Dip in Acceleration

[Niran]

Hey everyone!

Forgive my ignorance if this has been covered elsewhere, but i cant seem to find anything similar through the search function

I own a 1999 VR4 Manual Legnum Type S. I notice when accelerating hard on 1st, 2nd, and 3rd the acceleration/power dips at around 3500-4000rpms and then again at higher rpms sometimes when i plant my foot right down on the gas. Is this normal? It doesn't happen when i have the accelerator half or three quarters pressed.

Could it be the turbos? The car has done 130,000 ks. Or is this normal for twin turbos?

Thanks guys!

[Subaru ETA]

When were the plugs last done? Is it running standard boost?

[Niran]

Everything is standard. The previous owner had it for 5 years from 80,000k and didnt change the plugs

[Davezj]

When you say acceleration dips, do you mean all the power stops and the car jerks and slows for a second then picks up again.
Are you hitting fuel cut?

[elnevio]

Everything is standard. The previous owner had it for 5 years from 80,000k and didnt change the plugs

This had GOT to be the first port of call, as well as any other service items that haven't been done - oil change, air filter, fuel filter, etc.

Wouldn't surprise me if it's the plugs though.

[Niran]

When you say acceleration dips, do you mean all the power stops and the car jerks and slows for a second then picks up again.
Are you hitting fuel cut?

Its hard to explain precisely, but its almost like a loss in power? No a complete power loss. It could be as bad as a jerk as well sometimes. I thought it may have because of the twin turbos, but it happens at higher rpms as well sometimes?

[mattnz]

Not normal for parallel turbos. Also maybe clutch letting go, but could be a lot of things by that description. If it sounds engine-y would definitely try plugs.

[Niran]

This had GOT to be the first port of call, as well as any other service items that haven't been done - oil change, air filter, fuel filter, etc.

Wouldn't surprise me if it's the plugs though.

I have done the air filter myself. But i need to get the car serviced. Dont know when the owner did one last
Apart from the normal stuff, does the diff oil need to be changed as well? Oh and transmission fluid? or is that just for automatics? Thanks

[Niran]

Not normal for parallel turbos. Also maybe clutch letting go, but could be a lot of things by that description. If it sounds engine-y would definitely try plugs.

Awesome cheers Mattnz, will change em on the next service!

[mattnz]

Maybe also try looking at the piping around the dump valve (left-hand corner under bumper), air-leak could mean you hit fuel cut

Diff oil needs to be changed, not very often though. Easiest to take it to mitsi for that, as they can hook it up to the computer and pump it out properly.

No trans fluid for manuals

[Niran]

Is that pretty much the intercooler piping on the left hand side or something else? It goes pretty hard at low revs, if it was air leak wouldn't it be a power loss across the entire rpm range? lol thought so, no transmission fluids

[mattnz]

There probably are fluids tbh, but definitely not as finicky as auto. Yeah, the rubber pipes around the intercooler, they can get oil off the road on them, which degrades them and can make a little hole. A small hole can cause sudden loss of power because the ECU cuts the fuel above ~15psi, if unmetered air is getting in or out through a leak, that can mess with the fuel cut.

[kylereece]

Clutch could be slipping?

[wintertidenz]

If it's dipping around that rev range, it will be spark plug related. At the very least pull the front three plugs and inspect them.

[Niran]

Pretty sure its not the clutch, because it goes hard, and then dips. It definitely needs new plugs. From your experiences, with twin turboed cars, is the acceleration more or less smooth once the boost kicks in?

[elnevio]

These are smooth.

Change the plugs before wondering about anything else though!

[Nick Mann]

There are two types of twin turbo, sequential or parallel. With sequential you can get a change in power as the small turbo gives way to the large. I believe that some Legacys have this setup. But VR4's are parallel - they are both working all the time, there is no change over, so the power delivery should be smooth.

[Niran]

Awesome cheers guys! Will get the car serviced and have the plugs changed. Fingers crossed!

[Niran]

Finally got all my plugs changed, with new ignition leads. Turns out that oil was leaking from the rocker cover gasket too, so had that replace as well. It honestly feels like i am driving a new car now