Problem symptoms...

When I floor it the silver box under the dash on the drivers side fails to continue working (ecu). The fuel pump, ICM, coil, ckp, distributor, stop working. All said items are also new. I don't know what other symptoms someone is looking for. Engine cranks but doesn't start. I know 100% its a dead ecu because I've replaced it twice already. Wot is the only thing killing it. I don't know all of the sensors used during wot. This I could use help with. For some reason there is a spare tps that was in the globe box. I'm assuming the previous owner was having an issue. I originally bought the jeep with a bad ecu. The fuel pump wouldn't work. Once I replaced the ecu it ran fine. First time I floored it, it wouldn't down shift. It would only die. I spent about 8 hrs going through just about everything cruiser has tips on looking for a solution. Then I started throwing parts at it. Finally I asked a friend for a couple ecu's. Popped in the first one and was really irritated about all the money and time I spent when it was an ecu failure. Could the TCM have anything to do with this?

 

Picked up an ecu today. Going yo plug it it tomorrow and start voltage checks again. Check the resistance on the spare tps. Seems the low is 2.2k and high is 3.9k until it goes to open. This was checked from pins a/c and b/c while moving the arm.

 

RENIX TPS ADJUSTMENT

Before attempting to adjust your TPS, there are two things that need to be done.

1) Be sure the throttle body has been recently cleaned. It's especially important that the edges of the throttle butterfly are free of any carbon build-up.

2) With the Key OFF, and using the positive (red) lead of your ohmmeter, set on the lowest scale, probe the B terminal of the flat 3 wire connector of the TPS. The letters are embossed on the connector itself. Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it parallels the valve cover and also over near the MAP sensor on the firewall. If you see more than 1 ohm of resistance, or fluctuation in your ohms reading, some modifications to the sensor ground harness will be necessary. The harness repair must be performed before proceeding. I can provide an instruction sheet for that if needed.

TPS ADJUSTMENT FOR ENGINE ISSUES

Both RENIX manual and automatic transmission equipped XJs and MJs have a flat three-wire connector to the TPS which provides data input to the ECU. The three wires in the connector are clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. DO NOT UNPLUG THE CONNECTORS !! Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors. Note the voltage reading--this is your REFERENCE voltage. Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For example: 4.82 volts X .17=.82 volts. Loosen both T-20 Torx screws attaching the TPS to the throttle body and rotate the TPS until you
have achieved your desired output voltage. Tighten the screws carefully while watching to see that your output voltage remains where it is supposed to be. If you can't achieve the correct output voltage, replace the TPS and start over.

Sometimes, after adjusting your TPS the way outlined above, you may experience a high idle upon starting. If that happens, shut the engine off and reconnect your probes to B and C. Start the engine and while watching your meter, turn the TPS clockwise until the idle drops to normal and then rotate it back counterclockwise to your desired output voltage.

TPS ADJUSTMENT FOR AUTOMATIC TRANSMISSION ISSUES

RENIX automatic transmission equipped XJs and MJs have a TPS with two connectors. There is a flat three-wire connector, same as the manual transmission vehicles have, and it is tested the same as outlined above—FOR ALL ENGINE MANAGEMENT RELATED ISSUES.

However, the automatic TPS also has a square four-wire connector, clearly embossed with the letters A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module. THIS SQUARE FOUR WIRE CONNECTOR IS USED FOR TRANSMISSION/SHIFTING RELATED ISSUES ONLY. First off, DO NOT UNPLUG THE CONNECTORS !! Key ON, measure voltage between "A" positive and "D" ground by back-probing the connector. Note the voltage. This is your REFERENCE voltage. Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage. For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage. If you can't, replace the TPS and start over. So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and the other side feeds the TCU.

For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced. The square 4 wire connector is just not used.
Revised 12-15-2013

 

Got an ecu from a 90 model at the local u-pull-it yard. Tps, and grounds check out good. In proper adjustment. One thing I did notice is it doesn't like to downshift very well. I've adjusted the detent cable with no luck of fixing this issue. Curious if the TCM feeds back into the ecu. Maybe this is my underlying issue?

 

That cable is not a detent cable. It's a TV cable, meaning throttle valve. It moves a valve inside the trans to increase line pressure according to throttle load.

The TPS tells the TCU when to shift.

