Renix in Closed Loop at 120*

[GSequoia]

But he still isn't seeing the O2 heater being triggered.

 

[Ecomike]

I would be *very* surprised if you had one bad ECU, let alone two.

Personally if I were in your position (and I was recently) I would get very friendly with your multimeter. Start at the sensor and work your way back to the ECU.

Do you have the factory wiring diagrams?

But I agree, I doubt it is either ECU!!!

 

[Ecomike]

But he still isn't seeing the O2 heater being triggered.

If I understand him correctly, it goes closed loop, but stays rich in closed loop, does not reach stoich, or lean, or switch back and forth, and the ECU eventually gives up and goes back to open loop. He also has had a back fire issue IIRC.

Also not sure he has confirmed that his EGR is not sticking, or acting up.

But he has checked the wires, resistance and readings at the ECU and the sensors, and tested every ground to be >>.5 ohms

 

[Ecomike]

But he still isn't seeing the O2 heater being triggered.

He said the O2 heater is working with engine running, and while cranking. But not in run with the engine off. That is normal for the 89, but not for the 87.

 

[kcjeep6]

Mike you are correct it goes into Closed Loop & the O2 output will not reach stoich or lean, default to Open Loop. The ECU cannot drive the mixture lean.

• The only time it reads lean is the millisecond the key is turned to Start. This was verified using the Max/Min button on the Fluke 87.

• No voltage to O2 heater in the Key On position, voltage in Start & Run.

• All wiring has been checked with a Fluke 87, I know my DDM very well, well enough to use the Relative button so I am not reading the resistance of the leads.

• There are no vacuum leaks or exhaust leaks, verified with vacuum gauge & smoke test , a smoke test pressurizes whatever you are testing with smoke, the smoke will seep out of any holes in the system, very cool tool!

• Vacuum to MAP was verified by install a “T” at the MAP then connecting a vacuum gauge

• Fuel pressure is 31.5 with vacuum, 39 without vacuum

• Fuel Rail will hold 31.5 psi for at least 30 minutes

• All plugs equally fluffy black

• CTS, MAT tested

• New Sync, CSP, TPS, MAP, O2, all have been tested since installed

• I am trying a new O2 senor tonight, it seem there a 2 part numbers for a 88

• I will block off the EGR to make sure this is not an issue when running


I apologize if I sound a little testy, I am very frustrated! I am old enough to get a senior discount at Denny’s. Start my career as a Machinist, than a Foundry Maintenance Mechanic, move on to Overhead Crane Maintenance including fabrication, installation, inspection, troubleshooting and repair of mechanical, electrical & structures issues. I receive very instance training in motor control systems including Electronics while in Finland at the Konecranes factory. I am presently the Lead Maintenance Mechanic at a manufacture of medical radiation treatment machines, I am responsible for 2 CNC, 1 R&D machine shops plus a Vacuum Braze Furnace room This is not my first rodeo, although this is one of the most challenging troubleshooting job I have ever taken on!

Sorry for the rant and I am very appreciative of everyone’s input .

 

[GSequoia]

When checking your wiring did you go from the sensor to the ECU?

 

[kcjeep6]

When checking your wiring did you go from the sensor to the ECU?

3 times!

 

[GSequoia]

3 times!

I don't envy you. The ECU is in a mutha of a spot...

KOEOff would make sense to have the O2 heater disengaged, otherwise it would overheat (likely why they made the change). Have you checked the resistance of the O2 heater itself (don't recall the value offhand)? Either way I'd consider trying a different sensor. In my experience if the O2 heater doesn't bring the tip of the sensor up to operating temperature it won't go into closed loop (aside from a quick jump into it at first). When my O2 heater was not working my computer way saying I had a lean mix but my nose was saying it was rich.

 

[Ecomike]

I apologize if I sound a little testy, I am very frustrated! I am old enough to get a senior discount at Denny’s. Start my career as a Machinist, than a Foundry Maintenance Mechanic, move on to Overhead Crane Maintenance including fabrication, installation, inspection, troubleshooting and repair of mechanical, electrical & structures issues. I receive very instance training in motor control systems including Electronics while in Finland at the Konecranes factory. I am presently the Lead Maintenance Mechanic at a manufacture of medical radiation treatment machines, I am responsible for 2 CNC, 1 R&D machine shops plus a Vacuum Braze Furnace room This is not my first rodeo, although this is one of the most challenging troubleshooting job I have ever taken on!

Sorry for the rant and I am very appreciative of everyone’s input .

Oh, OK Now I see what the problem is, you have no formal Jeep Gremlin Hunting experience yet!

LOL!

 

[Ecomike]

3 times!

Did you try going from the ECU to the Fuel injectors, on the output control side of the process control?

The only Renix ECU failures we have head of here (the last 4-5 years) were 3 or 4 that had a bad injector grounding transistor in the ECU. IIRC the details. As I recall the ECU fires the injector by ground it at the ECU via a switching transistor?

