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Solved AFR Mystery

Prefix for threads that contain problems that have been resolved, and there is an answer within the thread.

2000StreetRod

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Joined
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City, State
Greenville, SC
Year, Model & Trim Level
00 Sport FI, 03 Ltd V8
Problem:
Wideband Air/Fuel Ratio (AFR) meter displays >16:1 for Bank 2 (driver side) after M90 kit installation.

Background:
Prior to M90 installation AutoMeter 5978 Wideband Air/Fuel Ratio Monitor kit installed in Sept, 2009 worked fine. After installation of M90, vacuum/boost and custom tune (vehicle wasn't started for about 5 months during installation) and custom tune, the meter counts down for 20 seconds allowing for wideband sensor to heat and then displays maximum ratio of 16:1.

Troubleshooting
1.Tested all meter associated wiring for power, ground, opens and shorts to other wires.

2.Purchased new wideband O2 sensor and sensor connector to meter wiring harness. Replaced sensor.

3.Purchased new AutoMeter 5978 Wideband Air/Fuel Ratio Monitor kit and replaced meter in Bank2.

4.Removed old Bank2 wiring harness. Installed new meter kit in Bank1 and old meter with new wiring harness in Bank2 with common wiring except for O2 sensors. Bank1 worked normal, Bank2 same 16:1 display.

5.Swapped Bank1 and Bank2 meters - no change.

6.Logged STFTs with adaptive learning disabled. For cold start (ECT=64 deg F) Bank1 STFT begins cycling as soon as PCM switches from open to closed loop (10 seconds after engine start). Bank2 STFT switches to 0.70 (lean) at idle.

7.Reloaded PCM and logged STFTs with adaptive learning enabled. For cold start (ECT=74 deg F) Bank1 STFT begins cycling as soon as PCM switches from open to closed loop (10 seconds after engine start). Bank2 STFT switches to 0.70 at idle. At 3 minutes LTFT Bank2 starts increasing until it reaches 1.13. STFT Bank2 remains 0.70 until 4 minutes. During the first 4 minutes logged Fuel Pulsewidth in Clock Tics Bank2 are 1.6 times Fuel Pulsewidth in Clock Tics Bank1 - the opposite of what I expected. After 4 minutes (ECT=122 deg F) STFT Bank2 begins changing at a very slow rate and Bank1 and Bank2 pulse widths become comparable. At 5 minutes STFT Bank2 reverts to 0.70. At 7.6 minutes (ECT=146 deg F) increasing engine speed from idle to 1500 rpms had no effect on STFT Bank2. At 8 min engine speed was pulsed from 1500 to 2500 to 1200 rpms (PCM still in closed loop) causing LTFT Bank2 to change from 1.13 to 1.0 and STFT Bank2 to begin cycling and was identical to STFT Bank1 until the end of the log. Several throttle blips were performed causing wideband Bank1 meter to display AFRs as low as 10.5:1 but wideband Bank2 meter never read below 16:1.

8.Loaded latest tune into PCM, regapped cylinder 6 spark plug from 0.044" to 0.030" but did not connect plug wire. Started engine, waited for idle speed to stabilize and then connected plug wire. There was no audible detectable change in engine speed or stability. Repeated several times with same result. Spark detected on plug wire using timing light. Removed plug and performed compression test - 190 psi on warm engine. Installed new plug gapped to .030" - connecting and disconnecting plug wire makes no idle difference.

9. Attempted to listen to cylinder 6 injector using mechanic stethoscope but couldn't access the injector directly.

Plan
1.Disable IACV so cylinder not firing impact can be easily detected and then test each cylinder by disconnecting/reconnecting plug wires as plugs as regapped.
2.Remove wideband Bank2 O2 sensor and check for an obstruction in downpipe at bung.
3.Swap Bank1 and Bank2 wideband O2 sensors.
4.Hope for ideas from forum members.
 



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EGR & IAC valves

1. For the possibility that EGR was being enabled at idle I disconnected the vacuum hose from the EGR valve and plugged it. I also capped the vacuum port on the EGR valve although that was unnecessary. There was no change in the idle AFR after engine start.

2. I disconnected the electrical connector from the IAC valve and adjusted the throttle cable length until the engine idled slowly a couple minutes after engine start. Then I checked for idle speed change while disconnecting and reconnecting the cylinder 6 spark plug wire. I still could not detect a change in idle speed by listening. The results were the same for cylinders 4 and 5. Compression on cylinder 5 with a cool engine was 170 psi and on cylinder 4 (a little warmer engine) was 180 psi. I checked compression on cylinder 5 about two months ago (engine cold) and the pressure was 165 psi.

3. I removed the Bank2 wideband O2 sensor and made sure nothing was plugging the internal end of the bung. I reinstalled my original O2 sensor that worked fine before the M90 installation. No change in AFR at idle.

I know I have spark to plugs 4, 5 and 6 because my timing light fires when connected to each plug wire. I also got shocked when disconnecting/reconnecting the plug wires even though I was wearing a thick, plastic glove approved for working with acidic chemicals. I'm wondering if the injectors are spraying. I had to modify all of the injector wires when reworking the engine wiring harness. I also replaced the easily broken stock connectors with an aftermarket, improved connector that has a retaining metal clip. I guess the next step is to perform PCM connector to injector connector continuity tests. I suspect it will be difficult to access the injector connectors.
 






running on 3 injectors

I realized that I could disconnect the PCM power relay which powers the injectors (among many other things) and measure the resistance between the PCM power relay socket and the PCM connector pins. The resistance for injectors 1, 2, and 3 was 13.1 or 13.3 ohms and the resistance for injectors 4, 5, and 6 was infinity. Obviously, there is an electrical problem. It's unlikely that I failed to wire all three wires from injectors 4, 5, and 6 to the PCM so I probably failed to wire them to the power source. I checked the other nine PCM pins that are connected to components powered by the PCM power relay (IACV, O2 sensors, PCM, EVAP canister purge valve, fuel pump relay solenoid) and the resistances were all reasonable. I thought about just running a jumper from the IACV to injector 4 but was concerned that the injectors may be misconnected to something else so I decided to trace their wiring. Unfortunately, to do that I need to remove the EGR tube, EGR vacuum regulator, coilpack and the looms between the IACV and the firewall.

