ECU testing

[hpaulb]

Anyone want to test my ECU for me. Can't get tach response or start. Changed everything. Last this was to get a used ECU from a Porsche recycler here in Ontario but its the same so I'm stuck for now.

[wwdwgs]

did you try to troubleshoot your problem according to clarks garage instructions?
and Pelican's post.

[hpaulb]

Did every test. Changed every part. Not sure if the car has a faulty alarm system. Powered the DME directly to switched ignition power. Does it control anything else other than DME power?

[wwdwgs]

many folks on this forum say that the factory alarm system causes many problems and recommend to carefully "deactivate" it. I was personally "warned" not to touch that second lock and not to use that alarm system.

[944 Ecology]

I can test it for you, but shipping across the Canada/USA border might be problematic.

[Jfrahm]

The DME relay is two relays in one package. One powers the DME and the other powers the fuel pump when it gets a ground signal from the DME. The DME sends this signal when it sees the signals from the Speed and Reference sensors so you don't get fuel pumping unless the engine is spinning (for lots of reasons).

I suggest jumpering the DME relay and then checking all the power and grounds on the DME harness connector. Power on 18 and 35, power on 4 when cranking, etc. All those grounds.

https://grassrootsmotorsports.com/forum/grm/megasquirt-install-in-a-924s-944-please-review-my-wiring-diagram/43120/page1/

I would guess that the alarm takes out some power and/or ground to the DME.

I would test with a test lamp, like a several watt turn signal bulb or the like so you see for sure that you are getting solid power and ground and not some ghost only a DMM can see.
You can steal your dome light bulb and tape wires to it if you have to.

[Monkey Wrench]

I like using test lamps for troubleshooting, then I can leave them within sight of the driver seat and monior as I muck with stuff.

a friend sent me some tiny grain of wheat bulbs. no socket needed as they have about 6" leads. they are only a tiny drain and good above 12V I figured maybe they woud be used for things like toy train displays.

Id like to buy a few more and soms small alligator clips, they are quite useful, and cheap, throw one in the trink and a 9V battery and you can check most things youd check with a meter and its only worth a couple dollars. a long lead with a fuse is good to check from battery to different points, backfeeding things, etc.

the ability to leave them in place while troubleshooting makes things easier and a little less confusing sometimes .. Meters have their place. meters work but they are a little less helpfup for things like intermittent pulses. easier to see at a distance.


two points im interested in monitoring are fuel pump power and one across the coil to show coil pulsations when cranking. I dont see a lot of reason to be troubleshooting sensors in a no start condition if I already have a pulse at the coil.

wiht this problem you might add one to verify the DME is latched on both the fuel pump and DME, maybe one for 12 V power and one for ground for the DME.

You can use a solid state relay with LED indicators. In my car its up under the dash and not easy to see from the drivers seat, youd pretty much need to be kneeling on the ground beside the car twisting your neck to look up there under the dash and turning the key.. super awkward. now try doing that while driving , impossible.


I hooked up an LED to the coil in my ford van thinking id leave it there but the LED burned up, Im thinking the grain of wheat bulbs ones with filaments. might be more durable.
i can see how installing a few and leaving them connected in the glovebox might work ok, out of sight until you have a no start issue or similar, and then faster and easier to troubleshoot the issue. you can just open the glovebox, crank and know instanty if you have power to the fuel pump if the coil has a pules and similar things. if its an intermittent its easy to see if the bulbs are going out , flickering etc even while driving.
load varies but 40 milliamps isn't too uncommon it seems, not much of an electrical load.

[curtisr]

Originally Posted by hpaulb

Anyone want to test my ECU for me. Can't get tach response or start. Changed everything. Last this was to get a used ECU from a Porsche recycler here in Ontario but its the same so I'm stuck for now.

Is the alarm deactivated (jumpers)?

Post #2