Skoda Fahia 2005 1.4L Stalling high fuel consumption high intake pressure

[FemiE]

Hello people. Car overheated while fixing non working coolant fan but after cooling was resolved the car started stalling every time after running idle for a few minutes or after throttling RPM above 1000.

 

Fuel consumption indicator on dash was about 0.7L/H before problem started but now very erratic and varies widely between 1.4L/H to 5L/H with black soot coming out of exhaust.

 

Also noticed with VCDS that intake manifold pressure now varies between 500 - 900 units.

 

No engine fault code is being logged while all these is happening.

 

Please help.

[LB123]

You have BBZ engine. That MAP is way outside limits for any steady state. Limits are lower 200 and upper 420. Might point to failed/failing MAP sensor or the sensor not talking to the new ECU properly.

[FemiE]

4 minutes ago, LB123 said:

You have BBZ engine. That MAP is way outside limits for any steady state. Limits are lower 200 and upper 420. Might point to failed/failing MAP sensor or the sensor not talking to the new ECU properly.

Hi LB123. Thanks for your prompt response.

I am also concerned about this. I can get a working a working MAP sensor from a similar car fixed to test.

 

Are you suspecting the MAP ismalfunctioning or what could be inducing this high MAP values?

 

Is it the high MAP values that is trigerring the high fuel consumption?

 

[LB123]

I've had idle problems with possibly an air leak on my BBZ engined fabia which I have been investigating with the help of 'cleverer than me' people on this board over the last month. Just so happened the MAP/AirTemp sender came under suspicion and I had run a couple of logs on it. These didn't show a problem but I did note the upper and lower limits permitted and immediately recognised yours were way outside. The figure VCDS reports rises with throttle opening towards atmospheric of around 1000. So the high MAP figures will be telling the ECU the throttle is wide open and it will be fueling far too rich. Hence your experience I think.

[FemiE]

3 hours ago, LB123 said:

I've had idle problems with possibly an air leak on my BBZ engined fabia which I have been investigating with the help of 'cleverer than me' people on this board over the last month. Just so happened the MAP/AirTemp sender came under suspicion and I had run a couple of logs on it. These didn't show a problem but I did note the upper and lower limits permitted and immediately recognised yours were way outside. The figure VCDS reports rises with throttle opening towards atmospheric of around 1000. So the high MAP figures will be telling the ECU the throttle is wide open and it will be fueling far too rich. Hence your experience I think.

@LB123, based on your advice i swapped the MAP/IAT sensosensor and the problem persisted.

 

I discussed this with a mechanic friend who indicated that the excess fuel being dumped into the engine may be due to faulty valves/valve seals or these not sitting well and thus allowing for unburnt fuel which I see as soot in my exhaust.

 

But I am still eager to know the actual root cause of this problem so I have asked him to pull the intake manifold and reinstall with good sealing. He will also be checking the valves with the seals.

 

[LB123]

That seems a bit random. The fuel entering the engine is injected, the quantities controlled and adjusted by the ECU in response to the input of the sensors. They include MAP, IAT, RPM, CTS, Lambda, sorry for any I missed. Valves and their seals can reduce compression and add some oil, make the engine a little less efficient, make a bit of smoke after overun but I can't see them having a major effect on fuel consumption or causing your symptoms. A good look and sealing effort on the intake system including EGR and all the various hoses that feed into the intake would however be a good plan.

[FemiE]

15 hours ago, LB123 said:

That seems a bit random. The fuel entering the engine is injected, the quantities controlled and adjusted by the ECU in response to the input of the sensors. They include MAP, IAT, RPM, CTS, Lambda, sorry for any I missed. Valves and their seals can reduce compression and add some oil, make the engine a little less efficient, make a bit of smoke after overun but I can't see them having a major effect on fuel consumption or causing your symptoms. A good look and sealing effort on the intake system including EGR and all the various hoses that feed into the intake would however be a good plan.

I agree more with your conclusion @LB123 so I will make re-installation of the intake manifold and its accessories the priority.

 

[FemiE]

While reviewing the activities that took place before experiencing this stalling & high fuel consumption, I was reminded by my partner with whom I was working on the electricals of the cooling system that the problem started after we asked a mechanic to pull out the exhaust manifold housing the catalyst and yanked out the catalyst which had become blocked due to overheating. Could it be that the exhaust manifold was not properly reinstalled leading to exhaust leaks causing either or both the pre-cat and post-cat O2S to send wrong data to ECU causing ECU to signal  demand for more fuel?

[sepulchrave]

Is it possible that the pre-cat lambda probe was damaged during the removal?

[Breezy_Pete]

Check wiring to MAP sensor, particularly the +5V (red/green) on pin 3 from engine ECU pin 98.

Other pins: Pin 1, brown,  earth; pin 2 green to engine ECU pin 85; pin 4, brown/white to engine ECU pin 109.

 

I don't see how anything exhaust side could be making those super-high pressure readings in the intake manifold. 

[sepulchrave]

The high readings could be a consequence of the ECU opening the throttle too wide, it's tricky to make sense of these symptoms.

[FemiE]

19 hours ago, sepulchrave said:

Is it possible that the pre-cat lambda probe was damaged during the removal?

