Cold Start Up Loop Fault Lean Code on REM

[oleskool]

I have had this happen randomly twice in the past and now two days in a row.  29 degrees this morning and yesterday morning when I went to start the truck up.  It fires up but idles rough (sound wise) (RPM wise it is fine) and noticeably sounds like it is skipping a little when you rev the engine.  After a few minutes I get a Loop Fault code on the REM and this morning I got Injector 2 and 4 fault as well.  If I let it idle and warm up to roughly 150~ water temp and cycle the ignition it fires up normally and runs great the rest of the day.  It appears the O2 sensor is cycling properly from 0-5V depending on the condition but I will try to reverify this.  It also appears that the O2 heater circuit is working and is at 14V.  Is it possible for the heater inside the O2 to burn out and if so is there a quick way to test it?  Or would there be another issue I am missing here.  It appears the engine wants to go into closed loop but cannot or will not do so when its cold.  After it warms up or the outside temps increase to ~40 or 50F its fine.

 

Thanks for all the assistance!

[Gojira94]

Heater circuits do indeed burn out but I don't think that's going to be your problem. For an 89 3-wire sensor I want to say red and black are the heater and grey is the 0-5V signal. I think the 89 electrical manual is around here somewhere, but should be the same as 88 & 87 and I know I've seen those manuals here.

 

Cold weather and injector faults at cold start - not to send you down a rabbit hole, but it suggests to me a slim possibility of moisture in the fuel, especially if you're running any ethanol blend these days.

 

Not to rant (again) about wishing to see the contents of the factory Renix calibrations, but I'd like to see if there is a cold start enrichment and corresponding stall saver IAC routine in there. IAC, TPS closed throttle, and idle screw relationship can jerk that cold start routine around if they're out of sync.

 

The fact that your problem goes away when warm would suggest to me it's not sensors, since those would be out of the equation before closed loop. I have an IAC tester for the old GM pintle style IACs but you can test it manually with a lawn tractor battery and a couple 14 gauge wires. You can run the pintle off the gear with the GM IACs of old, not sure about our Renix system IACs. Wouldn't hurt to just pull it and clean it with electronics cleaner to be on the safe side, make sure it isn't trying to move and getting stuck from buildup that acts worse when cold.

[Ωhm]

8 hours ago, oleskool said:

After a few minutes I get a Loop Fault code on the REM

 

Sounds like stumble is ECUs attempt at Closed Loop (LP). Which Loop Fault code did you get?

• Loop Fault Rich:
  ECU Closed Loop Attempt failed, too rich to correct.
  Possibly too large injectors, other fuel system imbalance.
• Loop Fault Lean:
  ECU Closed Loop Attempt failed, too lean to correct.
  Possibly faulty o2 sensor, weak fuel pressure, other fuel system imbalance.
  – TIP: This code is more common during cold weather starts as the first Closed Loop attempt may fail due to the Cold Fuel Enrichment value still being too high. This code can be ignored if the 2nd closed loop attempt succeeds.

 

 

8 hours ago, oleskool said:

and this morning I got Injector 2 and 4 fault as well

 

This can be a PITA but INJ2 & INJ4 cavities on the ECU are C202_A3 & C202_A4. Check this connector, visual, make/break it.

 

 

[pizzaman09]

Sounds like my truck when I had a Bosch O2 sensor in it.  I swapped it out for a new NTK and no longer have the issue and my idle is much smoother.  My Bosch sensor was brand new, but it just didn't work well.  My REM code was lean.

[Gojira94]

I gotta get my rig running so I can quit talking and guessing about these problems and start enjoying them myself. 

[oleskool]

12 hours ago, pizzaman09 said:

Sounds like my truck when I had a Bosch O2 sensor in it.  I swapped it out for a new NTK and no longer have the issue and my idle is much smoother.  My Bosch sensor was brand new, but it just didn't work well.  My REM code was lean.

My fault code is lean as well as Injector #2 and #4 short to ground...  Couldn't tell you what O2 is in it, the truck sat for 10 years and I have not replaced it lol.  Seemed to be working fine up until now though.

 

The Injectors run this code until a let the truck warm up a bit ~ 100 degrees F water temp.  If I cycle the power no more codes .  I have not had time to check out the injectors themselves or the wiring.  I have checked the wiring grounds in the past and all were good but that does not mean they can't change.  Its almost like the injector short out inside and as they thermally grow it goes away lol.  I have seen this with other systems but I an not sure how our injectors work so it may not be possible.  

 

Any assistance on injector test besides manually swapping 2 and 4 with other locations to see if it follows them or stays with the wiring is greatly appreciated!

[oleskool]

Here’s what I get code wise. 
 

 

[oleskool]

Here is how the O2 responds after I shut it off and crank it up.
 

 

 

 

[Ωhm]

I wonder why Battery Voltage (VLT) is lower than O2 Heater Voltage (vHT)? Maybe just a REM thing, if so, good to know.

[oleskool]

2 hours ago, Ωhm said:

I wonder why Battery Voltage (VLT) is lower than O2 Heater Voltage (vHT)? Maybe just a REM thing, if so, good to know.

I was wondering the same. 

[oleskool]

I went through and re verified the ground circuit and cannot find any type of short in the wiring.  I measured off the FI harness, TPS harness, etc and no indication that a ground is bad.  I did look at the #4 and #2 injectors and noticed a little green corrosion on the plugs in the dielectric grease I applied when I swapped out injectors 2 years ago.  I cleaned all that out, used a contact file to polish the terminals down and reapplied dielectric grease.  I did use my voltmeter to probe around while the connectors were off and they all read the same as the #1 injector so.... I am not sure where to go from here lol.  It doesn't make sense that I have a short to ground on Inj 2 and 4 when it is 30 degrees out but not after it warms up a little unless the injector ground internally is shorted.  I believe these injectors are fired by grounding through the PCM.  After it warms up for a few minutes and you do a restart the truck runs like new again and continues to do so all day long repeatable.  

 

On a side note it was upper 40's this morning and it fired up perfect   Everything on the REM looks to be in spec, and the truck went into closed loop at around the 45 second mark which means the heater circuit and coils in the O2 are good.  I find it hard to believe that I have 2 injectors internally shorting ground when its cold but I have seen stranger things happen.  I will swap injectors if this happens again after my connector refresh and see if the code stays or follows them.  It sucks that I can only repeat this in the morning after the truck sits all night and is completely cold soaked lol and the temps need to be below freezing apparently which are few and far in between this time of year...  At least my fuel mileage is still between 16 - 20 mpg depending on how much stop and go traffic I end up in.

[Ωhm]

3 hours ago, oleskool said:

I believe these injectors are fired by grounding through the PCM

 Jeep (RENIX) are in the 5%'ers.

 

Waveforms Injectors pg_9.pdf

 

 

23 hours ago, Ωhm said:

I wonder why Battery Voltage (VLT) is lower than O2 Heater Voltage (vHT)? Maybe just a REM thing, if so, good to know.

 

Battery Voltage less than O2 Heater Voltage, I’ll bet has something to do with Reverse Battery Protection for the REM, if that even exist. Note the 0.7vdc (diode voltage drop) difference between the two readings.