Loss of power

[Stephen w]

Hi can anyone help, I have just purchased a old 2003 rav4. When I drive it at normal running temperature it intermittently loses power. When I push the pedal to the floor it hesitates and suddenly cuts in on power again. More noticable when I put my foot down on approach to a hill. I have had the Egr valve replaced and the rac plugged the car in and it is showing no faults, please can someone help thanks Steve. 

[IanML]

Petrol or diesel?

[Stephen w]

Diesel 

[IanML]

I suspect an electrical problem associated with fuel supply.  An independent diesel specialist would be the best bet, as they see more of the obscure problems than do the dealers.  

[Devon Aygo]

A likely cause would be SCV ( Suction control valves ) a relatively common issue on 2.0 D4d Rav and there is a repair kit of Two valves available,

The valves control fuel pressure from the pump in to the common rail depending on throttle input, as the valves fail they slow down and stick then release, the slow valves causes the lack of power the stick/release the surging.

[Avalon]

Personally i'm going with VNT's being sticky, put a tank of Shell/BP ultimate and two bottles of forte turbo cleaner through, ideally manually actuate the control arm on the turbo and make sure it operates stop to stop easily. Also consider a fuel filter change while you're at it - it's often skipped by disreputable garages.

[KTH]

Steve I’ve got a similar issue. 2005 D4D. Complete service, all filters changed (they were filthy), oil changed, system cleaned & flushed, just replaced SCVs. Car running and starting much better (starting was weak) and eliminated stutter on acceleration, but still get loss of power at speed. Accelerate to 70mph, back off to just above 60mph, ask again for power and engine won’t let me go above 2000 rpm. Decelerate, change down & eventually acceleration comes back suddenly. No engine cut out, no warning light, nothing showing up on diagnostics.  Any advice what to try next? 

[Avalon]

1 hour ago, KTH said:

Steve I’ve got a similar issue. 2005 D4D. Complete service, all filters changed (they were filthy), oil changed, system cleaned & flushed, just replaced SCVs. Car running and starting much better (starting was weak) and eliminated stutter on acceleration, but still get loss of power at speed. Accelerate to 70mph, back off to just above 60mph, ask again for power and engine won’t let me go above 2000 rpm. Decelerate, change down & eventually acceleration comes back suddenly. No engine cut out, no warning light, nothing showing up on diagnostics.  Any advice what to try next? 

So you come off boost when you back off, the variable vanes (theoretically) go from wide open to fully closed so that the turbo can spool up quickly at a lower pressure/flow, the problem is due to carbon buildup the control ring doesn't move smoothly, this leaves the turbo unable to spin up properly till boost reaches a point that can overcome the incorrect vane position. As I suggested in the post immediately above, you need to decarbonise the dirty side of the turbo.

In order of cost/agro:

1. Replace turbo, new fitting kit/oil pickup, prime it before starting up. Expensive and will have the same issue long term.

2. Dismount, strip and clean the turbo, cheaper assuming the turbo itself is serviceable, takes longer, still requires a new fitting kit/priming, will have the same issue long term.

3. Use a cleaning treatment, this is potentially the least invasive option, but also the least effective. Forte works well and is just added to the fuel tank, generally two bottles is enough to notice a significant improvement, not using crap fuel helps a lot. If you fancy removing the heat shield and the exhaust (new gasket is a few quid), oven cleaner works well (Mr. Muscle) and is £3-4, it's way cheaper and more effective than Forte, but it requires more effort and it's still not as effective as a full strip/clean.

[KTH]

Avalon, thank you, this is really helpful and would make sense. We’ve done fuel cleaner and aerosol cleaners through air I take, cleaned MAF sensors and done the EGR. Turbo strip and clean is next on the list. Car goes like a rocket otherwise ...!