Decat Woes
 

MY00 Uk Turbo with PPP

I have within the last couple of weeks fitted a Magnex Twin Dump D/Pipe. Seemed to be fine originally but over time the car seems to have developed a fault. It kind of felt like a misfire so plugs have been removed and gapped from 0.8 to 0.7 - they are PFR6B's. I have replaced the O2 sensor with the oem Subaru part (old one looked knackered). However to try and explain the problem = it feels as if you acclerate with light throttle upto 2-2.5Krpm the car is fine as soon as it gets to 2.5K rpm...hesitation as in the light throttle I was using is no longer accelerating and you seem to have to put your foot down to sort of accelerate throught it. However engine note goes louder (as if under load) car does not accelerate until you get to just under 3Krpm and then the car pulls. This problem got so bad yesterday that whilst driving on the motorway (with 2 up) the car would accelerate ok with light throttle - anymore throttle and nothing apart from a lot of noise coming from the Exhaust. Interestingly I disconnected the Boost Solenoid yesterday but the car still did it ?
Have fitted an MBC today thinking that the problem may be boost spiking ? and whilst its better it is still hesitating at around 2.5K rpm. I have performed an ECU reset and had no CEL faults.

I am at my wits end with this now and am beginning to think that it could either be a sensor playing up (wheres the Throttle Position Sensor BTW) or could it be overboost/boost spiking ? I would have thought that an MBC would have sorted this though ?

Any help would be very gratefully appreciated.

Just a question: When you fitted the decat...did you reset the ECU BEFORE you drove it anywhere, and realised there was a problem...or did you reset it AFTER you noticed a problem.

If you reset it straight after fitting the decat without driving it, the decat pipe could just be coincidental. And I would be pointing my finger at the MAF sensor, as any error correction data stored would have been lost during the reset.

Also how many miles / old are the plugs?...platinum tipped spark plugs like the PFR's shouldn't need re-gapping.

Hi Nelson

How old are your plugs ?

Had same prob with my MY96 UK Turbo. Changed to PFR7B's misfire went.

Red

interested to know, not being that technicaly minded why would you have to reset ecu. specialy as i just put a de cat down pipe on today.

Thanks for your replies guys :)

1) I didn't perform a reset when the decat was done. I drove it around for about a week with no problems. Then I decided to replace the O2 Sensor having seen what state the existing one was in. I then changed the oil and plugs (used NGK iridiums) and noticed that having done the mini-service the car was beginning to hesitate below 3K rpm ? Decided to do an ECU reset and originally problem seemed to have gone but again the hesitation returned. Now I reset ECU and the hesitation is there almost immediately :( I did in fact replace the MAF Sensor on the Scoob just after I bought it (last September) I was also running with an ITG filter from this time until the end of December when I began reading about the problems MY99/00 have with fragile MAF's. In January this year replaced the ITG with an STI but still running with the MAF that was fitted last September.

2) The plugs that I have fitted now have done 15K Miles (these being the PFR6B's). As the problem still exists I think I'll refit my newly purchased NGK iridiums. I only fitted these recently and they are gapped too 0.7. It was interesting to note that the PFR6's were gapped to 0.8/0.9, cos I thought they had to be 0.7 ?

I must admit that having reset the ECU today I did notice that whilst the needle sat steady the car did feel a bit lumpy on tickover (its usually very smooth) ?? I assume you guys are thinking that I have a sensor problem rather than overboost ?

You mention hesitation, and on light throttle, the Turbo would not really be up to full pressure. Which to me would seem as a lack of boost rather than too much! Do you have a gauge to confirm anything?

Symptons of serious overboost would be noticed by the fuelling being cut. Giving a sudden complete loss of power (like hitting a brickwall is a favourite term). This is uaually due to clogged or faulty pipes/boost soloniod/ valve / MAP sensor, or an aftermarket boost controller.

Symptons of boost spiking, would give more of a surge of power and it slightly dropping off then you may feel another surge and dropping off, with it going on until you back off or change to the next gear. This is due to the ECU having a bit of a mare at keeping the correct boost and basically overacts, you may also hit the fuel cut too if it's serious. This usually a known side effect of decats on later models, which is caused by the restrictor to the wastegate being too small.

I've run out of ideas on relating the symtoms to any other fault :( You could try swapping back to your old o2 sensor, same with the MAF (presuming you changed the original as a precaution)...obviously do them seperately though ;)

Daz - ECU reset basically forces it to re-learn its fueling and ignition settings. It's beneficial as your recalibrating it to the mods you've just done. You can acrry on without doing a reset but the ECU maybe slow in adapting itself - this especially applies to the older classics.

thanks for that ALi-b

The O2 sensor uses the downpipw as it's ground path.
Make sure that everything is nice and clean and that the path to ground is a good one.