ECU failure?

[KTPhil]

I am usually the first one to call these rare, but I think I've got one.

The car started missing a bit when I was doing a break-in run on the freeway, and then when I got home it was hard to start. When it did start it sputtered and couldn't idle. Then it seemed to clear up for a short drive down the street. It then sputtered again, so I pulled into the garage for some checks.

I checked timing, spark, hoses, and all was well. All wires were tight, with the exception of the 2-pin injector connector on #3, which was flaky and pulled apart when I put the motor in last month. I had re-crimped it (badly) to get it running for the break-in, but I now figured this was letting go, and so I properly spliced in a replacement connector with new boot when this recent problem came up. But this fixed nothing!

So I got out my EFAW 193 tester and hooked up my fuel pressure gauge. All the resistance and continuity tests came back nominal.

Pressing the PUMP button on the tester made the pump run, and it jumped right to 28psi every time.

But here is the tell:

The pump does NOT run when I turn the key on. I hear the main FI relay click, but I get no click from the pump relay, and no 1-second pump run. This is now consistent... just one click and no pump run.

I have checked the relay connections (visually and wire tugging) and they seem fine, though I will make another check with a VOM and be sure.

But the odd thing is that my EFAW 193 tester can always trigger the pump to run. Functionally, this is simulating the grounding of pin 19. Since the tester is talking through the same wiring and relays... and it works... but the car does not... that suggests the wire 19 circuit inside the ECU is the fault, not the wires and relays.

All parts of the circuit are common whether I am turning the key on, or using the PUMP button... EXCEPT for the ECU itself.

I remember posts about rare but real ECU failures. IIRC, this included injector output transistors, and the pin 19 fuel pump grounding circuit.

In the short term, and as a diagnostic, I will ground the FI relay terminal 85 with a jumper (bypassing the ECU safety interlock), but it will tell me where the fault is (or isn't).

I also have a spare ECU, which is a better mid-term fix.

Then I'd like to fix my original ECU for the long term and have working spare.

Has anyone had this problem? Has anyone fixed the pin 19 circuit in the ECU?

[Bobnotch]

[KTPhil]

Yes, I just heard from Jim also, and he confirms it is likely the transistor in the ECU.

I have a little tinkering to confirm the diagnosis, but it is looking pretty certain.

Yes, he does the repair, and my only question is how many ECUs do I have on hand to send him, so I'll also have a reliable spare ECU.

Thanks!

[Ceckert64]

You should be able to send just the one ECU. Maybe it’s bad luck but I have had 2 ECUs that the fuel pump transistor rotted off of. The one was in my Squareback and it was like that when I got it. Then I got a junkyard ECU and it worked well then one day the transistor broke off, similar to what happened with yours. There is a piece of foam that goes under the transistor and the foam disk holds moisture rusting the legs of the transistor and eventually causing them to break.
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1964 sunroof Beetle Restoration "Herbie"
“Joann” 1970 Elm Green Squareback
1972 Sierra Yellow Tin Top Westfalia Camper
“Fitz” 1971 Westfalia Poptop

[KTPhil]

Partial success: Grounding wire 19 in the engine bay (which defeats the safety shutoff) makes it run the pump and the car starts right up. So that was the basic problem.

But I still am getting some missing once warmed up, and it seems to be running a bit rich, so I have more digging into the MPS, TPS, and get out my spare ECU. No vacuum leaks I can find, but I'll check again.

As it has 100 miles on the rebuild, I'll probably check/adjust the valves again to be sure one hasn't slipped.

No more time this holiday weekend, so stay tuned next weekend for more updates...

[Tram]

Zipping through on a rare chance to check in, but yes, faulty ECU. Keep in mind that as these cars and parts age, a lot of the old "facts" are changing, such as ECUs being either good or bad. Try the spare ECU before going anywhere else because I have seen this movie before. Solder joints are getting weak and corroded in these ECUs, among other things. Had a '69 last year that intermittently ran rich enough to cause misfiring and heavy smoke/ fuel from the exhaust- once warmed up. Every time i thought I had it fixed... it did it again. Finally, out of complete desperation and lack of further options, I replaced the ECU and it's been fine since.

