electrical tests. No start.

[hpaulb]

Rebuilt the engine years ago. Anyone out there that wants to help me test some stuff. Car stopped running 7 years ago and have done almost everything. Car started stalling at lights then next year in spring. Nothing. Trying to test speed sensors now. Measure ok with ohm meter but not with a scope. No speedo flicker? Also can't test coil. Maybe the ECM so i got another from a Porsche parts yard but the same.

[Jfrahm]

Obviously you should test with a DME relay jumper in place as that's a common failure point.
Also the 9 pin connector, disconnect and clean:
https://forums.pelicanparts.com/porsche-924-944-968-technical-forum/481251-88-924s-9-pin-engine-loom-connector-pinout.html

https://rennbay.com/DME-Relay-Info.html

[944 Ecology]

Originally Posted by hpaulb

Trying to test speed sensors now. Measure ok with ohm meter but not with a scope.

The ECU needs to see the proper waveforms from both sensors in order to start. It doesn't car what the ohm meter says. Compare to the waveforms in the factory workshop manual.

If you have to replace one, better to have both on hand, since the likelihood of breaking one or both is very high.

[hpaulb]

How do you grab hold of the sensors. A long wrench with a wise grip got them loose. Lots or wd40, but can't pull them out. Can't get my hand down there and youtube shows it without the brake booster in place. Will try the bulb thing for the coil but what if its a week coil.

[944 Ecology]

I've probably removed 100 of these things, with about a 50 percent success rate. If there is corrosion between the sensor and the bracket, just about the only thing that you can do to remove them is to break the bracket. Some have had luck with a vise grip attached to a slide hammer.

Good luck...

[Monkey Wrench]

I was going to post a link but instead, just google " how to test an ignition coil" Id just check the primary and secondary to make sure it isnt; open and that you have somethign clost to the number of ohms expected and move foreward. sure one can fail, yes it's possible, but it is a lot more likely that the coil is not issue. engine sensors I;d replace for reliability..

if things dont come easily, Id soak it with bolt loosener, applying heat? well you'd have to think about what's nearby that could be damaged ,, but the basic theory is if you soak something with bolt loosener and then apply a few heat cycles,,, the heating and cooling things moves things some microscopic amount and that expansion and contraction can work to your advantage..

in general the dissimilar metals like iron and aluminum have different expansion rates which means the temp changes are actually moving them in relation to one another. and you dont need to get it red hot, just hot to the touch.. some rather gentle tapping may help as well to dislodge things, generally once you get them to move even, just slightly. then you "win" shortly thereafter. I'd try not to mange the bracketry.
.. and no way Id re-use use a sensor that was heated up with a torch,, it'll have coatings on the wires and maybe plastic parts so heating will destroy it.

You could get to a state where saving the old sensor is the least of your worries. so then your main issue is removing it without destroying other things around it. before you go in with a torch maybe ask the others if they think there is a problem with nearby components , that could be very bad advise for that sensor area, so be cautionary.

you can check the sensor with a meter and expect some resistance, maybe 100 or 2000 ohms not open circuit, not zero ohms either. replacing those old sensors is likely improving reliability, I think less so , with the coil. also a lot of sensor issues arent; the sensor but a problem with the wires which vibrate, see many heat cycles and also have oil residue so that hardens up the wire, oil soaks connectors etc.

sooner or later you'll come across some small bolt and if you crank on it you'll snap it off flush and then that will present a "learning experience" next time you will stop yourself , use bolt loosener, use heat, put a little wrench on ti and pull moderately,, but while you pull use a small hammer and tap your wrench, combining torque with a little tap will often get things to move whereas ore torque will result in trouble. drilling out a 6 mm bolt and using a ez out or similar is a lot more difficult than stopping yourself and doing all you can not to snap it.

if you wonder what it takes to snap a 6mm
just put one in the vice and go ahead and snap it.. I believe breaking stuff is a way of learning and its best if its not something hard to get to or that you care about. experienced mechanics have a feel for this and get themselves into trouble way less often, due to these sort of memorable experiences..

[Chalt]

I didn't know how to use a scope, but I bought a DSO Shell type oscilloscope from ebay for about $30 and it was dead simple to use. I just followed the test instructions on Clark's Garage. My speed and reference sensors were actually fine, I had a bad DME temp sensor. It was worth the price of the tool to know for certain if the sensors were good or bad.

[944 Ecology]

Originally Posted by Chalt

I didn't know how to use a scope, but I bought a DSO Shell type oscilloscope from ebay for about $30 and it was dead simple to use. I just followed the test instructions on Clark's Garage. My speed and reference sensors were actually fine, I had a bad DME temp sensor. It was worth the price of the tool to know for certain if the sensors were good or bad.

I bought one of those, just to check it out. I can carry it with me in my go bag, doesn't take as much space as my pico 4425a or my pico 2204. For the money, it's a no brainer.

[Chalt]

Originally Posted by 944 Ecology

I bought one of those, just to check it out. I can carry it with me in my go bag, doesn't take as much space as my pico 4425a or my pico 2204. For the money, it's a no brainer.

But don't you miss just replacing random parts, hoping you'll guess the right one that was bad? (I am joking...) But yeah, it's always nice to have a new diagnostic tool in the arsenal to help actually test and troubleshoot rather than load and fire the parts cannon. These forums are so great. These young people don't know what it was like to only have a manual, no forums, to try to learn to work on these cars.

[Monkey Wrench]

Originally Posted by Chalt

But don't you miss just replacing random parts, hoping you'll guess the right one that was bad? (I am joking...) But yeah, it's always nice to have a new diagnostic tool in the arsenal to help actually test and troubleshoot rather than load and fire the parts cannon. These forums are so great. These young people don't know what it was like to only have a manual, no forums, to try to learn to work on these cars.

Yes the forums are such a huge help! You might be preaching to the choir ;-)