TheSamba.com :: View topic - Explain Fuel Pump, DigiFant Relay Schematic

Mon Oct 29, 2012 5:08 pm

1. it looks like the relay labelled Fuel Pump Relay does NOT control the Fuel Pump??

2. where the thick lines cross, is there a wiring connection or not??

3. finally, do these relays have diodes in them? I thought I saw a thread where someone said they did...

I am trying to test each relay on the bench and don't want to push 12 V in the wrong way...

Mon Oct 29, 2012 5:30 pm

Yes, it is a labeling error in that diagram. The relay labeled Fuel Pump is really the ECU Power relay. You can tell because the other relay connects to the fuel pump.

The stock relays don't have diodes, just a resistor if the relay is Type 53 as both should be for 86.

Is your VIN# really within the first 55,000 of 86 models that that diagram is for?

If it is, you may easily get confused trying to match what that diagram says you should have in that wiring area and what you do have. No time for details at the moment.

Mark

randywebb wrote:

1. it looks like the relay labelled Fuel Pump Relay does NOT control the Fuel Pump??

2. where the thick lines cross, is there a wiring connection or not??

3. finally, do these relays have diodes in them? I thought I saw a thread where someone said they did...

I am trying to test each relay on the bench and don't want to push 12 V in the wrong way...

Mon Oct 29, 2012 5:48 pm

The relay for the ECU in 88 and later vans is protected by a diode.

Sounds like there is more to the story according to Mark..........

Mon Oct 29, 2012 6:22 pm

Some of the 88/89 models have a slightly different fuel injection harness that uses a different ECU power relay than vans before and after have. That relay has a diode in it but not for protection in the normal sense that many relays have a diode for.

Mark

Syncro Pilot wrote: The relay for the ECU in 88 and later vans is protected by a diode.

Sounds like there is more to the story according to Mark..........

Mon Oct 29, 2012 6:40 pm

Hi Mark,

I only figured out about the diode in this relay when I tried to swap in a ECU relay from my 87 to test it for some reason a few years ago. After I figured out what the extra pin was for, and how to read the symbol for diode on the wiring diagram, I then read up on diode function and the best that I could do was understand it as if it was a one way valve to prevent high voltage current from reversing into the ECU and doing damage.

What is the function of the diode, other than what I see as "surge protection"?

Looking to learn more....... Thanks.

Mon Oct 29, 2012 6:53 pm

If you look at the diagram for 88/89 , the ECU section shows a ECS Mal led and a switch. Page 97.123 current track 20. This is an OBD function, a "check engine" type of thing that was planned for 88 models. VW got an exemption and ultimately didn't have to implement it but some of it is there. The 022D version ECU actually stores fault codes and that switch was supposed to let you read them from the light. My 88 owners manual shows the light and switch on the instrument cluster though my 88 didn't have it. Anyway that special ECU relay was part of the OBD function that was planned and the diode is there to prevent any back feeding from the ECU to the power relay coil that could otherwise keep the power relay energized even after the key was turned off.

Mark

Syncro Pilot wrote: Hi Mark,

I only figured out about the diode in this relay when I tried to swap in a ECU relay from my 87 to test it for some reason a few years ago. After I figured out what the extra pin was for, and how to read the symbol for diode on the wiring diagram, I then read up on diode function and the best that I could do was understand it as if it was a one way valve to prevent high voltage current from reversing into the ECU and doing damage.

What is the function of the diode, other than what I see as "surge protection"?

Looking to learn more....... Thanks.

Mon Oct 29, 2012 7:12 pm

Great detail to have explained. Thanks again for sharing your knowledge on this. Interesting to discover a hidden "feature" that might have been.
Imagining the evolution of a VW wbx powered Vanagon for the 90's and beyond.....

Mon Oct 29, 2012 8:41 pm

I don't know what you mean by the "56" relays - mine have "24" stamped on them

Tue Oct 30, 2012 1:28 pm

my VIN = WV2ZB0257GH 025 811 - is that the wrong diagram?

Tue Oct 30, 2012 1:45 pm

In the diagram above they are labeled "Fuel Pump Relay I and II" the way I read it. They are connected on the power side (terminal 30) with a 1.5 R (red) wire.

Tue Oct 30, 2012 5:05 pm

1. Simplified explanation is fuel pump relay II controls fuel pump relay I which controls the fuel pump.

2. No

3. Don't know- not that it shows on the schematic.

Tue Oct 30, 2012 5:42 pm

The key switch turns on the ECU power relay, and that powers up the ECU.

The ECU controls the fuel pump relay, by switching the "ground" for the fuel pump relay coil on and off as needed.

That diagram is flat wrong in the relay label. Just look at the later versions of the diagrams.

97.72 is that diagram
97.89 is the later 86 diagram, correctly labeling the fuel pump relay but mis-labeling the ECU relay as the Digijet Control Unit Relay, should be Digifant.

Randy, your vin# GH 025,811 decodes to an early 1986 model, the diagram you show above is for up till GH 055,689 so it is the one.

The bad news is that VW made some changes after the early vehicles were built and the VW Dealerships were expected to retrofit those changes to some or all of the early 86 models. As a result the early diagram is often wrong after the dealer hacks made wiring changes. They did not always do them correctly so people with early 86 can have real head scratchers when they try to make sense of the diagram while looking at their wiring.

The proper relays for your van are Type 53, the enhanced version of the earlier Type 24. Lots of people are using the Type 24 and the difference isn't likely to be causing you any issues.

Mark

Fritz wrote: 1. Simplified explanation is fuel pump relay II controls fuel pump relay I which controls the fuel pump. ....

Tue Oct 30, 2012 8:50 pm

thx - just one more question: in the box which is the Fuel Pump relay - LH side or RH side?

Wed Oct 31, 2012 10:35 am

You may want to seach as i did a post on this a while ago (year or two ago ?) I have a 1986 vanagon, US spec, original family owner. My vanagon was wired unlike the manual, for both the ealry and late 1986 model. Mine was more like a hybrid of both electrical diagrams, was a pain to trouble shoot. turns out my relays in the engine bay box were doing nothing, yes they actuated, but no power was going thru the contacts. all the power for the spark coil O2 sendor, and pump was run thru the ignition switch, wired such that there was no relay for the current. I had huge voltage drops to the spark coil and pump. only getting about 8-9 volts as I recall.
the stock factory wiring in my van was unlike the Bentely diagrams It came from the factory this way. allt hese years the power was running thru the ignition switch, and the relays carried no current. all the jumpers and wires to make this happen appeaed as orignal factory install, Just is it was all wrong.

I ended up correcting it, adding two extra relays to keep the currect out of the ignition switch. Now i have full voltage to my coil,pump O2 sendor, idle controller etc....

So beware, some vanagon are not wired at all like the factory diagrams. In my opinion, it looks like the factory had bits of both the early and late 1986 stsyle wire harness in my van, plus some extra wiring to make it work, however it the way they did it resulted in low voltage to some critical componets ran fine this way for 20+ years. only when I took a volt meter to it did I find the huge voltage drops and then the detective work to figure out how it was really wired, heck even some of the color coded wirtes where wrong color. This was a factory modification.

If you find inconsistancies in the Bentley diagram, it might be the way th4e van was made. go figure

PS yes that is an error in labling of the pump circuit as prior poster has pointed out, so you got both errors in the diagram labling, plus the fact that some Vans where shipped with non-standard wiring.

Wed Oct 31, 2012 2:32 pm

holy kee-rist!

can you post the VIN of your van?