Walbro 341 pump upgrade

[dandan]

Can anyone give some definite answers to the following questions?

Many people upgrade to a Walbro pump at some stage, some tuners recommend this as a matter of course for J spec owners, others do not.

Does this pump have to be fed a constant 12v and have the 9v-12v "on boost" switchng disabled?

Will running 12v constant cause an overly rich idle and light load condition?

Why did Toyota design a switched system, was it to prolong pump life rather than for a fuel flow reason?

Let's take a car where air fuel ratios are perfectly acceptable with stock fuel system at all levels of boost encountered for that car. If a Walbro is fitted will this have any effect on the afr's? Will it cause an over rich condition at certain load/speed sites in the fuel map at all?

Or, will the pump make no difference to afr's because the stock regulator maintains (a maximum) flow pressure at all times?

The reason I bring these last two points up is beacause I know of several owners (including me) running higher than stock boost but with perfectly acceptable afr's and "if it ain't broke, don't fix it" comes to mind.

However, if somebody can tell me that the pump will not cause over rich conditions and will only perform different to a stock pump when stock pump flow falls due to increased demand then I am happy to fit one. (ie at the point when fuel demand exceeds stock pump's capabilities).

It would be a shame to fit one and end up having to buy one of the piggy back "fudges" just to correct any over richness incurred by its fitting in the first place.

Looking forwarded to some (no doubt) differing responses...

Dan

[Martin F]

Quote[/b] (dandan @ May 06 2004,21:14)]Can anyone give some definite answers to the following questions?

Many people upgrade to a Walbro pump at some stage, some tuners recommend this as a matter of course for J spec owners, others do not.
Ok........

Quote[/b] ]Does this pump have to be fed a constant 12v and have the 9v-12v "on boost" switchng disabled?


No, you can leave the switching between 9v and 12v as stock. However make sure your rail pressue or AF ratio is checked to ensure when the Walbro is at 9v it is not running below the stock specifications.

Quote[/b] ]Will running 12v constant cause an overly rich idle and light load condition?

Nope, the fuel pressure is regulated by the fuel pressure regulator so the injectors will still only be injecting the same amount of fuel. What will probably happen in reality is that there will be a bit more fuel passing back to the tank on the return pipe.

Quote[/b] ]Why did Toyota design a switched system, was it to prolong pump life rather than for a fuel flow reason?

Good question. Think there's two trains of thought on this one. One being for pump life (longevity) and the other being reduction in noise. However it may be neither of these somebody needs to see if this one is mentioned in the NCF

To answer your other points, if your AFR is spot on now and your running at BPU you should not see any great changes when fitting a Walbro. AFR may shift a few points but not enough to warrant any concern or re-tuning.

This small shift in AFR can be brought about by a slightly higher fuel rail pressure because the Walbro pump is higher specced than your JDM original. Therefore with a higher fuel rail pressure your injectors will not have to open for quite so long to get the same amount of fuel into the intake. This in essence gives you more headroom on your fuelling allowing you to increase boost further (neagting the fact that stock twins will be out of their efficiency range, SMIC may not be so efficient, etc) and your fuelling system will still be able to manage the increased demand.

Now i apologise if there are any errors or omissions in the above but its getting late and i need to get to bed, so will re-read in the morning to make sure it makes sense. http://www.mkivsupra.co.uk/iB_html/non-cgi/emoticons/biggrin.gif


Dan - haven't forgot about your parts, just been short on time in the evenings. Will let you know over weeekend

[Nathan]

Quote[/b] ]some tuners recommend this as a matter of course for J spec owners, others do not.

We are one of the tuners that do reccomend fitting a Walbro for all BPU cars now. I agree, there are no doubt some Jap cars out there that will be OK at 1.2 bar with the stock pump but by far the majority are right on the edge. AFR's are one thing, but we have checked the fuel being returned to the tank and most cars will show just a dribble. Hardly a nice situation. In addition, running 1.2 bar against the OE boost places demands on the OE pump it was never designed for and whilst I agree that AFR's might be OK straight after the upgrade, they might not be in a few months time as the pumps rapidly wear. As a commerical enterprise, we can't take that risk. What I have said above we say to all of our customers too and ultimately the decision lies with them but we make it quite clear on the invoice that no uprated pump was fitted although it was reccomended.