I removed and checked the pre-cat probe today and found it was physically okay covered with soot which we wiped clean. However, I could not ascertain its real performance with vehicle running as a rainstorm interrupted the diagnosis.

I will plug in VCDS and take some data as soon as possible.

[FemiE]

10 hours ago, Wino said:

Check wiring to MAP sensor, particularly the +5V (red/green) on pin 3 from engine ECU pin 98.

Other pins: Pin 1, brown,  earth; pin 2 green to engine ECU pin 85; pin 4, brown/white to engine ECU pin 109.

 

I don't see how anything exhaust side could be making those super-high pressure readings in the intake manifold. 

 

[FemiE]

10 hours ago, Wino said:

Check wiring to MAP sensor, particularly the +5V (red/green) on pin 3 from engine ECU pin 98.

Other pins: Pin 1, brown,  earth; pin 2 green to engine ECU pin 85; pin 4, brown/white to engine ECU pin 109.

 

I don't see how anything exhaust side could be making those super-high pressure readings in the intake manifold. 

I checked these 2 days ago and confirmed wiring between MAP sensor and ECU was okay for all those pins.

[Breezy_Pete]

Did you confirm that the 5V supply is actually 5V?

[FemiE]

10 hours ago, sepulchrave said:

The high readings could be a consequence of the ECU opening the throttle too wide, it's tricky to make sense of these symptoms.

I am at a loss why the ECU will be doing this. Could it be due to dodgy or broken cabling between the ECU & throttle body?

Which wires/pins on both side should I be checking and what voltage/resistance values should I expect other than simply confirming continuity?

[FemiE]

36 minutes ago, Wino said:

Did you confirm that the 5V supply is actually 5V?

I missed the voltage check and tested only for continuity but I will go back to confirm that. It skipped my mind. 

[FemiE]

On 22/10/2018 at 20:21, Wino said:

Did you confirm that the 5V supply is actually 5V?

Hi Vino, quite some time out as I was busy attending to other cars,

 

I finally checked the voltage on pin 3 and it was 4.96v and same voltage was recorded on pin 2. Is this normal?

 

I still can't figure out why the MAP errors are occurring. I have swapped all these devices (MAP sensor, EVAP, throttle body & EGR)  but the high absolute pressure values, correlation errors and high fuel consumption of the order of 4-5L/hour in idle mode and in motion eventually resulting in car stalling persisted.

[Breezy_Pete]

4.96V sounds perfect for a 5V supply, that's not the problem.

I will try to have another look at this thread tomorrow.

[FemiE]

On 13/11/2018 at 23:16, Wino said:

4.96V sounds perfect for a 5V supply, that's not the problem.

I will try to have another look at this thread tomorrow.

Hi Wino and all helpers.

I am finally back to this car after being away to attend to other cars and other matters.

 

To continue the troubleshooting of this Fabia can someone help with ECU pinout for the throttle body and other vital components that may be affecting the fuel consumption rate and/or manifold pressure?

 

I want to doublecheck all this again before asking the mechanic to take down the intake manifold and possibly top cylinder and reinstall.

 

Many thanks for your ongoing assistance.

[Breezy_Pete]

ECU=J687

TB=J338

br=brown, bl=blue, ws=white, ro=red, gn=green, li=purple

 

[FemiE]

Hi Wino, thanks for the prompt response. Let me chip in an incident that happened while working on this car if it may have resulted in what I am facing now.

 

I noticed a very red hot glow on the catalyst immediately after the exhaust manifold which was very unusual. I took out the catalyst unit and it appeared to have fused and blocked so I yanked out the whole catalyst and fitted it back.

 

Could this alone result in the very high fuel consumption (1.5L - 5L/hour on idle) and car stalling?

 

Of did I damage the precat lambda probe or something related to the pre and post cat lambda probes?

 

Can a stuck open EGR be responsible?

 

Thanks.

[Breezy_Pete]

Has the coolant temperature sensor been replaced?

That can give very bad info to the ECU resulting in the fuelling being way off, without generating any fault codes because the possible range of 'real' temperatures is so wide.

I think faults with lambda probes would give fault codes, as would faults with the EGR system.

[FemiE]

On 19/12/2018 at 10:12, Wino said:

Has the coolant temperature sensor been replaced?

That can give very bad info to the ECU resulting in the fuelling being way off, without generating any fault codes because the possible range of 'real' temperatures is so wide.

I think faults with lambda probes would give fault codes, as would faults with the EGR system.

Not replaced but I can do this today as I should have an old spare which I think is in good working condition.

 

In relation to the catalyst incident related above I know that happened at about the same time the engine overheated as the fan control module failed to automatically start up the fan as the engine warmed up and got very hot.

 

I will update later today with result of changing coolant thermostat and confirming throttle body-ECU mapping.

 

Is there also an engine thermostat that may be causing this problem and if so where should I look for it?

[Breezy_Pete]

The sensor I'm talking about is a grey two-pin one that tells the engine ECU the coolant temperature. The coolant thermostat is different, non-electrical, and regulates flow through the radiator, it is in the same black plastic housing as the coolant temperature sensor on the side of the engine head.

I'm suggesting the grey one may be causing overfuelling if it is reporting a very low temperature.