Need ECU tested

[Amskeptic]

I am starting to worry about the afm i had rebuilt. I think I'll measure voltages while plugged into the system.

Heres what I got
Pin 7(neg) Pin 9(pos) Starts at 7 volts half on the wiper 4 volt wiper all the way 3 volts. incremental movement of 4 volts but the first 3 volt change was in the bottom half of the wiper sweep.


Pin 7(os) Pin 6(neg) Starts at 2 volts Half way wiper travel 5 volts Full travel 5.8 volts incremental movement of 3.8 volts but again first 3 volt change is in the first half of the wiper sweep.

Kind of echos what I feel on the gas pedal. But I don't know what these number are suppose to be. Are they normal?

Make sure you have a good tester and go follow the procedure in the Bentley. It does have discrete steps as it travels through the potentiometer sweep.
Colin

[flyfisher111]

The Bentley measures resistance, only states resistance should not be lower than 40 ohms and not above 500. It doesn't say what the reading should be at any peculiar sweep angle.

[Amskeptic]

The Bentley measures resistance, only states resistance should not be lower than 40 ohms and not above 500. It doesn't say what the reading should be at any peculiar sweep angle.

The actual potentiometer track is delivering a proportion of the voltage supplied to the wiper. It is a bit of a zig-zag as you measure continuity across the etched board. If get any reading, you at least have connection, which gets dicey if the board burns through. Symptoms of board burn-through or lousy contact are hard skips.

Now, we left off with decent running in the lower gears, yes? AFM good.
Colin

[flyfisher111]

Yes isn't runs in first and second gear. I don't know if AFM is good. I don't have a linear progression on the voltage. out put. Tomorrow I ll try fiddling with wiper arm.

[asiab3]

If it runs well in the first two gears, the AFM and ECU are likely fine.

Let’s go WAY back. What are your valves adjusted to? What about your points? What about your ignition timing? Give us specifics in how you set all of them, and what you set them to.

Robbie

[flyfisher111]

Valves; are adjusted to .006.
Points; are .016 I bought a real timing light and was able to check the dwell its 47degrees
The timing; I bent the stops out a bit and with my new timing light was able to set the max advance at 28* with vacuum off.

I feel certain that all the mechanical aspects are set per "Bentley" and "How to rebuild your aircooled engine".

I checked the wiring plug at the ecu per Bentley

I was able to raise the rpm up 4800 and it wasn't yet at full throttle, I was afraid to go any farther even though the acceleration was smooth and had no misses. Don't know if that accounts for anything.

Do those upgraded ignition coils really do anything, the ones that claim to have 45k volts?

I

[flyfisher111]

Today I am going to re check my valves and do another compression test.

[flyfisher111]

I got my distributor in seems to have smoothed out the advance response.

My spark is short but is white will jump 3/4 of an inch.

[flyfisher111]

Anyone know why the air regulator is grounded through the ecu ?

[Amskeptic]

Anyone know why the air regulator is grounded through the ecu ?

That's a great question, and I cannot answer why. Get back to us with the answer after you research it.
The community thanks you.
Colin

[flyfisher111]

I bought a used distributor cleaned it ,put in no change. I bought a air flow meter for a renault 1980 -83 the meter s last three digits were 027 my vw AFM is 028. This gave a nice linear voltage read out on my analog tester. The voltage was about 1 volt higher than the vw 028. I adjusted the cog spring about 8 spaces clock wise. But what really made the difference was a rebuilt ecu from the bus depot. I paid through the nose but the ECU was the problem. The morale of the story is to eliminate all other possible problems before you buy an ECU. But it can be the ECU.

Thanks for all help. And this thread has a happy ending

[Amskeptic]

I bought a air flow meter for a renault 1980 -83

But what really made the difference was a rebuilt ecu from the bus depot.
The moral of the story is to eliminate all other possible problems before you buy an ECU.
But it can be the ECU.

Thanks for all help. And this thread has a happy ending

Wow.
a) did the Renault AFM bolt right up to your air filter box?

b) I have never run into an ECU problem yet. Perhaps ECU problems will begin to show up as they get older and older?

Congratulations! Your tenacity will put you in good stead with your Volkswagen.
Colin

[flyfisher111]

The Renault AFM needed some gasket sealant between the the unit and the air box, but the bolt pattern was the same. The idea came from this forum or the thesamba. Also the ECU was rebuilt by Cardone. I saw ads for these units but could never find one in stock. Maybe someone bought them all up. Bentley says to to short circuit the wot switch and if you don't get a rise in rpms to replace the ecu so i considered the ecu suspect.

Couple of things to point out;

I tested the upgraded distributor and found that there was not enough advance time span. Replaced it with a bosch unit.

My "rebuilt "AFM meter was not putting out a nice linear 5 volt progression. Replaced it with the Renault( which was cheaper)

When I added the Cardone ECU it was like adding a conductor to a meritable symphony orchestra.

Doing any of these things alone would not have produced the result i got.

So many thanks to all who contributed and ain't the internet wonderful! Knowledge is power....... literally.

[asiab3]

I am glad you are pleased with your diagnostic path! That’s what it’s all about.

Does Bentley have an ECU rest that doesn’t utilize the full throttle switch? Many FI T4 engines do not have those, from the factory.

Though in my life I have never witnessed a bad ECU, I did indict one just last weekend with a bus that wouldn’t start. I swapped ECU’s because I had one, and morale was dangerously low after trying for hours. After, the engine immediately fired up... But then I put the “broken ECU” back in, and it ran just fine. My diagnosis: ECU tabs were corroded because the bus hadn’t been sitting outside for years without an engine. Unplugging and plugging it back in probably cleaned off the electrical connections just enough. Sometimes these cars are mischievous like that :)

See you on the road,
Robbie

[flyfisher111]

Ok I put the other ecu back in and report back.