mfi idle on max, still lean on idle?

[svandamme]

my idle adjust is at full max
first i thought it was the little screw thingy that didn't connect on the inside, but i opened the pump , and the hex nut just won't go any further in the clock wise direction, i can turn anti clock wise, but that's leaning out


lm1 says it's lean on idle
and rich on load

however, if i lean out the main enrichement , the car stops idling


is this dyi fixable? anyone seen this before?
or am i screwed and is my pump overdue for a rebuild?

[jluetjen]

Thinking laterally for a moment, if your idle is too lean, might you be getting too much air (rather then not enough fuel)? To put it differently, what's the idle speed your at, and have you ensured that the butterflies are fully closed?

Are the butterflies too worn?

What's the clearance between the butterflies and the throttlebodies when the throttles are closed?

[svandamme]

my idle speed is a nice 1000 rpm
and the idle is to lean to adjust with the butterflies, if i squeeze it anymore, it runs out of air to idle

i disassembled the TB's, cleaned all the bores, and then benchflowed them with a unisyn and a vacuum cleaner to get proper correlation
there is no play on the butterfly shafts

so i used the cma suggestion , of setting the throttle stops so the butterflies stick, and then turn back a little till they no longer stick


when i installed it in the egine , it wouldn't idle properly
turns out it was not getting enough air ( disconnect fuel pump, open throttle engine idles )

but this was with a main set to very , very rich
as i leaned out the main , the idle went leaner as well
couldn't lean out more or the idle went away

i kept leaning out till my main afr improved
but it's still rich now ,and now my idle is lean


that made me look at the idle enrichement
which seemed stuck, turns out , it's not stuck, it's just at max inside the pump.


i'll run some more tests, but i think i'll have to admit defeat and get the pump overhauled

[Grady Clay]

Page 24 of CMA states:

“Always observe the following sequence:
First part load
then idle speed
Reversing the sequence results in incorrect values.”

Page 32 of CMA states:

“Reason: An incorrect part load CO value
influences the exhaust-gas composition so strongly that it
can be no longer corrected with the idle-speed adjusting screw.”

I would guess the main mixture screw has 5-10 times the
“…so strongly…” effect as the idle mixture screw.


On the diagram below, the main mixture adjustment (Part Load)
#2 is on the end of the rack and is the basic mixture setting.
The idle mixture adjusting screw #15 is in the centrifugal
governor and affects only the idle end of the operational range.
IMAGE: MFIpumpDiagram01.jpg "
"
(C) Dr. Ing. h.c. F. Porsche A.G.


Try setting the idle screw lean (CCW) two turns (12 clicks) and
then get it to idle using the main mixture adjustment. Once you
have it where it will idle, change the idle mixture screw and
confirm it has the expected result. This will tell you if this part
of the pump is working.

Be sure to keep track of your adjustment changes so you can
back-track if necessary.

Best,
Grady

[svandamme]

wildo! thx Grady

[Tyson Schmidt]

Stijn, Grady is right on.

I think what you might be experiencing is the fact that you have to set the part load mixture pretty rich for it to run right. If you set it to factory specs, it'll have poor driveability and a flat spot around 3000rpm at part throttle/part load.

When I use the 4-gas analyzer, I set them at 8% CO at 2500-3000 rpm free rev. That usually gets it right. MFI gets leaner under load, so you have to compensate.

[cmcfaul]

check the linkage. Make sure the linkage to the MFI pump is not too long and thus fooling the pump into thinking someone is pressing on the gas.

Chris

73 911 E

[svandamme]

i did the 114 mm from the manual, made sure of that one
and also checked that the pump is on full stop when the loudpedal is out

i'll run some more tests , hopefully this weekend, if my oil tank is welded up again ( the mounting bolt in the top left corner broke off )

i'll keep y'all update when i get some more data

thanks for the suggestions

[svandamme]

little update, finally got my stuff , and did some more testing


Peterfrans came over, and helped out , the ignition timing is now spot on , so is dwell (whiteout on the timing mark... should ave done this long time ago , at least now i can see the mark with the light)

but it still looks like the pump does not put out enough on idle , it's way lean , and i can't lean out the main adjust , or i have no idle left....

