From Audi 100 to urS4 in a week

[hunker7]

[UrS4boy]

Motronic ECU opening procedures

Not being funny, but how the hell do you get it apart? Got the metal casing off, but that's about it.

Lots of ECU accessing and opening info at the long version of my Engine Bay Device Map

(the links are not live under the labels, go to the listed links below the diagram):

http://forums.quattroworld.com/s4s6/msgs/22625.phtml

[hunker7]

Photos showed up. Okay both are 551AAs which = non-immobilizer. When you open the one from the red avant, I will be curious to see whether it has factory socketed boost and fuel chips. However with your VIN NN123###, it is probably a 3rd week in April 1992 build, past the date when they switched away from the socketed ECUs (mid-Feb 92) and the tuna can "dizzy" Cam sensor.

But still, I am curious.

Not being funny, but how the hell do you get it apart? Got the metal casing off, but that's about it.

[UrS4boy]

Photos showed up. Okay both are 551AAs which = non-immobilizer. When you open the one from the red avant, I will be curious to see whether it has factory socketed boost and fuel chips. However with your VIN NN123###, it is probably a 3rd week in April 1992 build, past the date when they switched away from the socketed ECUs (mid-Feb 92) and the tuna can "dizzy" Cam sensor.

But still, I am curious.

[hunker7]

At the moment, like yesterday, neither IE9 or Mozilla Firefox will display any of your photobucket photos, so I can't see the PNs on the two ECUs.

It would seem that the revving issue in 5th/6th is NOT related to the ECU and therefore is related to fuel delivery (fuel line kinks, weak fuel pump, etc) or a mechanical drag. I have made suggestions about these before.

PN for both ECUs is 4A0 907 551 AA.

I will start with checking vac line at the FRP, fuel hoses that are in the fuel tank, also swap FRP, and then work from there.

Can't really do the speed thing you suggested, as I am in Leeds, and there isn't any flat roads I could do it on

[UrS4boy]

I hope this makes things clearer

At the moment, like yesterday, neither IE9 or Mozilla Firefox will display any of your photobucket photos, so I can't see the PNs on the two ECUs.

It would seem that the revving issue in 5th/6th is NOT related to the ECU and therefore is related to fuel delivery (fuel line kinks, weak fuel pump, etc) or a mechanical drag. I have made suggestions about these before.

[hunker7]

Let me start from the beginning.

I have/had 2 issues with my red S4;

• Bad fuel economy (14mpg around town)
• Not going over 4000rpm in 5th/6th gear

I thought, that bad fuel economy is down to the fact that it's not running properly.

NOW!!!

Yesterday I took ECU out of the grey S4, and put it into my red S4 and went for a test drive, so 3 things I noticed

• Fuel economy was inproved drastically (18-20mpg)
• ..but car still won't go past 4000 rpm in 5th/6th
• and car takes longer to boost, but still boosts to 1.9bar

Here are pictures of both ECU's;

RED S4 ECU


GREY S4 ECU


I hope this makes things clearer

[UrS4boy]

At the moment i fitted grey S4 ECU into my red one, and fuel economy has gone up considerably. Is there a way to determine what is wrong with the red one's ECU that the fuel economy is *****.

Okay, a few comments:

1. What are the part numbers on these two AAN ECUs? I am asking so you will confirm that one (or both) of them are NOT immobilizer ECUs. Due to the fact that the grey UrS4's ECU is working at all in the red UrS4, it implies that it's PN ends in 551AA, i.e. non-immobilizer.

Your choices, based on list provided by prj, are:

"551A early UrS4 with pseudo dizzy and 8k boost chip
551AA UrS4 non-immo, Europe and America
551B UrS4 same as 551AA, but auto
551C UrS6 incorporates all software updates from RS2, different codebase, more diagnostics
551D UrS6 same as 551C but auto (see photos at the end of this post)
51E UrS6 has a small tweak to fuel on cold start
551F UrS6 same as 551E but auto."

Reference: http://forums.quattroworld.com/s4s6/msgs/21009.phtml

2. Why are you concerned about fuel economy? I thought your number one concern with the Red UrS4 avant was the problem with not getting over 4000 RPM in 5th or 6th. With the grey UrS4's ECU in the red UrS4 avant, are you getting over 4000 RPM in 5th or 6th? I know you say that it isn't boosting as fast (which will be another issue for another thread (HINT HINT (again)) but the issue should be is there still an RPM restriction with the grey ECU in the red avant.

You have a good diagnosis tool with this alternative ECU but you are not using it.

[hunker7]

Has the red one's ECU ever been apart?

In my experience the ECU is hardly ever at fault. But the vac line may be split or disconnected inside.

I did open the red S4 ECU, when I had the issue with boost and I couldn't see anything wrong with it. But I can open it tonight, and take some pictures, maybe someone can see something wrong with it.

Before I took ECU out, my average mpg was 13.5

[newsh]

In my experience the ECU is hardly ever at fault. But the vac line may be split or disconnected inside.

[newsh]

Has the red one's ECU ever been apart?

[hunker7]

Same thing applies with the vac line to the ECU, if it's original it may well be leaking, especially where it clamps at the ECU end

I've replaced vac line clip on that already

[hunker7]

I have NO idea which ECU/which car you are talking about anymore.

You need to start a new thread for the grey 93 S4 avant. It is hard enough to try to help you with the red one without mixing comments about the grey one into the red one's thread. Seriously does our (mine at least) head(s) in.

OK, will start.

At the moment i fitted grey S4 ECU into my red one, and fuel economy has gone up considerably. Is there a way to determine what is wrong with the red one's ECU that the fuel economy is *****.

[UrS4boy]

Gutted about the ECU though, not a cheap thing to buy. Is there any way of determining what's wrong with it?

I have NO idea which ECU/which car you are talking about anymore.

You need to start a new thread for the grey 93 S4 avant. It is hard enough to try to help you with the red one without mixing comments about the grey one into the red one's thread. Seriously does our (mine at least) head(s) in.

[newsh]

Same thing applies with the vac line to the ECU, if it's original it may well be leaking, especially where it clamps at the ECU end