Way Toooo Rich, And No Idea Why...!!!!

Bernard Fife · Post by **Bernard Fife** » Thu May 18, 2006 4:04 pm

bluetrepidation,

Chances are that the fuel pressure was controlled by PWM on the fuel pump. Since the ECU knows the intake pressure, it can set the PWM to compensate without additional sensors or pressure regulators (presumably from a look-up table, but possibly from a fuel pressure sensor).

Some cars have a 'semi-returnless' system in which the fuel presuure regulator is located near the fuel tank, these typically have a long vacuum line to the intake manfold.

Apparently the main reasons for goigng to returnless sytems was to avoid returning heated fuel (from passing near the engine) to the fuel tank, which causes evaporative emissions concerns. It also has fewer components, so it may be slightly cheaper.

Lance.

ptegler · Post by **ptegler** » Thu May 18, 2006 11:29 pm

odds are...you're ECU is controlling the speed of the fuel pump. This is one of the newer 'tricks' used these days.
No return is used on the '96 (and post '96?) Jeep Grand Cherokees. The 'deadhead' mode eliminated returning heated fuel fro mthe rail back to the tank, thus reducing emissions.
Â
Paul Tegler
ptegler@cablespeed.com (ptegler@cablespeed.com)
www.teglerizer.com

----- Original Message -----
From: bluetrepidation (bluetrepidation@sbcglobal.net)
To: megasquirt-tuning@msefi.com (megasquirt-tuning@msefi.com)
Sent: Thursday, May 18, 2006 7:33 PM
Subject: Way Toooo Rich, And No Idea Why...!!!!

This makes me wonder. My Saturn has a newer fuel injection system. There is no return hose from the fuel rail. Instead the fuel pressure regulator is located in the fuel filter which is just forward of the fuel tank. So really there is no vacuum feedback for the regulator. So how does this work really? I guess it could sense the fuel pressure on the injectors very quickly but that doesn't seem to accurate to me. Anyhow the stock ECU ran off it so I guess it shouldn't be a problem. Just a thought.

A.J.

1999 Saturn SC2 1.9L DOHC 4 cyl 5 speed
EBC Green Stuff Pads and EBC Dimpled and Slotted Rotors
17" Enkei RS5 Silver Wrapped with Kumho Ecsta 711 Tires

This post is at: http://www.msefi.com/viewtopic.php?p=120821#120821

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quattrodave · Post by **quattrodave** » Fri May 19, 2006 11:33 am

Lance,

Just added the vacume line and its made a vast improvement...!!!!
It swings a little rich and then a little lean but far better than it was...

One slight problem still sounds lumpy and when i dab the throttle it wants to die then suddenly revs....

I've been reading about similar engines / cars converted to MS, they all seem to have injectors far smaller than the ones i have (55lb siemens 3102 low imp.). What would happen if i have injectors that are far too big???

Many thanks

Dave