New O2 sensor, and a strange burning smell

[NckT]

Apologies(it's early for me!). Of course you weren't talking about that harness; you were referring to the 4 pin white harness at the idle ECU. Duh. I checked that; yes, it's open across black/yellow and black/slate. One follow up question: is it possible that this would be due to anything other than the electrical harness at the thermister? I will of course go back in there if need be, I just want to see if protocol would call for any other diagnosis, before stripping down to go back to the thermister location. Thanks.

I live in the north of England so I'm in a different time zone. ..

As what Bitsyncmaster said, the wiring from the ecu goes to the church window shaped multi plugs that are located behind the ignition coil cover in the engine bay. Look for the black/yellow and black/skate (grey) wires on the bottom right multi plug connector that has 9 cables going to it and then put the multi meter problem on those wires (without taking the multi plug off). If you get a resistance reading then the wiring problem is from the multi plug to the engine. If not then it's likely to be at the thermistor itself.

I would recommend to do a continuity test of the wiring from the multi plug to the ecu first to confirm the integrity of these cables before re-stripping the inlet manifold off again.

Just one tip, I've only seen it on 2 cars where the wiring plug for the thermistor and frequency valve were put on in each others place, so if your frequency valve is operating then at least your connectors are on the correct way. Double check the wiring colours at the thermistor if you need to take the inlet manifold again based on your diagnosis.

Good luck with it

Ps, the 10k resistor is a temp fix. I've done this at tech events by making short make to female wires to extend the multi plug at the ecu to the ecu for the non thermistor cables, then used 2 female blade connectors on a 10k resistor and connected this direct to the pins of the ecu where the black/yellow and black/slate (grey) cables were to go, as at the event there wasn't time to step the engine down to fix the thermistor connection.

[rjd2]

thanks much-if I get a resistance reading of 0 ohms across black/yellow and black/slate at the white 9 pin connector next to the ignition coil, when the harness is seated, what does that tell me? Cause that's what I get.

I live in the north of England so I'm in a different time zone. ..

As what Bitsyncmaster said, the wiring from the ecu goes to the church window shaped multi plugs that are located behind the ignition coil cover in the engine bay. Look for the black/yellow and black/skate (grey) wires on the bottom right multi plug connector that has 9 cables going to it and then put the multi meter problem on those wires (without taking the multi plug off). If you get a resistance reading then the wiring problem is from the multi plug to the engine. If not then it's likely to be at the thermistor itself.

I would recommend to do a continuity test of the wiring from the multi plug to the ecu first to confirm the integrity of these cables before re-stripping the inlet manifold off again.

Just one tip, I've only seen it on 2 cars where the wiring plug for the thermistor and frequency valve were put on in each others place, so if your frequency valve is operating then at least your connectors are on the correct way. Double check the wiring colours at the thermistor if you need to take the inlet manifold again based on your diagnosis.

Good luck with it

Ps, the 10k resistor is a temp fix. I've done this at tech events by making short make to female wires to extend the multi plug at the ecu to the ecu for the non thermistor cables, then used 2 female blade connectors on a 10k resistor and connected this direct to the pins of the ecu where the black/yellow and black/slate (grey) cables were to go, as at the event there wasn't time to step the engine down to fix the thermistor connection.

[NckT]

In that case there could be a bad connection on the thermistor or bad wiring from the coil church window multi plug to the thermistor.

Shove in a 10k ohm resistor at the church window multi plug and see if the car now idles correct

[rjd2]

In that case there could be a bad connection on the thermistor or bad wiring from the coil church window multi plug to the thermistor.

Shove in a 10k ohm resistor at the church window multi plug and see if the car now idles correct

Thanks, NckT. so, to be clear, I want to jam a 10k resistor across the black/yellow and black/slate pins at the white church window harness, and keep that harness seated, right? is 1/4W a problem? I have about every resistor value known to man here, but they are all for audio electronics, so most are 1/4W or 1/2W 10k's.

[NckT]

Thanks, NckT. so, to be clear, I want to jam a 10k resistor across the black/yellow and black/slate pins at the white church window harness, and keep that harness seated, right? is 1/4W a problem? I have about every resistor value known to man here, but they are all for audio electronics, so most are 1/4W or 1/2W 10k's.

Yes that's what I mean. 1/2 w would be fine and probably easier because of the thickness of the resistor legs.

It'd be better if you could fit it between the black/yellow and black/slate (grey) called at the idle ecu. It's the same difference.

[rjd2]

Sorry, I somehow may have gotten a "misread" on my previous DVM reading. When I first checked that resistance reading, I got 0 ohms. I just went back to the white church harness at the bulkhead, unseated it, and reseated it, and took the readings again; this time I got 8.95k Ohms across black/yellow and black/slate pins.

[NckT]

You've probably had a bad electrical connection at the church window multi plugs then that's causing intermittent problems. Use electrical switch cleaner to clean the pins and be careful reconnecting the plug as sometimes the male pins can get pushed back if forced.

Recheck the resistance reading at the idle evu plug

Good luck

[Jonathan]

IMG_4536.jpg

This is approximately what the jumper being described to you is going to look like once installed. I did not get the 10-Ohm resistor part of the advice when I needed to do this, so you'll just see a short jumper wire in my set-up.

The jumper fools the ECU to think the thermistor signal is present and good to go and the other short wires basically connect the other connections in that white connector to also convince the ECU that they are plugged in normally. This didn't work perfectly for me (perhaps the lack of resistor?) but it did get me to the end of the driving season and then I had the justification I needed to tear into the valley for the first time in my ownership of the car. I had other projects to do in there but sorting out the bad thermistor connection was the main one.

Another test of course if you find your car idling more or less ok, is to disconnect that white plastic connector on the ECU and it should jump to exactly 2,500 RPM and sit there. It's sort of the fail position for that part of the idle system and a good way to narrow down where your problems are.

[rjd2]

Man, you guys are the best! THANKS SO MUCH! This community is a huge resource for a guy like me in Central Ohio. Kudos!

Ok, I will clean those harness pins(they are coated in a conductive grease; must have been from the previous owner, as I generally go for clean, dry metal to metal connections).

I will read at ECU and report back.

Also, I know it's not perfect, but I did manage to get some images of the temp sensor, and the thermister, using a GoPro camera taped to a stick. While not pretty, I would like you guys to take a look at it if you have a moment, just to possibly confirm what I'm seeing. As best I can tell, the harness at the thermister looks to be seated.

Ok, thanks again-will report back soon; here's the link to the video:

https://wetransfer.com/downloads/917...ecipient_email

[rjd2]

Alrighty, last post for the day, I'm gonna wrap this up and dig in tomorrow after this:

I thoroughly cleaned and reseated the white 9 pin bulkhead harness. Upon re-reading at the ECU, i got 18.7k Ohms across black/yellow and black/grey.

The car idles solidly at roughly 2300-ish RPMs. Hope this piece of data is relevant: if I unseat the white 4 pin harness at the ECU while its running, I get NO change in behavior of the idle. It sits bang on at 2300-ish; it did not even slightly nudge up or down when I unseated it.

So...does it look like I am revisiting the VoD?