When I finally get the Bank2 injectors working I'll have to start back at the beginning of the custom tune process. I'm anxious to feel the power difference of six vs three functional injectors.
 






Vpwr

Oh.. VPWR missing on the one bank. This is going to be interesting. I love this kind of diagnosis stuff. During all this testing with finding OL from the PCM power relay to the injectors did you check for voltage at the injectors too?
Just wondering. Once I helped a student out with a RX7 that broke up at 4500 rpm. He told me he bought the vehicle that way and the previous owner said he did something to the vehicle to make it slower so his son would not get any tickets. Turns out it was bull. We found a connector at the Injector resistor(not used on explorers) that had just got bent over. It was one of the two power wires to the two secondary injectors that came on at 4500 rpms so only one was working. That made the one rotor run lean after 4500. We straightened it out and all was good to 8500 or so. I am sure his parents didn't appreciate me helping him fix that one.
I hope you find your open circuit quickly. That thing is going to come alive when the other three cylinders start working.
 






checking the voltage

I haven't checked voltage to the injectors yet. The continuity test was easy to perform. Now that I've pulled enough things for access I can check for power. I guess there's a possibility they had power but the only other +12 volt source in the wiring harness is the keep alive supply and I never cut that yellow wire or spliced anything to it.
 






Isolated injectors

After removing the coilpack I was able open the main loom enough to access the wiring for injectors 4, 5 and 6. As I suspected the control wires from the injectors to the PCM are present. However, the power source injector leads are all wired together but not to the source.
Bank2Injectors.jpg

I think I originally had planned to splice the IACV source to the injectors but the IACV was one of the last things wired because I hadn't selected a box for it. I must have just forgotten. The plugs don't look heat damaged from running lean but I only have about 200 miles on them. I've been careful not to exceed 5 psi of boost and have avoided high engine speeds at WOT. Burning premium fuel and the knock sensor retard seems to have prevented detonation. Today I spliced the IACV source wire to the common injector source wire and started redressing the wiring harness. I'll try the resistance test tomorrow but won't bother with a 12 volt test. I should be ready for an engine start Monday using the original tune calibrated for six functional injectors. I'm anxious to see what my wideband meter reads.
 






Vpwr

That sounds like something I would do. lol.
Just wait till you got all 6 of them cylinders and the boost from the supercharger. Going to feel like a jet plane!
 






Bank2 O2 sensor fault?

As I mentioned in item 7 of my first post at 8 minutes the STFT for Bank2 began cycling at normal range even though my AFR meter still indicated an AFR greater than 16:1 and that Bank2 STFTs were exactly equal to Bank1 STFTs. I suspect that the PCM determined that the Bank2 O2 narrowband sensor had failed and used the Bank1 sensor for both banks. Since my instrument cluster is not installed I couldn't see if there was a CEL. I'll check for any DTCs before loading another tune.
 






O2

That makes perfect sense. It thought that the one sensor failed so it went into "closed loop fault" where it was using one O2 sensor for both banks. That should have caused a code at the time and an illuminated the check engine light.
Is your instrument cluster all back in now?
 






smoking

I realized that any stored DTCs would be cleared since I disconnected the battery ground terminal to work on the wiring. I repeated the resistance tests for the Bank2 injectors and all were less than .6 ohms different from Bank1 injectors. After tightening the valve cover bolts I put everything back together under the hood, adjusted the throttle linkage and cranked the starter. The engine fired but then stalled. I tried it again and it started and ran at a fast idle and steady. Since the instrument cluster is still not installed the engine was running on the battery so I had to manually start the AFR meter O2 heaters countdown. After anxiously waiting for the 20 second countdown the meters for both banks displayed cycling AFRs of normal range. The exhaust note was noticeably different with six cylinders firing instead of three. After about two or three minutes I thought the engine had caught fire or was running excessively rich because smoke was filling up the garage. I immediately shut the engine off and then realized that the driver side exhaust has never been hot since I started the M90 installation because the cylinders weren't firing. Oil that had leaked from the valve cover onto the downpipe was causing all of the smoke.

While in Boone, NC on vacation for a few days I purchased from Michaels a small spool of 49 strand bead stringing wire and some crimps. Tonight I plan to restring my PRNDL indicator for the instrument cluster which I will install tomorrow. After that I'll gap the Bank1 spark plugs to 0.030" like I just did on Bank2. I'm not going to repeat the no load step test until I get the wiring done for the AFR meter analog channels so I can datalog the values. After the step test I'll install the seats and center console with the added A/C compressor defeat switch. I have pulled all of the wires to the A pillar for the oil pressure gauge but still have to install the connectors, pod and gauges. However, that is not required for driving or datalogging. My first trip may be to take Sidney (my parrot) to the vet for his past due beak, nails and wing trimming. Yes, I'll take a photo of him in my Sport and post it.
 






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