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Sat Sep 27, 2025 3:30 pm

Is it strange to have what is marked as pin 20 in this diagram not have a pin to connect to on the ECU?
You can see the pictures of my harness, ECU and the most accurate pin out chart I could find.
I confirmed that pin 20 does indeed connect with 86b on the double relay which is supplied with 12 v from the afm when the engine is running and the afm flap is open.

Sat Sep 27, 2025 4:11 pm

I must be looking at it wrong, I'm pretty sure I see a terminal in the plug and a matching one in the ECU.

Sat Sep 27, 2025 4:21 pm

I circled the spot in question. See below. The bus ran fine for years with this but after a rebuild the injectors are not firing, I suspect the ECU isn’t grounding them out.

Sat Sep 27, 2025 5:00 pm

I see it now, I was looking at one upside down.
If it ran before it's not the reason it's not running now, it's common for Bosch to not use terminals or circuits as these systems evolved, changes occured almost monthly to keep up with changing smog laws.

How are you confirming the injectors are not getting a signal?, noid light?

With all 4 injectors unplugged test for power on one pin in the harness side of the injector plugs on each one. Also confirm all three grounds are secure on the grounding star under the plenum. And finally make sure the single white FI harness wire is connected to coil #1 (same terminal the green wire from the distributor is on). Also confirm the backup light harness with it's inline fuse is connected to coil #15, the fuse is for the backup lights, but the branch leading forward to the DR powers the FI system.

Sat Sep 27, 2025 5:13 pm

Thanks for the reply.

I have spark and the engine tries to ignite with the cold start fuel.
I used an old injector that bench tested good and connected it to the harness while turning over and got no spray.

I also used a test light with the probe on the injector plug and the other grounded to the other terminal, per Bentley. No flickering light.

I tested fuel pressure and it is fine.

All 3 grounds on the spade under the plenum have fresh connectors.

The long white wire from ECU to coil is connected to terminal 1, the same as the distributor.

The hot like from coil terminal 15 is getting to the double relay, ( the same power line that feeds backup lights.)

I thoroughly tested the double relay for proper functioning with ignition off, on and in start position.

Injectors aren’t firing.

Sat Sep 27, 2025 8:18 pm

KMO wrote: .......... No flickering light. ......
So then solid light?, or no light? There should be constant power at one of the injector plug pins, no power means no squirt. Test each of the terminals to case ground with your light.

Sun Sep 28, 2025 6:18 am

busdaddy wrote: KMO wrote: .......... No flickering light. ......
So then solid light?, or no light? There should be constant power at one of the injector plug pins, no power means no squirt. Test each of the terminals to case ground with your light.

Each pin of the injector plug on harness has constant light when I ground it to the engine. I think I read somewhere that this is normal, both sides have positive charge until one side is grounded through ECU logic to close the injector solenoid. But when I bridge the two pins and turn it over I get no light and no flickering light when I turn the engine over.

Sun Sep 28, 2025 7:23 am

Both terminals show power because the other three are still plugged in to the injectors, it's a batch fire system and the power is backfeeding through the injector coils. A regular test light doesn't usually show anything when testing injector pulses, you need a noid light, kits are cheap on Amazon, or your FLAPS will rent you one.

How were the injectors stored during the engine rebuild?

Sun Sep 28, 2025 8:41 am

I’ll get a noid light and test it out. Injectors were stored in a ziplock bag in garage. The injectors bench tested with a good spray this week so I know they are functional.
Is there a good way to test if the ECU is grounding the injectors? I’ll get a noid light and try that. Wonder if there’s another way to test the ECU for this function.

Sun Sep 28, 2025 8:56 am

Some of the Control Modules fit more than one system. Remember VW utilizes the cheapest method of construction. So, sometimes shit does not look right, as it may fit on other car systems.

Regarding the problem. One question. Is there a white wire, labeled (1) going to the 1 side of the coil? That wire is the trigger wire for the injectors.

If you do have that connected. Are the 3 ground wires attached to the alternator body and clean? Is there a ground strap between the front tranny mount and the body and clean? Is the negative battery cable clean?

