3.2 engine harness - engine drop?

[Johnr352]

Originally Posted by ErrorMargin

That looks bad, can you give us the detail on how this happened?

Hi, yes. I installed a new O2 sensor. The heater and ground wire connector shifted in the metal bracket and shorted. It sits in the same sheath as the Coil wires and so this melted too.

[Johnr352]

Originally Posted by pmax

Recommend dropping the drivetrain just a tad, don't have to go all the way just a couple inches and a little more would do, so you can access the harness and see it all.

I’ve made some progress but agree that dropping the motor a bit would make testing and then installing the new harness section (if I get lucky and show the rest intact) easier. How best do I drop the drivetrain an inch or two? Never done it.

[Johnr352]

While I’m at it. As I described, the O2 heater and ground shorted which in turn shorted the Coil wires. This was a hot mess for those five wires and three that are part of an unused (on my car) plug on the engine fuse box. Two questions: 1. Did I kill the Coil when the coil wires shorted? 2. Can anyone identify the plug’s use from my pictures? I can’t find it described but would like to replace the wires anyway.

[pmax]

Originally Posted by Johnr352

I’ve made some progress but agree that dropping the motor a bit would make testing and then installing the new harness section (if I get lucky and show the rest intact) easier. How best do I drop the drivetrain an inch or two? Never done it.

This is a good guide.
https://www.pelicanparts.com/techarticles/911_partial_engine_drop/911_partial_engine_drop.htm

Disconnect the shift coupler since that would lever up as the rear drops.

Support the engine with the jack, loosen the engine mount bolts. There will be no or little weight on them given the jack. You don't even have to remove the entire bolt to lower the engine a couple inches. Go slow, stop if any of the hoses e.g. breather, fuel lines on the driver side or harness at the connector in front of the engine, AMHIK about that connector, are at the end of their travel ...

Use blocks of wood, 4x4s are good, under the heat exchangers just in case, you can leave the engine sitting on them while you work.

[Johnr352]

Originally Posted by pmax

This is a good guide.
https://www.pelicanparts.com/techarticles/911_partial_engine_drop/911_partial_engine_drop.htm

Disconnect the shift coupler since that would lever up as the rear drops.

Support the engine with the jack, loosen the engine mount bolts. There will be no or little weight on them given the jack. You don't even have to remove the entire bolt to lower the engine a couple inches. Go slow, stop if any of the hoses e.g. breather, fuel lines on the driver side or harness at the connector in front of the engine are at the end of their travel ...

Use blocks of wood under the heat exchanger just in case.

Thanks VERY much.

[pmax]

Originally Posted by Johnr352

Thanks VERY much.

Stay safe ! I never get under there without the tires resting on something sturdy, 4x4s for example.
If you're new to jacking up the 911, read this thread Car slipped off the jack stand


The breather hoses are an easy disconnect so consider removing them at the oil filler tube, one less thing to worry about dislodging.

On the 3.2, watch out for the brake booster contraption as well, might wanna disconnect that, one of the sections being a $200+ item.




BTW have you removed the driver's seat yet and taken a look at the DME/relay end of the harness ?

Also inspect the fuse panel in front.

[911obgyn]

That plug is used to center the idle air contoller for adjusting idle and CO. Do you have a bently manual? Only 2 wires are used for that. Not sure where the other wires go.

[Johnr352]

Originally Posted by 911obgyn

That plug is used to center the idle air controller for adjusting idle and CO. Do you have a bently manual? Only 2 wires are used for that. Not sure where the other wires go.

Thanks for this, I learned, to your point, this is a test connector for setting the idle, etc. I think there are three wires to that test connector, and one is a ground. (The other wires I killed are the O2 sensor, O2 Heater, O2 Heater ground, Coil Green and Black)

(Good point on the Bently Manual. Ordered...

[Johnr352]

Originally Posted by pmax

Stay safe ! I never get under there without the tires resting on something sturdy, 4x4s for example.
If you're new to jacking up the 911, read this thread Car slipped off the jack stand


The breather hoses are an easy disconnect so consider removing them at the oil filler tube, one less thing to worry about dislodging.

On the 3.2, watch out for the brake booster contraption as well, might wanna disconnect that, one of the sections being a $200+ item.

BTW have you removed the driver's seat yet and taken a look at the DME/relay end of the harness ?

Also inspect the fuse panel in front.

Thanks! Not sure I know where the Brake booster contraption is... is it in your picture? I thought that was the breather hose you mentioned.

I did remove the driver's seat. I can see that the O2 heater wire burned almost to the relay. I haven't pulled apart to DME connector yet, but presume the O2 Heater ground wire is in there and also sad. Aside from the DME Relay Heater wire, I haven't figured out yet which pins are for the O2 sensor wire, O2 Heater ground wire, Coil Green wire and Coil Black wire, and Idle speed adjustment wires (white, Black/White), and idle speed adjustment ground (brown).

I'm presuming the DME Relay is dead. I'm hoping the DME itself is not. I'm unsure if the shorted Coil wires would kill the Coil and/ or damage the DME.

