Holding back under acceleration

As the title says the car is holding back under heavy acceleration, then it'll just take off, doesn't do it all the time but more often than not, any idea's? Thanks John

Could be a lot of things :

- could be the prodrive sports cat with an unmapped car
- could be maf sensor
- could be O2 sensor
- could be some bad fuel

had the sports cat on over a year,been fine,until now we did have the p0420 cat below threshold bank1, nocked cel light off 3weeks ago and never came back on

P0420 will keep coming back on til mapped tbh but it sounds like overboost with the cool weather. It is most prevelant at around 0 degrees.

boost leak

I've just had the car out again with a passenger this time, to try and give some more info, when i accelerate the boost gauge goes up to 0.9 bar then it will drop off to around 0.6 a couple of times then back up to 0.9, without me easing off the accelerater, as i said it doesn't happen all the time.

Thanks guys Will check boost pipes etc tomorrow, but think your right Duncan it's about time it was mapped.

I reckon Duncan is well versed to give an accurate diagnosis Lian. Sounds like that CAT fault may have something to do with it bud or the MAF.

Its not really a cat fault so much as the cat efficiency code being activated as the sports cat isnt quite as efficient as the original 2 cats that were on there. Switching that code off in the map is a matter of course and literally takes 5 minutes and it will never appear again.

The underlying issue is that the map on the car is designed for the 3 cat system but with 2 of those cats missing there is much lower back pressure and the boost is building up much quicker than the ecu expects it to. It then goes past the boost target before it has a chance to react.... so it tends to over-react and kill boost too much. This feels hesitant and is easily seen on the boost gauge with it showing the symptoms you describe.

After a remap (whether it is by me or any other recommended mapper) the boost will build quicker but to a much higher level and hold that consistently and smoothly. This gives more power, more torque and a much smoother driving experience.

If you have a rise and fall in boost pressure it is more than likely going to be the a faulty boost control solenoid or sticky actuator rather than a map or sensor issue.

Start by disconnecting the pipes from the boost control solenoid and cleaning it out with brake cleaner, also make sure the actuator can move free and still has plenty tension with no sticking points.

Thanks guys, will do that today Jonny.

Jonny Gav wrote:

If you have a rise and fall in boost pressure it is more than likely going to be the a faulty boost control solenoid or sticky actuator rather than a map or sensor issue.

Start by disconnecting the pipes from the boost control solenoid and cleaning it out with brake cleaner, also make sure the actuator can move free and still has plenty tension with no sticking points.

I am sorry but I disagree Jonny - if it was a std car or the car had been mapped for the mods then yes i would start at the actuator/solenoid but in this instance where the fundamentals of the exhaust system have been changed it will be unlikely to make a difference.

Either way, there is huge potential that isnt being used. 0.9 bar is no fun at all

Duncan, I looked at this car after the sports cat had been fitted, fueling was spot on, boost was holding at .9bar (as it should be on a standard car) and it was det free, this was well over 6 months ago.

It has been fine until recently so IMO something has deteriorated in order for the boost to start fluctuating between .6 and .9bar.

You know as well as I do a standard (safe) MAF based system, Subaru or otherwise can handle a lot of changes before the ecu is working past the parameters of its array of sensors.

Look at all the unmapped cars out there running full de-cats and filters etc WITHOUT issue.

IMO a remap is not the answer to this issue, although you are right, it would improve the "fun"

I wasnt aware that it had been checked over Jonny - it does change the diagnosis. But as you know the boost control has temperature dependencies which cannot all be truly checked at the time. Most of these show when between 0 + 10deg intake temps.

Yeah, but logic says it would be a reduction of under 10% in boost pressure not 33%?

Jonny Gav wrote:

Yeah, but logic says it would be a reduction of under 10% in boost pressure not 33%?

The overboost is the potential issue (caused by whatever reason be it mechanical, modifications or temp related wgdc compensations/map issues) - the cut back afterwards is the ecu's way of responding to it. Dropping it significantly is a result of the stadnard turbo dynamics tables in there. As the std set up is fairly unresposive it needs quite large movements in wastegate duty to make any difference in boost level. Use those std responses on a system that is more free and it will over-react and cut boost back significantly greater than is necessary resulting in the hesitation.

Obviously if there are mechanical issues alongside it then the effects will be exaggerated.

Hummmmm, but we haven't established that it is overboosting, it certainly wasn't when I checked it out, to be honest we could debate this all day ( this isn't 22B ) but without the car in front of us neither of us can be sure what the problem is.

Lian/John, have you had a look at it yet?

Yeah jonny had a go at it today, I cleaned the boost solenoid and took the car out but that didn't make any difference, so then I cleaned the maf which was really dirty, took it up the road and it ran perfect, didn't have time to give it a good ride out before coming to work but lian will tomorrow, so fingers crossed it's sorted, thanks for the advice, although most of it went straight over my head lol, uz sure know your stuff!

well guys it still really holding back when you drive it hard,it ticks over ok and drives ok until you give it some,cleaned maf and boost solenoid still no difference,cel light has been back on once since last post, its clearing and staying of but the p0420 code is staying in the memory,we are wondering if this has something to do with the holding back problem, as in the past when the light has come on showing this code,the car has ran lke it is at the mo holding back and a little spluttery when driving hard,its annoying us now not that we drive it hard much but you still want it to be right.

jonny maybe john could take you out in it when youre free,as we have no idea now,we could maybe try that resistor thing you suggested,see if it makes any difference

When did you last change the plugs??? Also coil packs could be at fault, this would cause the cel for the lambda sensor due to the fuel not getting burned.
Can check for it with the laptop on Friday afternoon if you are free.

sticky acuater on turbo just an idea

thanks jonny, plugs have been in about a year & half , yeah friday afternoon ok jonny got valet on the morning but will be finished for after dinner, i will send you my mobile number and you can text me with a time,thanks jonny

leakey exhaust or dodgey sports cat?

This happened to Steviedoo's car a while ago, we found a split in one of his boost pipes from it rubbing on the intercooler, changed the pipe and it was spot on