Checking my work before buying a new ECU

[vanagon89]

Hi everyone, longtime reader first-time poster.

My engine abruptly cut out while I was driving last week. I had some minor acceleration hesitation (so minor I convinced myself I was imagining it) leading up to the cut-out, but no rough running.

This is my first no-start troubleshooting process and I think I know what to do, but wanted some other perspectives before I swap the ECU.

Some initial checks I did

Checking spark:
Pulled each plug, all were golden brown / no soot or oil fouling.
Grounded each plug and cranked 5 seconds. No sparks visible at any of the plugs.
Grounded center wire and cranked, spark visible.

Checking fuel (out of due diligence):
Fuel pump buzzes when turned on.
Exhaust smells like gas when cranking with fuel injectors plugged in.
I have not done a spray test yet (couldn't find a pan that would fit)

Checking air:
No obstructions above air filter
Exuast puffs out air when cranking

Zeroing in on Spark
Pulled the cap and rotor. A small amount of carbon buildup. I replaced the cap and rotor 2 years ago. And have probably driven less than 15k since. I'm doubting it's a cap/rotor issue since there were no sparks available at any of the plugs. Seems unlikely all contacts would go bad at once?

I tested the hall sensor plug with the center spark plug cable grounded. Checked voltage / ground on the outside terminals and it was normal. When connecting the center terminal I heard a swishing noise (fuel returning from the FPR?) but no spark at the center cable.

My working hypothesis is that the ECU is fried and not sending the coil the signal to fire at the right time. Is there anything else you'd check before trying to do an ECU swap? I don't want to jump to conclusions since they're scarce. Unfortunately I don't have a spare so I'll need to order one.

Thanks in advance for your help!

[4Gears4Tires]

Welcome!

What year is your van? Engine?


When I had hiccups while driving it was the ECU. Resoldering all the solder points fixed 95% of it. My hiccups went from 15-20 minutes to 2-3 hours. Maybe try taking the ECU apart and looking for any blown item and try resoldering. No spark at all points to something larger though.

Have you gone through this thread? https://www.thesamba.com/vw/forum/viewtopic.php?t=474332
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'87 Syncro Ferric Oxyhydroxide Superleggera Edition
'85 Westy Sciuridae Domus Edition

[vanagon89]

Skipping the basics! It's a 1989 2.1. Thanks for that thread. Reading through now...

[hdenter]

Why not ask if there is someone in your neck of the woods who has a good one you could swap in and test with. Either that or do more testing of leads and harness before pulling trigger. Throwing parts at it is not an economical way of fixing things...
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'79 triple white convertible bug
'84 sunroof vanagon
'85 weekender

[E1]

So spark’s going into the cap but not coming back out of it?

Regardless of cap age, that’s where I’d start!
— Any chance it’s not seated fully?
— Do all the little wires aside the distributor look attached and unharmed?
— Then swap rotor if still no spark

Distributor?

I’m probably wrong but don’t see how the ECU would do this… and FWIW, after eleven years’ ownership of two vans and six digits of miles, we’ve had many no-starts and it’s never been an ECU (despite repetitive opinions of “It’s the ECU”).
_________________
1984 Westfailure/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans

"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere." — Colin Chapman

Jonathan Weisheit, Race in Peace:
https://www.youtube.com/watch?v=z3dS7xiFn7I&t=500s

[MarkWard]

A timing light is the easiest way to check for spark on the coil wire and the plug wires. No risk of getting shocked.

With vehicles this old and the fact that even the manual troubleshooting chart eventually ends at trying a known good ECU. I carry a spare and recommend that anyone that travels also carry one.

So, nothing wrong with getting a second one. The ECU does control spark on the Digifant system. That doesn't mean the problem is the ECU. I'm lazy, did you try a known good coil? You should also one by one ohm out the plug wires and the coil wire.

[E1]

We’ve carried a spare since 2016, taking up the space of five good movies.

Yes, could be the ECU, and Yes, maybe you get a spare. Mostly I’m suggesting exhausting a lot of other things first — at least, before getting a spare and trying that.

Worst that can happen is you learn a ton, to refer to again later.
_________________
1984 Westfailure/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s
AI has spoken to further illiteracy, to steal, to cheat, and to replace humans

"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere." — Colin Chapman

Jonathan Weisheit, Race in Peace:
https://www.youtube.com/watch?v=z3dS7xiFn7I&t=500s

[kamzcab86]

Before condemning the ECU and going to the expense and trouble of replacing it, I'd thoroughly test it:

https://oldbluesblog.com/files/DigifantProTrainingManual_SingleSided.pdf

PDF pages 46-47 (manual pages 40-41).

You have an '89? See page 48. It may not be the source of your current issue (but it's worth checking), but it might be the source of a future issue (ask me how I know).
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~Kamz
1986 Cabriolet: www.Cabby-Info.com
1990 Vanagon Westfalia: Old Blue's Blog
2016 Golf GTI S
"Real knowledge is to know the extent of one's ignorance." - 孔子

[vanagon89]

Thanks all, this was the sanity check I needed. Going to start with some basics:

- Checking the rotor is even spinning!
- Replace rotor (cheap enough) and maybe cap.

The wires coming from the hall sensor all look good. I'll also test the ECU pins, thank you for the resource. Also looking through Bentley 24.61.

[thebaz67]

this thread may have some help.

https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0

[Abscate]

The job of the distributor is to distribute the incoming spark to the cylinders.

I bet you have a cap rotor problem
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[Jake59]