rayqblue94

Hoping somebody might be able to help with supercharger problems. I have a 94 gts auto, fitted with a Murf 2 (Vortech) supercharger, SFMU and 30 lb injectors.
The problems are:-
1. When the Idle Fuel pressure is set to recommended 30 psi the fuel consumption(normal driving) increases by about 30%.
2. When the engine is turned off, the fuel pressure reduces to zero almost immediately.
3. When idle fuel pressure is set to 22 psi (to get normal fuel consumption), on a hot day (30+ deg C) I think fuel is vaporising as a restart causes difficulty in driving off for a short time - then everything is normal.
4. (At idle FP 22psi) the Air Fuel Ratio is about 12.5 at cruise and less than 10 at WOT/boost.
I have access to a sharktuner, and it has been recommended that I replace the SFMU with stock regulator, increase injector size to 42lb and sharktune.
I wonder if the SFMU is faulty, but would like to simplify the system where possible so I'm happy to ditch it if I have a good alternative.
99.9 % of my driving is sedate within speed limits, 75% highway cruising and 25% suburban/city.
TIA
Ray

Shane

Ray,

Go with the 42's and sharktune, ditching the SFMU. Mine is running the 42's with the MAF restrictor, has a cruse A/F of 14.7 and a WOT of 12.5's, and I still get 19mpg.

Tim Murphy

Hi Ray,

Does your car have an o2 sensor, from the factory? If it does, I don't think it is working properly. If your car does not have an o2 sensor from the factory, then there are some other adjustments that you can make to help you out. The chips I have for the Stage3 were initialized by tuning without the o2 sensor closing the loop but were tuned with a Wide Band o2 and targeting 14.7:1 under cruise and idle.

The (original) Stage2 that you have will run rich until the car warms up and then should go into closed loop via o2 sensor feedback with idle and cruise at 14.7:1 AFR.

The SFMU is not a great piece of engineering, to put it politely. I think the Vortech unit is the best on the market but that still does not make it anything more than typical automotive aftermarket quality. Make sense? (Wonder what that makes my sc kit? )

If you want to upgrade to what I now call Stage3, I can help you with that. It will require chips (or files from me if you have a ST), 42 lb injectors, putting the stock fuel regulator back in, and a custom MAF restrictor. Depending on how much boost you are making now, you might even turn that up a bit.

Kevin Michael

Replace your checkvalve on the fuel pump, I feel this is your problem based on OP. I hear conflicting opinion on idle fuel pressure. Mine is 57psi on the rail at idle and my fmu is not adjustable. Can someone clarify please.

rayqblue94

Thanks Guys,
I replaced the O2 sensor with an new OEM sensor, shortly after installing the kit, also a new fuel pump check vale -which I tested and is ok.
Kevin, I believe the stock regulator idle fuel pressure is 55 psi.

Hi Tim, My engine (by the LED AFR gauge) idles (after warm up) just in Stoich range, otherwise just a bit rich at cruise or over idle(12.5 on dyno cruise) To be honest, I'm quite happy with the amount of power the SC generates - still learning how to get my lips back over my teeth after a boost. I see a pattern of thought here with the larger injectors a stock regulator and ST. thanks for the advice and I will keep my options open on stage 3.
Shane, the figures you quote are exactly where I am trying to go but what is a MAF restrictor and where do I get it ?

Thanks Guys
Ray

hacker-pschorr

It's part of the stage 3 kit.

rayqblue94

Thanks for the detail on MAF restrictor, sounds like I have a plan,
Murf 2 + MAF restrictor +42lb Injectors -SFMU +stock regulator + Sharktune
Thanks for your advice Guys, also happy to hear if I've got the formula wrong1
Cheers
Ray