7A Diagnostic Code Reader that Works!

[S2central.net]

Looking at it now... I was mistaken - this funky relay fuse business predates the 7A, NM and AAH... dates back to before 08.88.

[4WheelDrifter]

On a 7A IIRC you can use a fuse in the top of the fuel pump relay to trigger the blink codes and output tests. The same as you would with the jumper wire/switch. If that's the thing you are referring to?

I've only ever used an LED on both my 7A and 3B.

[mcandmar]

Just had another quick read of the Bentley manual, someday i will write a guide on how to setup the 7A as the closed throttle position, idle switch position, idle speed, and idle CO are all adjustable.

The preferred method to set the base idle speed is to use VAG Tool / VAGCOM to set the ECU in "Basic mode" which does the following,

-fixes ignition timing at 12degrees
-idle valve set to a fixed position
-O2 control disabled (i.e. open loop mode)
-all adaptive values set to 0
-carbon canister valve switched off
-engine coolant temp fixed at 80c

From there you use the measuring blocks function to read the idle speed and twiddle everything until there within spec.

If you DONT have vagcom you can enable the "Basic Mode" by placing a fuse into the fuel pump relay, then set the base idle speed via the rev counter.

To set the CO adjustment you need a CO meter plugged onto the take off pipe on the manifold. That metal tube on the manifold with a rubber cap on it. You can get it in the right ballpark by reading the O2 sensor input via measuring blocks, Bentley manual states you want to see measuring block channel 8 with an average valve of 128.

Only catch is the two settings play off each other, adjust one and it changes the other so you can end up going around in circles if your not careful.

[cexley]

Fuse in fuel pump relay.

We're waiting...

Found this link, which relates to using fuse in fuel pump relay method to dumps fault codes.

http://www.gtquattro.com/ECUcodes.html

The blank fuse holder is present on my 1991 7A fuel pump relay. Has anyone tried this? I don't want to go frying my Hitachi ECU now I have finally got everything sorted....

[4WheelDrifter]

That was the only way I did on my 7A. IIRC my car came with a fuse in the relay.

[mcandmar]

Interesting, i've never used it for reading fault codes Never bothered looking into the engine check light, i thought only US models had it but read we can use it by fitting a bulb to the instrument panel. Maybe Paul can help us out there, think an S2 has the same?

@4WD, sounds like a previous owner stuck one in thinking it was missing, i should put one in mine and drive it around the block to see how it runs..

[quattro20v]

I checked codes with vagcom on my -91 7A just fine. No promlems.

[cexley]

I checked codes with vagcom on my -91 7A just fine. No promlems.

Now I am really curious.

After months of swearing at various versions of VAG-COM and trying every option in the book I was eventually told by the VAG-COM people that their diags don't work with the Hitachi ECU.

How did you set things up with your version of VAG-COM to get your 7A to play ball?

[S2central.net]

There's at least two ECU variant on the 7A - maybe one plays nice with VAGCOM and the other doesn't...

[Mikes2]

it's only the early 7A engines with tubular manifolds where this is a problem. VAG Com works fine on cast manifold cars.

same applies to the fuel pump relay slot that Paul's referring to

[S2central.net]

The fuel pump relay slot is just a jumper to the L wire on the ECU to kick off blink codes.

I didn't know the ECU changed with the exhaust manifold on the 7A - thats curious.

[mcandmar]

Yes there was two ages of 7A, upto 1990 had the tubular 5-1 manifold and an ECU with two connectors (part number ending 266). Post 1990 has the cast 5-2-1 manifold, ECU with four connectors (part no 266D), and a few other changes like different ISV and throttle body. Interestingly the chips availble for the 7A are almost always for the earlier version of the ECU.

[cexley]

Yes there was two ages of 7A, upto 1990 had the tubular 5-1 manifold and an ECU with two connectors (part number ending 266). Post 1990 has the cast 5-2-1 manifold, ECU with four connectors (part no 266D), and a few other changes like different ISV and throttle body. Interestingly the chips availble for the 7A are almost always for the earlier version of the ECU.

In that case, my 20VCQ must be an early model 7A on a late registration as it has the tubular manifold and definately won't talk to VAG-COM. I have also checked the ISV and according to 20V.org, it is the earlier Hitachi unit (see link) so all is starting to make sense now.

http://20v.org/engprob.htm#isv

Every day is a school day. Thanks all for helping out on this one.

[S2central.net]

Wondering if I need to try one of these with my old V6Q on its MMS200 ECU which singularly fails to want to talk to anything. Pity its only a limited code scanner as there is quite a lot of useful 'measuring blocks' that can be extracted from the AAH.

A better project would be to reverse out the OBD from a later Hitachi ECU that likes VAGCOM and port that into the MMS200... Not enough hours in the day for that though. Very tempted to look at sourcing a later ECU from a scrappy though.

[Flat on my back]

Ecu?

Which ECU you want?

I have a spare early and late model 7A, up to you?

Oh, and a MAP late 80q v6.