3.2 engine harness - engine drop?
 

I aim to post a thread on this unexpected project resulting from my f!$&#!g mistake tomorrow. Tonight I’m searching for info. Found a lot but not clear on: is it required to drop the engine to replace the engine wiring harness?

I suspect yes but hope not.
Thanks for any heads up on experince others have had.

It might be easier to remove the engine but definitely not necessary
You'll have to remove the alternator and work around the intake
You'll also have to get the starter wires and reverse lights from underneath
A big pain in the butt but definitely doable

Thanks for the reply. I'm hoping it can be done (by me) without engine drop.
Then I read this while searching/reading - a wareaglescott thread, quoted from a 14Dec2018 post by timmy2 "Engine and transmission out, and everything comes out the back."
I though my fuel line replacement of 2018 was a challenge (...but then with this forum, Len/BoxsterGT lines and advice it got done). Not confident on electrical as impending post to demo why...

do the engine drop, you'll be happier. If you are good with it, you can drop it in 2 hours.

No need. If you need room, just drop the rear down about 3-4” just make sure you unhook the shift coupler. The intake isn’t that difficult to remove either. You probably need to replace the intake gaskets anyways if you have never done it.

Following up on this old post. It appears I've fried some of the harness on the left side of the engine from shorting the O2 heater wire and ground wire... It seems I need to remove the harness and fix some damaged wires. This post is helpful but I'm wondering if there any more specific tutorials on how to do this?

Thanks in advance.

What year is your car? On my 1984, it looks like the O2 sensor goes into the body DME harness.

If this happened to me I’d have to pull the harness from the engine bay to underneath the driver seat…repair and then reinstall.

no need to drop the engine, remove the intake and its all there. replace intake gaskets and new spacers at the same time and you're good to go

Thanks very much to both of you. Mine is a 1984. So pulling the intake will give me access. I’m hoping enough to inspect and repair the harness. I’ve heard pulling it through the tunnel is hard.

I’ve seen a couple of images of motors where it seems there is a connection between the engine harness and the main wire that connects to the DME and relay. Is that later (or earlier) model cars?

Have you done this? Any tricks to make this a bit easier?

This

I can drop mine really far down without removing, but I have no heat or AC to deal with.

I have not pulled that harness from the car.

However, as I do have the engine out of the car right now, I made you this video:

https://youtube.com/shorts/DLIs2S2ncAM?si=DX4XWol_uPw7s5pp

If I were in your shoes, I’d check the continuity of all the DME wires from the engine bay to the DME connector.

If only a few were bad, I’d think hard about running separate new lines just for the bad wires from the engine bay connection points and then splice them in right at the DME connector.

Thank you VERY much for this and agree. My thinking of my process is:
- Undo the harness connections on the left side of the motor to see how much access I have to inspect.
- Try to access the bracket/clip holding the harness in the front of the motor to help give me a bit more harness length to inspect and test. What else can I do here to get more room on the left side? Maybe remove the fuel filter and lines right here? Remove the Intake (ugh).
- Try to replace/ repair bad wires
- Test continuity from each sensor to the relay and DME.
- Determine if the harness needs to be removed.
- Replace (at least) the O2 Harness
- Replace any other sensor wires independently, as needed.

Other considerations?

My thoughts:

1. Disconnect all wires on the DME harness from their various connection points in the engine bay, this will include the injector control, O2 sensor, etc, etc. See this link for a list of everything that the DME harness connects with that you will need to disconnect.
2. Disconnect the harness connector from the DME....now all wires are disconnected at both ends...hopefully this only took an hour or two to get to this point
3. For each wire...
3a. Check that it has continuity from the front of the harness to the back using a separate wire you run from front to back outside the car just for the purpose of testing continuity. For example, let's say you pick the first wire (let's call it wire A) in the harness to test. Connect a test wire to the end of wire A where it terminates in the engine bay. Run that test wire back to the DME (run the wire outside the car, just laying on the ground) and then connect a small battery and light to both the end of the test wire and the end of Wire A where it terminates in the DME connector. Does it have continuity? Yes? Great, keep testing...
3b. With the test wire still connected to Wire A in the engine bay, test all the other wires in the DME harness for continuity to wire A. Do any of them have continuity to Wire A? No? Great, keep testing
3c. With the test wire still connected to Wire A in the engine bay, check to see if Wire A has continuity to Ground. No continuity to Ground? Great... Now connect the test wire Wire B in the engine bay and run tests A B and C again.

