D-Jetronic Fuel Pump Circuit Troubleshooting, Flow Charts Options

[pbanders]

These charts used to be available on my page but the javascript has been broken for years. Here are the individual charts, you start with the first one and branch to the other charts as needed. I'll come up with a new way to put them on my page so that they're accessible there.

Note that these charts were intended to help diagnose problems where the fuel pump isn't running at all. If your fuel pump runs for 1.5 sec after key on, but doesn't run after starting, you likely have a fault in your trigger contact (TC) points, the ECU, or the ECU wiring harness connections to the TC's.

Note that the DMM should be set to DC voltage, and either in auto-range or on the manual 20V range. In the flow charts where it says "ground", that's the same as reading 0V on the DMM. I used "ground" and "0V" interchangeably, sorry for any confusion.

Here's a diagram of the relay board so that you know what relays and connections are being referred to. This view is from the top side.

[pbanders]

Start here, when you reach a red oval, go to the corresponding flow chart below:

[pbanders]

Pwr to Relay Board:

[pbanders]

ECU Pwr-Gnd Conn:

[pbanders]

From previous flow chart, "Circuit is OK, leave DMM probe on pin III plug ECU back in and reinstall, reinstall air box assembly":

[pbanders]

FP Pwr and ECU Control:

[pbanders]

End Fault Area Diagnostics:

[Spoke]

Start here, when you reach a red oval, go to the corresponding flow chart below:

Nice flowcharts. These should be very useful.

On this chart, I was ok going down the chart but on the way back up at "Connect a DMM to pin III", I think an adjustment is needed in the flow.

I believe the intent is to check the driving capability of the ECU to the FP on pin III. The ECU grounds pin III to turn on the FP. Here it should be mentioned to have the DMM set to Volts.

On the next box, "Remove relay 74 turn key on" I am lost. Relay 74 is the power supply to the ECU. Removing relay 74 will disable the ECU permanently. Relay 74 should remain installed. The box should say "Turn key on".

The next decision box "Ground for 1.5sec" should say "Measure 0V on DMM for 1.5sec after key on, then 12V.

For the ending green box "FP System OK" only indicates the wiring to/from the FP including relay 75 and the ECU capability to drive relay 75 is ok. The FP system also includes the contacts on the distributor which tell the ECU the engine is turning and it should power the FP. If the contacts on the dizzy are not functional, the FP won't operate when starting the engine. Maybe this is a minor point in your flowchart and can be ignored.

OT: BTW, I hate tracing the wiring on the relay board by seeing the routing of the relay board instead of having a real schematic of the board. It makes this job much harder. Anyone have a real schematic of the relay board?

[pbanders]

Spoke, will check all of your comments, I haven't looked at these in about a decade and needed some eyes on them to check for errors, thanks.

[Tom_T]

Thanx for posting these Brad!
(IMG:style_emoticons/default/beerchug.gif)
Tom
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[draganc]

Thanks for an excellent job done!

[pbanders]

On the next box, "Remove relay 74 turn key on" I am lost. Relay 74 is the power supply to the ECU. Removing relay 74 will disable the ECU permanently. Relay 74 should remain installed. The box should say "Turn key on".

Looks like I copied a version of the initial flow chart with an error on it, the version that's on my page references relay 75 instead, which is the fuel pump relay and not the power supply relay. I uploaded the correct flow chart. I added some text in the first posting about DMM settings and the interchangeable use of "ground" and "0V".

I agree with your comment that "FP System OK" doesn't include verification that the fuel pump runs after starting, which is enabled by the ECU when it sees the TC's switching at above the cut-off level. I'll add a comment to the first posting to this effect, the charts were intended to address the "no fuel pump operation" problem.

Thanks again for looking at these and please let me know if there are other issues that need fixing.

[thomasotten]

Excellent flow charts. One thing to note, it appears that the relay board diagram is wrong. Specifically, Pins 85 and 86 are reversed. Here is a photo from my well worn Haynes manual which has it correct. I also verified with the actual relay Pins. I am not sure if your flow charts reference the actual Pins or if they also carry over the error.

Nevertheless, I appreciate the work.

Thanks

[ClayPerrine]

You can always use this relay board diagram.

(IMG:http://www.914world.com/bbs2/uploads/post-1143-1694107603.jpg)


It didn't exist when this thread was started. It is much easier to read.