Quote[/b] ]Does this pump have to be fed a constant 12v and have the 9v-12v "on boost" switchng disabled?

We always run our Walbros at 12v, no question. The pump is not designed to work at lower voltages, and fuel delivery can become very unstable. In extreme circumstances, it won't run at all.


Quote[/b] ]Will running 12v constant cause an overly rich idle and light load condition?

Absolutely not. As Martin says, the regulator returns any unused fuel to the tank. The injectors don't know any different.

Quote[/b] ]Why did Toyota design a switched system, was it to prolong pump life rather than for a fuel flow reason?

To this day I'm still not 100% sure, although both of Martins suggestions are viable.


Quote[/b] ]Let's take a car where air fuel ratios are perfectly acceptable with stock fuel system at all levels of boost encountered for that car. If a Walbro is fitted will this have any effect on the afr's?

No.


Quote[/b] ]Will it cause an over rich condition at certain load/speed sites in the fuel map at all?

No.


Quote[/b] ]Or, will the pump make no difference to afr's because the stock regulator maintains (a maximum) flow pressure at all times?

Correct.


Quote[/b] ]The reason I bring these last two points up is beacause I know of several owners (including me) running higher than stock boost but with perfectly acceptable afr's and "if it ain't broke, don't fix it" comes to mind.

My reasons for maybe adjusting your attitude towards this have been explained above. It's a 'peace of mind' thing. Whilst I generally agree that spending money where it's not immediately needed is wasteful, Jap soops at 1.2 bar (and more and more UK spec too) are known to generally be on the edge of the OE pump and do you really want to be worrying about it at 150 leptons in the summer? If you can afford to run a soop at 1.2 bar, you can afford an uprated pump. It's not exactly an expensive component (relatively). Bit like running stock plugs at 1.2 bar as well IMO.


Quote[/b] ]However, if somebody can tell me that the pump will not cause over rich conditions and will only perform different to a stock pump when stock pump flow falls due to increased demand then I am happy to fit one.

That is correct.


Quote[/b] ]It would be a shame to fit one and end up having to buy one of the piggy back "fudges" just to correct any over richness incurred by its fitting in the first place.

You won't need to.

Do yourself a favour, buy a pump. I don't care who from, just get one.

In case no-one knows how I feel about this...

All 1.2 bar Jap supras should be running with a Walbro and colder plugs!

I might add that many people report of their car being 'more responsive' after having a pump fitted. We can only assume, even if AFR readings seem OK, that the sharper boost rise of a BPU car is actually out-gunning the pumps ability to supply fuel at certain rpm's/loads. Most AFR readings are taken either at stable loads or 'flash' readings where the car is nailed from a low rpm. It may just be that the AFR reader itself can't react quick enough to show any leaness, and by the time it has caught up the pump has caught up. Just a thought. I've never spent too much time pondering over it TBH.

[dandan]

Thanks for the replies chaps.

Nathan, I've known for a while that you recommend a Walbro upgrade and I was hoping you'd respond. Your comment about the return line to the tank is an interesting one. http://www.mkivsupra.co.uk/iB_html/non-cgi/emoticons/smile.gif

I am not worried about spending ?100 or so on a pump at all, not exactly big spending compared to the other items we treat ourselves to!

My only concern was afr's dropping and having to do something to correct that, but as suspected the regulator should keep things in check.

It's next on my list then.

Cheers all

[Martin F]

Nathan are you coming across many lazy (read *ucked) fuel pressure regulators ?

Maybe a consideration to check out this component when you do this upgrade as well. Its even cheaper than the pump but just as critical.

[Nathan]

No, not seen a faulty reg yet. The only time we've changed them is when going to the HKS rail.