View Full Version : Strange boost
Millen99
05-01-2006, 19:13
Mate owns a mk4 turbo with 888 engine gearbox etc. Normally the car feels great under acceleration but recently the boost hasn't been holding at the normal level...
Normally the car overboosts to around 15 then holds between 9 and 11 depending on the rev range.
Now it overboosts to around 10 and only holds at around 5:omg. The performance doesnt feel like it has decreased alot. Has anyone got any ideas of what could be causing the problem.
We've checked out the air intake and all the piping seems ok, there is a slight leak in the exhaust although it has been that way for a fair while.
Any help much appreciated.:)
coupe_turbo_jon
05-01-2006, 21:40
First thing to change is the air flow meter, I almost guarantee it will be this if anything
Do you have a fault code light on?
I had the same problem, and it was the air flow meter.
Millen99
06-01-2006, 18:42
Thanks for the suggestions guys, there is no fault codes anywhere. Will check the actuator.
AFM's cost a fair whack don't they?? might have to be left as is if thats the case:mad:
bally_gsi
06-01-2006, 19:10
Go for the cheapest options first, i had a similar problem a while ago,
1.Boost soleniod ( on top of turbo) about £20, i think.
2.temp sensor ( on top of intercooler, this is what caused my boost loss) about £70.
3.dreaded air flow meter :mad: about £100.
ballysri
Do the boost soleniods go ofted as i have an unstable boost at 18 to 20 psi (just replaced amm and both o2 sensors, petrol filter) and still doing it
bally_gsi
07-01-2006, 17:11
Do the boost soleniods go ofted as i have an unstable boost at 18 to 20 psi (just replaced amm and both o2 sensors, petrol filter) and still doing it
Not sure how often they fail but at not alot of cost it's worth changing. i changed mine last year when my car was standard due to a fluxuation in boost between 3000-4000 rpm and it solved that problem. when the car got more powerful the next thing that went was the sensor on the intercooler which wouldnt let the car overboost, replaced and sorted :)
Hope this helps :)
Millen99
07-01-2006, 18:38
Cheers ballysri. Think it could be the solenoid then, the fluctuation appears around 3-4k rpm. Boosts up as normal if you give it some welly in the low revs.
Should be able to get this sorted:)
Millen99
16-01-2006, 18:55
Turns out that it was a split in the vacuum pipe attached to the dump valve.
All sorted now:)