ECU reset lower MPG...?

[Trig 0]

After new exhaust was fitted on the VR6 and all the problems sorted on the drive home I got about 34MPG :-P

 

Was advised to do a ECU reset so I did and took the car for a varied drive etc. for 30mins. Now the car is averaging about 26MPG :x

 

I figure either:

 

1. The ECU has never been reset and the old figures were innacurate for my car and 10 years on its not as economic as it was. (The new MPG reading is accurate)

 

2. I messed up the reset or something and the ECU (or somethinng connected to it - lambda jobby) isn't working properly. (The new MPG reading is wrong)

 

Can't really tell yet if it is actualy using more fuel...

 

Any ideas?

[RW1 0]

What are you mpg figures based on? dash or pump litres filled?

 

Sounds also as though haven't done the second part of the procedure for Basic Settings.

 

ECU reset is a VW term. It doesn't mean reset per say. The term translates as ECU is "rapid learning" in the first half ie. battery disconnect & drive sequence, and ECU is "harmonising" in the second half ie. harmonising the ECU and sensor inputs so it knows where everything is.

 

I suggest you do Basic Settings with VAG-COM noting early VR6 ECU's do it differently to later ones in the procedure and see how you go from there, plus get accurate mpg figures for comparison.

 

http://the-corrado.net/.archive/forum/viewtopic. ... highlight=

 

The battery disconnect can always been done again but I doubt you'll get anything different providing that when you started the engine and immediately within the first 10 minutes (from starting) were driving the car not leaving it idling.

 

This sort of change doesn't usually happen when disconnecting the ECU. 3 mpg maybe but not 8.

 

 

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[Trig 0]

MPG figures from the dash.

 

Correct, I didn't do the second part of the procedure...

 

Do you think thay I am using more fuel than I should be then or is the MFA just displaying it wrong? As far as I can tell the car is performing exactly the same as before I did the "reset".

 

I need to get hold of a VAG-COM then...

[RW1 0]

The comparison is like for like, so although the reading has slight inaccuracies, it’s good enough.

 

What you’ve done so far is put the ECU through a rapid learning mode for 10 minutes after starting the engine. If the lambda probe wasn’t changed when the exhaust was renewed, it wasn’t that necessary. In doing the battery disconnect, you’ve lost everything in what the ECU knew about it’s sensors. Basic Setting restores that by putting the ECU into an offset mode whereby it samples it’s sensors and makes adjustments. Mainly very fine tuning for emissions.

 

One of the things that’s been lost is the throttle position through the throttle position sensor. So at lower rpm’s the ECU doesn’t respond well and given you got 34 mpg on the way home, I assume that was on relatively light throttle settings most of the time. Cos the throttle is unknown to the ECU, you may not really realise it but your foot in combination with MAF is giving a coarser fuel mixture. This usually results in about 1 to 2 mpg typically but 8 mpg difference does seem a lot. Sure you are not now enjoying the car’s performance J

 

When you get VAG-COM plugged in, to do Basic Settings on Group 000 or 001 depending on the ECU part number your see in VAG-COM v instructions above, it will have to be a licensed copy as this facility is not in the “freeware” download. Also while you are in the engine ECU, I suggest you take a note of the fault codes for later discussion on here if they exist, clear them down, then drive 30 minutes, then look at the fault codes again in the engine ECU and note what has re-appeared.

 

Also, just do again the ECU battery disconnect & then drive it around followed by Basic Settings about an hour or two later (ignition/engine running on timed hours!) when initial settling of the lambda probe should have happened (in other words, do the disconnect and 10 minute drive one day and do BS a few days later) and see what happens to the mpg.

 

 

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[Trig 0]

Thanks a lot for the help RW. get the feeling that i'm speaking to the right guy! Just need to sniff out a VAG-COM in cornwall now...

