Another speed reference sensor question

[HWG09]

So have done some reading up on this and pretty sure this is my issue but want to throw it out. This weekend took my '86 951 out and while getting onto the freeway engine completely died. Pulled over, put into neutral and started up no problem and continued on. Drove home later no issues. Then that evening go to get in the car and start backing out, engine dies again and now wont' turn over. Has good crank but just can't turn all the way. I examines the connections on the sensor harnesses and they look pretty worn. I've heard to jiggle them (or the sensor themselves) but seems like might be time for a replacement.

This sound like sensor issue to you guys? Oh and so I'm clear there are two identical sensors to replace correct?

[944 Ecology]

Could be the sensor or its connection to the wiring harness.

If your tach is bouncing, your sensors are fine.

If your tach is not bouncing, it could be a number of things, including DME, KLR, DME Relay, sensors, or coil.

The only definitive way to test the sensor is using an oscilloscope and checking the waveform against what is published in the factory service manual.

[HWG09]

Originally Posted by 944 Ecology

Could be the sensor or its connection to the wiring harness.

If your tach is bouncing, your sensors are fine.

If your tach is not bouncing, it could be a number of things, including DME, KLR, DME Relay, sensors, or coil.

The only definitive way to test the sensor is using an oscilloscope and checking the waveform against what is published in the factory service manual.

I'll check the tach bouncing tonight.

[HWG09]

This might be a stupid question but car had been running just fine until this past week I put some cup replicas on there that are 17" instead of 16". Fit is good, no rubbing or anything but is there a chance that might've messed something up?

[mytrplseven]

Nope. No way wheels cause engine problems.

[RRRacing1970]

Wheels causing Engine Problems... well heck yea' they will cause problems... I put a set of go-cart wheels and tires on my 951 once and could not get the car above 35 MPH IN 5TH GEAR @ 7000 RPM on the engine... I know for a fact it... (the problem) had to be the engine... U think! I'm almost crying causing I'm laughing so hard! THIS IS WITHOUT A DOUBT THE BEST ONE I'VE HEARD IN OVER 20 YEARS!

#1 Pull out all the spark plugs and read them / if they look ok... put them back in.
When u turn on the key (before u try to start the engine)... do u hear a humming noise (behind the passengers side rear wheel), if yes your WF Pump is spinning and hopefully pumping (93 Oct.) gas... if the fuel WF Filter is not plug up, then take off a spark plug wire and short it out with a screw driver to ground (about a 1/4" of an inch away from any ground)... do u get a spark to jump when the engine is cranking over... if yes the the ECM, DME, Dist. Cap & Rotter, Timing Sensors (1), Spark Plug (1) wire and the coil are all good to go... especially if the tack is bouncing while cranking over the engine! Then I would ck the WF Fuel Pressure Regulator or the WF Damper on the WF fuel rail... it sounds like a Fuel Problem... when the car stopped running while driving did it seam to just run out of gas, even when you pushed down on the gas petal or did it run and stop again?

I don't quite understand this statement... ("Then that evening go to get in the car and start backing out, engine dies again and now wont' turn over. Has good crank but just can't turn all the way?") . I need a little of clarity here... what do u mean by the statement? Check your battery / alternator & cables for shorting out or corrosion at their connections and they are all tight and clean.

I'd be more than happy to help... but their are a ton of good people on this site that can help u out and point u in the right direction much better that I can.
Best Wishes...Good Luck... Ron
PS: I do recall this happening to me once a long time ago... when my 951 stopped running and it went bang... with 21#'s of boost ("Loud Popping Sound") when the car stopped running... I don't think this is your (951 Culprit)... problem('s)!

[HWG09]

Originally Posted by RRRacing1970

Wheels causing Engine Problems... well heck yea' they will cause problems... I put a set of go-cart wheels and tires on my 951 once and could not get the car above 35 MPH IN 5TH GEAR @ 7000 RPM on the engine... I know for a fact it... (the problem) had to be the engine... U think! I'm almost crying causing I'm laughing so hard! THIS IS WITHOUT A DOUBT THE BEST ONE I'VE HEARD IN OVER 20 YEARS!

#1 Pull out all the spark plugs and read them / if they look ok... put them back in.
When u turn on the key (before u try to start the engine)... do u hear a humming noise (behind the passengers side rear wheel), if yes your WF Pump is spinning and hopefully pumping (93 Oct.) gas... if the fuel WF Filter is not plug up, then take off a spark plug wire and short it out with a screw driver to ground (about a 1/4" of an inch away from any ground)... do u get a spark to jump when the engine is cranking over... if yes the the ECM, DME, Dist. Cap & Rotter, Timing Sensors (1), Spark Plug (1) wire and the coil are all good to go... especially if the tack is bouncing while cranking over the engine! Then I would ck the WF Fuel Pressure Regulator or the WF Damper on the WF fuel rail... it sounds like a Fuel Problem... when the car stopped running while driving did it seam to just run out of gas, even when you pushed down on the gas petal or did it run and stop again?

I don't quite understand this statement... ("Then that evening go to get in the car and start backing out, engine dies again and now wont' turn over. Has good crank but just can't turn all the way?") . I need a little of clarity here... what do u mean by the statement? Check your battery / alternator & cables for shorting out or corrosion at their connections and they are all tight and clean.

I'd be more than happy to help... but their are a ton of good people on this site that can help u out and point u in the right direction much better that I can.
Best Wishes...Good Luck... Ron
PS: I do recall this happening to me once a long time ago... when my 951 stopped running and it went bang... with 21#'s of boost ("Loud Popping Sound") when the car stopped running... I don't think this is your (951 Culprit)... problem('s)!

Cheers for all this. Good timing as well. What I meant about not starting was that the engine turns but won't fire.

