tappaja

Hi guys,
I need advice how to replace engine harness. Is it necessary to remove engine to replace harness? My brother told me that there is no way to do it with engine sitting underhood? Is he right?
Thanks

dougbfresh

What harness? The main electical harness?? It would be VERY hard to replace it with the engine in, you would most likely have to disassemble large parts of the engine to get access.

BLOWNBLUEZ06

The heads and intake block the main harness in the back and it's made even more difficult by the air tubes running across the back.

tappaja

Oh sh*t,
seems that he is right. OK, will tell him that there is no way to replace it without engine removal. But I guess it will be better solution that to cut ECM connectors and attach it to old harness which is gamaged after accident. Don't want to have any electrical problems in the future based on soldering and patching "new" cables to old harness...
Thank you

runamuk

Removing the intake will get you access to the ground stud on the back of the left cylinder head and removing the right exhaust manifold will get you more than enough access to everything there.Sure the air tube runs behind the engine along with the harness but it's not like they are twisted together.

Why do you have to replace the harness?

tappaja

OK, maybe it's not too late
Will tell him about this possibility, I guess that intake must go anyway during engine removal from the top.

Harness must be changed because of accident when right wheel goes off and crushed everything behind.



Frame is repaired, just needs to be doublechecked if it's not bent. Alignment is OK but front right wheel is out of position about 20mm but this can be set by shims on upper front arm+lower arm I guess. But let see.

tappaja

What do you mean with AIR TUBE?

runamuk

Ouch, I guess that harness is beyond repair.

The air tube that deliver fresh air to the exhaust on cold start up. It runs from the air pump to the left cylinder head and crosses behind the engine to the right cylinder head.

lucky131969

ut oh...

keliente

Technically I think you could do it without removing the entire engine. If you could remove the alternator, disconnect the steering shaft, and maybe a couple other small things, you could back out the nuts that hold the cradle to the engine, and drop it down just a couple inches. Between that and removing the intake I believe you could change the engine harness without removing the whole thing from the car.

The problem is I think the engine harness/trans harness/etc is one giant thing. It's not like the engine harness just unclips behind the heads as a separate unit, it runs down the length of the torque tube and then plugs up to the rear end/trans sensors. It is also attached to the bellhousing via the top two bolts. But, lowering the engine a bit makes the bolts far easier to get to.

Here is what it looks like without the engine, so you can get an idea of how the harness runs.

dougbfresh

MAN, I can only guess what else got shorted when this happened-this WILL be an adventure no matter what way you go about it.

runamuk

The engine and transmission harness are not one gigantic harness, and why, if you don't know would you be telling this person he could lower his engine out of the way???

The engine harness starts at the PCM goes up over the frame rail where he showed all of the damage, from there it crosses around behind and in front of the battery tray, it crosses over to the engine and hooks to a clamp at the back right cylinder head, some wires go down to the starter, oil level sensor and crank shaft position sensor, the harness continues across the back of the engine where it T's off and goes across the top right side of the intake manifold for the injectors and throttle body as well as T'ing on the top left side of the manifold for those injectors, throttle body, EVAP solenoid, engine coolant sensor and MAF sensor, the harness continues across the back side of the left cylinder head with a ground wire attached directly to the head, a short harness for the knock sensors, a connector for the cam position sensor and a vacuum hose that connects to the intake manifold as well as continuing down to the oil filter for the oil temp sensor. The harness is thickest from the PCM up around the battery tray where it's an inch to an inch and a half in diameter, and this is probably the trickiest part.

There is a second harness in the engine compartment that may also be damaged, this one runs along the top right frame rail and goes to the parking & headlights as well as the horns and then crossing over to the left side for the EBCM (if yours is a front mount) and to the air pump.

There are also a half dozen small round plugs in the battery area, I can't remember if any of these have to do with the engine or if they are just other systems but either way they all have their own colored tape at the plugs, ie. one is green, one is pink, one is blue, one is red etc. and they are Murphy proof.

MattB

Well, good luck with this one, its gong to be a b!@ch.

The wiring harness is attached with metal clips to the bell housing. You would need to drop the engine enough to get to the clips. They are held on by the bolts for the bell housing.

I've only worked on a 2000, so it could be a little different for a 97. But, there are two wiring harnesses for the under hood area, one for the engine and one for the abs, fans and such. They both go to the PCM and the under hood fuse box. So, try and get a used harness (A new one will run around $2,500) that has the engine, under hood fuse and front harness. You have to get one from the same year and same transmission. This will make it much simpler. The transmission harness and under dash should then plug into it and keep the splicing to a minimum. Otherwise, you would end up with splicing in new connectors and running new wires to compensate for incompatibilities.

I’d get a set of manuals from www.gmpartshouse.com.

It looks like your missing some of the vacuum lines and such as well.

Good luck!

keliente

I am sorry for offering my advice.

On my car where the harness runs up from the back end, the engine & rear harness were intertwined with tubing & electrical tape. I wrongfully assumed they did not come apart, but after reading your post I took a razor to the tape and saw that the engine harness is separate.

I still feel it is valid to offer that lowering the engine a little would make the process go a little smoother. My engine harness was attached to the two top bellhousing bolts, and they were far easier to get to with a little more room from above.

tappaja

Thanks to all for advices!

Complete engine harness looks like:


diference between automatic and manual harness is that biggest round connector vs. smaller black square connector. I bought harness from 99, which is different from 97 because different ECM used and I planned to make swap to 99' ECM, but then I said that will be better to go with 97'. Maybe later will do re-pin of ECM, but want to run it first.


And last question, I asked here before but no clear answer, do anybody know this cables? Goes from passenger side (probably from BCM) to somewhere, no idea where

runamuk

Are the wires your holding coming from that harness sticking through the firewall?

If so, thats the dash harness and it will connect to the underhood fuse box and I believe there is also one or 2 round connectors in the battery box, there should also be a vacuum line in this harness as well that runs from the vacuum solenoid on your HVAC module over to the vacuum manifold next to the vacuum accumulator.

One more thing, someone above said that the engine harness is secured to the bell housing with metal clips??? that is not correct, but since you have the harness out, you've probably figured that out already.

tappaja

Will ask brother to take better pics and write down colors of wires one by one and try to find where it goes. If there is any connector, then I am in deep sh*t to find good one.
Original damaged harness is still sitting in a car, I have two spare, 99' MANUAL which I will not use and 97' AUTO (from one great CF member)

I found some pics how harness is attached to the engine:


And yes, vacuum line is part of harness, near to ECM connectors goes to vacuum canister and other end goes somewhere to manifold or HVAC unit I guess.

runamuk

My 04 harness only had two clamps, one on the right cylinder head and one on the left. I didn't have the other 2 clamps that it's showing there but either way with the intake removed I'm sure you had more than enough room.

If any of the forum vendors can't help you out with a replacement harness then Ebay may be a good place to look for a replacement. Look for a username Karstuffs, he's always got a Corvette or two that he's parting out.

camaro69

I think the wires your holding go the throttle control actuator. I just rewired my 99 same problem. and you can't go by just wire colors there are so many duplicates in the harness. good luck.

kh400

I just bought an 03 with similar damage, almost an exact duplicate. Today I removed the old engine harness. Took about six hours. I had to remove the intake manifold and thermactor tube,but was able to get at all the grounds and sensor connectors [with great difficulty]. Just take your time and try not to lose your cool. The wiring on these is ridiculously thin guage. Email me at rwill10590@verizon.net. Good luck. Let me know if you found a source for a used harness.