No boost after engine/turbo upgrade

[gmac78]

Ah thats good info on F96, cheers. I'll strip it down and have a wee play with it to see if i can get it reading correctly. With a bit of luck thats all thats causing the reduced pressure.

The other fault code was for Vehicle speed sensor G68, not the usual Engine speed sensor G28 that shows up with the car switched off.

Any ideas?

[K Simmonds]

G68 is the speedometer sender located on the nearside of the gearbox just above the drive shaft flange, is your speedo working?

You can unplug this and the car will still perform the same.

[gmac78]

Ah right ok, i'm just in the door so haven't had time to check out what G68 is. Yeh my speedo was working fine actually, hmmm

[gmac78]

Just been reading possible effect of fault code 00281 and this applies to me-

"Engine speed briefly drops below idling speed when disengaging clutch in overrun phase"

Basically the car stalled once today when coasting to a halt and i also noticed the revs seem to drop to around 3-400rpm every time before raising to around 800rpm idle speed when slowing down to a halt.

I would thought this would be an idle control valve issue but perhaps the Vehicle Speed Sensor Fault is the cause of it?

[newsh]

I don't think you should have moved the dizzy, if it was really wrong then the car would not start (read the 3B troubleshooting link posted above) so I'm leaning towards a poor connection to the hall sensor.. Maybe in moving it you disturbed the connection, then driving and it brief went o/c again thereby bringing up the fault code.

[UrS4boy]

G68 is the speedometer sender located on the nearside of the gearbox just above the drive shaft flange, is your speedo working? You can unplug this and the car will still perform the same.

Not really. There is no G68. It is a G22 Vehicle speed sensor as shown in this 3B S2 diagram.



From what I understand, when you are coasting (moving) and the throttle is closed, the ECU uses that T55/50 signal to say, "Hey this car is moving but since the throttle is closed (at the idle position), I might as well stop sending signals to the fuel injectors and save some fuel. We're coasting baby. " (As opposed to sitting at a stop, no G22 VSS signal, throttle closed = keep the injectors working").

So in my opinion a faulty G22 signal could confuse the ECU regarding coasting, need to keep injectors working, etc.

REFERENCE: G22 Vehicle Speed Sensor (VSS) 012409191D Info - What it is and where the signal goes:

http://forums.quattroworld.com/s4s6/msgs/168463.phtml

[LHD_Kid]

I don't think you should have moved the dizzy, if it was really wrong then the car would not start (read the 3B troubleshooting link posted above) so I'm leaning towards a poor connection to the hall sensor.. Maybe in moving it you disturbed the connection, then driving and it brief went o/c again thereby bringing up the fault code.

If the dizzy was out, it wouldn't start. Stinks of intermittent dodgy electrical connection to me...

[gmac78]

When i put the engine back together a few months ago after the head work etc, that was the first time i had ever set the timing on the dizzy. Ever since then the car has been started many times in the garage, left running for quite a while, revved up etc to make sure all was ok. Not once did it have starting issues or the hall sender fault code activating the blink light. All of this has just started last week when i took it out for it's first run on the road after the rebuild. I also had the ECU open for the second time changing chips and fitting the R201 resistor which i initially thought might have started all of this, due to possible damage on the tracks within the ECU but perhaps there is no damage at all?

Certainly when i first got the Hall sensor code last week the distributor had not been moved in anyway since it was installed and set a few months back. However, i think when i refitted the distributor a couple of days back after the new hall sensor fitment i did not set the timing correct. I was tired that night and made a mistake i reckon. Today, when i moved it slightly to what it was set at previously the codes disappeared and i was able to make boost. I have checked the wires from the dizzy plug to the ECU and all check out ok so don't think a problem lies there.

There are several markings on the dizzy, two of which are under the distributor cap, and another mark externally which i believe is meant to be in line with a wee notch on the head itself. Maybe i've not been setting it correctly, is there a guide on how to do this properly? I've seen reference to the two marks under the distributor cap lining up whilst the dizzy is pointing to plug 1 on the cap and the engine at TDC etc but no mention off the external marks on the body of the dizzy?

Where is the 3B troubleshooting link? Think i've missed that.

Cheers

[220bhp]

Forgive me if this has already been covered, but if the marks on the side of the dizzy do not line up perfectly you will not get full boost.
This is not an easy job with the engine in the car,as the dizzy is well hidden under the inlet manifold.
It is possible to see it better using a mirror, but the best way is to bight the bullet and take the inlet maniold of.
You dont have to remove it completly, just the manifold studs. Then you can lift it up
out of the way with all the plumbing still attached.

[K Simmonds]

Not really. There is no G68. It is a G22 Vehicle speed sensor as shown in this 3B S2 diagram.

From what I understand, when you are coasting (moving) and the throttle is closed, the ECU uses that T55/50 signal to say, "Hey this car is moving but since the throttle is closed (at the idle position), I might as well stop sending signals to the fuel injectors and save some fuel. We're coasting baby. " (As opposed to sitting at a stop, no G22 VSS signal, throttle closed = keep the injectors working").

So in my opinion a faulty G22 signal could confuse the ECU regarding coasting, need to keep injectors working, etc.

REFERENCE: G22 Vehicle Speed Sensor (VSS) 012409191D Info - What it is and where the signal goes:

http://forums.quattroworld.com/s4s6/msgs/168463.phtml

I stand corrected, G22 it is. I'm just use to seeing G68 when I pull the codes on a mates car with a duff speedo sensor, it certainly doesn't stop the car from boosting properly though.

Dave is quite right the ECU does use the signal when coasting off the throttle.

I think you may have a damaged wire or bad connection as the other guys say.

[gmac78]

Morning All,

There seem to be a bit of difference in opinion with regards to the dizzy setting and boost. One view being is if it's off timing it will simply not start, and the other view sounds like if it is slightly off timing it will start and run but full boost will not be achieved.

I have no knowledge on this matter so relying on you kind gentlemen out there to help. Is there a guide to ensure i am doing it 100% correct? I find access not to bad actually since there is no plugs leads in the way and i'm quite tall so can get the head in about enough to see the marks etc.

Thanks guys

[twoqu]

Some pics here:

http://www.quattro123.com/Audi200DistributorRepair.htm

On the 3B as John said earlier, it seems to like you to sneak up on the marks with the engine being rotated by pushing the car forward in gear rather than just rotating the engine. That seems to take all the backlash/slop out of the adjustment and leads to a more accurate setting.

[220bhp]

http://forums.quattroworld.com/v8/msgs/13192.phtml

[twoqu]

The difference in opinion is probaly due to the 3B/ABY difference. With the distributor and HT leads the physical position of the distributor alters the timing of the firing order as well as the hall sender position whereas on the ABY there is no adjustment and the timing is calculated electrically.
You have a mash up but ideally the ecu should not be throwing up a hall sender fault!

[newsh]

Mac, do you have the correct MAP sensor in the ECU for the chipset? Just askin [emoji6]