Engine Swap; Diode In 15 Circuit or Resistor In Relay?

[Vanagon Nut]

Hi all.

From this thread

https://www.thesamba.com/vw/forum/viewtopic.php?t=682821&highlight=diode

[MarkWard]

Neil, I would forge ahead and not worry about the diode. If you shut the engine off with the key and it keeps running, then you can work on a solution. My diode is still there. Mark
_________________
☮️

[crazyvwvanman]

Neil, I think the problem you are trying to prevent isn't going to be a problem with the later instrument cluster in your 88. Starting in 85 VW added a diode to the cluster foil to prevent back feeding of the circuit 15 by the alternator blue wire.

The issue arises when the black wire 15 is used in the engine compartment only for a low current and low voltage load like a small relay coil. The relay coil gets turned by the key switch power but but takes less voltage/amps to stay turned on once it is already on. On early clusters the blue wire from the alternator charging led circuit back feeds the 15 circuit in the cluster but with a weak voltage/amps. Too weak to power the ignition coil like the 15 circuit originally powered but enough to keep an already energized small relay still turned on if an engine is later wired to put everything on relays. VW figured this out and started putting a blocking diode in the cluster foil trace that connects to the alternator blue wire circuit.

You can see a tiny diode symbol in the wiring diagram for the cluster, where the alternator blue wire connects to the cluster, in 85-91 wiring diagrams.

Mark

[Vanagon Nut]

[crazyvwvanman]

The 87 cluster has the extra diode already.

Mark

[Vanagon Nut]

[Vanagon Nut]

[crazyvwvanman]

No. The cluster diode is in the blue wire power feed from the cluster to alternator field control input.

A relay with suppression should have a diagram on it showing the type and location of the suppression. Usually a resistor symbol if a resistor.

Mark

[Vanagon Nut]

Thanks for the quick reply Mark. Ya, it was a long shot thought I had. Given all the wiring work I did, wanted to rule that out asap.

This is obviously only a small sampling of relays but the ones I've opened up had what appear to be resistors in them and each had what looked like a generic icon for the suppression device. i.e. not the

-/\/\- symbol.

Looking through my images again, I'm reminded that the "coil/ECU" relay I installed in this swap is a Pico brand shown below.

Neil.

_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[Abscate]

Those are resistors to absorb the pulse from release of the electromagnet

They will bleed a bit of current from the relay but won’t get torched if you reverse polarity , so they are preferred in auto apps for Gorillas
_________________
.ssS!

[Vanagon Nut]

thanks Abscate. Yes. That was my understanding and interesting point re: Gorillas. That makes sense. It's my understanding that when the switch opens, the suppressor quells any pulse back to sensitive things like an ECU. I gather the suppressor also helps prevent arcing at the switch contacts.

So, alternator at rest: 12.5 Volts. Running: 14.5

Vacuum hose to FPR ok but I swapped in a VW nylon hose with braided hose transitions to be sure. (no new braided hose on hand) I didn't check to make sure the vacuum port at the intake plenum was clear though.

Ran a new ground from a different (better) point on engine to OE ground point at frame.

The only possible vacuum leak I found visually might've been at the EVAP purge valve hose connection at throttle body (loose clamp) but the hose was tight to the nipple.

Still stalls. Time to get VAGCOM on it see if there's a DTC(s). I'm wondering if the TPS is doing something funky to fuel shut off on decel. Maybe I'll be able to measure resistance (edit: voltage drops) a la Tencentlifes WBX AFM method (measure with analogue meter, power applied to TPS)
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[crazyvwvanman]

That icon on those relay cases does refer specifically to a resistor even though it differs from the traditional zigzag icon.

If you look at Bentley page 97.5 it shows some of the various icons you can expect to see in automotive applications.

Mark

[Vanagon Nut]

Ah yes. Ok. Makes sense. And in sticking in the Bosch realm of things, I now see that it's pretty obvious if the relay has a diode

[Tbob]

Neil, my 86 with the Audi 3B engine does the same thing after I replaced the orphan Eurospec/Tiico Fuel Injection system with a Digifant system from a 90-91 Jetta. I haven't solved it yet either. I tried all the same sorts of things you did with no success. Since I was moving the van down south for winter storage,(towing, not driving) I cheated the timing forward a few degrees to make it less annoying. This is not a solution, and I do not recommend what I did, but it made it possible to move it around the yard and into storage without it dying when I let off the throttle. Running with too much advance is not the answer,and could be very detrimental to the engine. I won't be able to go after it until January, so I will watch this space for your solutions!
_________________
1969 Deluxe, owned since 1973
1973 Westfalia, owned since 1983
1980 Westfalia, watercooled conversion
1985 Westfalia, stock!
1986 Westfakia, Audi I-4 conversion
A couple of trucks and a couple of Jeeps

[Vanagon Nut]

hi Tbob.

The stall issue mostly appears to be incorrect engine timing:

https://www.thesamba.com/vw/forum/viewtopic.php?t=...d7e167ecee

The TPS was likely a red herring though it did show to be faulty.
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[Tbob]

Neil, that's great news! Timing really does matter! I doubt that my problem is the same, as I never had this problem with the old F.I. system, and I did nothing to the cam and belt in the interim. However, it did get better by cheating up the ignition timing----hmmmm.
I really admire your diligence and willingness to chronicle your journey, both good things and things that you learned. You analyse each and every problem, and rather than throwing parts at it and getting nowhere, you methodically think through the process, seeking to understand how the systems were suppose to work together, and just what part may or may be working properly. I live in an area of the country where those kind of skills, indeed even the understanding of why those skills are important, just does not factor into most peoples lives, even those service people who one needs to rely on to fix those things I do not have time to fix. So I come to the samba to get my diagnostic thought process fix. Thanks again Neil!
_________________
1969 Deluxe, owned since 1973
1973 Westfalia, owned since 1983
1980 Westfalia, watercooled conversion
1985 Westfalia, stock!
1986 Westfakia, Audi I-4 conversion
A couple of trucks and a couple of Jeeps

[Vanagon Nut]

Thanks a lot Tbob. Appreciated. With list help and patience, my methods have improved over the years ...... somewhat.

Truth be known, I did kind of throw parts at this but not w/o some thought, reading, measuring.

Sometimes I think I post too much, and write too much, but if it helps at least one person, great.

On these old rigs, there's so many potential factors behind a given issue but I'm reminded each time I run across an issue to sit down and read the Bentley(s) and after checking the basics, deploy the VOM.

Does your version of Digifant use an idle control valve? If it does, I bet you've already cleaned it and put a meter on it.

Neil.
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN