• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Renix in Closed Loop at 120*

K

kcjeep6

NAXJA Member
NAXJA Member
Location
Castro Valley,CA
I am having an issue with my 88 4.5 Stroker, it seem to worse when cold, it is backfiring thru the exhaust when accelerating and cruise.This motor has run great for 3 years, new MAP & CPS
All inputs test OK and the distributor is indexed. Sensors have been tested with a Fluke 87 and a Snap-on MT2500. The one unusual thing I see is it is going in to closed loop with the coolant at 120*.
I’m thinking the ECU is defective. Anybody have a thought on this?
 
Renix goes closed loop with a cold engine seconds after ignition, no problem. Have you checked the vacuum hose-tube from the throttle body to the new MAP? If it is loose at the throttle body it will back fire..... IF it is clogged, or collapsed it might do it as well.

If it is not the MAP vacuum line or MAP to ECU wires being fubared, the next suspect is a bad TPS, but a bad ground wire on those 2 sensors will also cause all sorts of headaches, so check the ground at each sensor, TPS and MAP, they should be no more than 1 ohm to the battery negative post.
 
Have you ever checked the sensor ground circuit as Mike mentions?

Or ever refreshed the grounds on your Jeep?

You have the dreaded C101 connector on your firewall. Ever addressed this?

Individually, and combined, the above can cause the issues you describe, along with a bad TPS. If it were mine, I would perform all the preventative ground refreshing, C101 cleaning, and sensor ground testing before proceeding.
 
Thank for giving me a direction to go. I believe I check the grounds, I had less than 1 ohm but I will check them again, 2 years ago I redid all the grounds and soldered all the connections. The hose is clear, the fitting seem tight, I will take a closer look at the hose.
I do have an adjustable voltage regulator with a bypass switch for the MAP that is not potted; I installed it when I did the Stroker. I soon found it was not needed thru a wide band A/F meter. I will take it out of circuit and see if that helps. I still have a C101 connector and I have cleaned it.
 
kcjeep6 said:
I am having an issue with my 88 4.5 Stroker, it seem to worse when cold, it is backfiring thru the exhaust when accelerating and cruise.This motor has run great for 3 years, new MAP & CPS
All inputs test OK and the distributor is indexed. Sensors have been tested with a Fluke 87 and a Snap-on MT2500. The one unusual thing I see is it is going in to closed loop with the coolant at 120*.
I’m thinking the ECU is defective. Anybody have a thought on this?
Click to expand...

The point of the HEGO (Heated Exhaust Gas Oxygen sensor) is to allow the sensor tip to reach operating temperature independent of the engine.

If a HEGO won't give a valid signal for Closed Loop Operation within 60 seconds, the heating element is likely shot.

Closed Loop is independent of engine coolant temperature (although ECT sensor output does play a role in fuel metering, the HEGO provides a feedback loop to trim fuel - whatever inputs go into calculating fuel delivery in the first place. "Open Loop" and "Closed Loop" operation simply refer to whether or not a valid signal is being generated - Open Loop runs a bit on the rich side of stoich - simply to help keep chamber temps down and to keep the engine running. It's just rich enough to keep NOx and knocking down, but no so rich as to run close to RBL or to cause washdown.)

Since your MAP adjuster is neither sealed nor potted (by your own admission,) troubleshooting that circuit box may prove instructive as well - it may have gotten contaminated. Or you could simply remove it ("test by elimination," as opposed to "test by substitution.")
 
I removed the AVR and re-soldered the original wires, this made no difference. I was concerned that the switch contacts were flaky. MAP ground to battery is 0.1 ohms and the TPS is 0.6 ohms. I tried a new piece of hose from the TP to MAP, no luck so far. Think I will start working on removing the C101 tomorrow; I am really trying to avoid this. If that does not do the trick I will replace the MAP and TPS. I have tried switching the MAP with a use one that I had laying around, that did not make a change either. Both of my MAP’s are used.
 
From your post above, I can't determine if this was done.

Cruiser’s Renix Sensor Ground Test
Set your meter to measure Ohms. Using the positive (red) lead of your ohmmeter, 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 runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.
 
