Hi All

1990 S4 Auto, with Ken's EZK

I've had a problem with hot start (it would start, but not idle unless helping a little with the throttle pedal).

I've had the following work done, which has cured it, but I have a new problem...the gearbox changes up into 3rd & 4th with a massive "thunk" and a large jerk....

I've included everything done, just in case it is something related to the work...

Any advice?

Cheers

John

• Confirm fault - Vehicle fires and then cuts out unless throttle is applied.
• Vehicle also stutters when pulling away under load intermittently.
• Checked fuel pressure - measuring 3.3Bar at idle and 3bar with engine off (within spec) Fuel pressure does not drop or leak back at operating temperature. Note - Threaded union on bank 1 fuel rail in poor condition - union previously painted red
• Checked fuel pressure regulator - holding vacuum and no trace of fuel in the vacuum line.
• Strong vacuum supply to regulator present.
• Removed air box, checked both fuel dampeners - holding vacuum and no trace of fuel in the vacuum line. Strong vacuum supply to both dampeners present.
• Checked resistance of NTC temp II sensor in coolant water bridge at operating temperature Pin1 - 196Ohms (Spec - 100-210ohms) Pin 2 - 195Ohms (Spec - 100- 210ohms) Sensor is reading 2.9kOhms at cold (Spec - 1.6-3.6kOhms)
• Disconnected temp sensor to default control unit into default settings for hot start however vehicle still stalls when started when hot.
• Checked for spark - present when car cuts outs
• Checked for air leaks as engine sounds like it stalls from lack of air. Air leak present at top of inlet manifold for the intake plenum resonator flap.
• Checked throttle butterfly during hot start, butterfly in closed position just before activating idle switch
• Removed inlet manifold, checked throttle body, ISV, vacuum lines and gaskets.
• Checked idle switch - all ok.
• Found vacuum supply loose under inlet to distribution piece. Applied vacuum pump to supply and created vacuum of 50kPa - vacuum leak present and bleeding back. Traced leak to line for HVAC - Disconnected the vacuum line and blocked off.
• Cleaned throttle butterfly and minor oil residue from inlet manifold. Clean all sealing surfaces. Adjusted throttle butterfly end stop just just before idle switch activation (approx 1/2 turn adjustment) Refit inlet manifold and test.
• Run car to operating temperature and hot start is correct. Fired and idles nicely.
• Allow car to cool down - Road test vehicle to operating temperature - Hot start is correct.
• Carried out test for 3rd time and vehicle started stalling during hot start.
• Fault logged in LH control unit - 23 Oxygen regulation control (Rich)
• Unable to communicate with EZK control unit (control unit has been chipped)
• Checked wiring at LH and EZK control unit for all engine sensors - all present and within spec
• Disconnect battery for 20+ minutes to reset control units and reset idle adaption
• Carried out idle adaption with full load Reset EZK control unit
• Tested vehicle - hot start correct
• Carried out multiple road tested and heat cycles - vehicle performing as it should and starting each time without stalling.

 

John,

Have you measured the vacuum at the tranny vac regulator connection when the engine is warm and idling at 670 rpm? You should see about 20 inches Hg.

 

Hiya Fred

Thanks for your quick reply - as usual!

I'm afraid I have no idea how to do that - could something have become disconnected with all of the work above?

 

John,

The vacuum line through to the gearbox is a composite construction involving connectors, rubber tubing, steel tubing and nylon tubing. All you need to do is connect your vac gauge to the connector that slips over the nipple on the gearbox mounted vac regulator and run the engine. The vac regulator itself has a rubber cap - that must also seal tight to the body.

 

John,

Forgot to ask but I presume you are noticing the "thump" on lightly loaded changes. If you push the throttle hard in 2nd and let it change at full throttle into 3rd do you still get a thud or is it more like a normal change?

 

Yes that's right. I haven't had a chance to do any full throttle driving today.

 

Tends to confirm that your vac modulator is not doing its job - prime cause for that is not seeing vacuum.

Could also be a problem with the modulator but more logical to eliminate the vacuum source as being the cause first.

 

Thanks Fred - and do you think something could have become disconnected in the work above? I can speak to the tech tomorrow, if you think it's all to do with the work?

 

It is possible that in re-connecting the spurs from the multi way rubber manifold at the backof the manifold, the process of fitting the line from the gearbox may have been accidentally pulled out of the connector that links to the steel tubing that runs along the side of the torque tube. Not likely to happen with new connectors but if the original connectors are still in there they become hardened to some extent and thus less resistant to being pulled out as it were. Thus the smart thing to do if it has ot been done already, is to refresh the various constituents or more to the point, the connectors. The steel tube should be fine but even that may be corroded given the UK salt laded roads during the winter season. I was able to re-use the steel tube section on my vehicle but then my underside is like it left the factroy- no corrosion whatsoever - just a layer of desert over the "sticky" coating.

 

Thanks Fred!

 

I spoke with the tech and we both think that he has blocked off the vacuum line to the gearbox and NOT the HVAC controls....

I have some new flappy valve parts coming from Roger, so will wait until they arrive to continue the fault finding.

 

John,

The passive vacuum system is taken from the brake servo inlet as that provides a constant vacuum source. Te vacuum system at the rear of the manifold is a dynamic vacuum source and provides vacuum at whatever level is being pulled on the engine side of the throttle plate.

If th eintent was to disable the flappy then the 4- way connector in front of the servo unit needs to be blocked off too keep the HVAC system functional.

 

OK thanks Fred - I've passed that on

 

UPDATE

The vacuum line to the gearbox was found to be disconnected causing the jerky gear change.

The flappy valve bearings have also been changed with a kit from Roger.

But.....now the vacuum line is connected back to the gear box, the hot idle problem has returned....!

So, how is it related? Could it be that there is a vacuum leak at the gearbox end causing inlet manifold issues?

Thanks!

John

 

There could be a leak at the gearbox end but i doubt that would cause an idle issue but...?

Easy to test for leaks - disconnect at the back of the manifold and connect to a Mityvac tester it should hold a fullish vacuum.