Renix in Closed Loop at 120*

[GSequoia]

What are the actual fuel pressure readings?

What if the fuel pressure is actually higher than is read? Faulty gauge?

The ECU doesn't read fuel pressure, there is no fuel pressure sending unit; you can only read fuel pressure from a fuel pressure gauge you hook up to the schrader valve on the fuel rail. With the fuel pressure regulator vacuum line hooked up and engine running it should read 32 PSI, with the fuel pressure vacuum line disconnected it should read a bit north of 40.

 

[Ecomike]

The ECU doesn't read fuel pressure, there is no fuel pressure sending unit; you can only read fuel pressure from a fuel pressure gauge you hook up to the schrader valve on the fuel rail. With the fuel pressure regulator vacuum line hooked up and engine running it should read 32 PSI, with the fuel pressure vacuum line disconnected it should read a bit north of 40.

Cruiser knows that, he was referring to a test pressure gauge on the schrader valve.

FWIW, both my 87 and 89 have always read 29 to 39 PSIG (8 years and 4 years). Both have new FPRs (the last year), and still read 29 and 39. The 89 has a good tight engine, great compression and vacuum, and the 87 is weak on compression now, 278,000 miles. My 87 has no ballast resistor and the 89 does. Both are very old, maybe even OEM, fuel pumps.

 

[GSequoia]

Both of the Renix Jeeps I've owned gave me clean 32 on a good pump/FPR. The only times I've seen bad readings is when the hose between the fuel pickup and pump pickup was faulty or with a failed pump or FPR.

 

[kcjeep6]

I just got back from lunch at the local brewery with my Beer Buddy Bonding buddy so I’ll keep this short till after my nap.

I checked my resources, I have 3 a pdf Jeep Cherokee Manuel, pdf Jeep 4.0 Jeep Renix Manuel and a Snap On Jeep Reference Manuel. Jeep Cherokee Manuel state that high voltage is high rich & low is lean. This is the same manuel that told me the forward relay is for the Q2 heater,I lost a good 8 hours on that wild goose chase! On my XJ the O2 relay is the rear relay, on a friend on mines it’s #3!

The Jeep Renix Manuel state Low Voltage is Rich and so does the Snap On Jeep Reference Manuel. This is what I’m seeing on the 2500, DMM & wide band! The thing is running rich, that’s my story and I’m sticking to it!

I spent some time looking at the wiring diagram and noticed there are 2 grounds that are available at the diagnostic connector. One is the sensor ground on the left side of the motor, the other is the ECU ground on the right side. I found the Sensor Ground at the Diagnostic plug to be less than 1 ohm. The EPU Ground is 2.5 when tested at the plug. My next step is to improve the ECU Ground.

I have screen shoots and MAT/CTS information but that will have to wait till after my nap.

 

[cruiser54]

Cruiser knows that, he was referring to a test pressure gauge on the schrader valve.

FWIW, both my 87 and 89 have always read 29 to 39 PSIG (8 years and 4 years). Both have new FPRs (the last year), and still read 29 and 39. The 89 has a good tight engine, great compression and vacuum, and the 87 is weak on compression now, 278,000 miles. My 87 has no ballast resistor and the 89 does. Both are very old, maybe even OEM, fuel pumps.

Yes, I do know that. Just throwing something out there. I had a supercharged car with a FPR that wouldn't drop the fuel pressure low enough and it ran rather rich. OP has not said what his readings are I thought possibly if he had read them with a manual gauge, perhaps it might be inaccurate.

 

[cruiser54]

The ECU has two grounds that terminate at the dipstick tube stud. One is 18 black and the other 16 black.
The O2 sensor ground is there, too. There is a connector # C116 above the master cylinder that the ground travels through along with the other O2 sensor signals. It's a five wire connector BTW.

 

[Ecomike]

Both of the Renix Jeeps I've owned gave me clean 32 on a good pump/FPR. The only times I've seen bad readings is when the hose between the fuel pickup and pump pickup was faulty or with a failed pump or FPR.

Are you at sea level?

 

[Ecomike]

I just got back from lunch at the local brewery with my Beer Buddy Bonding buddy so I’ll keep this short till after my nap.

I checked my resources, I have 3 a pdf Jeep Cherokee Manuel, pdf Jeep 4.0 Jeep Renix Manuel and a Snap On Jeep Reference Manuel. Jeep Cherokee Manuel state that high voltage is high rich & low is lean. This is the same manuel that told me the forward relay is for the Q2 heater,I lost a good 8 hours on that wild goose chase! On my XJ the O2 relay is the rear relay, on a friend on mines it’s #3!

The Jeep Renix Manuel state Low Voltage is Rich and so does the Snap On Jeep Reference Manuel. This is what I’m seeing on the 2500, DMM & wide band! The thing is running rich, that’s my story and I’m sticking to it!

I spent some time looking at the wiring diagram and noticed there are 2 grounds that are available at the diagnostic connector. One is the sensor ground on the left side of the motor, the other is the ECU ground on the right side. I found the Sensor Ground at the Diagnostic plug to be less than 1 ohm. The EPU Ground is 2.5 when tested at the plug. My next step is to improve the ECU Ground.

I have screen shoots and MAT/CTS information but that will have to wait till after my nap.

Wow, have a good Nap, LOL. Wish I could take one...Did that "Jeep Cherokee Manuel" cover 91-96? As they use an entirely different sensor, voltage, etc....Or are they all just Renix?

Since your wide band says it is rich, I agree, you have independent data so it must be right, must be rich, and open loop should be rich, unless it is fuel starved.

