speed/ref. sensor wire covers crumbling

slojet · 12-31-2010, 09:53 AM

I have a 1986 Carrera...was going to replace CHT sensor and discovered that the other two wires that run with it, (from the 3 wire bracket to sensors) have the insulating covers disentegrating/crumbling off and exposing the metal sheath underneath. Any problems with this ? Can they be wrapped with tape or should they be replaced ? Thanks.

slojet

slojet · 12-31-2010, 10:25 AM

forgot to mention on first entry...engine just spins, won't fire at all...could this be result of grounding of either sensor wire or defective CHT sensor...any way to isolate problem

Joe Bob · Joe Bob's Garage

On the wires, replace or attempt to paint on a rubberized coating to see if that works......

As to not firing, could be the CHT.

Gotta do the Air, Fuel or Spark dance. Give the intake a shot of ether and try to start. If it coughs and tries to start or runs a bit, it's fuel. If nothing check spark......no spark, do the DME dance.

PM me if you need help.....hope you have a test light and multimeter.

slojet · 12-31-2010, 10:47 AM

Thanks for the input...I'll try to recoat wire after I get them out and inspect them. I'm not much into the techno electro side of things but I do have a multi meter and test light. Might need help in that dept. On the spark aspect..do I assume correctly that this can be checked at distributor with coil wire ?

rick-l · 12-31-2010, 10:49 AM

Do a search for DME no start

feel idle air controller for vibrations
check for spark
jumper DME relay for fuel pump

j911brick · 12-31-2010, 10:58 AM

Are you getting spark? Are the injectors firing? I've run with bad connectors on 944s for years. You can actually buy replacement connectors.

Dixie · Dixie's Garage

Coating the wires may make them look better, but it won't fix them if they're bad. If you really think it's the sensors, replace them. I used Bosch sensors for a BMW. They were a touch longer, but way less money. A search will lead you to the part numbeer to order.

Joe Bob · Joe Bob's Garage

Checking spark is best done by pulling a plug wire, putting a spare plug in the boot, running a ground wire from the threads to a grounded bolt, cranking the engine and looking for spark at the electrode.

You have a PM.

rick-l · 12-31-2010, 01:23 PM

Quote:

Originally Posted by slojet

Thanks for the input...I'll try to recoat wire after I get them out and inspect them. I'm not much into the techno electro side of things but I do have a multi meter and test light. Might need help in that dept. On the spark aspect..do I assume correctly that this can be checked at distributor with coil wire ?

Make sure you provide a path to ground for the spark wherever you do it. If you just disconnect it and crank the engine the voltage will build till the weakest link breaks down typically with a hole bored in it for future headaches.

JerP · JerP's Garage

Were you having problems with the engine prior to the no start issue?

KTL · 12-31-2010, 03:52 PM

Common occurrence for that wire sheathing to go bad, given their location near exhaust heat and road debris. I don't think recoating them will work and i'd bet your no start problem is the sensors, if you disturbed the wiring while under there looking at CHT sensor.

I also agree the BMW sensor is the hot ticket. No reason to buy the Porsche part no. Both systems are similar Bosch Motronic, so no worries about interchangeability and hence the reason the swap works.

rick-l · 12-31-2010, 04:14 PM

You can do a search for the part numbers for the sensors but you have a few rudimentary checks do do first, most revolve around the DME and the DME relay.

tom.stiller · tom.stiller's Garage

...as far as the no-start problem goes, I had a similar issue and fixed it by replacing ref/speed sensors. You can get the BMW sensors for half the price and they are working great in my 84 Carrera.

Here is a link to my diagnosis and resolution: no-spark problem finally resolved