402;406..........402;406

[C1RUN]

These are my O2 readings on my Scanmaster. Rinse and repeat 402;406. Millivolts do not change whether in neutral, drive, 800 RPM or 2500 RPM. Car has been down now for 8 months, have run through and replaced all "obvious" parts and pieces (and not so obvious) to try to get my O2 readings back in operation.

Have replaced O2 sensors 3 times using multiple manufacturers, different ECM, new CHIP, vacuum hoses and check valves, Exhaust Headers (original were FUBAR), TPS, stock to TR6 Ignition and several other sensors that have nothing to do with the O2 readings but needed to be replaced anyway.

Car starts and idles OK, but with the constant 402;406 readings car is running pig rich. In drive and any load put on the motor I'll get a backfire and instant stall, can barely pull the car out of the garage. Last ditch effort before requesting for assistance on this board was to hotwire new leads from the O2 sensor to PIN D7 on the ECM connector and to run a new ground from a grounded source to PIN D6...............nothing changed.

On a running car if you disconnect the O2 sensor the car will run 406mv as a default. Not sure where the 402 comes into play but the ECM is acting like it is not getting a signal from the oxygen sensor.

I'm tapping here, have run out of ideas and my other sources for technical info have come up short. Has anybody on this board heard of or experienced a similar condition? Will try any and all suggestions to fix this gremlin.

TIA

 

[turbocamino1]

Which MAF sensor?

 

[C1RUN]

LT1 with Translator. MAF was changed early on with no change in readings.

 

[Eric Stage I]

That really sounds like no O2 connection to the ECM. When you made your new leads, did you replace all the terminals also (the O2 connector, and the ECM terminal)?

 

[TType85]

Have you checked ALL grounds? The ones to the back of the head, the one to the head/turbo bracket?

 

[C1RUN]

That really sounds like no O2 connection to the ECM. When you made your new leads, did you replace all the terminals also (the O2 connector, and the ECM terminal)?

Got a set of new PINS from Caspers for the ECM connection (both O2 and Ground) and put on a new Weatherproof Connection at the O2 sensor.

 

[C1RUN]

Have you checked ALL grounds? The ones to the back of the head, the one to the head/turbo bracket?

Have not checked all the splices in the wire harness, but the ground connections at the back of the motor and the one at the turbo bracket have been removed, wire brushed and re-installed.

 

[Eric Stage I]

I would go through this diagnostic tree for the O2. I'm attaching a PDF. You can skip step one in the tree, since we know it will never go into closed loop with those O2 readings.

 

[C1RUN]

Thanks for the chart, will go through those to see if any of these tests will resolve my issue.

I ran some Data Logs just to confirm what the Scanmaster was telling me and you can see the first 4 Logs were from random previous scans over the years just to get a base. The last 7 were taken shortly after my issue started. Don't believe there's any additional information in these Logs that are not explained by a bad O2 reading but then again I'm not a tuner........

 

[C1RUN]

One more item just to confuse things, the car never threw a CODE 13. ESL was never introduced during this whole situation.

 

[Eric Stage I]

Code 13 is disabled in most chips these days, so that's why you didn't see it.

 

[C1RUN]

Code 13 is disabled in most chips these days, so that's why you didn't see it.

Finally had some time to spend with the car, ran the O2 diagnostic chart and found the following;

Step 1 - Open Loop
Step 2 - .39 volts (less than .2 preferred)
Step 3 - .40 volts (.3 to .6 preferred)
Result - Faulty ECM

So I changed to a different ECM (used) and found the following;

Step 1 - Open Loop
Step 2 - .38 volts
Step 3 - .39 volts
Result - Faulty ECM

So I picked up a spare ECM that had the same issue?

With the swapped ECM I did notice the Scanmaster readings were reading mostly 378 - 390 mv instead of the 402 - 406 from the other computer. And numbers did vary a little bit below 378 and above 390 from time to time....so it did change up a bit, but the end result is still stagnant O2 readings and car dies immediately under load.

Want to add that this all started last year after driving to a local Cruise. Car ran fine from the house up to the cruise-in. Parked the car, it sat for a couple hours, and when I went to leave the car would barely run.....and here we are today. Has to be a single point of failure somewhere in the system. Think I'm getting close only because I'm running out of things to change. Frustrating as hell!

 

[C1RUN]

So if I'm assuming the tests that I ran were to diagnose a Code 13 (that does not exist anymore) the final outcome of "faulty ECM" really does not apply. What it did determine is that the O2 is working as it should, but I still have a fault somewhere in the system that is causing an inaccurate reading across D6 and D7 in the ECM.

Are there any other sensors/fuses/relays that could be faulty that have a direct correlation to the O2 sensor readings within the ECM? I can't think of anything obvious, and not knowing how the internals of our computers function I am at a loss.

Only other suggestion that I have had was just to remove the old wiring harness and replace it with a new one, in that somewhere there is a ground that frayed loose or some other cable that got cut/shorted out causing this issue. Not a job I'd be happy to take on right now but will after all other options have been looked at.

