Should I consider using 18awg twisted pairs of TXL wire for my engine harness? Would that be an alternative to using shielded wire within the harness for knock sensors, crankshaft position sensor, oxygen sensor.

 

crankshaft poistion sensor...maybe. most CPS systems use deep teeth. That generates a sufficient amplitude to overcome most noise. I dont think it could hurt though.

When I was working on the Distributorless ignition setup I was doing my initial development with 2 crank position sensors. At one point I had has exposed wires twisted together by hand and was way beyond spec on the air gap. It still ran fine even at higher RPM's. This tell me CPS system are not so sensitive.

On the other hand my work with ABS systems tell me they are very sensitive to signal quality and air gap. The shallow teeth on the rings probably has something to do with it.

 

Twisted pair is useful at reducing induced EMI, these circuits have a transmitter and filtering in the receiver to remove all but the transmission information. For VR sensors you will need to use shielded cable. Vehicle manufacturers use shielded cable for a reason.

I would not bother twisting wiring the engine bay harness ECUs are designed to work in this environment, they have their own signal conditioning/filters.

I often twist cables but this mainly for aesthetics not noise reduction.

 

A good source for twisted pair wiring with a consistent
twist is ethernet cable of at least Cat5 grade. These
cables are intended for high signal rates at lengths
far longer than found in an automotive application.

Under the outer sheathing there will be 4 twisted pairs.

The individual wires will be AWG 26 or smaller.

Most will be stranded, but solid is obtainable in plenum
rated cables.

Everyone on the internet has a spare patch cable laying
around by now right?

 

All I can share is my personal experience. I purchased a 89 XJS with Marelli ignition. I purchased it on eBay from a shop that had taken it in to get it running for the customer. After running through 6K, including a new ignition harness, the car would try and fire occasionally, but mostly sounded as though it had jumped timing. I bought it not running of course. The owner basically abandoned it at the shop. After MANY hours work, and finally just taking the ignition harness out, I came across twisted pairs going to the front, and rear crank sensors. I replaced this with NOT shielded wire (as the diagram says it is, but it isn't}, I used a automotive coax. The car fired up very nicely. I don't understand why, I just know that on this, and another forum, I had guys respond that were much more understanding of it try and explain that it had something to do with Hertz? The twisted pair can somehow interrupt surrounding wiring, or even worse, its own signal?

 

Hmmm. Bizarre. However, since no one seems to be using twisted wire in engine harnesses now, Ill pass and stick with what I intended to use....automotive coax.

Thanks for the insight. I probably wouldn't have understood the explanation anyways.

 

Good idea.

Put simply coax has much better noise suppression than TP.

One VERY important thing with coax, ground it at ONE END ONLY when it's transmission, like the shielded wire from the ECU to the ignition module. This prevents noise on the shield which can get into the centre conductor. Things like VR sensors need the shield connected to signal ground at the ECU, this is ok as this signal is crappy anyway and needs a significant amount of signal conditioning.

 

Thank you. I did enough research to have read that several times.

I'm going through each wire in the harness and it definitely appears that all shielded wire (I think there's 8 of them) are all grounded together from one end.