Engine wiring loom?

[redsupra]

Next issue. I've been getting some higher than normal revs at idle when the engine is warm (sitting about 850rpm instead of 600 or so) and my mechanic said the issue appears to be the wiring loom that connects to the coil packs under the rocker cover.

Apparently heat has deteriorated the plastic casing and is causing some signal problems to the spark plugs. He patched up the lead and the engine tends to return to normal idle more often now, but he suggested to get it replaced.

I contacted a mob (suprastore.com) and the guy told me these looms don't exist any longer and the fix was to get a new set of coil connectors and rewire the loom near the coil packs and solder the connection.

So, question is, does anyone sell these wiring looms and is this suggested "fix" the way to go, or is there a better solution? Also is there a way to rehabilitate the loom cover to protect the wiring?

[redsupra]

OK, so to answer my own question.

I took the car to a local auto electrician who tested the coils and found the front two were harldy suppling any signal. Being 18 years old I guess it was time they expired. So I got a new set of Super Spark coils and connectors shipped in and fitted. The sparky said the wiring was perfectly ok, (says little about what a mechanic knows about this stuff, and he wasn't complimentary about mechanics either when talking about their knowledge of auto electrics).

So the existing loom was re-wired to the new coils and the car is running perfectly well now. I'm a happy camper

With that last major "under the hood" issue dealt with I can now plan on some new rims, complete re-spray and new sound system.

[pwpanas]

Originally Posted by redsupra

OK, so to answer my own question.

I took the car to a local auto electrician who tested the coils and found the front two were harldy suppling any signal. Being 18 years old I guess it was time they expired. So I got a new set of Super Spark coils and connectors shipped in and fitted. The sparky said the wiring was perfectly ok, (says little about what a mechanic knows about this stuff, and he wasn't complimentary about mechanics either when talking about their knowledge of auto electrics).

So the existing loom was re-wired to the new coils and the car is running perfectly well now. I'm a happy camper

With that last major "under the hood" issue dealt with I can now plan on some new rims, complete re-spray and new sound system.

1) The Mkiv's coils can't be properly tested, except under load
2) I'm pretty sure that Toyota still sells the plastic coil connectors. The oem plastic gets hard, brittle and cracked. Let me know if you need the part number.
3) Did you replace all of the coils? If not, they all usually begin to 'wear out' within a few thousand miles of the others, so you'll likely need to replace the others eventually if you haven't already. However, you should get at least 125,000 miles out of a set of coilpacks.
4) For whatever it's worth, your symptom and the fix don't really go together. Weak coilpacks fail to ignite the air/fuel mixture under hard boost. They don't cause "higher than normal revs at idle when the engine is warm". If you ask me to guess, I'd say your so-called mechanic fixed a vacuum leak he didn't mention to you, while selling you coils you probably didn't need. *shrug*
5) I'm pretty sure that Toyota would still sell you an entire primary wiring loom. Warning - it's quite expensive $850USD+. Not sure why you're concerned about replacing the 'pig tail' ends. *shrug*
6) You should never solder a harness/loom. A proper 6-sided crimp with shrink-wrap is the only thing that should be used on any wiring in a moving vehicle.
7) Those plastic connectors go bad because of heat. Anything you can do to reduce under-hood heat will help them last. For example, have you considered a vented hood?

Either way, congrats on the fix. Glad it worked out for you.

[redsupra]

Originally Posted by pwpanas

1) The Mkiv's coils can't be properly tested, except under load
2) I'm pretty sure that Toyota still sells the plastic coil connectors. The oem plastic gets hard, brittle and cracked. Let me know if you need the part number.
3) Did you replace all of the coils? If not, they all usually begin to 'wear out' within a few thousand miles of the others, so you'll likely need to replace the others eventually if you haven't already. However, you should get at least 125,000 miles out of a set of coilpacks.
4) For whatever it's worth, your symptom and the fix don't really go together. Weak coilpacks fail to ignite the air/fuel mixture under hard boost. They don't cause "higher than normal revs at idle when the engine is warm". If you ask me to guess, I'd say your so-called mechanic fixed a vacuum leak he didn't mention to you, while selling you coils you probably didn't need. *shrug*
5) I'm pretty sure that Toyota would still sell you an entire primary wiring loom. Warning - it's quite expensive $850USD+. Not sure why you're concerned about replacing the 'pig tail' ends. *shrug*
6) You should never solder a harness/loom. A proper 6-sided crimp with shrink-wrap is the only thing that should be used on any wiring in a moving vehicle.
7) Those plastic connectors go bad because of heat. Anything you can do to reduce under-hood heat will help them last. For example, have you considered a vented hood?

Either way, congrats on the fix. Glad it worked out for you.

All I can say is that the new coils have solved the problem, but to answer your comments:

1. No idea. I'm not an auto electrician, but the guy I went to knows his stuff.
2. Toyota do sell the OEM coils, but far more expensive than the after market ones available. The Super Spark I got claim better performance than the OEM too. They are also available locally surprisingly enough. http://www.superspark.com.au/
3. All 6 coils and connectors replaced. Wasn't going to stuff around any more. If 2 were bad the rest were on their way out already.
4. It was an auto electrician that replaced the coils. He wouldn't be fixing a! vacuum leak. Also I had to source the coils, he just did the labour. And still what can I say: new coils, problem is gone. Revs sit rock steady at idle now where they should.
5. Toyota don't make the wiring loom any longer, not that I needed it anyway. The auto elec said the wiring was fine.
6. The advice from the guy at Suprastore.com was to solder the connection. In the end it's up to the auto elec, he's the expert so he did what he knows best.
7. Nope. They last coils went nearly 18 years before going bad and I don't drive the car as much these days anyway, so not an issue. Vented hood is another expense I don't need just now!

[pwpanas]

Originally Posted by redsupra

...6. The advice from the guy at Suprastore.com was to solder the connection. In the end it's up to the auto elec, he's the expert so he did what he knows best...

The guy from Suprastore.com was wrong. Solder should never be used on automotive connnections. It's all in TSRM Electrical manual. Those soldered connections seem to work okay for awhile, then they fail due to vibration over time. HOWEVER this assumes you (or your "mechanic") have the tools necessary to do a proper crimp joint.

Here are the types of wiring splices generally seen in automotive work, ordered from best to worst:

1. ROCK-SOLID RELIABLE PROPER CRIMP - USED BY TOYOTA, MERCEDES, BOEING and LOCKHEED MARTIN (etc.)!
   - Step 1: Materials
   
   - Step 2: The Right Crimp Tool
   (ratcheting, with interchangeable dies):
   
   - The Result:
   
   
   .
   
2. UNRELIABLE SOLDER JOINT* (for ANY/ALL moving vehicles):
   
   .
   
3. CRAPPY CRIMP (EVEN MORE UNRELIABLE THAN SOLDER):
   
   
   .
   
4. ABSOLUTELY TERRIBLE!!!
   
   .
   
5. THE WORST - JUST TWIST UP THEM WIRES REAL GEUD, AND IT'LL HOLD FER-SHER:
   

*Note: Soldering is just fine for solid state applications, like circuit boards, and stationary applications (like home stereo wiring). The unreliability comes when vibration and movement is applied to the place along the wire where the solder wicking ends (typically up under the insulation, making it extremely difficult to troubleshoot).