User 52121

Just want to make sure I have this right.

The "speed" sensor is the one that measures engine RPM. The "reference" sensor is the one that syncs up to tell the DME where the motor is when starting. Correct?

So in theory, the "reference" sensor is not really needed/used once the car has started, correct again?

Having a random no-start issue (no tach bounce - textbook S/R sensor issue) - the sensors themselves are recent (well, maybe 2 years old now). I re-did one of the sensor harnesses a few weeks ago (the one that I KNEW was in bad shape) with all new shielded wire and connector and I still get a random no-start. (Only did one because I ran out of time and had to button the car back up.)

My theory is that the sensor I re-did the harness for was the "speed" sensor and not the "reference" sensor and thus the car is still having issues. I'm just trying to decide if it's worth building another harness for the other sensor this weekend, or saying "screw it" and order the official replacement harnesses from Lindsey (thinking that somehow perhaps the shielded wire I picked up from Radio Shack isn't quite shielded enough). I already have the parts, so the only crap part is digging into it... just trying to think it through now before I start.

Oddjob

Reference sens. is identifying TDC for the DME. I think it is necessary for running, not just starting.

User 52121

I guess what confuses me is why they don't seem to "fail" once the car is running? (**** did I just jinx myself?)

And once the car "learns" where TDC is... does it constantly check? I figure once it figures out where TDC is, as long as it has RPM, it always knows where TDC is. I guess maybe Joshua or somebody that knows the software can confirm...

doabarrelroll

*Makes sacrifice to Stuttgartrian Gods* We promise we didn't ask for reference sensors to fail!

V2Rocket

Reference sensor used to calculate spark timing...

User 52121

Ok. So it's conceivable that if the reference sensor wiring is crummy, and the signal can drop in/out, that the ignition timing could be bouncing around too?

hp18racer

Yes

Bri Bro

The reference sensor tells the DME when it has reached a set point on the crankshaft rotation, only one point. The speed sensor counts starter gear teeth so it can determine how far from the reference mark it has moved. Lots of teeth on the starter ring so you can dial in timing by degrees. If you search you can get into details of front vs back gear speed sensor counts which determines the amount of timing degree accuracy and find the number of degree from TDC the ref sensor is set.

The chip inside the DME that gets the sensor inputs is a custom IC developed by Bosch. It looks like a Phase Lock Loop IC to me which means it averages out missing pulses so you don't get a jittery signal. I did melt one sensor lead on the track...don't remember which one, and the car ran like crap, but it still ran. The speed sensor can miss a pulse or two without causing problems because the ref sensor resets the position of the crank every revolution of the engine.

You need them both working for proper operation. Get the LR harness and the injector harness and you will not be disappointed.

Tom M'Guinn

I second that. I tried several times to replace the connectors on the harness and continued to have issues. I finally gave up and got the lindsey harness, and it solved all issues. I concluded that the issues with the original harness were not limited to the connectors under the hood! You could always make your own replacement harness, but when all is siad and done, the Lindsey harness is cheaper than collecting all the parts and tools needed to replicate it...

Bri Bro

What is bad about the design? Cars are still running 26 years with the original parts on it. It has a top speed of 150+ with no mods... stock.

The Bosch DME was a major development that revolutionized the car industry using fuel injection and a catalytic converter to make emission standards. You can thank Volvo for contracting Bosch for making this happen.

Lots of 240 Volvo went over 250K mile with this setup. I would have to say that most would state the the factory system was the least problematic running setup that they had.

V2Rocket

Think about it though, are the Bosch ref/speed sensors really any different than the ones on the LS1?

V2Rocket

magnetic pickup for a wheel with little teeth on it?

Bri Bro

They are both reluctors that count teeth to determine engine timing. The GM sensor has signal conditioning built into the sensor instead of having the ECU condition it like the DME does. You find relutors in all type of cars for cam, crank and ABS position sensing.

Basic LS1 components
Crankshaft sensor (CKP)

The crankshaft sensor is a 24X (58X on 2004 and later engines) pulse sensor that controls ignition coil firing and injector pulse. The 24 tooth reluctor wheel is mounted on the back of the crankshaft. This location is known as the "quiet" deflection zone that minimizes any false signals to the pcm that can be misinterpreted as a fault. As with the CMP, the crankshaft sensor is a magnetic sensor that has the field interrupted by the passing the the teeth on the reluctor. This signal is conditioned by the sensor circuitry so I can be properly used by the pcm.
http://www.chevythunder.com/ls1_page_1.htm

houstonj52

I have had intermittant problems with 944 turbo speed and reference sensors. In each case, the problem occurs on the track when under acceleration. The car will buck for approximately 15 seconds then go away.

I had a worn out reference sensor in one case, a melted reference sensor wire in a second case and metal shaving on the sensor in the 3rd (it was just after changing the clutch and flywheel). The symptoms were the same, and in every case where I have either changed or cleaned the sensor, the problem has gone away. Through the process of upgrades and replacing components, I have ruled out other sources of the problem.

BTW, I highly recommend the Lindsey Racing wiring harness. I was very straight forward to install.

Darwantae951

I sometimes wonder why Robstah posts at all. His constantly pessimistic attitude gets quite old, quite fast.