Reference sensor issue

[944Nick]

So I just got a new Bosch reference sensor for my 88 944S and installed it fine but the car won't start still. I checked the sensor for resistance (I dont have an oscilloscope) and the first 2 plugs are showing a good amount but the first and third show OL. Does that mean it has infinite resistance or the sensor is broken?

[944Nick]

Also how can I test the plug to the computer because I did some sketchy wiring and that could be the problem

[944 Ecology]

Originally Posted by 944Nick

Also how can I test the plug to the computer because I did some sketchy wiring and that could be the problem

Sketchy wiring can be checked with an ohmmeter: zero ohms end to end good, more than zero ohms bad.

Send me your flywheel sensor and I will test it with my oscilloscope.

[curtisr]

Are you experiencing a no-start or a no-crank condition? If it's the latter, an updated reference and speed sensor platform with shielding (an aluminum sleeve) should fix things. If it's a no-start situation, it might be a spacing issue. May I ask why you are replacing this particular piece?

[944Nick]

Originally Posted by 944 Ecology

Sketchy wiring can be checked with an ohmmeter: zero ohms end to end good, more than zero ohms bad.

Send me your flywheel sensor and I will test it with my oscilloscope.

Thanks, ill check when I get a chance and I was just about to go get a cheap oscilloscope, but thank you for offering

[944Nick]

Originally Posted by curtisr

Are you experiencing a no-start or a no-crank condition? If it's the latter, an updated reference and speed sensor platform with shielding (an aluminum sleeve) should fix things. If it's a no-start situation, it might be a spacing issue. May I ask why you are replacing this particular piece?

Its a no-start situation and because thats what my no start condition steps took me to.
So I take the sensor out again, glue on a .8 mm washer, and put it back in and thats all?

[Chalt]

Here is what I bought. The brands vary, but I think I paid $35 or so on Amazon or ebay. It worked great for testing my speed and reference sensors. I know nothing about o-scopes but this one was basic enough that I could use it. It works off a 9v battery OR the wall wart that comes with it.

[Chalt]

This video shows what happens if the sensor gap is too wide – the signal becomes weaker as distance increases. If there in no gap at all the flywheel teeth will hit the sensor.

[curtisr]

Originally Posted by 944Nick

Its a no-start situation and because thats what my no start condition steps took me to.
So I take the sensor out again, glue on a .8 mm washer, and put it back in and thats all?

Gapping is critical (as Chalt pointed out already) and it's possible that a replacement sensor is, in fact, a tiny bit shorter. However, that's NOT likely (impossible?) to be the case with a Bosch. The write-up at Clark's Garage should provide you with all that you need to know.

The aluminum sleeve and accompanying platform should be considered if the situation is no-crank.

[944Nick]

Originally Posted by curtisr

Gapping is critical (as Chalt pointed out already) and it's possible that a replacement sensor is, in fact, a tiny bit shorter. However, that's NOT likely (impossible?) to be the case with a Bosch. The write-up at Clark's Garage should provide you with all that you need to know.

The aluminum sleeve and accompanying platform should be considered if the situation is no-crank.

It cranks, and I looked at the 2 sensors when they were both out and they looked perfectly the same length

[curtisr]

Hoping that this might be of value in case you haven't had a chance to check Clark's Garage.

[Sirlapsalot]

Maybe elaborate on the "sketchy wiring" you did....

Those sensors are probably the last place you want to be doing any kind of sketchy wiring.

Just FYI, there is no condition in which an issue with a speed/reference sensors will not allow cranking. The starter will turn over regardless of what the DME is seeing regarding the speed/reference sensor inputs. The sleeve added to the sensor bracket is to protect against EMI from the starter during cranking, causing a hard to start due to missed or invalid trigger inputs. Has nothing to do with no crank.

Also, as seen in the picture posted above, pins 23 and 78 are the sensor shield wires, which is not connected to anything sensor side. It is only grounded at the DME. So your reading is fine.

If your car was starting and running fine before replacing sensors then they probably aren't gapped correctly or whatever wiring you performed that you refer to as sketchy is the cause. Does the tach needle bounce when you crank?

[944Nick]

Just inspected my sketchy wiring and indeed a wire did pop out so I fixed it right this time and now she runs fine

[944Nick]

Runs fine except after soldering the wires together and starting it there was a loud noise and a plume of smoke from the exhaust and now the engines knocking

[944 Ecology]

Originally Posted by 944Nick

Runs fine except after soldering the wires together and starting it there was a loud noise and a plume of smoke from the exhaust and now the engines knocking

Something mechanical?