MFI Pump - Open Heart Surgery

[911st]

Can any one compute what that might be in peak TQ?

Or Hp peak, probably assuming about 80% flow as HP peak is at a lower TQ number or fuel per RPM.

I forget, is 3500rpm at the pump like 7000rpm at the crank?

[911st]

Originally Posted by kenikh

...Jeff Higgins car runs basically perfect AFRs now that he has dialed in the tuning...

I think he has very good AFR's from about 4300rpm on under WOT or at the meat of the power curve.

However, before that and probably under light load it is probably not very good but I am guessing.

[dicklague]

Can you give me more information on the thermostat thumb screw? I think I have seen one before. Do you have a photo? Maybe some specs?

I would love to remove my thermostat. I have a push button primer and live in a fairly warm area.

fill me in. I am intrigued.

[911st]

Sorry, that was 10 years ago.

I just had a plate made to cover the Thermostat's opening. I measured the max length that the Thermostat could extend for reference.

I then taped a hole in its place and cut a SS bolt to the right length so could not extend to far. I am not sure but I think the bolt may not have had threads all the way up but I did put a spring under it thinking it would keep it from turning unintentionally.

At the hardware store I found a knob that fit over the head of the bolt so I could turn it with my fingers.

I then set my bolt to the hot length I believe as a starting point.

Or something like that.

[Flieger]

I think Tony and Marco at TLG Auto may have done mine. Not sure, since many mods and many mechanics have been in my car's history.

TLG Auto Porsche Service in North Hollywood, CA

[haycait911]

here's mine. seems pretty straightforward.

[kenikh]

Originally Posted by 911st

I think he has very good AFR's from about 4300rpm on under WOT or at the meat of the power curve.

However, before that and probably under light load it is probably not very good but I am guessing.

Before, yes...under WOT it blew fuels smog and hunted a bit at light load. His latest tuning session resolved these issues. She's a kitten now...that still throws a fuel cloud occasionally.

[dicklague]

thanks guys. I am going to build one of these covers.

I got to know the thermostat quite well a couple of years ago. I had the pump resealed and Fairchild set everything up to factory settings. The shop did not fully warm it up on final testing. The first long drive I took......wow when heated up fully the it would just not run.

Now that I am suing an AFR gauge and data logging all the time, I at least know what is going on and take advantage of extra tuning.

Just to be clear does the "thermostat screw" adjust mixture over a wide range? Or a specific RPM??

Thanks.

[356RS]

Originally Posted by dicklague

Just to be clear does the "thermostat screw" adjust mixture over a wide range? Or a specific RPM??
Thanks.

Yes it will affect the main rack which is the complete range. The thermostat rod mechanically connects to the balance lever and then to the main lever "posted in photo yesterday" that moves the main rack. Small changes in the thermostat rod will make very large changes in the AFR.

[356RS]

Why just put a bolt in and set it when you can use a lever assembly. With a lever, like in the photo below, you can control the main rack for "cold starts" then adjust till warmed up, or just richen up the AFR when needed by simply moving a knob on the dash.

[911st]

Nice!

[kenikh]

I asked a question long ago - and who knows, the answer may be buried in this very long thread - but just in case...

Mark, it sounds like that in your assessment, there is enough range in the thermostat adjustment and/or barometric adjuster to facilitate a very wide range of enrichment adjustment.

The question: would it be resonable to assume that an ECU w/ wideband O2 could adjust fuel trim using a solenoid on either of these to basically make an MFI system as dynamic to AFR as an EFI system? Thus the computer could control cold start enrichment, load dependent fuelling, etc. EMFI would be very, very trick.

I was going to try this project at one time (and still may), but was never able to get a qualified answer regarding the range of these adjustment mechanisms for this purpose.

Thanks!

[911st]

If I may, a lot of us have wondered about something like this. Probably not a solenoid but a stepper motor with the right controller could work.

If doing that one might just remove the space cam and use the steeper motor to determine the rack's position. Might be easier than trying to reprogram over the programing of the existing space cam.

The new D-WUR that is being used for the 930 turbo's has most of the bassic atribuites including a steeper motor controler than might be adaptable witout to much issue. One could even add 02 correction if so motivated.

[kenikh]

Originally Posted by 911st

If I may, a lot of us have wondered about something like this. Probably not a solenoid but a stepper motor with the right controller could work.

If doing that one might just remove the space cam and use the steeper motor to determine the rack's position. Might be easier than trying to reprogram over the programing of the existing space cam.

The new D-WUR that is being used for the 930 turbo's has most of the bassic atribuites including a steeper motor controler than might be adaptable witout to much issue. One could even add 02 correction if so motivated.

I agree in principle, but it seems it would be much easier to simply actuate the compensation lever like the 935 LDA, since the fabrication required would be near zero. Stolen from another thread:





Redoing the guts of the pump to adjust the rack's position seems as if it would require a lot more work. That said, this would be "doing it right" versus doing it "good enough".

[356RS]

Originally Posted by kenikh

Mark, it sounds like that in your assessment, there is enough range in the thermostat adjustment and/or barometric adjuster to facilitate a very wide range of enrichment adjustment.
The question: would it be resonable to assume that an ECU w/ wideband O2 could adjust fuel trim using a solenoid on either of these to basically make an MFI system as dynamic to AFR as an EFI system? Thus the computer could control cold start enrichment, load dependent fuelling, etc. EMFI would be very, very trick.
Thanks!

Might not be able to control 100% of it, but it could definitely control a major part of fuel trim. The thermostat control side of the balance lever will provide a greater range of fuel control than the Bar cell end.

[Flieger]

Could you put a linear actuator on the front of the pump where that silly rubber cover is all that separates the main rack from the outside?



Then the whole governor end could be eliminated...

[jeffc280sl]

Mark,

Actually, the solenoid ends up lifting the stylus off the space cam and shuts the fuel off.
As your RPM drops towards idle, the solenoid is then deactivated and fuel flows again.


Can you clarify a point for me. The depth of the solenoid pin is adjustable and i agree it does lift the stylus off the space cam. Have you tested the pump with the solenoid energized to confirm fuel is 100% shut off? It seems more appropriate to have a minimal (idle level) amount of fuel present during this condition. An extreme case would be coasting down a long rocky mountain road. The ignition system is still firing but there is zero fuel in your senario. Just doesn't sound right to me.

[Flieger]

I have done just what you say- coasting down a long mountain road- Kanan road in the Santa Monica Mountains. Before I had the speed switch working, it would pop and backfire. With the speed switch working, it makes no such protests. The engine note is "cleaner" and there is a significant amount more engine braking. If I rest my foot on the throttle pedal just enough to open the microswitch, it will give a little pop and speed up a little as the idle fuel comes in. Towards the bottom of the hill, I can feel the engine "start" again due to the increase in sound.

I am quite confident that it shuts off fuel.

[356RS]

You could, but the main rack movement from idle to WOT is only about 4.75mm to 5.00mm. The ratio between the throttle bodies and rack movement might be a challenge.

[Flieger]

Also, if the fuel still remained at "idle" level, the diagnostic test for the speed switch would not work. Opening the throttle to 2000rpm with one's hand whilst depressing the microswitch will cause the engine to cut out until the revs drop to 1300 and the speed switch turns off the 12V to the solenoid and the revs climb back to 2000rpm.

I have worn throttle bodies and my idle is high since the motor sounds/runs better like that. The idle sometimes creeps up at stop lights on warm days. So, with the throttle on the stop, the revs get to 1500 rpm and then the speed switch cuts fuel and the revs drop until 1300. They then start to creep up again.