Techno Duck

Did 928 Motorsports ever finish the 951 engine harness replacement? They started making one for the early 944 a few years ago.

I am really surprised LR hasnt come up with something, i mean they are like 1/3 of the way there with the replacement harness legs!

Before i parted my engine out i was in contact with a local-ish guy that was rebuilding engine harnesses for w124 series Mercedes which suffer from the same issues as our cars, aging harnesses. It uses all the same types of connectors so it wouldnt have been too difficult for him. Ultimately i decided to goto the darkside though. The only thing that would really stop me from doing it myself is simply the cost of purchasing enough wire to complete it. I mean one could probably do the entire thing with red and black wire, but sort of makes future troubleshooting difficult!

User 52121

Yeah looks like their website still says the 951 harness is "in development".

I acquired all the connectors and pins. Just need to get the wire. 20' spools of "automotive grade" wiring (high temp) seem to run about $20. I'm thinking I can get by with 10 color combinations... so $200 in wire. The connectors were a bitch to source, and assembling is pretty tedious though. If 928 sells them for $600 then IMO that's a steal.

PF

Hi.

Has anyone bought a new engine harness and/or ground cable set from Porsche?

Is it just a price decider? I mean that must be the best harness if one needs to replace it!

Maybe I will end up this route when we are done searching for faults on my Turbo cup.

//Peder

blown 944

I went through everything else prior to figuring it out. I posted about it years ago. It was misfiring if the headlights were on, but not during day driving. It happened after an engine install iirc. It's been awhile. I looked closely at the routing of the Sr wires and found one to be wrapped around the alternator cable. Pulled it all out, re routed and all was good.

It was a pain to find. Especially since I was trying to figure it out at night and on the weekends.

Not sure about the kick back. I don't remember that.

User 52121

I don't know if they're even still available?

I'd just buy the battery wiring kit from Robby. Nice quality stuff.

User 52121

Hmmm. Will do a search now.

Found it: https://rennlist.com/forums/944-turb...e-fixed-2.html

I suppose I can try running new ref sensor wires, and just make sure they stay far away from the power leads - though yours were also pretty crusty. Mine are in decent shape. Still, it's easy enough.

I'll try some of the other stuff first (measure for AC current, voltage drops, I'll also try disconnecting the alt and running it to see if it goes away) but will put this in the 'ol back pocket.

Tom M'Guinn

Sunset quoted me about $2500 for a new engine harness...

Dwane

Not to derail....who's Robby?

PF

I checked with my local PC and it seems they still are. I will look into that "Robby kit" if its needed.

Thats alot of money but in the big picture cheap since you can then trust you have good wiring and hopefully dont have to spend countless hours searching for weird fualts and spending money on parts that are ok.

Thanks
//Peder

Droops83

Once you get the engine hot and acting up, check voltage at terminal 15 (positive wire) on the ignition coil. This voltage comes from the ignition switch, but through the electronics box. My hunch is that you'll find a low voltage reading at the coil and will need to trace the circuit backwards till you find the source of the voltage drop; the real tip-off is the fact that the problem is worse with the headlights on.

It is unlikely to be the ignition switch itself, as the switched KL15 power that goes to terminal 86 of the DME relay (and then to the DME, to which your logger is connected) comes from the same part of the ignition switch. However, there are a number of connections within the E-box between the ignition switch and terminal 15 on the coil . . . .

As for A/C voltage, one of the main functions of an alternator is to rectify alternating current into direct current to be able to operate a vehicle's DC electrical system and charge the battery. Each of the stator windings of the alternator are connected to at least one pair of diodes that are reverse biased to each other. They are arranged in such a way that only positive DC current is passed to the battery (this arrangement is shown in the factory 944 wiring diagram, and should be the same or similar in the Nissan alternator).

The positive diodes that do the blocking of the negative current are subjected to a lot of heat and are mounted in a heat sink. They live a hard life and can sometimes fail, and one of the failure modes is the passage of AC voltage into the system, which can cause odd electrical issues. Inadequate cooling is often what kills diodes and other parts, hence the cooling duct on the factory alternator. I would expect that you would be having other electrical/charging issues if this were the case, but it is so damn easy to check that you should do it (set your voltmeter to AC, connect the positive lead to the B+ connection on the back of the alternator and the negative lead to the alternator case; there shouldn't be any AC voltage).

