fuel pressure - FPR problem maybe??

[leeroy_25]

I had to go and put the car on the dyno again at the weekend as I had changed my coils which had been dodgy for a while. I had fiddled with the FPR to check for a fuel leak but set this back to 40psi static before going. First run the car was way short on fuel mid range onwards with the biggest shortage being somehwere around 4k-6k. I watched the gauge on the FPR during a run and it starts at around 20psi on low rpm then builds to just over 60psi with throttle open then as the revs build the guage starts to drop again back to around 40psi where it holds and if anything just before you lift at full chat it will start to rise a touch over 40psi. I am wondering if my misfire I thought was coils may partly have been fuel although the plugs were plenty dark when I swapped them out and I know for a fact the coils were dicky as it was eating plugs!
Car is running 850s all round, FSE FPR, a bosch style pump, and 15psi boost. I remember that the fuel pressure tended to drop off full chat when it was first tuned a while ago but not so much as this. In the end we set the base pressure to 47psi to compensate and now it fuels fine if not a touch rich for safety. (still behaves the same pressure wise)
Any thoughts would be grat.

Thank you
Lee

[leon]

Are you saying your fuel pressure drops to 20psi when your at low RPM? It should be static at 40psi when out of boost if this is what you set it to.

[leeroy_25]

See that\'s what I thought although I have never been too sure how the work. I assumed maybe the vacuum on the inlet at low rpm was drawing the regulator pressure down hence the initial drop as I guess they use boost pressure to work? but yes it drops to 20psi on light throttle. It does not seem to cause a problem to it there. (that said my knock warning flashes a lot at low rpm 2000-300rpm. Having tried a couple of sensors and other things it has been put down to noise/interference from something. Funnily enough when I changed the coils and had fiddled with the FPR there was no flashing knock light. but now the pressure has been turned up the knock light flashes again in the 2000-3000rpm band. No flashes at high rpm high load though.:Thumbs-up
I would like to try and get to the bottom of this though..

Cheers
Lee

[leeroy_25]

Okay I have thought about this some more. Hoping someone will reply..

When you set the static pressure you are supposed do it with the engine off right? And then ground the Fuel Pump so it keeps the pressure in the system and adjust to 40psi or chosen base pressure.
Hopefully I have got that bit correct to start with.?!

Now the vac/pressure line connected to the FPR connects after the throttle so at idle this is seeing vacuum which in turn would make the fuel pressure at idle lower. Your static pressure would then not be reached until throttle is open and boost gauge reading 0. then after that as the boost rises so does the fuel pressure. Why mine drops again and then appears to go back up a bit that\'s another story? Tried a couple of pumps that should flow the juice all the same.

Cheers
Lee

[SiH]

Bosch \'style\' pump? That woudl be my first thing to look at - what is it?

What you say is correct - base fuel pressure is set without the vacuum feed, or with the engine off.
Vacuum in the inlet drops this pressure and takes the pressure down, however 20PSI seems a little low - I\'m sure mine\'s closer to 30.
The fact it\'s dropping off on boost is very worrying tbh - I wouldn\'t be boosting until you address that issue!
What FPR is it?

[leeroy_25]

Okay.. First off new information I just recieved. My FPR is an FSE one. (some people say they are great others sh!te!?) I gather this is rising rate. I think 1:2 but need to check. Have just been told I should really be using 1:1? Is this true? That would explain the increased drop in fuel pressure as I guess the ratio works on vac as well as pressure?

Are SARD ones any good? I found one for a good price. Will check if its 1:1 if that is the case.

The pump is a DA-27 270lph from http://www.driven2automotive.com/. rated better than the walbro and bosch. We tried a genuine bosch and walbro when I had fueling problems before and they were no better at all.

AFR wise I am running safe even with the pressure dropping off to 40psi on boost. If anything at pressent it is a touch rich to be sure. Nevertheless I would like to try and sort it properly.

[leon]

The pumps are fine from Driven2Automotive, I drove to germany and back on two of them! Ill report back in a year or two on the reliability x3

Your pressure should not be dropping that much when off boost! Mine used to drop only to about 30-35psi from memory when I reved the engine while static.

From memory the rising rate fuel pump ratio works as follows for every psi of bost you gain it will increase the psi of the fuel pressure in acordance so 1:1 = every 1 psi you go in boost the pressure goes up 1 psi.

1:2 should be fine but you will get a high fuel pressure very quickly if your running big boost. 10psi would = 20 psi of extra fuel pressure using the above..

if im wrong with this stament please sombody correct me

[leeroy_25]

Thanks for the reply.. Good to hear someone else on the same pump system! Are you saying you have 3 pumps on one motor? What on earth are you running?!
Or do you mean you have buggered 2 and are onto your third. I was assuming the comment about driving to Germany on two just meant you had two on the car at the time and not you broke one halfway there?!

From what my tuner says and a few things I have read it is most likely the FPR that is Sh!te? I read an old post on a supra forum with almost exact same symptons and pressure changes.. Same FPR!! Never said whether they cured it with a new FPR but I am going to get a SARD one I think and try that.

Cheers for info.
Lee

[BlitzBoy]

FSE FPR = S H I T E for rotary turbo setup IMO

I have seen one making honking noises on boost LOL

Go for a 1:1 FPR a lot easier to tune for as well, Aeromotive or SARD

[hairyhoover]

Ive got a sard fpr knocking around.
 
Let me know if your interested
 
cheers

[leeroy_25]

Hi There mate.. Defo interested. Just looking at a new one now.. Can get them pretty cheap so let me know which one, how old and how much.. Can send pics/details to Leeroy_25@hotmail.com if you like.

Cheers for the advise chaps! If only I new this before trying now two FSE FPR\'s!! Shortly I will have a couple of spares if anyone wants a paper weight!!

Lee

[leeroy_25]

Any thoughts/opinions on a Tomei FPR. Looks identical to the SARD one to me??!

Cheers
Lee

[Furb]

1:1 FPr is the way to go, i had the SARD, but i replaced it by a aeromotive.
they are better IMO, as the Sard also tends to make a lot of noise.
 
what also might help, is rewiring the fuelpump to make sure you get decent voltage.
i got mine connected straight to the batt switched through a relais, fuelpump now gets 13V instead of 11.5 going through the stock wiring

[leeroy_25]

thanks for the info. Fuel pump re-wire was doe the first time it got mapped!! Was hoping hairyhoover would come back to me about his FPR.

Regards
Lee

[leon]

sorry x3 was a smile face. I am running 2 pumps on the car at the moment they have not missed a beat yet.