Digifant hall unit, spark, and fuel injection system testing

[crazyvwvanman]

Here is a quick and simple way to test a lot of things, even working alone.
This test can show if the distributor hall sensor works, the ignition coil works, the relays work, the ECU works, the Fuel Pump works, ( and if the injectors spray.)
In spite of all the words to explain it this should take maybe 5 minutes for the basic test and putting things back.
Read the whole post before doing it.

1. _ pull the center wire out of the distributor cap and set the loose wire end on engine metal
2. _ remove distributor cap and wires leaving the spark plug wires in the cap
3._ MAKE NOTE of exactly where the rotor is pointing and make sure the 10mm nut of the distributor clamp is tight
4. _ loosen the 13mm nut that holds down the distributor clamp bracket to the engine block. Leave the nut on the stud by just a couple threads so the distributor won't lift much.
5. _ wiggle and lift up the distributor body slightly and make sure the rotor now spins freely with your fingers.
6. _ turn on the key but DON'T crank the starter.
7. _ rotate the rotor slightly by hand and you SHOULD:
_a. feel the fuel pump relay click and hear the pump run for a second.
_b. hear the injectors click for EACH 1/4 turn of the rotor. (see the fuel spray if injector pair pulled out)
_c. _ there should also be a strong spark from the loose dizzy center wire end for EACH 1/4 turn. careful!

when done testing:

8. _ turn the rotor till it again points to where it pointed in step 1
9. _ push the distributor back down fully into place while slightly rocking the rotor to make sure the distributor engages down into it's keyed slot. tighten the 13mm nut
10. _ put back the dizzy cap and center lead
(_ put back the injector pair and hold down screw if pulled to check injector spray)


The ECU powers the hall unit in the distributor.
Turning the distributor shaft should cause hall pulses to be sent to the ECU.
If the ECU sees a hall pulse it should do ALL 3 of these things for each pulse.
1. fire the ignition coil to make a spark
2. fire all 4 injectors at once
3. turn on the fuel pump relay to make the pump run

If ANY of the 3 things happen when you turn the distributor rotor shaft then a hall pulse was sent to the ECU but that pulse should signal the ECU to do all 3 things at the same time.

(if desired you can use this test approach to also visually verify that each injector sprays properly if you remove the hold down screw and lift an injector pair up enough to expose the injector tips.
This must be done with CARE since gasoline is highly flammable and a FIRE could easily result if a spark hits the sprayed gas.)

IMPOTANT NOTES:
a. if you turn the rotor fast enough with a finger the hall pulses should occur fast enough the keep the fuel pump relay on and thus keep the pump running constantly
b. there are different versions of the Digifant harness so there is some variation in the expected idle control valve behavior during the test.
In some vans the idle valve vibrates all the time when the key is on and so it will be buzzing the whole time during the above test.
In many later vans the idle valve runs only when the fuel pump relay is on and this means it will buzz each time the rotor is turned in the above test.


Mark

[ragnarhairybreeks]

Thnaks agajn for this . It’s copied and pasted to notes. It’s a very good head straightener when you have a no start.

Alistair
_________________
'86 7 passenger syncro, converted to westy pop top, project still in progress
'82 westy, diesel converted to gas in '94, now gone...
https://shufti.blog/
Old address still works...
http://shufti.wordpress.com

[DuncanS]

Mark--Yes, excellent. I've printed it up and added it as an appendix to my ProTraining manual along with your direct from battery to relays and coil test wire post. And made one and use it.

If my current exploration fails after the steps I just outlined in https://www.thesamba.com/vw/forum/viewtopic.php?p=9981468#9981468 then I'll do this. A little nervous about lifting the rotor, but if you say it's OK to do, then I know it is. Do you know if it is OK to do the test light at the number 1 terminal to ground if the plug is off the coil to check if a signal is coming from the ECU and not being corrupted by a potential coil malfunction. Is there any danger of ruining the ECU?

Duncan

[tjet]

Thanks!!!!!

[crazyvwvanman]

Never use a test light other than an LED one when working with the fuel injection.
Like VW says and shows.

Mark

[bobhill8]

Thanks Mark - another one of your posts copied and filed away, both physically and electronically.
_________________
1986 Westy
1971 Squareback

[do.dah]

Thank you Mark. You are a godsend!!
Hope you have a GREAT NEW YEAR!!

[djkeev]

Thanks!

Added to the FAQ guide ........
I put it in with the Hall diagnostic tool and Digifant test loom.

Dave
_________________
Stop Dead Photo Links how to post photos

Ghia
http://www.thesamba.com/vw/forum/viewtopic.php?t=392473

Vanagon
http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537

Beetle
https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert