what could be the cause?

**mike 850** · Wednesday 28th April 2010, 20:56

my s60 t5 2001 is being a little odd.

it starts perfectly, it idles perfectly and there are no fault codes and all sensors are in there ranges and no reported misfires (according to my code reader)

sometimes on acceleration it feels like its holding back (then takes off again) and sometimes a bit of hesitation when coming on boost
i have a boost gauge which shows no fluctuation in boost(constant 12 psi)
there are no vac leaks(as far as i have looked)
new plugs, air filter, fuel filter. swapped coils for 2nd hand others.
i did a test a little while ago with the maf unplugged and it seems to be faster and smoother so i have a new Bosch maf but has made no difference.
the car is still very fast and smooth just something doesn't seem 100% also when slowing down in gear at 1500 rpm it has a little surge, even with the brakes on.

anyone have any ideas please?

the only other thing i can think off is etm? but could it cause issues and still have a solid idle etc?

thanks

Mike

**p fandango** · Thursday 29th April 2010, 07:08

i thought the ETM normally throws a fault code?

are you 100% sure there are no leaks

**princepugh** · Thursday 29th April 2010, 10:01

I think the small surge at 1500 rpm is a red herring, mines done that since I bought it and it's had a new ETM + various other sensors since.

Has the problem started suddenly or over time?

**timbo_1975** · Thursday 29th April 2010, 13:57

I would be looking for a leak also, as we know intercoolers on these love to leak, as do the intake pipes.

A run with a scan tool connected and showing live data would be the next job, looking especially at short and long term fuel trims. If these are elevated then this definately points to an intake leak somewhere.

Also look to see if it is detecting some knock, and pulling the timing back because of that- is it any better with super unleaded??

**t5_monkey** · Thursday 29th April 2010, 15:27

mine surges on rundown at about 1500rpm too - i think it's something to do with no fuel being injected on coast, and that's when it starts injecting fuel again to make sure you don't stall as the rpm drops.

**princepugh** · Thursday 29th April 2010, 16:15

Originally Posted by t5_monkey

mine surges on rundown at about 1500rpm too - i think it's something to do with no fuel being injected on coast, and that's when it starts injecting fuel again to make sure you don't stall as the rpm drops.

Agreed - seems to stall the stall, so to speak.

**jez.w** · Thursday 29th April 2010, 16:47

Originally Posted by mike 850

my s60 t5 2001 is being a little odd.

it starts perfectly, it idles perfectly and there are no fault codes and all sensors are in there ranges and no reported misfires (according to my code reader)

sometimes on acceleration it feels like its holding back (then takes off again) and sometimes a bit of hesitation when coming on boost
i have a boost gauge which shows no fluctuation in boost(constant 12 psi)
there are no vac leaks(as far as i have looked)
new plugs, air filter, fuel filter. swapped coils for 2nd hand others.
i did a test a little while ago with the maf unplugged and it seems to be faster and smoother so i have a new Bosch maf but has made no difference.
the car is still very fast and smooth just something doesn't seem 100% also when slowing down in gear at 1500 rpm it has a little surge, even with the brakes on.

anyone have any ideas please?

the only other thing i can think off is etm? but could it cause issues and still have a solid idle etc?

thanks

Mike

I have posted up similar question a couple of times regarding slight drop in performance as if holding back slightly, i have found using fuel injector cleaner cured mine. The problem came back after a few thousand miles and i put some more injector cleaner in the tank which cured it again. I think i need to send my injectors off to JIMATHAN to get them cleaned properly. I have noticed that fuel injector cleaner really improves MPG for a couple of tank fills after application, so maybe its a good idea to use some good fuel injector cleaner once and a while anyway.

Cheers

**princepugh** · Thursday 29th April 2010, 17:02

I'm running some Redline Si-1 through mine this weekend as it goes although I'm expecting to have to pull the injectors and ship to Jimathan also, at some point.

http://www.vpcuk.org/forums/showthread.php?t=28858

As an outside shot, a sluggish o2 sensor might also cause these symptoms and might not throw a code. Just a thought.

