big66440

I replaced the ECM because the one I had was for an older model Manual transmission MJ and I wanted the power increase and better "manners" of the 89-90 ECM's. My old O2 sensor had a bad heater element causing a rough idle and open loop at idle. According to the Renix monitor the MAP sensor is within specifications as well as the other sensors.What ever it is it's now common to both ECM's since the one I removed from my Jeep originally is doing the exact same thing.

That's the monitor I have as well, my readings were exactly as you described before I decided to swap ECM's. Now my O2 reading is stuck at 4.98V all the time and the ECM will go into closed loop for a few seconds then pops back into open loop. I've checked all the relays and have completely taken apart the relay sockets to thoroughly clean them ( one wire at a time). I have never been so frustrated with my Comanche, I give it the best I can and can't help but feel a bit betrayed.

Something is very weird then I have verified 12V reference to O2 5V reference to the O2 0-1 Ohm on ground circuit 2 working O2's ( one with an open heater circuit but still showed voltage oscillation) 2 ECM's one definitely working Good connection at ECM I know somethings wrong because mileage has suffered and I can see and hear the engine struggling really bad to stay in closed loop. I think I can see why you dislike Renix systems so much Hornbrod :rotf: All I did to "cause" this was literally disconnect my battery and replace the ECM,,,, I re installed my old ECM to verify and still no luck.

Thanks,So the 5V reference at terminal C is normal?

Just checked voltage again and I'm getting 12V on terminal A, and a 5V reference from terminal C. I did this test on the harness side with the engine running, is this normal ? if so does anyone know where the ground for terminal B is?. I apologize once again for the ignorance.

I'm sorry but what do you mean by " 02 signal circuit" ? I understand the heater needs a ground but I thought the "ground" for the O2 signal was the oscillating voltage the ECM needs to calculate air fuel ratio :hmm: . Thank you for the diagram Hornbrod

I Don't think they exist, not saying it's impossible but I don't think there are any readily available on the market.

The monitor was working perfectly before I replaced my ECM with the new replacement O2 sensor, so that rules out the O2 sensor and monitor issues. I'm running 89 Unleaded, I have the Renix fuel injection manual and have studied the O2 sensor diagram and I'm a bit confused. The diagram shows the solid gray wire ( terminal C ) to be return voltage to ECU Pin D9 but I'm getting a solid 4.98V with the key on engine running and not running which leads me to believe that gray wire is actually the 5V reference TO the O2 sensor FROM the ECM?. If I am correct that means the Black wire ( terminal B )is the return voltage signal and ground for the heater element to the ECM? if that is true what pin on the ECM is the return signal and ground for the O2 sensor?

Anyone want to take a shot at this? I'm stumped right now and could use some brain storming. I'll do a quick recap, my Renix monitor shows my O2 voltage stuck at 4.98V ( all the time)and goes into closed loop intermittently for about 3-4 seconds. I have battery voltage to the heater circuit as well as a 5V reference from ECM. I have a brand new O2 sensor as well. I have also done cruisers renix tips for the ground upgrade and splices. I have checked and double checked the connection to the ECM and it's fine.

Never mind I figured it out, I'm seeing a voltage reading going up and down but my monitor still shows 4.98. I'm going to check the resistance of the harness when I get a chance.

I replaced my ECM recently with part number 8953005428 and ever since then my Renix monitor shows the O2 voltage to be stuck at 4.98V and only goes into closed loop once in a while for about 3-4 seconds, the ECM I replaced showed normal voltage readings for a good O2 sensor circuit. I have battery voltage for the heater and 4.97V reference from the ECM and show 0 ohms when I check resistance on the third wire. I tried replacing the new ECM with the old one and it's doing the same thing ( constant 4.98V and open loop) as well as installing my old O2 which I'm sure works except for the heater element being busted no difference. I looked at the terminal pins on the harness side and ECM and seem to be fine, I've wiggled the harness with the engine running and made no difference. Can you guys please tell me how to hook up my voltmeter to check the voltage of the O2? I'd like to be 100% sure what I have and don't have for my diagnosis, thank you.