[Trig 0]

Ok, just been down to RK Enginering in St Agnes (thanks andrewdowd), we did the basic setup 2 faults found:

 

00537 - Lambda Regulation 08-10 Control Limit Surpassed - Intermittent

 

00525 - Oxygen Sensor (G39) 29-00 - Short to Ground

 

Took the beast for a 30min drive, MPG much better (averaged 33mpg on the way home)! Re-connected the VAG-COM still the same fault codes. We also noticed (before the drive) that when measuring the engine sensors the Active Lambda reading would stay at 1.20 when idle, if we engaged the throttle and the car rev'd to 3000 then released the throttle and let it idle again the reading would quickly count from 1.00 back to 1.200 again. This reading should be 1.00 +/- 0.02 all the time shouldn't it (rhetorical)? I thought this might be something to do with the throttle position..?

[Kevin Bacon 5]

537 is a result of 525 and your reduction in mpg is a result of both :-)

 

The lambda should be constantly varying from 0.1 to 1V (0.8V max in reality) at idle after the lambda goes into closed loop mode (2 minutes). Being stuck at 1V doesn't ominous, not seen that before. When dead, they sit at 0.45V usually....regardless of temperature.

 

I would ignore VAG-COM's interpretation of Lambda activity as it's too slow, instead, connect a high impedance meter (at least 1Mohm input resistance) across ground and the white wire in your 02 Loom (rear engine mount) and monitor the voltage in closed loop mode (hot idle).

 

As said above, the voltage should move rapidly between those ranges.

[RW1 0]

Lambda probe is goosed. VAG-COM 0.95 to 1.04 oscillating about every 0.5 seconds to 1 seconds at idle. Your's isn't.

 

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[Supercharged 2]

I think i'd be going back to the exhaust fitters!!

[Trig 0]

One of the guys at RK noticed that one of the wires (yellow one i think) going to or from the probe looked dodgy. They are going to take a closer look when I go back for an engine tune in a week.

[RW1 0]

Yellow wire is one of the signal wires into the ECU. ECU plug pin 42. At the plug break in the lower engine bay it's pin 3.

 

They've probably disturbed it! While doing the exhaust. Grrrr... clumbsy.

 

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[jezzaG60 0]

Hi tris,

 

This is jeremy from rk engineering. What i'll do when we have your car back for a go on your rollers is to get it on the ramp and hook a good old analogue multimeter up to the lambda. That will soon show if it is cycling rich/lean ok.

I'm not entirely sure what the O2 value vag com gives.... its not a usual lambda voltage (i.e 0-1v). The only thing i can think is that it is a simulated "lambda value" i.e stoichiometric = 1 1 = lean

This would probably make sence as the ecu would be seeing a lean situation and cause an adaption towards the rich side increasing the fuel consumption.

 

Anyway, when we hook it up to the wideband lambda kit and get it on the rollers i'm sure all will be revealed

[RW1 0]

The only thing i can think is that it is a simulated "lambda value" i.e stoichiometric = 1 1 = lean

 

Yes about sums it up..

 

Lambda probe is goosed. VAG-COM 0.95 to 1.04 oscillating about every 0.5 seconds to 1 seconds at idle.

 

Value range on an "good" car. Typically it's about 0.98 in value +/-0.03. View measuring block on Group 006, field 1. Field 2, 3 & 4 are ECU map offsets so ignore these values in your checks and they may have been disturbed by the wildly changing probe values.

 

If probe is changed, then the full ECU set-up procedure will need to be performed after the probe is replaced. Could also be necessary considering the miss-readings affecting the ECU offset values.

 

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[Trig 0]

Ok, spent hours down in St Agnes today to no avail...

 

Changed the lambda probe to a new one still the same problem, overfueling and displaying 1.2 etc. on VAG-COM. We checked the voltage to and from ECU and (I think - bit tired) it read fine. The boys at RK were stumped and even phoned Stealth, who also seemed unsure what was wrong.

 

The lambda I think thinks that it is running lean all the time therefor adds fuel and runs rich but continues to think its running lean...? confused myself.

