Fuel pressure

[paulcundy]

Trevor wrote in the exhaust thread;

"However, whilst checking the fuel pressure, in line with something we would normally do and also suggested by Jools, we noticed the fuel pressure was dropping during the power run. I believe we have a solution to this but will have to confirm tomorrow and Friday on the rollers. Whilst the pressure drop is not massive, it does have a slight effect (shifted half an afr or so) on the fuelling which, whilst not unsafe for the engine, is something I'm not that comfortable with right now".

There are a few people who've noticed fueling to be marginal in some circumstances over in the USA. Trevor have you any other more general comments? A few of us have power upgrades and I'm wondering if we need fuel pressure regulation or boosters? I don't know a lot about the issue but presumably a low pressure leads to a weak mixture which can end up roasting the internals.

Any pearls of wisdom?

Regards
Paul C

[actech]

Paul,
I seem to remember Jools having a bigger fuel pump fitted to get around (t)his problem on the recommendation from JNMS.
Anthony

[joolski]

I have had an uprated fuel pump installed on my car.

When my car was originally upgraded with the 3L exhaust, the mechanics were informed that no upgrade of the fuel pump was required.

As a result of this very bad bit of advice, my engine was lunched and then required a rebuild.

JNMS checked my car after the rebuild, and warrantied the engine. I was amazed by how professional they are, and I was shocked to find after spending a few hours on their rolling road just how many things needed to be adjusted. Top blokes !

If you do upgrade the fuel pump, the cables to the pump will also need upgrading as they are puny 24awg, wired up to a 30a relay.

BTW, on standard boost with a beter flow exhaust and upgraded pump my "little" 2.5L was putting out over 360bhp on the rolling road.

Very impressive stuff.

Paul, you may want to give pete dibble a call .... might save you a few quid ....


--Jools

[gizard]

Do you have an M400 pump then?

[ThatPhilBrettGuy]

There's also a potential problem with the 2.5l fuel rails. The return is right next to cylinder 6 feed and a number of people believe is subject to pressure drops. This causes 6 to run lean with predictable expensive results. Vegantune have seen more than one cylinder 6 failure, believed to be due to this.

The 3l rail is different in design. It also fits on the 2.5l engine I believe.

[joolski]

gizard said:

Do you have an M400 pump then?

We tried the stop M400 pump and it was not upto snuff.

JNMS sourced a motorsport pump which they felt would provide enough kick.

[joolski]

ThatPhilBrettGuy said:

There's also a potential problem with the 2.5l fuel rails. The return is right next to cylinder 6 feed and a number of people believe is subject to pressure drops. This causes 6 to run lean with predictable expensive results. Vegantune have seen more than one cylinder 6 failure, believed to be due to this. The 3l rail is different in design. It also fits on the 2.5l engine I believe.

I don't think the 3L rail is a straight fit on the 2.5L, however one of the guys at vegatune was working on fitment. Not sure how far it has been taken.

This is because the relief valve is next to the cyl 6 injector. And as a result robs the injector, when under high loads.

However, point aside, upgrading the pump ensures that the fuel rail is at the correct pressure, even at the end of the rail.

This topic is very close to my heart (can you tell ?) as a result of the lack of knowledge on this subject my car was off the road for some time.

--Jools

[paulcundy]

Jools,
I have the M400 pump so I'm a little worried if you say its not up to scratch.

Does anyone know about fuel pressure boost regulators?
Regards
Paul C

[washy]

Surely it's flow you need not just pressure Paul? I can't see how a fuel pressure regulator's going to help if the pump doesn't flow sufficient volume?

As an M400 owner who likes the occasional track day I must say this is a tad worrying!!

[paulcundy]

I don't claim to understand it all. Its a combination of flow and pressure and the two are clearly linked. The injectors are designed to work at certain operating pressures so even if the potential flow can be supported it isn't any good if its not being pushed hard enough? Laymans language works best for me!

I am suprised that Jools found the M400 pump to be inadequate. M400s don't seem to have a problem generaly. Jools could yours have been a duff pump?

What are the differences between the standard M400 one and your new one?

Regards
PauL C

[gizard]

paulcundy said:

I don't claim to understand it all. Its a combination of flow and pressure and the two are clearly linked. The injectors are designed to work at certain operating pressures so even if the potential flow can be supported it isn't any good if its not being pushed hard enough? Laymans language works best for me! I am suprised that Jools found the M400 pump to be inadequate. M400s don't seem to have a problem generaly. Jools could yours have been a duff pump? What are the differences between the standard M400 one and your new one? Regards PauL C

Just to put more spin on it - If I understand him correctly YellowShed mentioned to me that if you go bigger than the M400 pump - you need to upgrade the wiring to be man enough to cope with the electrical power requirement (at least that's what I think he said - maybe he will be along in a minute to clairfy this).

[yellowshed]

The standard fuel pump fitted to the 3 and 3R (and to the 2.5s I believe as well) is only good really for the standard car's power - 350bhp - it will deliver fuel for more power but at an ever decreasing pressure as the flowrate (power) goes up. During the development of the M400, we noticed this (we even had 400bhp during the development on that original pump but the pressure had gone down a lot and I was compensating for it in the mapping). Therefore we ended up specifying a higher flow pump for the M400s.

I have to say that all the testing I did during the M400 development and since, hasn't shown an issue with the fuel pressure with the pumps specified for the M400. Unless you're in excess of 450bhp, I would think the M400 pumps are fine.

As stated on the exhaust thread, I am planning on testing an M400 next week, and I'll have the results to say yay or nay.

Updated:

As gizard said, I have heard that the higher spec motorsport pumps do draw more current and the standard wiring loom is not up to that level of current draw. From memory, the specs on the M400 pump were more flow with not too much more current draw, hence they should work fine in the M400s. Also, the motorsport pumps were deemed too noisy for road cars.....

YellowShed



>> Edited by yellowshed on Thursday 2nd March 16:21