Full Throttle High Rpm Problem

[HotRodderJoe]

Hi, I have a small issue with my RB25DET. Under full throttle from about 5,000rpm to redline I get a strange slight surging. If you back off the throttle slightly to 90% it's fine. It kind of feels like boost is going up and down slightly.

The car is a '96 R33 5 speed with BOS importing front pipe, Catco wide body cat, Trust PE2 cat back, Apexi pod filter and R34 GTT intercooler apart from that it's stock.

I've recently done a full service on it including new NGK plugs and fuel filter and it runs very smooth and powerful except for this small issue. Anyone got any suggestions on what could be causing this? Would be glad to hear any ideas.

[DVS JEZ]

Very likely to be hitting rich and retarded mode. Or the fuel pump is being lazy

[HotRodderJoe]

Thanks for that. I thought maybe the fuel pump isn't supplying enough pressure or AAC valve fluttering. The car seems to have a lot of power and must be right on the limit for the stock fuel pump, injectors and ECU so when you back off the throttle slightly reduces the air going in and everything is OK. Might just leave it and not worry too much about it. Could it be the factory boost controller sticking or stiff might try a Turbotech manual boost controller and see if that has any effect.

[KiwiRS4T]

Consider getting a new pump. It may be on the way out and a more grunty new pump isn't too expensive.

[HotRodderJoe]

Could put in a Bosch 040 in a few weeks.

[DVS JEZ]

R33's are tricky to get an 040 setup at the correct height, research it first, or try a walbro which uses the stock filter and mount

[gotRICE?]

Did they change the walbro pumps?

There wasnt a shit show of fitting the stock filter sock to mine when i put it in. Faced the wrong way and wouldnt let the pump sit down.

Ended up breaking off the circlip tab too And apon my last pump inspection, the walbro sock is also gone. lol. Wonder how long ago it fell off...

[rondofj]

Just remember to rewire the walbro pump to get constant 12 volts. Theres threads on this

[DVS JEZ]

Did they change the walbro pumps?

There wasnt a shit show of fitting the stock filter sock to mine when i put it in. Faced the wrong way and wouldnt let the pump sit down.

Ended up breaking off the circlip tab too And apon my last pump inspection, the walbro sock is also gone. lol. Wonder how long ago it fell off...

Ive never had any drama's. U have to cut the bottom of the bracket off though and use a hose clamp to mount the pump theye bracket

[HotRodderJoe]

Something like this looks pretty good. A direct replacement with no mods would be best.

http://www.prospeedracing.com.au/products/Walbro-Fuel-Pump-Uprgade-Kit-%252d-Skyline-GTS%252dT.html

[gotRICE?]

Ive never had any drama's. U have to cut the bottom of the bracket off though and use a hose clamp to mount the pump theye bracket

Yeah i never had any drama fitting it as such. It fits fine without cutting the bracket at all.

It was just where the circlip sat. Didnt allow the factory sock to point in the right direction, therefore holding the bracket up. And unfortunately for me the circlip snapped off when i took it back off lol. And the walbro sock went for a dive.

Need to fish it out or get a new one and try the hose clamp trick. Although from memory there isnt really the space for a hoseclamp.

[HotRodderJoe]

I've been reading up on fuel pumps for Skylines. The Walbro's are cheaper but there seem to be some fakes floating around and they max out at 60psi also for them to run at max they need a wiring mod, easier to get a better pump. The Bosch 040 seems very good but more expensive. If you measure the stock pump and install the new pump so the intake is at the exact same height inside the tank it should avoid any issues.

Think I'll get one of these looks like good value.

http://www.prospeedracing.com.au/products/DeatschWerks-300%252b-LPH-High-Flow-In%252dTank-Fuel-Pump-suit-Skyline-GTS%252dTs.html

The Walbro without the wiring mod would be OK for my setup but don't want to risk getting a dodgy fake.