Let’s see if I have this right, A Valid Signal could be over or under a set value. The ECU is using both the O2 & MAP at all times to keep the engine running.
The TPS wiring harness passed the wiggle test as did the C101
 
kcjeep6 said:
Let’s see if I have this right, A Valid Signal could be over or under a set value. The ECU is using both the O2 & MAP at all times to keep the engine running.
The TPS wiring harness passed the wiggle test as did the C101
Click to expand...

The ECU will run with out an O2 signal, it defaults to table values in the program for air and fuel rates, rich stoich. It will also run with out a vacuum line to MAP, and with out a TPS signal but it requires a V signal from the MAP to run, even if the signal is not changing due to loss of the vacuum input. But with out the correct MAP and TPS signal rapid acceleration and deceleration can kill the engine and cause it to back fire.
 
I’m ready to pull my hair out. I have tested the all of the sensor and tried at least 2 of every sensor. I removed the C101 plug, soldered the wiring, all grounds and sensor wiring have been tested back to the ECU. I have tried my spare ECU and added a ground from ECU to battery. I have verified all Brick readings with fluke 87, vacuum gauge and Innovate wide band gauge. Fuel presser is good. Compreesion a little low, valves good, vacuum steady.

The motor is running rich, when started it is lean then goes rich and stays there. It will go into closed loop, the Short Term Trim goes from 128 to 0 then back to open loop, LTT never changes. As the STT is decreasing the Injector Pulse drops from around 10 to 6, the O2 voltage only comes up about 0.5 volts. It will do this 3 times then goes into open loop and stays there. When in open loop the F/A is around 10, when it goes into closed loop the F/A comes up to 11.5.
As I see it the system knows it is rich, tries to lean out but will not lean out so it defaults to open loop.

Any clues?

Is someone looking for ECU’s? I have one that was given to me, there is a transistor that fell out. If someone would like it to play with PM me your contact information and will send it to you.
 
The fuel pressure will remain steady for at least ½ hour after the motor is shut off. I feel this rules out a leaky injector, also all plugs are equally fluffy and black.
It goes rich in less than a minute. I have also tried running it with the cat disconnected.
 
cruiser54 said:
As for who might like your ECU, contact Jon Kelley in San Jose just over the hill from you. www.kelleyswip.com.

Leaky injectors? How long is it lean before going rich after starting?
Click to expand...

AKA as 5-90 here.

Have you checked the FPR vacuum nipple while running to see if it smells of a fuel leak, leaking into the vacuum line, while under vacuum?

AVR=??
 
Last edited:
kcjeep6 said:
I am having an issue with my 88 4.5 Stroker, it seem to worse when cold, it is backfiring thru the exhaust when accelerating and cruise.This motor has run great for 3 years, new MAP & CPS
All inputs test OK and the distributor is indexed. Sensors have been tested with a Fluke 87 and a Snap-on MT2500. The one unusual thing I see is it is going in to closed loop with the coolant at 120*.
I’m thinking the ECU is defective. Anybody have a thought on this?
Click to expand...

Is it just running rich now, did you solve the backfiring problem, if so, how? What work did you do shortly before the problems started?

Is the O2 sensor getting 12-14 volts to the internal heater? Have you checked the ground, on each and every sensor, power off, on ohms, and power on with standing voltage ground test?
 
cruiser54 said:
As for who might like your ECU, contact Jon Kelley in San Jose just over the hill from you. www.kelleyswip.com.

Leaky injectors? How long is it lean before going rich after starting?
Click to expand...

Just include a note letting me know the original application and the diagnosed failure, please.

RENIX is a hobby...
 
kcjeep6 said:
I’m ready to pull my hair out. I have tested the all of the sensor and tried at least 2 of every sensor. I removed the C101 plug, soldered the wiring, all grounds and sensor wiring have been tested back to the ECU. I have tried my spare ECU and added a ground from ECU to battery. I have verified all Brick readings with fluke 87, vacuum gauge and Innovate wide band gauge. Fuel presser is good. Compreesion a little low, valves good, vacuum steady.

The motor is running rich, when started it is lean then goes rich and stays there. It will go into closed loop, the Short Term Trim goes from 128 to 0 then back to open loop, LTT never changes. As the STT is decreasing the Injector Pulse drops from around 10 to 6, the O2 voltage only comes up about 0.5 volts. It will do this 3 times then goes into open loop and stays there. When in open loop the F/A is around 10, when it goes into closed loop the F/A comes up to 11.5.
As I see it the system knows it is rich, tries to lean out but will not lean out so it defaults to open loop.