 

Could it be the ECU? bearing in mind this all started after an ECU reset. I'm going to book up some work with (and take the very long drive to) Stealth so hopefuly they will be able to sort it with the car there.

[RW1 0]

Given the number of times peeps have done this, you've either been unlucky for some reason with the ECU or there is something else disturbed when you did the procedure.

 

Have a think what you did on the day, mainly how and what was done while disconnecting the battery. Anything else. The drive should have had little impact on the electronics and given the probe is not the problem, it's what went on while loosing the ECU memory.

 

How did you disconnect/reconnect the power, which battery terminal first and so on and what else did you do while in the engine bay at the time and elsewhere before driving off?

 

 

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[Trig 0]

I simply unplugged the possitive terminal, left it for 15mins, 20 tops. reconnected the terminal then drove for about 30mins doing all of the acceleration procedures etc. I very much doubt if it would mean anything but my ipod charger was probably plugged into the cigarette lighter!

 

From start to finish I don't recall doing anything else to the car. After a few drives I noticed the MPG was down and here we are!

 

(Thanks for the continued help & advice btw :wink: )

[RW1 0]

Hmmmm.

 

Should always disconnect the earth -ve. It's good practice to take off the negative first when isolating the battery and reconnecting it last if the positive is removed. The main reason is because first reason is that your spanner on touching the car's body will not spark etc. Once the earth is off, the positive if the spanner touches anything won't spark 12 volts as with the earth side gone (isloated) there is no possible circuit.

 

Secondly, taking the positive of first can cause a voltage spike on disconnection if it is not cleanly done and this will be across the car's electronics because the earth is still connected.

 

It could be that the ipod has reversed current flow through the ECU. Only small current is sometime necessary to damage electronic circuits through circuit reversal.

 

This occurs in the VW Digifant fitted cars if an earth in the engine bay is left off and the reverse current fries the ECU.

 

Or as I wrote, you've been very unlucky with disconnecting the positive terminal.

 

 

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[Trig 0]

Well when you put it like that!

 

Apart from the O2 Sensor reading though, the ECU is working fine. All the other readings are fine and it performed fine on the rolling road. Could it be that during the disconnect I fried only a minute portion of the ECU?

 

I guess the way to be sure is to try another ECU. RK Engineering didn't have one (or we would have tried it), which is another reason to take it to stealth.

[RW1 0]

See what they find.

 

Maybe worth asking your local VAG dealers where they send ECUs for repair. May be cheaper than a replacement unless you get hold of a scrappie car's ECU.

 

I'm not convinced the ipod caused it or disconnecting the positive. You are not the first in the world to have something in the power socket or disconnecting the positive first.

 

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[Trig 0]

UPDATE

 

Taken the car to Stealth and they have discovered it is the ECU that is causing the problem - for anyone who was wondering. I can only assume that this happened at some point in the reset/power cut procedure, so you have been warned!

 

http://the-corrado.net/.archive/forum/viewtopic.php?t=33166

[jezzaG60 0]

Glad to hear you have got it sorted now mate. Seems our diagnosis wasn't far out! Did you get your new suspension kit fitted while you were up there?

 

We are gonna be having a VW only rolling road day.... probably in the new year so i'll let you know when cos it would be good to see a few corrados there!

[Trig 0]

Well unfortunately not sorted yet mate, we know the problem but now I need a new ECU or need to get the knackered one repaired... Credit where its due, you guys (and myself) thought it was the ECU all along.

 

I did get my suspension sorted, Koni TA's and H&R springs are the weapon of choice and I can report even this early on, they are great (and not too low to get up your lane!)

 

RR sounds good, let me know. If you find any VR6 ECU's hangin about let me know!

[buttles 0]

I used All Car Electronics when my ABS unit went awol. They let you try a unit and keep it if it solves the problem. For a cost of course! http://www.all-car-electronics.com/stock.html