Here's where I'm at.

Last night I go out to check the speed/ref sensors. Connections are pretty worn so I'm jiggling them around and still not starting.

Tach bounces when I first hit the ignition but dead after that.

While i'm under the hood, check the oil. Pretty low so I top that up. About 15 minutes car fires up no problem and is purring like a kitten. I take it out for a spin around the block and it's driving fine. Yay me!

This morning get in, fires up head off to the gym. Leave gym, fires up and just down the road at a stoplight engine dies, won't restart. Battery still works fine.

I push it to a nearby parking lot check oil again. Still seems kinda low, put some more in no luck. Tach bounces while trying to start. Had it towed home.

So bit more research and I need to address spark/fuel. Not sure I will get to it tonight but will take your advice on these bits. Pretty sure my plugs are about 1.5 years old. Fuel filter/lines were all replaced in the last two years.

Hopefully it's nothing too major. Maybe a new cap/rotor?

[RRRacing1970]

Do u have a spare DME or can you borrow one from a friend... Try it!

You can make a (3) wire connector with (3) lugs & (3) short wires all (3) tied together at the top with a screw on electric connector...then plug the other ends (the) (3) individual wires w/the lg. lugs into the DME's (3) "Large" Pin Ports (Only) where the DME plugs into your fuse box... this will give u (Spark and Fuel Pump On and running if your DME is bad! The car should start and run just fine!

Do not drive the car like it is fixed... u can drive it a while close to home and see if it happens again when it gets hot, (try driving a short distance around the block and stop and go, stop the car (park it)...wait ten min's and have a beer...then try to start it again... (do this a couple of times untill u have consumed at least (3-4 Beers) if this works go out and pay about $30-$35 for a new (OEM) DME!

Old DME's... sometimes short out after driving for a while when they get hot...when they get hot they will short out... and the eng. will stop running (WF Pump Stops Running and The Spark Circuit is turned off)... then the next day they will do the same thing over and over till they melt the top of the plastic out of the center of the DME! This can lead to a major melt down in side your lower fuse box under where it plugs into your fuse box and may be as bad as starting an electrical fire in your car!

Does the car back fire or runs rough at any time while driving it... and then just clears up for no reason?

When the car's engine... dies (stops running) does it sputter 1st or just dies instantly, like it has run out of gas?

I have never bought a new cap and rotor button but only once when my rotor button completely melted and blew up (with a loud "POP") & blew out the center of the rotor button! I can take emery cloth and clean the posts on the cap and rotor button (edge that spins and makes .030 - .060 thos. clearance to the cap slotted pins) and put them back in and they are good for another 10K miles!

If it's a fuel problem it still smells like, sounds like and looks like a... WF Pressure Regulator going bad or a (Bad Leaking WF Damper... this allows fuel to be sucked into your vac.system if the diaphragm is leaking!)
Good Luck...
Ron...

[HWG09]

Originally Posted by RRRacing1970

Do u have a spare DME or can you borrow one from a friend... Try it!

You can make a (3) wire connector with (3) lugs & (3) short wires all (3) tied together at the top with a screw on electric connector...then plug the other ends (the) (3) individual wires w/the lg. lugs into the DME's (3) "Large" Pin Ports (Only) where the DME plugs into your fuse box... this will give u (Spark and Fuel Pump On and running if your DME is bad! The car should start and run just fine!

Do not drive the car like it is fixed... u can drive it a while close to home and see if it happens again when it gets hot, (try driving a short distance around the block and stop and go, stop the car (park it)...wait ten min's and have a beer...then try to start it again... (do this a couple of times untill u have consumed at least (3-4 Beers) if this works go out and pay about $30-$35 for a new (OEM) DME!

Old DME's... sometimes short out after driving for a while when they get hot...when they get hot they will short out... and the eng. will stop running (WF Pump Stops Running and The Spark Circuit is turned off)... then the next day they will do the same thing over and over till they melt the top of the plastic out of the center of the DME! This can lead to a major melt down in side your lower fuse box under where it plugs into your fuse box and may be as bad as starting an electrical fire in your car!

Does the car back fire or runs rough at any time while driving it... and then just clears up for no reason?

When the car's engine... dies (stops running) does it sputter 1st or just dies instantly, like it has run out of gas?

I have never bought a new cap and rotor button but only once when my rotor button completely melted and blew up (with a loud "POP") & blew out the center of the rotor button! I can take emery cloth and clean the posts on the cap and rotor button (edge that spins and makes .030 - .060 thos. clearance to the cap slotted pins) and put them back in and they are good for another 10K miles!

If it's a fuel problem it still smells like, sounds like and looks like a... WF Pressure Regulator going bad or a (Bad Leaking WF Damper... this allows fuel to be sucked into your vac.system if the diaphragm is leaking!)
Good Luck...
Ron...

Sounds like a new DME relay could be a fix regardless for $35. I'm an electrical retard so would rather just put a new one in than try to rig something up like that.

Car does not backfire and runs fine. When it died no sputtering or anything just dead engine. No warning sounds. Last night after I put oil in it was purring, better than it had for awhile (probably needed oil for a bit). My guess is if it were spark plugs there'd be some sputtering or misses.

Will look into the WF Pressure Regulator or Damper. I'll prob just get fuel pressure tester and hook that up.

Thanks for all the advice!

[HWG09]

Happy to say it looks like a replacement DME Relay did the trick.

Went out and tried to fire it up to no avail. Replaced relay and she turned over nice and easy. Purred like a kitten on the test drive around the neighborhood. Now I'll be sure to keep an extra one of those in the glove box.

Thanks for all the help.

[RRRacing1970]

Cograts...Now you are a certified ($200 an Hr. Porsche Mech.)! Have a 6 Pack on me!
Cheers... Ron...