With this process you will check that each wire has continuity and is not leaking current to any of the other wires in the harness or to ground.

If you only find that 2 or 3 wires are fried and all of the others are fine then without removing the existing harness, run new wires along the same path of the existing harness and splice the new wires into the harness at the DME end and splice them into their connectors/connection points in the engine bay. This is just a temporary fix to get things going. It might work very well.

In any case, I'd start looking now for a DME harness. Make a WTB post in the Pelican 911 parts for sale forum, and start looking on eBay. Maybe give LA Dismantlers a call.

Are you planning an engine out service soon? That would be the ideal time to replace the harness.

I'll do this. Thanks very much.

Was hoping not a soon engine out service....famous last words.

A good voltmeter will check for continuity without the need for a battery. The 'outside' wire is still needed for the continuity check. Better electricians than myself tried to explain using ohms for the same check without the extra wire. Above my pay grade though.

For continuity, I wouldn't use a voltmeter but an ohmmeter. Preferably with the car battery disconnected. With an ohmmeter you can still use an extra wire to extend one of the ohmmeter leads, as the two of them are too short to test continuity between both ends of the engine harness that runs from engine compartment to driver seat and beyond. Also you should "calibrate" measurements by excluding the extension wire resistance and the probes resistance. They may well add up to 1 ohm. So a continuity test reporting up to 2 ohms from one end of the harness to the other end is presumably a pass.

One way of not using an extension wire for the continuity test with an ohmmeter is to short two of the wires to test at one end and measure/test resistance at the other ends of these two wires. This time you are measuring forward and return circuits, that is twice the resistance that is expected for one wire. Once the two wires test good, you can test them against ground to ensure no leak to ground and against another wire, or another pair of wires, to ensure no leak to these wires.
Sorry for the confusing explanation, English ain't my mother thong. :p

With an ohmmeter, you should always test / take measurements with no external power source interfering with the circuit tested. In automotive, that means disconnect the battery ground or even both terminals.

An update. I’m using a continuity tester from Milwaukee. It beeps.

I spent the day preparing to test the different harness sensor leads against the DME connector and Relay connector. As described above. I quickly learned that the O2 heater wire to ground wire short was pretty bad as it’s in the same sheath as the two wires going to the coil. It melted those which caused them to short to each other. Lots of current in those and took the other three wires that go (fortunately) to an unused connection in the rear fuse box. So, I was able to remove and then cut those 8 wires (3 for the O2 sensor, 3 for the unused connection, 2 for the Coil). I stripped the grey sheath back under the car where the bad harness integrated. The wires look ok but now I’ll test the rest of the wires for the sensors. If I’m lucky the wires will be ok and I can have a harness made to replace the O2, Coil, Connector section.http://forums.pelicanparts.com/uploa...1712361648.jpg
http://forums.pelicanparts.com/uploa...1712361648.jpg

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

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.

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.

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.

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. http://forums.pelicanparts.com/uploa...1712436286.jpg
http://forums.pelicanparts.com/uploa...1712436286.jpg

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.

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 http://forums.pelicanparts.com/porsche-911-technical-forum/1144744-car-slipped-off-jack-stand-3.html#post12170264


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.

http://forums.pelicanparts.com/uploa...1712449556.jpg


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.

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.

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...

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.

http://forums.pelicanparts.com/uploa...1712510055.jpg
Meanwhile this may help

http://forums.pelicanparts.com/uploa...1712510236.jpgthe other page

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.

http://forums.pelicanparts.com/uploa...1712513043.jpg

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.

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.

http://forums.pelicanparts.com/uploa...1712519553.jpg

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.

[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.

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.