would a blocked fuel return cause higher emissions?

21st February 2011, 15:26

ive got my mot coming up soon and atm ive got a blocked fuel return on my 16v engine so basically could this cause me to fail emissions?

cheers
sam

21st February 2011, 15:35

It'd cause your fuelling to be all funny and I suspect beyond compensation of the trim levels in the ECU - so yeah your emissions would be out.

Why's it blocked?

21st February 2011, 15:40

i haven't fitted a fuel return from when i did my 16v conversion, i did buy 4m of fuel line to do it but never got round to do it i might buy the parts from pug/cit to make life easier if im gonna do it

21st February 2011, 15:42

ah. i see... I'm surprised you haven't had any issues with how much fuel the car goes through or anything?

21st February 2011, 15:46

lol ive only just fitted a lambda sensor for the up coming mot been running without one for nearly a year, it does love to drink the fuel

21st February 2011, 15:51

Bet you been getting mad bore wash, which could be killing your bottom end.

21st February 2011, 16:39

the injectors will only send through as much as theyre told to by the ecu.

i had no problems with no return hose on my vts conversion

21st February 2011, 16:42

Quote:

Originally Posted by pjm300

the injectors will only send through as much as theyre told to by the ecu.

i had no problems with no return hose on my vts conversion

That's the problem... the ecu couldn't tell how much was going through dude.

21st February 2011, 16:44

Yer I know that but he said he been using alot of fuel, which if so then will be getting bore wash.

21st February 2011, 16:53

is bore wash when fuel goes past the rings? Well i say it uses alot of fuel but i was used to a vtr enigne before hand, out of £20 id get 80 miles round town and 120 on motorway, the majority of my driving is round town so that's gonna make my mpg crap anyway, if i had bore wash would the fuel come out when doing an oil change as ive just done a service

21st February 2011, 16:53

Quote:

Originally Posted by adsayer

That's the problem... the ecu couldn't tell how much was going through dude.

it doesnt need to... it adjusts it to preset parameters in the ecu... thats the whole point of the ecu...

its just done on revs, throttle position and adjusted slightly on engine temp..

there arent any sensors in the fuel return...

the only problem reason for the high fuel usage would be the lack of lambda.... no?

21st February 2011, 16:57

as paul says, the injectors only flow what they are told to, which is a function of pulse width from the ecu and fuel pressure. The fuel pressure regulator should be controling the pressure in the fuel rail, even with a blocked return the pressure in the rail shouldnt change.

21st February 2011, 16:58

Well, I was just going on what you said about using alot of fuel, if it did then yes would could get bore wash.

And only on way to find out go and get tested, did you inform the dvla of the engine change or is it still down as a vtr?

21st February 2011, 17:06

still down as a vtr as it hardly gets used, i wanted to get it running 100% before i registered it

21st February 2011, 17:12

Quote:

Originally Posted by yr51ocw

as paul says, the injectors only flow what they are told to, which is a function of pulse width from the ecu and fuel pressure. The fuel pressure regulator should be controling the pressure in the fuel rail, even with a blocked return the pressure in the rail shouldnt change.

is this marc?

21st February 2011, 19:32

Quote:

Originally Posted by pjm300

it doesnt need to... it adjusts it to preset parameters in the ecu... thats the whole point of the ecu...

its just done on revs, throttle position and adjusted slightly on engine temp..

there arent any sensors in the fuel return...

the only problem reason for the high fuel usage would be the lack of lambda.... no?

Quote:

Originally Posted by yr51ocw

as paul says, the injectors only flow what they are told to, which is a function of pulse width from the ecu and fuel pressure. The fuel pressure regulator should be controling the pressure in the fuel rail, even with a blocked return the pressure in the rail shouldnt change.

Hence the problem gang. The ecu has no idea how much fuel is being injected on the closed loop (or for the open loop for that matter), the lambda has gone and the fuel pressure is not being regulated. Without a return the pressure is going to be higher than anything the ecu could anticipates surely?

Just for clarification (because I'm not basing this directly on a saxo system), how can the fuel pressure be regulated if the excess pressure (i.e. fuel) cannot be vented (i.e. returned via the fuel return)?

Sure the fuel pump may have a pressure cut off but that pressure is going to higher than normal, the fuel injected is going to be more than normal. Lack of lambda means the ecu has no knowledge of how much it's chucking in, even with all the other parameters reading properly.

21st February 2011, 19:43

well if jeffs car was original a single plug silvertop motor of some sort the fpr and fuel return bollocks is under the rear bench those cars ran a single line inlet on fuel system with the fpr and rturn as said under bench

21st February 2011, 22:23

but pressure regulators dont always have to vent "excess" off to a buffer. For example a rear brake bias valve on a vehicle, they are a simple restriction which reduces pressure after it. I have not taken a FPR apart yet, but I would imagine the return is there so that the fuel doesnt heat up as much.

However, all this said. If there is meant to be a reasonable return on the system, and it is not there now it is sensible to correct it as part of the fault finding process.

paul - jup its me.

22nd February 2011, 12:50

as marc said, the fpr on the vtr is on the tank, so it will be sending it at a constant pressure after that regulator

i presume the vts as a return rail so that it could always pump a shed load round so if you hoon i there wont be any excess running via the return as it will all be going down the injectors.

however even with 708's i didnt find there was any problem with lack of juice getting down the throats.

the OP asked whether the lack of fuel return would cause high emissions - ie overfuelling.

the answer is no - but the lack of lambda would

22nd February 2011, 13:40

ah... this is my error then. Assumed jeff had no return or regulation (based on the VTS setup), I wasn't aware of underbench return setup on the vtr

Marc, the regulator (on the VTS) is downstream of the injector rail, so I would assume it would be a venting type regulator as opposed to an upstream one which would be a restriction type.

Quote:

Originally Posted by pjm300

i presume the vts as a return rail so that it could always pump a shed load round so if you hoon i there wont be any excess running via the return as it will all be going down the injectors.

And for low load conditions...?

22nd February 2011, 15:40

had the return pipe unplugged on the vts, and when on idle the fuel p***es out of it,
and when you rev it it lessens and at full throttle barely any fuel comin out., this says to me its its a restriction type????

22nd February 2011, 15:46

Quote:

Originally Posted by adzvtr

had the return pipe unplugged on the vts, and when on idle the fuel p***es out of it,
and when you rev it it lessens and at full throttle barely any fuel comin out., this says to me its its a restriction type????

says to me it's a venting type lol

22nd February 2011, 16:31

Quote:

Originally Posted by adsayer

And for low load conditions...?

in low load conditions it goes back to the tank

22nd February 2011, 16:33

Quote:

Originally Posted by pjm300

in low load conditions it goes back to the tank

I read you post wrong

21st December 2012, 13:05

Huge bump I know! (But at least I searched!) - Mine has just failed the MOT on emissions, I have also got a blocked off return and the reading was miles out, high 5's, it's a 16v conversion in a silvertop VTR, with no return or anything. Is this likely to be my cause? Or should I be checking lambdas?

21st December 2012, 13:12

Quote:

Originally Posted by jeffchiz

still down as a vtr as it hardly gets used, i wanted to get it running 100% before i registered it

Quote:

Originally Posted by jeffchiz

lol ive only just fitted a lambda sensor for the up coming mot been running without one for nearly a year, it does love to drink the fuel

Wait, wut?!

21st December 2012, 17:01

Quote:

Originally Posted by mlawlan69

Wait, wut?!

the car didnt get used much but it still got used for a year... bloody hell this thread is almost 2 years old lol