Power loss, poor hot starting & info on wastegate

[20Vcqdriver]

CAr ran brilliantly from April to July but performance dropped off since then and put down to hotter weather but coming in today in cool conditions expecting it to fly and it feels as though it's holding back, it goes to take off in 3rd 4th upwards and then feels to back off a bit. It has also starting playing up when hot and takes a lot of starting if you have stopped to refuel etc. Also want to know if there is any benefit on a 3B of winding down the wastegate spring. Thanks. Comes off the road on SORN end September so 6 months to get it sorted. Any ideas

[max_s2]

Hi.
Could be coolant temp sensor, MAF, maybe a leak. First of all, connect ECU to a VAGCOM and check whats going on in there, maybe you'll find out smth.

[S2central.net]

Agreed with above - something is out of kilter if it ran so sweetly at first. Codes might not tell you anything though so don't ever trust them 100%. Would be worth swapping MAF with someone else - that is a common cause of all sorts of ills. But a faulty temp sensor could also make the ECU thing the car is too hot and so retard timing and such as result - hence the 'holding back' feeling - and make it run too rich also.

You are running 3B FPR aren't you at 3bar with 3B injectors ?

Other possibility is that the ECU has been detecting knock - perhaps falsely. A good way to check for that is to unplug the ECU for a minute or so. This resets it and forces it to start adaptation from scratch... If all performance has returned then that may be something to investigate further.

See if you can get a resistance test across the 2-pins of the air temp sensor (top of inlet manifold) and the coolant temp sensor (tricky at rear if head without a JPT extension plug). Do that with a warm engine (90 degrees) and we can see if the values are broadly correct.

[20Vcqdriver]

Agreed with above - something is out of kilter if it ran so sweetly at first. Codes might not tell you anything though so don't ever trust them 100%. Would be worth swapping MAF with someone else - that is a common cause of all sorts of ills. But a faulty temp sensor could also make the ECU thing the car is too hot and so retard timing and such as result - hence the 'holding back' feeling - and make it run too rich also.

You are running 3B FPR aren't you at 3bar with 3B injectors ?

Other possibility is that the ECU has been detecting knock - perhaps falsely. A good way to check for that is to unplug the ECU for a minute or so. This resets it and forces it to start adaptation from scratch... If all performance has returned then that may be something to investigate further.

See if you can get a resistance test across the 2-pins of the air temp sensor (top of inlet manifold) and the coolant temp sensor (tricky at rear if head without a JPT extension plug). Do that with a warm engine (90 degrees) and we can see if the values are broadly correct.

I have a spare MAF. But will disconnect ECU first and see what happens. Will measure sensor values when I get home tonight. One other item is that on starting from cold it starts instantly but after about a minute or 2 it starts to stutter as though missing a cylinder or two then recovers, revs rise to 1100 and then settles to normal and is fine from then on (only noticeable when left idling from cold), I'm suspecting the Lambda sensor, anyone agree?
Yes, running standard 3B FPR and injectors. Still boosts to 1.3bar on calibrated gauge in Sport mode which it has always done despite being told it should reach 1.4bar

[20vQC]

the lambda could be another reason if MAF and MAT are fine... Paul correct me if I am wrong whit ths, but the lambda when dies, the ECU protects you adding more fuel to avoid damages...oh and fuel consumption may be a lot higher! cheers!!

[S2central.net]

Yes lambda could be bad also... you should see mixture fault on ECU if it cannot adapt its way out of trouble...

[20Vcqdriver]

ok, got some readings.
Inlet air temp..
Cold = 427ohms (20deg outside temp)
Hot straight after raz home = 437ohms
reading after engine turned off for 5 mins = 476ohms.

Water temp.
Cold = 1852ohms
hot = 250ohms (taken after engine off for 5 mins and several burns )

What effect does turning wastgate screw have as seemed to run better on way home after unscrewing 2 full turns, or could just be my imagination

[newsh]

Oxidation build up on MAF connector? Give it a wiggle and let us know.

[S2central.net]

Gotta say the air temp readings don't sound right - look at the graph here - http://www.s2central.net/ds_G42.html

Your readings are always telling the engine it is very cold - and therefore runs too rich.

For example at 20 degrees ambient you should be seeing something like 480-490 ohms... Dunno how deadly accurate that graph is, but I will take a reading or two as well on my motor... same sensor on ABY as 3B.

Your water temp values look good though - http://www.s2central.net/ds_G62.html

[S2central.net]

To save you spending money swapping sensor just on this info - unplug it and wire in a variable resistor if you can - or just use a fixed 470ohm component. I can post you one if you want to try it.

[20Vcqdriver]

Thanks for info Paul, I have a complete set of resistors at work and taking car in tomorrow so will install a 470ohm and see what effect it has or Oops, Just read your post again, how about using a 47ohm in series to see what effect it has.

[S2central.net]

either way works

[20Vcqdriver]

Interesting development, I tested the sensor originally with the wires attached as they are soldered on as standard on the 3B, so during the planned install of the resistor I measured the IAT with the wires off and got a value of 519ohms, if anything slightly higher than I would expect looking at Paul's/ SJM graph. So fitted spade connectors to replace soldered versions and left as is for now.... Got a spare Lambda at home so try that tonight too.

[S2central.net]

That's just odd.

[20Vcqdriver]

That's just odd.

It does say in your attached sheet on the IAT that values should be taken with wiring disconnected, there must be a lowish resistance in the Ecu internal circuit associated with this sensor.
Lambda and MAF in that order are next...