The days of "it's either good or it's bad" with engine electronics is over, unfortunately. Same goes for ignition coils and condensers. I have seen probably 5 condensers now make people think they had fuel delivery issues with the car acting as if it was running out of gas intermittently- both old and new condensers.

Strange days and fun times indeed.
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[Bobnotch]

[KTPhil]

Okay, I dug thought my spares, and put in a replacement ECU and TVS. It seemed to work, and at least the ECU definitely solved the "no pump run" issue.

But the high-rpm miss came back, and it sputtered, and at the end of the freeway offramp, it quit and would not restart, just like before. The pump was running, but it took many minutes of cranking and a very heavy gas pedal to keep it running, though it did limp me home.

So my next suspect will be the condensor, and next the fuel pump. Or maybe a clogged filter. So little joy. Again, stay tuned...

But some interesting parts issues. The vintage Bosch-remanufactured ECU, still in the sealed box, looked great, but interestingly, was remanufactured to the "D" configuration, even though the metal casing cover still was stamped "C".

I can figure out why they would re-use a different box and put a D circuit card inside. But I would think they would scratch out the old indented "C". Stickers can come off, indentations do not. Odd.

Old ECU pump transistor. The tilt of the bad ECU's transistor suggests the lead corroded:

Remanufactured ECU pump transistor:

Looks fine, but looks to have the same (water-porous foam?) base pad.


Next up was the TVS issues. I substituted a used 4-pin with the proper part number. It works and was easy to do the basic external adjustment.

What is odd is that THREE NOS TVSs I have with the same VW part number are NOT compatible with the original! Yes, they are 4-pin, but the connector polarization is not the same, and the terminal numbers are not the same. New but incorrect TVS:

The original parts have a pin 14 instead of the combo 12/47 which is a terminal label that is seen on the 5-pin TVSs.

Very strange! I'll take one apart and see if they can be used, despite the wrong terminals, but as configured, the lack of pin 14 means I cannot adjust the damn thing! It must be for a different year. Weird that all three NOS units have this issue. Oddly, all my old used units gathered over the years lack terminal numbers, and work like my original.

I will review this thread, which talks about the 4 and 5-pin wiring.
https://www.thesamba.com/vw/forum/viewtopic.php?p=3740423

[Tram]

Don't you have a 123 kicking around? Try it. That'll eliminate the condenser AND the other possibility here- trigger points.
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[KTPhil]

Yes I do have a 123, but with it not always starting, getting the initial timing might be a problem. Can you time those statically, or does it have to be running?

I don't want to change too many things at the same time. I figured once it is running consistently, I'll drop the 123 in, and have my old points distributor as an on-the-road spare.

[Tram]

[KTPhil]

"Instructions? We don't need no stinkin' instructions"?
Thanks

Since it's a PITA to remove the distributor anyway, maybe this is the time to move to the 123 and be done with it. Hmmmm...

[Mike Fisher]

Mine starts/runs great with a 123 ignition.
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69 FI/AT square Daily Driver
66 sunroof,67,70,71,71,71AT,72,72AT,73 Parts
two 57 oval ragtops sold
'68 Karmann Ghia sold

Society is like stew. If you don't keep it stirred up you end up with a lot of scum on the top! - Russ_Wolfe/Edward Abbey

[KTPhil]

So installing the 123 distributor (which was easier than I expected) didn't solve it. I am tearing my hair out, and will miss next Sunday's Meet in the Middle (Solvang area).

I replaced the ECU, installed the 123, checked fuel pressure, timing, replaced the coil, replaced the TVS... and I still have these symptoms:
1) It started, but soon ran rough and would not increase RPMs with throttle opening, then died; did this a few times in a row.
2) Now it cranks and cranks with no hint of starting.

Compression, spark, fuel... is there a forth ingredient (magic)? I'm missing?!

It's gotta be something simple, but I haven't hit on it yet.

So my next steps are to really really verify fuel and spark.

1) I'll use a spare plug hooked to a wire and crank the motor, looking for a spark. The timing light flashes (any least it did long enough for me to set timing with a strobe), but that doesn't prove an actual spark.