Sun Sep 28, 2025 10:27 am

KMO wrote: ...... Injectors were stored in a ziplock bag in garage. The injectors bench tested with a good spray this week so I know they are functional. ......
OK, that rules out stuck injectors.

As Jimbo says nearly any L-jet ECU from the era will at least get it to run for a test. But in 998 out of 1000 cases the ECU is fine and there's something else wrong, they really are bulletproof.

If you are satisfied everything is connected properly the next step is to closely inspect every connector, the terminals sometimes get loose in the plastic and push backwards out of the plug as you connect it. Then there's the broken wire hiding inside intact insulation, they are super fun.

Sun Sep 28, 2025 10:28 am

VW_Jimbo wrote: Some of the Control Modules fit more than one system. Remember VW utilizes the cheapest method of construction. So, sometimes shit does not look right, as it may fit on other car systems.

Regarding the problem. One question. Is there a white wire, labeled (1) going to the 1 side of the coil? That wire is the trigger wire for the injectors.

If you do have that connected. Are the 3 ground wires attached to the alternator body and clean? Is there a ground strap between the front tranny mount and the body and clean? Is the negative battery cable clean?

The white wire from coil terminal to ECU is installed correctly.

3 ground wires on FI harness are on a spade terminal attatched to engine under plenum. Nothing to alternator except alternator harness.

The one thing you mentioned that I haven’t checked would be the ground strap from tranny to body. I’ll go ahead and clean that up.

Sun Sep 28, 2025 11:56 am

The grounds attach to the alternator body on type 1 (beetle), on a bus they go on the star on the case bolt below the plenum. Some also have a small ground on one of the DR attachment screws, or the DR has to be cleanly attached to the firewall.

Sun Sep 28, 2025 1:22 pm

KMO wrote: VW_Jimbo wrote: Some of the Control Modules fit more than one system. Remember VW utilizes the cheapest method of construction. So, sometimes shit does not look right, as it may fit on other car systems.

Regarding the problem. One question. Is there a white wire, labeled (1) going to the 1 side of the coil? That wire is the trigger wire for the injectors.

If you do have that connected. Are the 3 ground wires attached to the alternator body and clean? Is there a ground strap between the front tranny mount and the body and clean? Is the negative battery cable clean?

The white wire from coil terminal to ECU is installed correctly.

3 ground wires on FI harness are on a spade terminal attatched to engine under plenum. Nothing to alternator except alternator harness.

The one thing you mentioned that I haven’t checked would be the ground strap from tranny to body. I’ll go ahead and clean that up.

Sorry man. I knew it was a Bus. Sorry for the incorrect info on that. But regardless. The electron path to ground has to be clean, intact and fully functional.

Sun Sep 28, 2025 6:44 pm

Thanks for the input. I’ll get all grounds squeaky clean… I also went ahead and bought an ECU, I’ve wanted a spare for a FI type 4 start stand anyway so if it doesn’t fix the issue then I’ll have an extra.

Wed Oct 01, 2025 10:57 am

Continuing my troubleshooting while I wait for a new ECU. Coul a bad AFM create a no start/no injection situation?

Wed Oct 01, 2025 11:53 am

No, the engine will run (idle only) with the AFM unplugged.

Wed Oct 01, 2025 2:36 pm

Ok, I’m still reading a stack of tech articles to understand the pins on the ECU harness that actually trigger the injectors. I know the wires that lead to injectors but not certain of the process that switches the ground off and on.

Wed Oct 01, 2025 2:48 pm

No doubt you've read all of these already :o : https://www.thesamba.com/vw/forum/search.php?searc..._chars=200

The one about providing ground for the AAR goes down a rabbithole that leads to many diagrams and internal probing.

Tue Oct 07, 2025 9:03 pm

I tried the new ECU today and still have the same symptoms. I ran the below tests to check the harness and FI components. Everything checked out perfectly. except I’m confused about the first test for pin 1 ( coil to ECU wire). Can anyone explain how this should be tested if I am following the below instructions? Also, the pin one ALWAYS has continuity with ground. I’m hoping that this wire is shorting out on a ground in the harness or something and that I found my problem. I tested continuity from pin one to ground on the engine case and I’m always getting continuity. Is this wrong? Can someone explain the proper method for the first test below? Pin 1 to ground.