 

Installed the ecu (90model), and a new accelerator pedal. Also put my spare TCM in. Its not shifting any different but feel like it has more pep to it. I have not tried wot yet. I'd like to figure out the issue before frying another ecu. Still feels like it doesn't want to downshift, or at least its not downshifting like my 99 does. The power comfort switch also seems like it isn't working. Sometimes it lights up, but most of the time it doesn't. I noticed the e-fan wouldn't kick on with defrost either. Probably has something to do with the a/c system not being charged. I'll charge it after I replace the pressure line. Previous owner hose clamped it on. Only other thing not working is the cruise. I have to replace the piece of vacuum line I broke. For now, its plugged. I apologize for the rambling. Maybe more of these issues will help with bouncing around ideas.

 

I forgot to mention with the engine off and key on I opened the throttle all the way with no ecu failure. I know that not all systems are functioning unless the engine is running but figured I would give it a shot. Still thinking it might be because the engine is under too heavy of a load at wot because the transmission won't downshift quick enough.

 

Bypass the Power switch and put it in Power mode permanently. Be sure the "trans" fuse isn't blown.

Bypassing the Power/Comfort Switch on a Renix Jeep

Remove and unplug the switch. In the harness are 3 wires One has a stripe, one is tan, and the other black. Make a 4" jumper wire with a male spade at each end. Plug one end in the cavity for the tan wire and the other in the cavity for the striped wire and you'll be in permanent Power mode. Stuff the harness back in and reinstall the switch for looks.

 

I understand simple wiring with my electronics engineering background. the switch is good. it ohmed out when switched both ways. I even tested the light on my bench supply. so the light works and the switch works. also I ohmed the wiring. it has no breaks. what this is leading me to is a faulty tcm. problem is I replaced the tcm with a similar tcm that is know to work. same issue. no light and no change in shifting. I still haven't found the underlying condition to the ecu failures. after checking everything I cannot pinpoint the issue. the jeep drives perfect. I just cant use wot to speed up quickly. also I have to manually downshift if I want to pass someone. zero of cruisers tips have been helpful with this issue. I've seen only references to them instead of actual problem solving skills. Cruisers tips may work for those that don't know how a vehicle works, but some of us actually know a thing or three. I have a 99 model as well as this waggy. I'm used to working on the mopar system without fail. Some of my friends can tell me symptoms on their mopar jeeps and I can tell them which parts to replace. I guess the renix gurus aren't really gurus. Many have kept asking for problem symptoms. As I have said here are the symptoms. The ecu fries at wot. No ignition, fuel pump or injectors. I can solve this issue by replacing the ecu. My initial gaol of posting here was not to have the answer given to me as to why the ecu fries, but to find out specs on sensors i'm testing. I don't want to know the voltage at the tps. I want to know what the resistances are going through it. its a potentiometer. it will have set high and low resistance. Any testing done with the key on is not an option. I do not wish to fry another ecu.

 

Yours is a symptom that we've never seen before.

Gotta cover basics and we can't decipher your skill levels over the internet right off the bat.

 

I've never seen this symptom either. I've even swapped a tj/WJ engine into a renix and got everything to work. I just can't figure out why an ecu would die when trying to go wot.

In other news...
I found out my volt meter is out of calibration. I went and got another one and will start voltage checks again this week. Going to start with the tps again. Oddly my voltmeter still reads ohms correctly. I may go ahead and ohm everything again just to make sure.

 

IIRC, at 80% and above throttle the system goes open loop. So, is this happening only at WOT or in open loop?

 

Could you elaborate more on "open loop"? I am used to it meaning something to do with o2 sensors.

As far as I know I've fried 3 ecu's when putting the accelerator to the floor while driving. I have not tried putting it to the floor while sitting in the garage. I'm slightly afraid that a 430K mile engine might try to come apart and go through some walls. Also I would like to not have to go get another $4 ecu. After driving around town a little today I noticed that at half pedal the trans wouldn't downshift still. I pressed a little harder and still nothing. I didn't try any further due to fear of accidentally hitting wot. I do know at wot the fuel pump relay cuts out and the o2 heater relay takes over for the fuel pump. I'm still thinking the tps could be bad since I found my meter not working correctly. As you said the tps controls when the trans downshifts, and it is a sensor on the engine that is used during wot.

 

So your CPS ACV out-put to How meany ECU's is what?

You are fortunate Cruiser didn't can your ****. I still think it's your harness. In your shoes I'd check the ACV AT the ECU while it won't fire, AND the motor mounts and harness.

 

At WOT injector pulse is shut off while cranking, to help clear a flooded condition. While running, the 02 is ignored, (along with other sensors), and it provides fuel from the MAP signal. (the 02 heater relay is not an issue except to provide heat to the 02 sensor, sooner, as it warms up, (for smog).