But long story short, have you been able to check the Injector side yet? Check the loom for an intermittant ground? Pulled one injector wire set at a time to see if the engine operation changes? You have eliminated so much I leaning towards that EGR or the Injectors.

Could you have a weak spark? leading to missfires, and excess fuel? I am grabbing at straws there, but who knows, maybe look out side the box time.

One last wild idea, I criss crossed wires a few times over the years, TPS, O2 sensor, plug wires, and got very odd behavior when I did!!!!

 

[kcjeep6]

Oh, OK Now I see what the problem is, you have no formal Jeep Gremlin Hunting experience yet!

LOL!

Thanks you just made my day a lot brigther!

 

[GSequoia]

Renix ECU fires injectors through the hot side, ground is common. Chrysler works the other way around.


Blown injector circuits is the only failure I've heard of on a Renix ECU.

 

[5-90]

IIRC there is a relay for the O2 voltage.

For the heater circuit, but not for the signal.

 

[5-90]

Oh, OK Now I see what the problem is, you have no formal Jeep Gremlin Hunting experience yet!

LOL!

Just bear in mind that it can be a blood sport - the Gods of Automotive Repair occasionally demand sacrifice.

This sacrifice must be taken, it cannot be willingly given.

But, sometimes you get lucky and catch the Gods in a good mood, and they don't want your blood.

Just be forewarned. Cyanoacrylate esters ("super glue") are wonderful additions to your First Aid kit - germs can't grow in them, they'll stick a wound shut through blood, and they'll give a waterproof seal. Note that an allergic reaction is possible - to test, put a small drop of CA glue on your inner forearm, just past the elbow, and watch it for three days. Some mild reddening can be normal, but doesn't usually happen. If it gets violently red, blisters, hives, or some other drastic reaction, do not use it to stick wounds shut! Anaphylaxis really sucks...

 

[Ecomike]

LOL, I thought the Gods were just a myth!!!

LOL

 

[kcjeep6]

I may have earned my Jeep Gremlin Slayer Badge! I was at my buddies shop last night and installed a new O2 sensor, this made no change in O2 sensor output.

What we were seeing is at crank the voltage would start out at about 5 volts it would drop like a rock to less than 0.5 volts, it would stay there even though the ECU was reducing the Short Term Trim & Injector Pulse. This had us both stumped and we are coming up with ideals of what would drag the voltage down.

We had the XJ connected to his Snap-On Verus which displays all the information form the ECU on one screen, everything looked great except the O2 voltage, he tapped the arrow next to the O2 voltage line and a scope window popped-up, we could plainly see I had only 0.02 volts O2 output to the ECU, what we did see was spike in the voltage!

With the motor running I pull the O2 connector and to our disbelief there was no change. We plugged in my spare ECU and the spike became worst. This is clearly a case of having 2 ECU’s with defective power supplies for the O2 filament. I have a ECU on order.


I can’t find the yellow mountain and it says at the bottom of this tread that I cannot post attachments so I have posted a picture of the Verus showing the spikes in my album , if anyone would like to see what is happening. This picture was taken with the Key On with out the motor running

The Verus http://www1.snapon.com/diagnostics/us/verus is one awesome tool & for 9,200 bucks it better be! I do have a Fluke 123 Scopemeter but never used it to check out my system (silly me), you can be sure that the next time I have an issue I will be using my Scopemeter rather than a DMM

I will post an update & a scope picture when the the new ECU shows up.

 

[GSequoia]

There's your photo. :cheers:

 

[Ecomike]

I would be asking what damaged both ECUs, if indeed they are both actually damaged, before I ever risked installing a new one!!!!

They are nearly indestructible, ask me how I know!!!! LOL. I would look for bad O2 sensor wires, which is VERY COMMON!!! Especially if they get too close to the front driveshaft or exhaust manifold!!!! Ask me how I know!!!!!

Also doesn't the 5 volts from the ECU power supply feed all the sensors? In which case the bad part may be the resistor in the ECU that the 5 volts goes thru first on the way to the O2 sensor. I think Old_man told me it is part of the voltage divider circuit!!!:laugh3: It might be an easy fix if it has a cold solder joint, or got fried, (My guess is fried with an O2 sensor 12-14 volt heater short) if 2 ECUs are really bad).

 

[kcjeep6]

All of the other 5v signals are OK, it’s like the O2 filament is drawing to much current and shutting down the power supply for the O2 circuits , I have 3 O2 sensors that behave the same.

I will go thru the O2 wiring one more time before installing the replacement ECU, this time looking for grounded & shorted wiring. As I have said before I have removed the wiring from the loom and it looked good, never hurts to look again.

I opened up the third ECU I have (the one the transistor fell out of) the board looks like multiple layers & has a conformal coating, it indeed looks very well built!

 

[Ecomike]

I would disconnect the O2 sensor, and the ECU, and maybe even the O2 sensor heater power relay, and then check the three O2 sensor wires for any sign of a short or loss (partial short, xxx ohms) between any two wires, or a short to ground from any one wire. And wiggle wiring harness during the tests.

If they are all clean, then you may indeed be the first with two bad renix ECUs.