Fuel pressure sensor setup

Fuel pressure sensor setup

Author
Discussion

griggsy2

Original Poster:

126 posts

279 months

Tuesday 25th July 2017
quotequote all
Afternoon,

Would like to add a fuel pressure guage to the car. Not so keen on a mechanical version in the dash so has anybody installed a decent sensor fit for purpose (0-5bar range) they can point me towards?

Cheers,
Lee

DCL

1,215 posts

178 months

Tuesday 25th July 2017
quotequote all
I looked at the Stack and gauge but decided in the end to fit a removable mechanical gel filled unit at the fuel rail. And that's just used for RR and checks. Although seeing fuel pressure all the time may seem a good idea, it can be confusing for a couple of reasons.

Firstly the mapping will compensate for the fuel pressure, so if the pressure drops at high power, then the injector time will increase to compensate (provided there's enough duty cycle left) - so there is no 'correct' fixed fuel pressure as such. Secondly, and this was my main reason for not doing it, is that fuel temperature makes it extremely difficult to interpret. For reasons I don't fully understand, fuel pressure drops as temperature goes up (I suspect that it becomes less viscous), but more fuel also goes through the injectors too. It's a bit like measuring voltage when you don't know what current is flowing.

griggsy2

Original Poster:

126 posts

279 months

Wednesday 26th July 2017
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Thanks DCL, it was the Stack unit I was looking at.

Interesting what you say about the change in pressures though, that does indeed make a difference to the value of having a guage in car. I have the ability to measure inline from the engine bay so maybe will stick to that then.

Cheers again! smile

fergus

6,430 posts

274 months

Wednesday 26th July 2017
quotequote all
DCL said:
I looked at the Stack and gauge but decided in the end to fit a removable mechanical gel filled unit at the fuel rail. And that's just used for RR and checks. Although seeing fuel pressure all the time may seem a good idea, it can be confusing for a couple of reasons.

Firstly the mapping will compensate for the fuel pressure, so if the pressure drops at high power, then the injector time will increase to compensate (provided there's enough duty cycle left) - so there is no 'correct' fixed fuel pressure as such. Secondly, and this was my main reason for not doing it, is that fuel temperature makes it extremely difficult to interpret. For reasons I don't fully understand, fuel pressure drops as temperature goes up (I suspect that it becomes less viscous), but more fuel also goes through the injectors too. It's a bit like measuring voltage when you don't know what current is flowing.
That's a neat trick to increase injector time as a function of drop in fuel pressure. Which ECU handles this? I'm running a K6 Emerald, and get close to maxing out the duty cycle on my injectors (assuming a fixed 3.5 bar fuel pressure) so could benefit from something similar.

griggsy2

Original Poster:

126 posts

279 months

Wednesday 26th July 2017
quotequote all
Pretty sure DCL is not implying this is an 'automated' ECU option that adjusts the timings in real-time with fuel pressure. Rather saying the maps account for differing fuel pressure (and hence injector timings) at varying rev / loads when they are defined on the RR.

Also, if you are maxing your duty cycle then you need to review pressure, injector capacity, etc. What's your setup?

Edited by griggsy2 on Wednesday 26th July 14:34

DCL

1,215 posts

178 months

Wednesday 26th July 2017
quotequote all
fergus said:
That's a neat trick to increase injector time as a function of drop in fuel pressure. Which ECU handles this? I'm running a K6 Emerald, and get close to maxing out the duty cycle on my injectors (assuming a fixed 3.5 bar fuel pressure) so could benefit from something similar.
Maybe I didn't write that in the best way. What I meant to say was the mapping session would look at the mixture. So if the pressure is a little lower in parts of the map, then more inject time would be allocated to those sites to achieve the correct mixture. Not the ideal situation, but it is what happens in practice.


fergus

6,430 posts

274 months

Thursday 27th July 2017
quotequote all
DCL said:
Maybe I didn't write that in the best way. What I meant to say was the mapping session would look at the mixture. So if the pressure is a little lower in parts of the map, then more inject time would be allocated to those sites to achieve the correct mixture. Not the ideal situation, but it is what happens in practice.
Agreed. A la any mapping session done with a wideband lamdba sensor!

fergus

6,430 posts

274 months

Thursday 27th July 2017
quotequote all
griggsy2 said:
Pretty sure DCL is not implying this is an 'automated' ECU option that adjusts the timings in real-time with fuel pressure. Rather saying the maps account for differing fuel pressure (and hence injector timings) at varying rev / loads when they are defined on the RR.

Also, if you are maxing your duty cycle then you need to review pressure, injector capacity, etc. What's your setup?

Edited by griggsy2 on Wednesday 26th July 14:34
I'm using the "beige" injectors (can't recall the flow rate, but at 8k rpm, they're nearing 100% duty cycle. However, at lower revs, they do offer great atomisation for pin sharp throttle response!

I also have a "Dave Walker modified" fuel pressure regulator (i.e. partially squashed in a bench vice using a socket to increase the regulated pressure to around 3.5 bar.

To be honest though, I drive my car so little now, any more money spent fettling it is not money well spent.

griggsy2

Original Poster:

126 posts

279 months

Thursday 27th July 2017
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Picos? If the beige'y brown then these are the 330cc ones, same as I have. I've just shoved an adjustable FPR in ahead of an RR session with Dave on the 17th and plan to run somewhere between 3-4bar. Will let you know how I go.

fergus

6,430 posts

274 months

Thursday 27th July 2017
quotequote all
griggsy2 said:
Picos? If the beige'y brown then these are the 330cc ones, same as I have. I've just shoved an adjustable FPR in ahead of an RR session with Dave on the 17th and plan to run somewhere between 3-4bar. Will let you know how I go.
330cc rings a bell.

1800 k series, 1227 cams (both inlet & exhaust) on vernier pulleys. A "bit of headwork" from DVA = 222hp and 155 lb ft torque (on Dave W's dyno).

What are you taking up to Dave for mapping?

griggsy2

Original Poster:

126 posts

279 months

Thursday 27th July 2017
quotequote all
Northampton Motorsport Engine
-2019cc over-sized (Duratec)
-88mm Omega forged pistons
-12.6:1 compression ratio
-Saenz HB con rods
-ACL competition bearings all round
-Head gasket 0.6mm cushed
-Neil Roper developments hand ported high-port head
-Piper cams double springs
-Piper cams BP 300 cams
-Cam timing: 102 inlet, 104 exhaust
-Crank, flywheel balanced
-Head skimmed 0.95mm
-Increased inlet valve pockets
-Standard crank keywayed

Was up there last week but it only made 245bhp as opposed to the expected 265bhp, traced to fuel pump dropping off significantly to circa 2 bar. New one in now so hopefully problem solved smile