From what I can see, the front fuse box is ok. The impacted wires appear to be limited to the DME/ DME Relay.

[911obgyn]

Meanwhile this may help

[911obgyn]

the other page

[wazzz]

Can't find the other thread where you described what happened to your harness, but if I remember correctly you didn't start the engine. So you probably fried the DME relay, but the coil wires got cooked from being too close to the O2 sensor heater wire that shorted to ground. They didn't suffer from an electric issue, but only from high temp. So probably no harm to the coil and DME (ECU) itself. Hope so anyway.
If you know anybody with a 3.2, take your ECU and swap it in his car to check if it's still good.

[pmax]

Originally Posted by Johnr352

Thanks! Not sure I know where the Brake booster contraption is... is it in your picture? I thought that was the breather hose you mentioned.

Disconnect the hose if it looks like it will be strained, I borrowed that pic from another 84 ... the 87 onwards, same as mine, has a different booster setup shown in the previous pic I posted, sorry about that.

[pmax]

Originally Posted by Johnr352

I did remove the driver's seat. I can see that the O2 heater wire burned almost to the relay. I haven't pulled apart to DME connector yet, but presume the O2 Heater ground wire is in there and also sad. Aside from the DME Relay Heater wire, I haven't figured out yet which pins are for the O2 sensor wire, O2 Heater ground wire, Coil Green wire and Coil Black wire, and Idle speed adjustment wires (white, Black/White), and idle speed adjustment ground (brown).

I'm presuming the DME Relay is dead. I'm hoping the DME itself is not. I'm unsure if the shorted Coil wires would kill the Coil and/ or damage the DME.

From what I can see, the front fuse box is ok. The impacted wires appear to be limited to the DME/ DME Relay.

The short went thru the DME relay, power at 30 to 87b to the fuel pump, O2 sensor heating. Hopefully that and the ground wires bore the brunt of the current so the DME's unscathed.

The power to the coil comes from the fuse box. Have a close look at the black wire at the top of the fuse panel at 7 and 8, pic from my 87 your 84 might vary slightly. One of them goes to the coil, part of the 173 harness.

[Johnr352]

Originally Posted by wazzz

Can't find the other thread where you described what happened to your harness, but if I remember correctly you didn't start the engine. So you probably fried the DME relay, but the coil wires got cooked from being too close to the O2 sensor heater wire that shorted to ground. They didn't suffer from an electric issue, but only from high temp. So probably no harm to the coil and DME (ECU) itself. Hope so anyway.
If you know anybody with a 3.2, take your ECU and swap it in his car to check if it's still good.

Oh don’t I wish. No, I was driving down the road, came to a light and the motor died. Luckily, 200 feet from my house. Turns over, no start. Then discovered all of my wire damage.

[Johnr352]

[QUOTE=pmax;12228185]The short went thru the DME relay, power at 30 to 87b to the fuel pump, O2 sensor heating. Hopefully that and the ground wires bore the brunt of the current so the DME's unscathed.

The power to the coil comes from the fuse box. Have a close look at the black wire at the top of the fuse panel at 7 and 8, pic from my 87 your 84 might vary slightly. One of them goes to the coil.

Thanks for this. So the green wire to the coil goes to DME spot #1? And the black wire from the coil goes to the fuse box up front, as indicated in your picture (7 or 8)? Makes sense, but I’m a little confused on how the black wire gets from the coil to the front fuse box. Meaning only that, from what I can tell, all of the bad wires passed through the DME harness through the firewall. How/where does that black wire get to the front fuse box? Would tge short have blown that fuse? And, to your comment on the DME relay and 87b. Do those fuel pump wires go to the fuel pump relay or directly to the fuel pump? I might have to check/ replace something there too.

[pmax]

Originally Posted by Johnr352

Thanks for this. So the green wire to the coil goes to DME spot #1? And the black wire from the coil goes to the fuse box up front, as indicated in your picture (7 or 8)? Makes sense, but I’m a little confused on how the black wire gets from the coil to the front fuse box. Meaning only that, from what I can tell, all of the bad wires passed through the DME harness through the firewall. How/where does that black wire get to the front fuse box? Would tge short have blown that fuse? And, to your comment on the DME relay and 87b. Do those fuel pump wires go to the fuel pump relay or directly to the fuel pump? I might have to check/ replace something there too.

Have a close look at the pictures 911obgyn posted above, that's from the Bentley... so 87b to fuse #3 to fuse pump, one of the black wires at 7/8 goes to pin 86 of the DME relay, the other to the coil.

I assume you are opening up the harness from under the seat anyways. See if you can trace the wires and check for continuity etc. Post pics !

[Johnr352]

Originally Posted by pmax

Have a close look at the pictures 911obgyn posted above, that's from the Bentley... so 87b to fuse #3 to fuse pump, one of the black wires at 7/8 goes to pin 86 of the DME relay, the other to the coil.

I assume you are opening up the harness from under the seat anyways. See if you can trace the wires and check for continuity etc. Post pics !

I will! Thanks for this. Ordered Bentley too, feeling embarrassed that it took this long (well, frankly, for the whole mess). Be back soon with an update and pics.