Surge @ Low RPM.

[4agejet]

Hey guys, so yesterday and today, my car seems to surge minorly whilst taking off or cruising at low rpm's. No idea wtf it is, havn't touched nothing in over a week, which was running fine during that time..
16v Big Port.
Bosch 910 external pump fitted just over a week ago, and from the sound it seems to be working fine..
The surge goes away after about 3k revs..
Any help appreciated.

[haveaparty]

Keep it above 3 grand Hahaha. Wat bout blokage somewhere.

[4agejet]

i was thinking that, fuel filter maybe? but why after 3k its fine?

[haveaparty]

Hmmm. U got coil pack or dizzy??? Could be ur filter. Just replace it and see how u go. If u got coil packs on coils be failing on low rpm.

[4agejet]

Im sure i have a dizzy only.. My fuel pumps got a relay for it in the boot, and it wasnt working properly at one stage, but all of a sudden it was fine, and now the surging business, ill replace the relay and check out my filter, see how it goes.

[LittleRedSpirit]

Bosch 040 Fuel Pump Specs:
Bosch Part Number: 0580254040
Minimum Current: 12 Volts
Operating Pressure: 94 PSI (6.5 Bar)
Minimum Flow @ Outlet: 80 GPH (300 LPH)
Fuel Pump Location: In Tank
High Temperature Reduction: 8 GPH (30 LPH)
Weight: 930 Grams (2.05 Pounds)

There are the specs on your pump. I think you have way too much fuel pressure and volume. Its probably forcing more fuel out of the injectors than needed until such time as you are higher in the revs and requiring it and relieving some pressure as they open up more. I believe a JDM ae86 pump flows about half the litres per hour than your new oversize pump. Why did you buy one so big? OEM is best unless you have a massive turbo system. Did you check the fuel pressure yet?

[LittleRedSpirit]

From a euro ae86 forum:

BE CAREFUL!!!!!!

The AE86 stock pump has a flow volume of approximately 80 lph. Swapping in a pump designed to flow 255 lph is NOT... I REPEAT... NOT a good idea! I have this information on the best source........ Walbro engineering!!!

A 255 in a corolla will at the very minimum cause excess fuel heating by over circulating the fuel! Other problems besides overheating that can occur... poor idle, poor off idle response, poor fuel economy. This is because the 255 pumps flow soooo much fuel, that the return line becomes an obstruction. This raises fuel pressure in the fuel rail, cause excess fuel to flow past the injector.

Now... if you are running 30psi of boost, then by all means get a 255 and replumb all the fuel lines... BUT for stock, or mildly built EFI cars you want a GSS310 Walbro fuel pump. This pump is used in the Integra B18C... it flows 115 lph at the exact same pressure as the stock AE86 pump. 115 lph is enough fuel in N/A form to support 230hp. In boosted form it can support 195-200 hp. Boosted apps require more fuel, that is why the same pump supports less boosted hp, then N/A hp.

You will still need the AE86 install kit, but try to ask your Walbro dealer for a GSS310 pump

Thanks to

[4agejet]

Um thanks but im running a bosh 910 not a 040 or 044...

[haveaparty]

I'm not an expert on numbers but 910 is a larger number then 040 or 044 soooo...
Hahahaha

[LittleRedSpirit]

Yeah copied and pasted the wrong blurb, this is yours:

Bosch 910 Fuel Pump Specs:
Bosch Part Number: 0580254910
Minimum Current: 12 Volts
Operating Pressure: 72.5 PSI (5 Bar)
Minimum Flow @ Outlet: 34 GPH (130 LPH)
Fuel Pump Location: In-Line

Its still almost double the flow rate.

Im unsure how much of a problem it will cause, but its not ideal obviously. Ideal would be OEM spec. I think the Walbro in my car is 160lph but I have a 20v with slight greater thirst for juice, and I upgraded my return line to the same size as the supply.

I think you wont know till you try. Why did you decide to change it, did the old one die? I think a fuel pressure gauge would be the best way to see if this is the problem before you spend the money on a different pump or pull anything apart. basically the fuel reg should maintain a constant 40 something psi, unless anyone can confirm exactly, as Im used to 20vs and am unsure how exactly this pressure differs. It should however be constant as you rev the car up, if it isnt then you have the issue as described I would say. Im no expert, but I have seen a few curious issues like this caused here and there with fuel pressure issues.