]

went to go play with the tps arm like 8mud suggested and got a new symptom. doesn't like to start when it's hot... so that's a cps issue correct?

Could be the CTS or IAT (MAT) temperature sensors that the ECU uses for fuel trim. They maybe off spec. Have you tested their resistance at several temperatures? I had a bad MAT temp sensor give me fits with cold no starts and high idles when hot!!

They would not be related to the rev limit, but an overheating HV coil or Ignition control unit under the HV coil might be.

 

[8Mud]

went to go play with the tps arm like 8mud suggested and got a new symptom. doesn't like to start when it's hot... so that's a cps issue correct?

It can be a CPS issue, it can be a combination of things. The pulse has to make it's way from the CPS to the ECU. If the connectors are oxidized, oil covered or anything causes resistance, the signal gets weaker during the trip.

I had one CPS that went up 50 ohms of resistance when it was hot.

 

[shawnxj]

turns out my no start is a no fuel issue. think i've got a clogged strainer or filter cause i can hear the pump plain as day....i'll mess with it tomorrow when i'm feeling better

 

[cruiser54]

turns out my no start is a no fuel issue. think i've got a clogged strainer or filter cause i can hear the pump plain as day....i'll mess with it tomorrow when i'm feeling better

Interesting. Keep us informed. Hope you're feeling better.

 

[shawnxj]

turns out the computer was putting voltage out on both sides of the cam sensor whether it was running or not. not sure if that was the whole problem since i cut out the stock setup and installed a megasquirt 3 but it kinda makes sense