I am less suspicious of a ground issue, as experience has shown that bad grounds on a 944 usually cause several issues at once rather than an odd misfire. Still, it is always worth it to check the grounds for voltage drops and clean the connections . . . .

Good luck.

User 52121

Well... have an update, nothing good yet...

Had my dad stop over last night to be a 2nd set of eyes (he was a GM Tech for a long time before going to work for a manufacturer). Started the car (cold), .2v of voltage drop between alternator and battery. .02v of AC current, at best (though it moved around a lot... I think it's small enough to call it zero).

We hopped in and went for a ride to get it hot. Wound it up twice to start generating heat and get it to misfire (was already dark outside). Saw a set of cherries approaching behind me after the 2nd romp, wasn't sure if they were for me or not (*grin*) but dove onto the expressway to put a little distance just in case. 2 miles down the road on the expressway: car died.

Tach still read RPM.. but car was dead. Coasted to a stop on the shoulder. Car wouldn't restart. Didn't have any real tools with me so pulled the coil wire, stuck a key down in it and laid it next to the cam tower: no spark. Called tow truck, 2 hours and $140 later, got home. Brief investigation showed 12v at the coil, but no spark from the coil, and it didn't seem like the DME side was grounding. DME thinks everything is A-ok - I can smell the fuel from the injectors firing. Tach bounces when cranking.

Sometimes, a small problem has to fail into a bigger problem to be easier to find. Hopefully this is big enough now to find whatever the hell the issue is.

And Chris, your theory re: the coil wiring.... keep in mind, I ran FRESH wires to the coil. A straight, direct line to the battery, and a straight, direct line back to DME pin 1. (I have DME pins so I made a straight fresh line, no joints/soldering/splicing). Problem still existed. So I don't think the issue is with the coil wiring... but must be something related to it.

At any rate - it's going to be parked for at least a few days. Don't feel like futzing with it anymore. Have the last autocross of the season this weekend (which, now, for the 2nd event in a row, I will get to coordinate but not participate due to broken car - yay?), then maybe going to COTA for the Tudor races the weekend after... then maybe spend a few weekends doing nothing since driving season is about done anyways.

*sigh*

User 52121

Ok - thinking about this over lunch, I re-played a conversation in my head I had with my dad last night when he was poking around the wiring... he said, "You have the coil hooked up backwards." I didn't pay much attention to it - my understanding of a basic coil is that polarity doesn't matter. A friend of mine who was helping over the phone also DID suggest, "Is your coil backwards?" though I believe my response was, "It's a coil, it doesn't matter...."

Doing some additional, deeper research this morning... it may, in fact, matter for more extreme use cases (such as running a high performance engine hard). Normal operation might run fine but putting it under stress might no longer work so well. I also read that running a coil backwards may also actually kill a coil over time. (Some random internet searching said it might kill a coil in short order, actually...)

Dead car last night, no spark... could be a dead coil. I could have killed it running it backwards. Running it backwards could have been generating weak spark - causing a misfire under high heat and load.

One thing I'm not sure of yet (and will check when I get home): pretty sure the stock coil, the posts on the coil are different physical sizes, making it difficult to hook that up backwards. But I don't know if it's *impossible*.

I'll take a look when I get home. I'll yank the Blaster coil, put the stocker back in, paying close attention to the polarity. If the car STARTS, then that solves one mystery (dead car). If the misfire is still there, I may try stealing a coil from my buddy's car.

Hmmmmmmm......

User 52121

Old coil in, still a no-start.

So much for that theory.

mel_t_vin

Jim, have you examined the condition of the S/R sensor wires and connectors...on the harness side?

Pull the boots back, carefully, and have a peek.

Tom M'Guinn

Are you sure the polarity is right? The color of the wires is counter-intuitive. Which color wire do you have going to the positive coil terminal?