Any other crazy ideas out there that may be causing a bad O2 reading?

 

[Eric Stage I]

Since you do have about .4 volts at the O2 connector, but it doesn't drop low (.200 or less) when grounded, I would look at the grounds. The O2 ground at D6 needs to be good (connected to the engine block with the other ECM grounds).
Also make sure the engine was running when you did the test.
You unplugged the O2 sensor, connected a wire to the connector (car side), and touched the other end where? And you read the result on the scanmaster?

If the O2 reading doesn't drop low (engine running), then there is an incomplete path to ground, or the ECM is bad (but unlikely since you tried a few).

 

[C1RUN]

Readings were taken from a digital voltmeter. I only mentioned the scanmaster readings to confirm that there was a change in mv to confirm the ECM was reading what the voltmeter saw. The O2 ground at D6 was taken from the battery ground up front, not from the engine block. Ran tests as stated with engine running then ignition on, engine off.

The O2 sensor reading was taken from the car side connector and the other end to the Alternator Bracket bolt at the engine block.

If a ground is at fault somewhere in the harness (all connection points have been accessed, removed, wire brushed and put back on) then it looks like it's time to replace the whole 39 year old wiring and connectors.........crap!

Thank you much for taking the time to hear me rant and throw some sound advice my way, I appreciate you, other misc V6 folks who have commented on other posts, all the racers at BG who gave up some suggestions and the Turbo Farm Crew who also burnt some brain cells trying to figure this out.

The SAGA continues, will post up results after swap has been made. May be awhile but I'll be back.

 

[Team Canada]

Readings were taken from a digital voltmeter. I only mentioned the scanmaster readings to confirm that there was a change in mv to confirm the ECM was reading what the voltmeter saw. The O2 ground at D6 was taken from the battery ground up front, not from the engine block. Ran tests as stated with engine running then ignition on, engine off.

The O2 sensor reading was taken from the car side connector and the other end to the Alternator Bracket bolt at the engine block.

If a ground is at fault somewhere in the harness (all connection points have been accessed, removed, wire brushed and put back on) then it looks like it's time to replace the whole 39 year old wiring and connectors.........crap!

Thank you much for taking the time to hear me rant and throw some sound advice my way, I appreciate you, other misc V6 folks who have commented on other posts, all the racers at BG who gave up some suggestions and the Turbo Farm Crew who also burnt some brain cells trying to figure this out.

The SAGA continues, will post up results after swap has been made. May be awhile but I'll be back

 

[Team Canada]

Just wondering how this turned out.....Did you find the cause?

 

[C1RUN]

Just wondering how this turned out.....Did you find the cause?

Several knowledgeable folks I have talked to believe it has to be a bad wire/wires somewhere in the wiring harness. Have the old harness disconnected and almost removed from the car. Once that is done swapping in the replacement shouldn't be that bad. May take some time to get to, weather needs to break a bit and get back down to normal before I can spend any measurable amount of time working on the car.

Will post up with results once I get the new Harness in and everything buttoned up.

 

[C1RUN]

Well its been a couple days, weeks, months since this last post and am happy to say the issue has been resolved. After the wire harness swap and many other updates to old sensors and equipment finally found a reliable source on the engine that was causing my issues. For the slim chance that I could have had a fuel delivery problem I replaced the pump, filter regulator and injectors. After that was completed I still had the same problem. Last resort was to replace the injector wiring harness (even though all the connections ohme'd out) before selling the anchor and letting it be somebody elses problem. During the process of installing the injector harness I found out that I could start the car, disconnect Cylinders 2-4-6 injectors and pull the plugs without the car hesitating. Injectors all had pulse and plug wires had plenty of spark. Had to be a timing issue of some sort. Replaced CAM and CRANK Sensor with no change to the motor. What's left?
I started rechecking everything that I had replaced already and ended up back at the TR6 Ignition set up. When the unit showed up at my door I was quick to replace it figuring I just wanted a good Base Spark to my plugs, not even thinking about all the other settings this module is capable of. Never thought twice about the install, figuring all the settings would have been at default for a standard set-up. Well I was wrong. Dip-Switch #4 was in the off position, set up for sequential spark. This should have been set to waste-spark mode for a standard GN type ignition system. So each cylinder would exhaust all the gas and then fire with nothing to combust in the chamber. I probably should have checked, but I didn't.....my bad. Set the Dip to on and the car fired right up on all 6.

Now this was not my initial problem as the no run started before I began replacing stuff. I'm pretty sure my initial problem was in the wiring harness by the looks of things, so when I replaced it I had fixed the original issue but created a new one by installing the TR6 set up before the harness was changed. It's a little embarrassing but can't say I'm pissed off about it, this made me change everything on that motor that should have been changed 10 years ago, just never had a reason to. I do hope that my stupidity may help somebody else in the future that may run into this so if you ever hear of someone who's car is only running on 3 cylinders tell them to check Dip-Switch #4 on the Baileys TR6 set-up!

 

[HotAirWH1]

Perseverance pays off !!!