Any clues?

Is someone looking for ECU’s? I have one that was given to me, there is a transistor that fell out. If someone would like it to play with PM me your contact information and will send it to you.
Click to expand...

If you run rich long enough (which usually isn't very,) the porous ceramic that makes up the HEGO tip will clog - then you'll be permanently stuck in Open Loop and running rich (11.5:1-12.5:1 sounds about right. It's rich enough to keep combustion temperatures down and prevent knock, but not so rich as to cause washdown.)

Running rich will also coat the matrix in your catalytic converter - which means it will probably want replacing soon as well.

"Brick" = Snap-On MT2500? Any screenshots? (I have got to get one of those...)

As far as my contact information, my address is on my site (link given, direct is www.kelleyswip.com/contact.html.) As I said, please include a card with the original application of the ECU and the diagnosed failure (from symptoms, even if an internal part is loose,) and I'm in no hurry - cheap Parcel Post is just fine. Let me know if you want your shipping covered, and I'll kick it back to you after I get the box/package/whatever.
 
5-90 said:
If you run rich long enough (which usually isn't very,) the porous ceramic that makes up the HEGO tip will clog - then you'll be permanently stuck in Open Loop and running rich (11.5:1-12.5:1 sounds about right. It's rich enough to keep combustion temperatures down and prevent knock, but not so rich as to cause washdown.)

Running rich will also coat the matrix in your catalytic converter - which means it will probably want replacing soon as well.

"Brick" = Snap-On MT2500? Any screenshots? (I have got to get one of those...)

As far as my contact information, my address is on my site (link given, direct is www.kelleyswip.com/contact.html.) As I said, please include a card with the original application of the ECU and the diagnosed failure (from symptoms, even if an internal part is loose,) and I'm in no hurry - cheap Parcel Post is just fine. Let me know if you want your shipping covered, and I'll kick it back to you after I get the box/package/whatever.
Click to expand...

Note that he says he has replaced every sensor at least twice, which I assume includes the HEGO, MAP, TPS, MAT and CTS. Also note it is a 4.5 L stroker.

OP, have you verified that the HEGO sensor output voltage at the ECU is the same as the voltage at the HEGO? This could be done by verifying a low resistance in the ground and sensor output wires from the HEGO to the ECU, using a very long wire and ohm meter, testing each ISOLATED wire.

IIRC the Renix uses only three wires, and the heater and ECU signal wire use a common ground, so if that ground is not perfect, the 12 volts from the heater heading to ground can feedback into the ECU signal wire!!!!

Also, it may be time to consider a possible exhaust leak near the HEGO messing with the O2 readings!!!! Or an intake-exhaust manifold leak, one feeding the other. Does it still have a stock EGR system?
 
Don't be shy about the C101. It's easy. I heard EcoMike even did one once with success.

Renix Jeep C101 Connector Refreshing
　
The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of almost 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before.

Almost every critical signal between the engine sensors, injectors, and the ECU travel the path through the C101.
The C101 is located on the driver’s side firewall above and behind the brake booster. It is held together with a single bolt in it’s center. To get the connectors apart, simply remove the bolt and pull the halves apart. You will find the connector is packed with a black tar like substance which has hardened over time.
Take a pocket screwdriver or the like and scrape out all the tar crap you can. Follow up by spraying out both connector halves with brake cleaner and then swabbing out the remainder of the tar. Repeat this procedure until the tar is totally removed. This may require 3 or more repetitions. Wipe out the connectors after spraying with a soft cloth.
If you have a small pick or dental tool tweak the female connectors on the one side so they grab the pins on the opposite side a bit tighter. Apply a true dielectric grease, not the stuff that came with your brake pads, to the connection and bolt it back together.
　
　
Revised 11-29-2011
 
You must log in or register to reply here.

Similar threads

9
Renix lowish idle
Replies
10
Views
2K
90xj06
9
C
91 XJ missing at 2000 +rpm only when at operating temp
Replies
0
Views
1K
cptmiker
C
R
2001 California Emissions runs terrible at startup
Replies
3
Views
1K
tech1001
T
B
Renix engine issues
Replies
7
Views
916
cruiser54
C
B
Renix wont go into closed loop (O2 sensor) mode
Replies
5
Views
2K
Black1990jeep
B
Back
Top