**mike 850** · Thursday 29th April 2010, 17:43

thanks for the responses, i was planning to send my injectors of at some point, just wanted to wait until some came up on ebay as i use my car daily. would the boost gauge show me if i had a air leak? it sits at -15psi on tickover and -20 when in gear but no throttle. if i had a leak boost side would it not hold the boost as much? this morning it was hitting nearly 15psi and holding to the redline, the code reader i have measures some of the sensors but comes back with no problems. im always running normal shell fuel ans was wondering if it was holding back because of the fuel, arn't they supposed to be run on 98 ron?
anyway all suggestions welcome

cheers

**princepugh** · Thursday 29th April 2010, 18:00

I assume if you're running 1BAR of boost you must have a re-map, in which case you should really be using 98RON - 95 will work but at full chat/ heavy load, the engine will de-tune as it detects knock, which would go some way to explaining your symptoms.

From the advice given so far it looks like you have a few streams of activity, which in combination may well lead to to a result.

I'll let you know how the Redline snake oil goes.

**thebadger** · Thursday 29th April 2010, 18:29

Originally Posted by princepugh

As an outside shot, a sluggish o2 sensor might also cause these symptoms and might not throw a code. Just a thought.

I had really bad MPG for ages, then it threw the code for the front O2 sensor.

Long & short of it was a £70 sensor (bosch) and then it was back to normal!

My car had only 80K on the clock when the sensor failed.

**mike 850** · Thursday 29th April 2010, 19:23

what would you call really bad mpg? mines averaging about 25 which is pretty much what i was expecting. maybe it could have a remap then. i might try a tank of v power next time and see what happens

**Louie** · Thursday 29th April 2010, 21:14

No idea if its any help mate but I had a similar problem earlier in the week. Replaced Spark plugs, cleaned out Distributor cap and replaced fuel filter. No problems at all now. Failing that you may have a vaccum leak?????

**thebadger** · Thursday 29th April 2010, 21:32

My bad MPG was hitting 16mpg, down from 20-25mpg. Happened suddenly, but then stopped at 16, shortly followed by the O2 code being thrown.

The joys!

**princepugh** · Friday 30th April 2010, 13:14

Originally Posted by thebadger

I had really bad MPG for ages, then it threw the code for the front O2 sensor.

Long & short of it was a £70 sensor (bosch) and then it was back to normal!

My car had only 80K on the clock when the sensor failed.

Early 2001 Turbo cars run the Volvo 8627750 (Bosch 0258007070) O2 sensor which is actually a replacement schedule for 100k miles. I suspect most don't get changed though!

For information, 'powersparks' on e-bay can provide the genuine Bosch units for £70 - probably where the Badger sourced his?

Snake oil has now arrived:-

**mike 850** · Friday 30th April 2010, 17:34

are the o2 sensors easy to replace? and how can i make sure i get the right one?

cheers

**princepugh** · Friday 30th April 2010, 19:06

Originally Posted by mike 850

are the o2 sensors easy to replace? and how can i make sure i get the right one?

cheers

TBH I'm not sure it's worth replacing as yet, probably best starting with the easier/ cheaper checks and maintence tasks first?

To confirm the part, you can contact the parts dept of yor local dealer, they should be able to confirm from your registration. The sensor was changed half way through 2001 so you need to be sure which one is required for your car.

**mike 850** · Friday 30th April 2010, 19:23

cool, when i was driving it a min ago it was boosting to 10psi and holding there. I wonder if i do has a vac leak that would cause it to overboost a bit causing the hesitation etc? i have ordered some 6mm vac lines so i will replace all the ones around the turbo.

cheers

**thebadger** · Saturday 1st May 2010, 01:56

Originally Posted by princepugh

Early 2001 Turbo cars run the Volvo 8627750 (Bosch 0258007070) O2 sensor which is actually a replacement schedule for 100k miles. I suspect most don't get changed though!

For information, 'powersparks' on e-bay can provide the genuine Bosch units for £70 - probably where the Badger sourced his?

Snake oil has now arrived:-

Chocolate watch & a coconut to that man!

Originally Posted by mike 850

are the o2 sensors easy to replace? and how can i make sure i get the right one?

cheers

Hell no, they weld themselves onto the downpipe! If you want to do it, you'll need to have a ramp or a pit to do it with, loads of swearing & force involved.

It's a 19mm size bolt to the sensor, so it's a pain!

**mike 850** · Sunday 2nd May 2010, 22:22

well heres an update, I have now done nearly 300 miles on v power fuel and the difference is night and day (it even sounds different), its sooo smooth and feels like its got more power with no hesitation or holding back, I am guessing it might be remapped after all, its boosting 14+psi and judging by the play i had with a bmw 330 its all pointing that direction. I read somewhere that standard s60 should do 60-100 in about 11 secs i timed mine at approx 8 secs.
cheers for all the help guys