Seems kinda fishy, I know the guy has 100% feedback but looking them closely they look a bit used, he doesn't have boxes for them either. Nothing to prove he didnt pull them from junkyard cars, bench test them and now he's trying to flip them??? Guess I'm a bit cynical sometimes.

Like Hornbrod said, stock is fine.

I was wondering if anyone knew the MOPAR part number or ACDELCO ( If I'm not mistaken GM used the same MAP sensor for some of their vehicles) part number for the MAP sensor compatible with the Renix 4.0 ?. Since it's a very important sensor in our fuel injection system I'd rather use a high quality factory part than aftermarket, thanks.

Crown sells the replacement kits as well as Mopar ( Part number 83502745 )

And the wires that get melted on the exhaust manifold include oxygen sensor... You can unplug the O2, CTS, and knock sensors, fish the harness up by the power steering pump. Then remove the split loom and see what ya got. I soldered in some good clean 12g wire for all the sensors for that section that had made contact with the exhaust, according to the monitor the ECM is getting a good signal from the ECT, O2 and knock sensor.

Congrats Jeeptec1, she looks really solid.

Ebay, that's where I got mine recently

I would go with a Doug Thorley tri Y if I had a choice, since I live in California I have to keep my EGR to pass the visual smog inspection :fs1:

Welcome to the forum :thumbsup: I love the monitor, thank you.

I bypassed the ballast a few years ago. I've been running an airtex pump ( I know I know ) and so far so good. I had a Bosch 69302 before and it went out on me within a year and a half but I blame myself for always running the tank below a quarter.

Guess I jumped the gun and skipped a VERY important test,,,, my O2 heater was not working. I went to NAPA and grabbed a Bosch ( Made in USA) and it stays in closed loop at idle and I can see my O2 voltage fluctuating. Funny thing is I tested the voltage to the O2 while the engine was running at idle and I got battery voltage on the orange (cleaned the relay connections) and 4.97 from the ECM, my FSM shows you should have voltage at those connections with the key on engine off?. I completely screwed up on my diagnosis and should have checked the heater circuit first

Agreed, early small block mopars ( LA ) didn't have a "tensioner" for the timing chain but when Mopar introduced the Magnum small blocks they came equipped with a "tensioner" which a lot of people install on their LA small blocks as an upgrade.

I sure have,as well as the ground refresh ( which made a nice noticeable difference ). BTW I highly recommend using air gun cleaning brushes for connectors https://www.walmart.com/ip/5-Pcs-Airbrush-Spray-Gun-Tip-Tattoo-Machine-Tube-Cleaning-Brush-Kit-Set/110592332?wmlspartner=wlpa&selectedSellerId=2396&adid=22222222227051729285&wmlspartner=wmtlabs&wl0=&wl1=g&wl2=c&wl3=151513093122&wl4=pla-328099138517&wl5=9031218&wl6=&wl7=&wl8=&wl9=pla&wl10=113148173&wl11=online&wl12=110592332&wl13=&veh=sem. These things are cheap and you can really get into the connectors to clean them out. I've thought about getting a replacement harness from the junk yard and cleaning/ repairing it as much as I can since I've found some pretty bad repairs from the previous owner as well as him not routing the wires correctly and letting them rest on the exhaust manifold.

I checked the big orange wire for voltage on the harness side of the o2 with key on engine off and got 0 volts . I then shut the ignition switch off ( keys removed ) and did an ohm test ( red DMM lead on orange terminal of harness and black to ground) and got about 27 ohms, I then started wiggling the harness back towards the o2 relay and when I got to the passenger side of the firewall on the cowl the ohms reading went up to about 30-35 ohms and would change the more I wiggled it!!!. I'm going to go through the harness and see what the heck is going on.