Multimeter questions

[lolcantturn]

Actually, I have a good demonstration on many E30s. Anybody have a working aux fan that doesn't come on with the A/C button? (If it spins and the fuse isn't popped, it probably works, even if it never comes on)


lolcantturn, your car is actually broken at the moment? Motronic doesn't handle shorted injectors too well. Unplug the ones you are getting screwy readings from and see what happens. (two might be pushing it to start the car though, the M20 makes a shitty 4 cyl)

My car is currently dead, yep. They're unplugged and the car still isn't firing. Dead injectors would read 0ohms right?

[DaveSmed]

0 for shorted, OL for open.

Injectors are something that ohms is perfect for. There is even a spec for them.

When you get a shorted injector on an E30, Motronic has trouble dealing with the extra current flow and you will frequently lose function on the entire batch. (E30 injectors are in batches of three) A three cylinder M20 pretty much just doesn't start.

Now, fuel injectors.... They receive a pulsed voltage, controlled by the DME grounding the injectors when they should fire. Your meter's display cannot react quick enough to show that pulse. A test light is the better choice in this situation oddly enough. But first things first, with the key on, engine off, one of those fuel injector terminals should have battery voltage between it and a good ground (not the other wire in this case, as you are not cranking, and the DME is not commanding them to fire.)

[lolcantturn]

0 for shorted, OL for open.

Injectors are something that ohms is perfect for. There is even a spec for them.

When you get a shorted injector on an E30, Motronic has trouble dealing with the extra current flow and you will frequently lose function on the entire batch. (E30 injectors are in batches of three) A three cylinder M20 pretty much just doesn't start.

Now, fuel injectors.... They receive a pulsed voltage, controlled by the DME grounding the injectors when they should fire. Your meter's display cannot react quick enough to show that pulse. A test light is the better choice in this situation oddly enough. But first things first, with the key on, engine off, one of those fuel injector terminals should have battery voltage between it and a good ground (not the other wire in this case, as you are not cranking, and the DME is not commanding them to fire.)

I want to give you a hug right now.
So with 0ohms, my 1st and 2nd injectors are shorted, which means, since there are two sets of batches, that 1, 3, and 5 injectors should lose their function, as well as 2, 4, and 6??

I tested the fuel injector terminal by putting the key into accessory and multimeter on the voltage setting and putting the negative and positive multimeter probes into the injector terminal contact points-- is this not how it's supposed to be done? It should be the positive probe in, and then the negative probe touching the chassis (or some ground) ?

[DaveSmed]

I want to give you a hug right now.
So with 0ohms, my 1st and 2nd injectors are shorted, which means, since there are two sets of batches, that 1, 3, and 5 injectors should lose their function, as well as 2, 4, and 6??

That would be correct if we are talking about an M20B25, I think the B27 goes (1,2,3) (4,5,6)

I tested the fuel injector terminal by putting the key into accessory and multimeter on the voltage setting and putting the negative and positive multimeter probes into the injector terminal contact points-- is this not how it's supposed to be done? It should be the positive probe in, and then the negative probe touching the chassis (or some ground) ?

Accessory doesn't cut it, has to be turned to run and yes, both probes in the connector will not work to check an injector harness. You need a separate ground. The DME provides the ground to the connector only when the injector is to fire, and it fires such a short period of time you cant see it on the meter's display.

Going off topic in the thread, grab a 194 lightbulb out of a sidemarker or something and bend the legs down. Plug it into the injector connector and watch it while cranking.

[lolcantturn]

That would be correct if we are talking about an M20B25, I think the B27 goes (1,2,3) (4,5,6)



Accessory doesn't cut it, has to be turned to run and yes, both probes in the connector will not work to check an injector harness. You need a separate ground. The DME provides the ground to the connector only when the injector is to fire, and it fires such a short period of time you cant see it on the meter's display.

Going off topic in the thread, grab a 194 lightbulb out of a sidemarker or something and bend the legs down. Plug it into the injector connector and watch it while cranking.

So sweet. Thanks man, much appreciated. I guess I need to buy new injectors, which I'm fine about :)

And yeah, I tried a DIY noid light, I tried a 12DC rated LED and a 3.3V rated LED and both of them didn't light up when I was cranking it to start. I probably did something wrong, however, I'll try to use the multimeter to see if at least power is getting to the injector connector by actually finding a ground this time :)


Much appreciated!

[DaveSmed]

The 3.3v one prob just cooked, and all LEDs are polarity sensitive. If you don't install it right, it will not light up.

[lolcantturn]

The 3.3v one prob just cooked, and all LEDs are polarity sensitive. If you don't install it right, it will not light up.

tested both polarities and still nothing, though I'll try again tomorrow.