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Megane RS250 engine into R26 - using mk3 fuel pump

Ewan

Active Member
I am swapping the engine in my R26 with a RS250 unit retaining the R26 ECU and loom. Should clarify at this point that 'I' means 'I am paying Rentec in Edinburgh' ;)

Ok, so we are keeping the R26 ECU and loom and swapping in the RS250 engine with turbo and the mk3 inlet manifold, fuel rail and injectors.

I know that we should be able to run the RS250 engine with the existing mk2 fuel pump, although it won't offer the rising rate fuel pressure. The question is can we fit the mk3 fuel pump to my car and take advantage of the rising rate rail with the mk2 ECU and loom without a massive headache?
 
In regards to Marts post, the ecu will compensate for the pressure difference so fuelling will remain same as standard

There's no fuel pressure sensor fitted to the 225, no pwm feedback control of the pump, and with the lack of wideband lambda sensor fitted, there's no 'fuel to target afr' feature of the Sagem either, so how does the ecu auto-compensate (alter) the fuelling map when a raised rail pressure is applied?

Virtually every mainstream engine I can think of requires the fuelling map/injector dc value to be adjusted afterwards, as it'll otherwise simply run rich(er), or completely 'flood', the more the base rail pressure is increased.
 
The posts asking clarification are fine, we're here to learn!

It's just that i got a PM of 'someone' on here asking for stuff i wouldn't share, now he's on about the 'spirit of the club' blablabla. So you'd understand when that person 'takes my free, club spirit advice' in doubt you can expect a reply like that.....

Basically i've figured everything out and know what i'm talking about, then when people start doubting the advice it's when you get to a point thinking, why am i even sharing this?
 
Apparently people don't take my word for granted, fine, figure it out yourself then

Dont be like that dude. People might have other experience ( I have for instance on the duty cycle ) to challenge maybe what you have found. Its not the case of having a go , or asking you not to share but personal experience.
 
Basically i've figured everything out and know what i'm talking about, then when people start doubting the advice it's when you get to a point thinking, why am i even sharing this?

No-one's doubting your advice. My question at the top of this page is exactly that - A question, asking how (on what type of feedback) does the ecu auto-compensate the fuel maps for an increased rail pressure.

I'm an Engineer, so I like to know how something works inside-out, rather than 'it just works'.
 
Pretty big difference between personal experience and hearsay tbh. I remap these ecu's, made tons of datalogs etc. So i know what i'm on about.

Could be the one you've had/read about was a very weak example but fact is they run pig rich when standard. My stage 2 has less duty cycle then a standard one
 
No-one's doubting your advice. My question at the top of this page is exactly that - A question, asking how (on what type of feedback) does the ecu auto-compensate the fuel maps for an increased rail pressure.

I'm an Engineer, so I like to know how something works inside-out, rather than 'it just works'.

Apoligies for rumbling up the thread, got a bit aggitated by the combo but have solved it with the person in question.

Regarding the fuelling adaptation, it does have a narrowband sensor and it simply expects the fuelling to be 14,7:1 below 4000rpm and 1100mbar iirc. If it's out it will start to compensate so it get's back to 14,7. Which will mean it turns back PWM to the injectors.
 
No rumbling. All is good (y)

Ahh, I think there's been crossed wires (sorry!), as I was referring to @ full boost/wot conditions, with the increased rail pressure, rather than idle/closed loop. That's what I meant by having to wind back the dc (in the 'on boost' part of the map) otherwise it'll just run (much) richer? I assumed that's what we were discussing, as after all, upping the rail pressure is usually just to create an 'extended' working headroom for the oem injectors @ wot/when cranking up the boost.
 
It'll change the long term fuel trim based on the part where it does closed loop, so if by then you go into full boost (open loop) it still extracts by the same margin as it had to do in the closed loop part, to make things a bit more confusing, it also has a short term fuel trim to compensate for transient operations
 
Finally got a chance to lay all 3 side by side, from left to right, 197, 250 ,225:
i1230.photobucket.com_albums_ee490_tutuur_96264B92_0EF4_43E0_A2FF_4762800383DC_zpsyu0taw5f.webp

It appears the tip is thinner but that's about it, i had a look at the pump body but not much meat left there.

The solution would be to machine the fpr down in a lathe and fit the 225 seal ring. Job jobbed!
 
Or, if we can find an alternative fpr that is the same size as 225 but with increased pressure! [emoji23] might be easier said than done though..

Has there been any progress with the Lexus fpr?
 
I don't think anything needs machining - the bore where the tip O-ring sits is the same diameter in the 225 sender housing, a VW fuel rail I tried and an aftermarket (one of these) bosch-type FPR housing - 7.4mm.

I'm pretty sure they're just straight up interchangeable.
 
It does look like it yeah. I suppose it's possible that the 225 reg is a 'looser' fit in the 7.4mm bore but it matters not. As long as it touches all the way round, the O ring will seal. I've just measured my 225 reg and (as best you can measure something made of rubber with a vernier) it's 7.8mm OD. Same for the one out of the Specialist Components reg.
 
I will try and get some before I head back over to yours on Tuesday. They are surplus to requirement now so will be going up for sale along with the meg 250 pistons. I sold the R26 on Thursday. I had my sensible head on for 24hrs and realised 4 cars and two motorbikes between me and the wife was excessive. Especially when I'm out of the country for six months of the year. Besides I was on the verge of building something similar to the clio. Think I'll get something special early next year currently floating around mk2 escort RS, lotus elise or a kit car. But baby is due in Jan so that could change =D
 
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