850 t5 holding back under hard acceleration HELP!!

**t5cookie** · Friday 26th April 2013, 01:01

My t5 drives fine when driving normal but when i put my foot down it feels like its holding back dident know if it would be a boost leak or somthing?
merc85 (gav) has had a look at my car but is a bit stumbled to what is going on? please HELP

**glock19** · Friday 26th April 2013, 04:22

You'll know it's a boost by looking at the boost gauge on the dash.
Your case is most probably due to the fuel pump

**t5cookie** · Friday 26th April 2013, 05:05

the boost gauge gos 3/4 into the white.
How will i know if its fuel pump?

**t5cookie** · Sunday 28th April 2013, 11:33

could the problem lie with fuel does anyone think?

**PHIL V70R** · Sunday 28th April 2013, 11:55

read the codes...try a good working maf mate....

**merc85** · Sunday 28th April 2013, 12:03

Its feels like abit like fuel cut the guage goes 3/4's into the white then it starts to stumble, there is no power behind the rise in rpm.

Its either leaking boost causing a boost cut, or the fuel pump is getting week.

The car tbh really needs a stage zero tune before diagnosis

**t5cookie** · Sunday 28th April 2013, 12:06

what do i need to do for a stage zero tune gav

**merc85** · Sunday 28th April 2013, 12:15

a Stage zero tune consits of renewing all serviceable items with new parts.

eg Pcv (which have done)

Plugs, Cap. rotor, leads, oil, oil filter, air filter, fuel filter
Replacing all perished vacum lines in the process

Only then can you be sure the car should be runing correctly, i relise this is costly but its what every owner should be doing before starting to tune one of these vehicles.

**Dangerous Dave** · Sunday 28th April 2013, 12:17

Had this the other day when I messed with my recirc valve, car felt like it was 'stumbling' for power when pushed. There wasn't enough pressure getting to the recirc valve so it was opening and venting the boost. Perhaps check the vac lines to the recirc or take the recirc valve off and check it for leaks.

**t5cookie** · Sunday 28th April 2013, 12:25

ive done oil filter, fuel filter, air filter, plugs, i think i need leads as one of the is split isint it gav?

**t5cookie** · Sunday 28th April 2013, 12:25

Originally Posted by bomb192uk

Had this the other day when I messed with my recirc valve, car felt like it was 'stumbling' for power when pushed. There wasn't enough pressure getting to the recirc valve so it was opening and venting the boost. Perhaps check the vac lines to the recirc or take the recirc valve off and check it for leaks.

i have a forge blank plate on the turbo but will still check the vac lines.

**Kingsford G** · Sunday 28th April 2013, 14:55

If u had yr maf gone it`d through an emission light on its most likely to be the fuel pump or even a clogged fuel filter.

**Nealevo** · Sunday 28th April 2013, 15:21

I would always look for an electrical ignition fault, mine used to hesitate under load, it turned out to be faulty number 2 lead, genuine new set purchased and all is well!!

**Kingsford G** · Sunday 28th April 2013, 15:24

As Gav said a full stage 0 is a must and go from there.

**t5cookie** · Sunday 28th April 2013, 15:47

Originally Posted by Kingsford G

As Gav said a full stage 0 is a must and go from there.

yh ive done fuel filter, denso plugs, air filter, oil filter and oil, leads but they need replacing. ill get new cap rotor and leads and let u know the outcome.

**merc85** · Sunday 28th April 2013, 17:07

Originally Posted by t5cookie

yh ive done fuel filter, denso plugs, air filter, oil filter and oil, leads but they need replacing. ill get new cap rotor and leads and let u know the outcome.

ive a standard fuel pump, let me know if you want to give it a try. if it does cure it, get a uprated one. there cheap enough

**AndysR** · Sunday 28th April 2013, 21:01

MAF failure doesn't always bring the warning light on Kingsford, I'd complete the full stage zero first as sugessted then go from there. After that, personally, I'd be looking at the MAF first then the fuel pressure reg and then pump. Good luck with it

**Kingsford G** · Sunday 28th April 2013, 21:10

Originally Posted by AndysR

MAF failure doesn't always bring the warning light on Kingsford, I'd complete the full stage zero first as sugessted then go from there. After that, personally, I'd be looking at the MAF first then the fuel pressure reg and then pump. Good luck with it

My experience with MAF based on V and S70`s and both times had light on running like a crap also not going above 3000k,not sure on 850`s tho.Before u start replacing pumps and FP regulator save your money and time and get a fuel pressure gauge connected and that`ll tell u if your problem in the fuel supply but change your leads and dizzy cap cos a hairline crack in the cap can cause that as well as dodgy wire.

**merc85** · Sunday 28th April 2013, 21:17

s/v 70's run Bosch 4.4, 850' are 4.3 and arnt as fussy. This car has had a replacement MAF tho be it not a Bosch one. It boosts ok but there is no power behind the boost and hesitates feels like mild boost cut ease your foot off and the problem resolves.

Its similar to a crank sensor fault ive had in the past, but I believe a fuel pump is probably more likely

**Kingsford G** · Sunday 28th April 2013, 21:23

Originally Posted by merc85

s/v 70's run Bosch 4.4, 850' are 4.3 and arnt as fussy. This car has had a replacement MAF tho be it not a Bosch one. It boosts ok but there is no power behind the boost and hesitates feels like mild boost cut ease your foot off and the problem resolves.

Its similar to a crank sensor fault ive had in the past, but I believe a fuel pump is probably more likely

I c,it does sound like a fuel starvation therefore a quick pressure test will show up.A Wallbro for future mods would be good anyway.