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I have taken my GU back to (almost) standard. Only engine bits: exhaust plate and catch can.
I get a limp after a few minutes at 110 km/hr, no issues at 100 or lower.
Remedy is to back off for 1 or 2 seconds, then all good until next time. That is OK unless using cruise control,
Has anyone tried a hole in the exhaust plate, similar to the Common Rail models?
If it works, what size hole is best?
Help or comments welcome.
Putting a hole in the EGR plate won't help with the Di engines. What I do know, when I had my Di, I was getting limp mode on anything about 16psi. I bought the HPD billet hi flow air flow meter housing. Also the hi flow lid they do. After fitting these I had my max boost set at 25psi and the cruise boost to 18psi and I never saw limp mode again. .
The best thing I did to that motor. Hands down.
If you want to drill a hole, 8mm is the hole size I used to do in the plates I sold when I had my shop.
Reducing the MAF voltage suppresses limp, but also reduces power :
The quantity of fuel requested by the ECM to the pump is directly linked to the MAF voltage value.
The higher the MAF voltage, the higher quantity of air swallowed by your cylinders/ pushed by your turbo, the higher quantity of fuel is injected, and the higher torque and power you get out of your motor.
Only a remap,
or an electronic control of the MAF value taking the RPM info into account to make sure that the MAF voltage does not exceed 3.55V below 2000RPM
3.88V below 2500RPM
3.98V below 3000RPM
4.18V below 3500RPM
will kill any limp mode.
Nothing to do with boost by the way. Only the quantity of air (in g/s, measured in volts by the MAF) matters.
The way the ECM manages the turbo and its vanes, trying to avoid MAF to exceed 4.0V is also a real issue.
Here again, electronic vanes management is your friend. I tested all systems on the market, from the dawes+needle ( catastrophy as it keeps the vanes closed until the dawes open, converting your wonderful VNT into a two stage turbo ), to a uk-base electronic controller worst than multi-valves.
I ended-up putting together a multi-valves system, based on one dawes + two needles.
the dawes opens as early as 3 psi, and you add behind a second needle reducing the flow of positive pressure to ensure a 'gentle' opning of the vanes. This system greatly improves the one-dawes one needle arrangement, but canno't match the normal way of dealing with vanes opening :
keeping vanes closed until the exhaust turbine spins fast enough, then open them quite rapidly until mid-aperture, staying at mid-aperture until getting close to max boost and then opening rapidly again to control max boost.
So I had to develop my own electronic VNT turbo controller, together with limp avoidance :
Attachment 83524
you can see below the limp avoidance in action.
Attachment 83525
And the expected result speaks for itsel : plenty of air, controlled boost, plenty of torque down low.
Cherry on top of my cake: by reducing MAF voltage only when idling, fuel eco is improved by 30 to 40% when idling, as well as the smell.
I can even tweak the MAF value to increase fueling a bit more, although I don't feel it necessary.
I have maximum torque down low and above as I have managed to maximize the airflow at all Revs by managing properly the turbo.
So I got the HPD hi flow. I will try that first. If needed I will get the hi flow lid.
Thanks for the first hand information.
Report back on outcome in the next couple of weeks.
Unfortunately, what this device does is decrease the MAF voltage to make the ECM believe there is less air coming through.
As a result, the ECM requests less fuel to the pump, and you get less power at the end of the day.
No limp at the expense of torque/power. This is the end result with this device.
If you don't want to go for a remap, suppressing limp modes by increasing the limp thresholds "burnt' in the ECM, you need to go for the ultimate solution : electronic control of both the MAF voltage and the turbo VNT : Magic Box VNT.