DME Nightmare! No Signal to Fuel Injector #1

[AZ91525ia]

1991 525ia M50 all stock (Prod 10/1990)

Fuel injector #1 is not working, no clicking sound. I followed the Bentley's instructions to measure the voltages from the battery and DME. It showed 12 volts from the battery with the ignition key on, but there was no pulsed voltage from DME with engine running. Cables are ok after ckeck.

So, DME is the culprit? I pull out DME and opened it (Bosch 0 261 200 405). My DME has 2 circuit boards. I tried to separate these 2 boards, but no luck. Visual check seemed fine, so I used the electric cleaner to get rid of dirt and dust. Put it back in and ran the engine, but the fuel injector still failed.

Now, my questions:

1. How to separate 2 DME circuit boards? I know: one center pin mount, two tabs on DME harness, two snap-on plastic mounts. I can release the center mount and 2 snap-ons easily. However, even though I broke the 2 tabs on DME harness, I was unable to slide the top board out.

2. Other ways to fix the DME or fuel injector problems? Or, where to find a used or new, but cheap DME for my car?

3. Any one in the Phoenix area has the same car, so I can swap DME to see it work?

Thanks,
Jerry
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[Jon K]

1991 525ia M50 all stock (Prod 10/1990)

Fuel injector #1 is not working, no clicking sound. I followed the Bentley's instructions to measure the voltages from the battery and DME. It showed 12 volts from the battery with the ignition key on, but there was no pulsed voltage from DME with engine running. Cables are ok after ckeck.

So, DME is the culprit? I pull out DME and opened it (Bosch 0 261 200 405). My DME has 2 circuit boards. I tried to separate these 2 boards, but no luck. Visual check seemed fine, so I used the electric cleaner to get rid of dirt and dust. Put it back in and ran the engine, but the fuel injector still failed.

Now, my questions:

1. How to separate 2 DME circuit boards? I know: one center pin mount, two tabs on DME harness, two snap-on plastic mounts. I can release the center mount and 2 snap-ons easily. However, even though I broke the 2 tabs on DME harness, I was unable to slide the top board out.

2. Other ways to fix the DME or fuel injector problems? Or, where to find a used or new, but cheap DME for my car?

3. Any one in the Phoenix area has the same car, so I can swap DME to see it work?

Thanks,
Jerry
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You know its not pulsed voltage from DME right, its pulsed ground? So if you were checking the DME against ground it'd not show any voltage.

Additionally, the pulsed ground is very fast, you may not see it on a DMM.

Take the injector and ground it yourself to see if its the injector failed. Let us know what happens with that.

There's no polarity with an injector just put one pin to +12 and one to ground, watch out for gasoline and all that good stuff

[AZ91525ia]

Thanks for your reply. Yes, I should have said it is pulsed ground. There are 2 wires to each fuel injector. I meaured these 2 wires on all 6 fuel injectors. Fuel injector #1 showed 0.006, while all other 5 fuel injectors showed the spec. 0.3 ~ 1.0V.

Excuse my limited knowledge, I don't quite understand what you suggest. Would you please give more details:


Take the injector and ground it yourself to see if its the injector failed. Let us know what happens with that.

There's no polarity with an injector just put one pin to +12 and one to ground, watch out for gasoline and all that good stuff

Thanks,
Jerry
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1991 525ia M50 all stock (Prod 10/1990)

[bjl4776]

There are several things to do to try and break down what is wrong.

1) Disconnect the injector and connect a test light between the two pins on the pigtail and turn the key. If the light flashes than the DME is fine. And try next test.

2) Reattach the injector pigtail and stick pin in the ground side of the injector. Turn the key on and try grounding the pin to a chassis ground somewhere. If the injector clicks than you know the injector is fine. If it is fine than to the next

3)If one didnt work, but two did try this. Find what pin on the harness attached to the dme is for that injector and get your DMM out. Switch it to Ohms, and test between the ground side of the injector pigtail to the pin on the DME harness for that injector. You should read very close to zero. If you see anything over 0.5 Ohms, or OFL, than the wire leading to the Injector from the DME has a problem somewhere.

Chances are your DME has fried out that one injector and I have seen it happen, but its worth a couple of relatively eawsy tests before you buy a DME for no reason.

[Jon K]

Additionally if it fails check that wiring for that injector for continuity.

[Javier]

no mater DME is OK. Also, A fried DME output (shortcircuited) will read close to 0 volts but injector will be permanently opened (leaking gas continuosly).

If DME output was damaged to open circuit, you would have a closed injector and high voltage reading instead of 0.006.

You may also have a damaged injector (shortcircuited thern burned open), tht managed to fry the DME. Doubt it!

Javier

[AZ91525ia]

I followed bjl4776's steps to test DME and fuel injector #1 last night. Yea, still no signal to fuel injector #1. I even measured the injector coil resistance, it is right at 16 ohms as specified in Bentley's. So, DME is faulty.

Now, go back my original questions:
1. Is DME repairable? Is there any DME circuit diagram?

2. Where to find a used or new, but cheap DME for my car?

3. Any one in the Phoenix area has the same car, so I can swap DME to see it work?

Thanks,
Jerry
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