73 914, no voltage at injectors

[rockydrxrvr]

I have a 73 914, that has spark to the plugs, but no juice to the injectors, what is the next thing upstream to find why injectors have no power,short of starting to buy expensive parts. The fuel pump runs fine, I might add. Any help would be appreciated.

[Jared at Pelican Parts]

is this a 1.7 1.8 or a 2.0?

There's a difference in the way the injectors are triggered on both the 1.7/2.0 and the 1.8 cars.

[rockydrxrvr]

Yes,I should have been more concise, It is a 1.7 motor. And,,,what does DME stand for and it's exact function?

[pbanders]

How are you measuring "juice to the injectors"? They only receive a brief voltage pulse, no DC component. A cheap way to check them is with a $7 "noid" light you can get at your local auto parts store, make sure you get the one for Bosch injectors. See my web site for more info on debugging your D-Jetronic injection.

[rockydrxrvr]

We are simply using a small 6 volt bulb with leads in the injector plug, then cranking the motor over to look for a pulse of light. Then we used a high quality multi-meter set on a very low voltage setting to look for needle movement on the meter.....nothing......

[bowlsby]

You won't see any voltage if the FI harness grounds are not connected. Check them.

[Dave at Pelican Parts]

To answer the easy part of your question "DME" stands for "Digital Motor Electrics"--or something very similar to that in German. To Bosch, it means a complete engine management system that controls both fuel and spark.

Our 914s do not have anything digital in them (unless you've got a newer radio!); the EFI is controlled by a primitive analog computer! And the spark is generated completely mechanically, unless you've changed that in your own car. So our cars fail to have a DME on at least two counts.

When people talk about the DME relay in DME-equipped cars, they generally mean the relay that sends power to the DME system, and also to the fuel pump.

The D-jetronic EFI used on both the 1.7s and 2.0s uses two of the round relays on the relay board to run power to the EFI and to run the fuel pump. The website listed in pbanders' post above has a neat flowchart of fuel pump troubleshooting. A slightly different procedure is written up in text on the following page: http://www.914fan.net/fuelpump.html

--DD

[rockydrxrvr]

A large victory, the throttle switch sensor gave an Ohms reading when the throttle plate was close when we used a digital meter on the 17 and 14 wire connectors. It should have zeroed out when the throttle plate was closed. We adjusted the plate by loosening the two screws at the base of the throttle control valve after we took it off. No luck at first, but upon taking the black plastic cover off the throttle control sensor, cleaning the contacts with 4000 grit sand paper and contact cleaner, then passing a sheet of clean computer paper to buff and dry the contacts. Victory~ 0.0 ohms as specified in the manual. By the way this was done with the throttle control valve off the car and on the bench. Reinstalled-- and the car fired right-off. Apparently if the throttle control is not adjusted correctly when the throttle butterfly is completely closed, it sent a signal to the ECU to not give any electrical pulses to the injectors. I may be giddy and have my head in the but the car runs after being off the road since 1985.
Now if I can figure out what the previous owner did with the MPS. and why small adjustment to the center screw change the idle speed so dramatically I will breathe a little easier. No epoxy, no plug, and lots of previous screwdriver evidence. I wonder where this will end?

[Dave at Pelican Parts]

Small tweaks to the adjustments of the MPS have large effects on the amount of fuel going into the motor. Read through the Brad Anders site referenced above--he has a very thorough description of how the MPS works and what the adjustments do. It's gonna be a b--ch to get it set up if someone's been messing with it, though. Your best bet is to come up with a wide-band O2 meter (like the Innovate one we carry) to tell you what your mixture is. Then you can tune from there...

--DD

[bowlsby]

The MPS could also be sent to Geoff Bleyseng or me to evaluate and recalibrate...