2) Then I'll pull an injector pair and verify it's squirting. I have 28 psi while cranking even when it just doesn't want to catch at all.

Any other thoughts? I am usually the problem solver, but I'm running on empty here.

[Mike Fisher]

Fuel Return Line could be plugged up. BTDT
_________________
https://imgur.com/user/FisherSquareback/posts
69 FI/AT square Daily Driver
66 sunroof,67,70,71,71,71AT,72,72AT,73 Parts
two 57 oval ragtops sold
'68 Karmann Ghia sold

Society is like stew. If you don't keep it stirred up you end up with a lot of scum on the top! - Russ_Wolfe/Edward Abbey

[Tram]

[vwsquare2]

Have you checked the CHT (TS-2)? I know that's a long shot and I'm not an expert but I think the symptoms may fit. You've eliminated most of the usual suspects, the MPS, the ECU, and eliminated the distributor and it's trigger points by installing the 123 distributor. Since you're doing break in, I'd think all the hoses are tight so a vacuum leak is unlikely and probably would cause this all the time, not just when it is warmed up.

Since you are seeing the problem, once the engine is warm, could it be the CHT? You rebuilt the engine so I assume the CHT was pulled out and then reinstalled. There is not much to a CHT but it is 50 years old so maybe something happened to it when the engine was rebuilt and the CHT was reinstalled.

If you replaced the CHT as part of the rebuild, maybe the new one is bad?

[KTPhil]

I will check these things out, thanks guys!

A few notes regarding them:

- Fuel return line...
I didn't replace the lines when I rebuilt the motor, but they are not all that old. I did replace the leaky fuel pressure regulator a couple of years ago, and adjusted the pressure. My pump drains down pressure fast... like down to 10-12 psi almost immediately, so the internal check valve may be toast. But it instantly reached 28 when the pump runs.

Checking fuel pressure when it won't start is a problem, so I grounded wire 19 in the engine bay to make sure it was at full pressure while I cranked it with the key. It didn't change anything.

A plugged return line should still allow the injectors to fire, and might drive pressure over 28 while running continuously. But is there a different problem the plugged line can cause, creating a no-start condition?

- Battery charge
It cranks very fast, and I had trickle charged the battery a week or so ago, so I think it's in a good state. I'll add a voltmeter to the coil to see what it is while cranking. I still have the original generator. Red light goes out, and a couple of years ago I replaced the regulator with the new solid state style. I lent my charger to the community garden for their tractor, but I can get it back and make sure.

Coil resistor? You mean internal to the coil? I had the stock ignition coil originally, and swapped it for a latter day Bosch blue coil, with no change.

- CHT sensor
I wondered about this, too. The VW EFI tester passed it, but that's just a static or short-term spot check. Intermittent or temp-related symptoms suggest this still could be the cause.
With the latest problem, it's not getting warm enough to matter; it ran just for a few seconds before dying.
But they can be loose internally, or poorly grounded, so I'll check if I have a fixed resistor I can substitute, or jumper a spare CHT sensor, and try again.

Injector check: I can connect a spare injector and see if it squirts every other rotation while cranking (with the pump jumpered as before to know it's got full pressure).

Spark check: Similarly, I'll connect a spare spark plug to ensure I'm getting spark right at the plug.

Thanks, these will at least eliminate more causes until the "dope slap to head" moment that I hope is coming soon!

[Tram]

I thought you had the Bosch red coil with the red banded resistor on there. If you can check spark when it won't start, that would be helpful. Sadly, new blue coils can be defective more often than is acceptable.

I agree to check CHT as well.
Try swapping in the old ECU as a "WTF" Hail Mary pass if everything else checks out.
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[KTPhil]

OK, so I think I solved my engine issue... loose/dirty connection at the head for TS2, as several here guided me to.

I wire brushed it and reinstalled, and it is no longer jumpy when I measure resistance.

I ran it about 50 miles today in the 85 degree heat, and she did well... so I am planning on going to the Meet in the Middle event Sunday as a long (100 miles each way, lots of hi-speed highway) shake-down run in prep for the Invasion. Wish me luck!