 

[GSequoia]

Are you at sea level?

No.

I'm sitting at about 163 ft. ASL. :wierd:

 

[GSequoia]

On my XJ the O2 relay is the rear relay, on a friend on mines it’s #3!

The relay center can be inconsistent. If you notice all four of them simply snap together and they can be reordered. To make matters worse the AC clutch relay (if I recall) is not in the same loom as the rest and can easily be put on either side of the other three (assuming you have factory AC, if you do not then you only have a total of three relays).

Another tricky part of Renix is the cam sensor, it can be clocked in two different locations and I've seen a mixed bag on where it is per Jeep, I've never really taken the time to figure ut the pattern yet.

 

[kcjeep6]

Well bummer, I checked both grounds from the ECU to the battery and they are both less than 0.5 ohms. I will continue to check the wiring from the ECU to sensors this week. I still have the C116 connector, I have considered soldering it and may get it done this week. I have pulled the O2 wiring out of the loom, it looks good a the way back to C116.

The MAT/CTS both look good I warmed the motor till the CTS read 191F and the MAT was read 145F with a 78F ambient.

Just installed a new Fuel Pressure Regulator today, because I had one on the shelf. The fuel pressure is 31.5/39; it’s the same with the new FPR.

Yea the sync in the distributor thru me for a loop for a minute trying to remember which way to index it, I’m getting old!

If I can’t find an issue with the wiring this week I may throw in my set of stock injectors just for S&G’s.

Why can’t I post pictures?

 

[Ecomike]

Go to user control panel, then networking, them album, post the picture there, then link using the insert image tool (yellow looks like a mountain) in the post tool work area, or wrap the url with:

<img src="--------"> where ----- is the http address of the image

 

[Crashsector]

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.

This is 100% the exact same behavior I had with a bad EGR valve. The computer was trimming fuel as if it was closed, but it was really open, making a big vacuum leak under power and backfiring on throttle. It would be worth looking at.

--Andy

PS My Thread: http://www.naxja.org/forum/showthread.php?t=1077659

It starts in open loop, tries to switch over to closed, stumbles, then goes back to open. It does this maybe 2-3 times in two minutes after it starts, then it goes back to open for the rest of the trip.

 

[cruiser54]

Interesting, as you can't SEE the EGR valve leaking. Best to remove it and check if the pintle is fully seating.

 

[kcjeep6]

Here’s an update although I have not corrected the issue yet. I rechecked all my wiring and it OK.

I took the XJ to a friend that is an excellent diagnostic mechanic and has a professional shop at his house (3 lifts & all the goodies). I don’t have a vacuum leak, we hooked his Snap-On Smoke Machine up to the intake manifold and header, we could not find any leaks. I did find I have a hole in the rubber tube between the TB and FAIK, bummer!

We were checking the O2 heater voltage and found that there is no voltage at the O2 sensor with the key on, but I do have voltage when cranking and running. I was studied the Jeep Renix Manuel and noticed that on page 76 under "Modes of Operation, Key ON Mode" that the O2 heater should have voltage. I this what the rest of you have seen? I am starting to believe both of my ECU’s are defective, although the odds of having 2 ECU’s with the same defect is high.

So to recap; It is running rich and the ECU cannot lean it out. The O2 sensor never shows lean or more than 1.5 volts once the motor is started. I have no O2 heater voltage with key but have voltage in crank and run.

 

[old_man]

IIRC there is a relay for the O2 voltage.

 

[Ecomike]

Here’s an update although I have not corrected the issue yet. I rechecked all my wiring and it OK.

I took the XJ to a friend that is an excellent diagnostic mechanic and has a professional shop at his house (3 lifts & all the goodies). I don’t have a vacuum leak, we hooked his Snap-On Smoke Machine up to the intake manifold and header, we could not find any leaks. I did find I have a hole in the rubber tube between the TB and FAIK, bummer!

We were checking the O2 heater voltage and found that there is no voltage at the O2 sensor with the key on, but I do have voltage when cranking and running. I was studied the Jeep Renix Manuel and noticed that on page 76 under "Modes of Operation, Key ON Mode" that the O2 heater should have voltage. I this what the rest of you have seen? I am starting to believe both of my ECU’s are defective, although the odds of having 2 ECU’s with the same defect is high.

So to recap; It is running rich and the ECU cannot lean it out. The O2 sensor never shows lean or more than 1.5 volts once the motor is started. I have no O2 heater voltage with key but have voltage in crank and run.

Sounds like it is getting too much fuel, fuel source that the ECU can not control, leaking or sticking fuel injectors?

The 89 Renix seems to have a different O2 sensor heater voltage design than the 87.

The 87 is hot to the O2 sensor in run with the engine off, but I also know that after a few minutes in run with engine off, the ECU shuts down power to the sensors!!!!

The 89 does not feed power to the O2 sensor heater in run with the engine off. This was recently verified in another thread here.

Have you tested the O2 sensor, to verify that it is good, since it never (??) reads lean? There is a test using propane IIRC, and O2, welding gas?

What is FAIK?

 

[Ecomike]

IIRC there is a relay for the O2 voltage.

Yes there is.

 

[GSequoia]

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?

 

[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?

I think he has beat the electrical end to death, I think he is down to a vacuum or exhaust leak, or fuel injector issue, dirty injectors, poor atomization, sticking open......or something odd with the O2 sensors he bought?

It sounded like he found MAP sensor vacuum line leak at the throttle body on his last post? Which if true, might solve the entire problem?