so probably , i'll need a pump rebuild this winter

did have a little scary moment , while on a test run
there's a short righthander half a mile before the garage
60 is fast in that turn , and i'm closing in to the corner at 90+ something

when suddenly my throttle sticks at full open in 4th gear
i noticed it when i clutched in... revs went up , but i caught it in time
i reach for my pedal, hoping to pull it back
but it doesn't work , it's stuck

want to turn of the ignition .... right hand side ... duh , i'm not in my 924
meanwhile the corner is getting closer

left hand, ignition off, brakes, and crisis avoided


the draining tube from the air filter housing , had gotten inbetween the throttle linkage of the #4#5#6 throttle body...

well scary stuff


anyway , didn't have to much time today , since i spent some time putting back my fixed oil tank, but i'll give it some more tries tomorrow , and check how far i can close the throttlebodies before it stops idling ,i'm not convinced i'll be able to richen up the idle enough that way , but it's worth a try

[Peterfrans]

I was in the car at that time the throttle got stuck, my hart rate still needs to come down and I needed a clean set of underware I already thought Stijn was approaching that bend rather enthousiastically before the throttle got stuck, but in stead of braking we were getting faster.

I was looking at the LM-1 before it happened. It is obvious that something is wrong with the pump. We were getting an AFR of 12.6 cruising along at 3500 rpm. On acceleration the AFR went down to 10. At idle it was around 14. The car backfires through the exhaust on lifting the gas pedal.
One thing needs to be said. Stijn removed the cold start enrichment from the pump, this might contribute to this situation. Also the fuel cut off solenoid and associated micro switches have been removed.

But to follow CMA:

1. Air Cleaner Cartridge: ok
2. Compression Loss: engine has been recently rebuilt with new P/C's
3. Spark Plugs: ok
(Spark Plug Connectors)
4. Dwell Angle: ok
5. Ignition Timing: was wrong, now ok, we had an AFR of 20 before, it went to 14 at idle after setting the timing
6. Fuel Pressure and Flow: not checked
7. Injection Nozzles: not checked
8. Injection Timing: ok
9. Correlation: ok
10. Exhaust Emission Test
a. at part-load: ok
b. at idling speed: way to lean

[Grady Clay]

Stijn Vandamme
testing his MFI
with stuck throttle Hehehe




Best,
Grady

[Grady Clay]

Peter,

I'll have to edit the image.

Brst,
Grady

[svandamme]

LOL

it needed a small correction :

[Peterfrans]

Grady,

LOL

The wide open eyes should be on the passengers side, the moment it happened the driver dove under the dash to do something to his pedal cluster

[svandamme]

Originally posted by Peterfrans
Grady,

LOL

The wide open eyes should be on the passengers side, the moment it happened the driver dove under the dash to do something to his pedal cluster

like this ?



at least i took care of business

probably wasn't too elegant though

[Peterfrans]

how would a 2,2S pump work on a 2,4S engine?

[Grady Clay]

Stijn,

The backfire when you lift is because you don’t have the over-run
solenoid working. I encourage you to reinstall that. It is a very
simple system with microswitch, RPM transducer, relay and
solenoid. Not only does the MFI run better but you get better
fuel economy and less dilution of the oil with gasoline.

I agree with removing the cold start spray/dribble fire inducing
system so long as it still starts easily cold. Don’t get tempted to
use the cold running thermostat to get it started. All that will do
is dump a LOT of gas in the oil and damage your new cylinders.

One of the best features of the ’69-’71 MFI is the cold start
solenoid on the pump. It forces the main rack full rich. You
can wire a momentary switch to control it if needed. This way
you can set the cold running thermostat to very lean, just
enough to have the engine run. The ’69-’71 MFI pump front
governor cover with two solenoids will fit the ’72-> MFI pump
or you can mod the later cover.

Peter, e-mail me about your 2.2 pump question – gradyclay@hotmail.com.

“I was in the car at that time the throttle got stuck, my hart
rate still needs to come down and I needed a clean set of
underwear. I already thought Stijn was approaching that bend
rather enthusiastically before the throttle got stuck, but in stead
of braking we were getting faster.”

Come on guys - - - I want you to solve MFI issues, not become
victims of a traffic “incident.” PLEASE be careful.

I don’t see anything that changes my mind about my above post.
Don’t assume anything on CMA. Some movie had the
line “Assumptions are the mother of all f***-ups.” This is very
true of CMA. When chasing an elusive problem, I can’t tell you
how many times I have repeated the same tests – all with the
same results. Too often something can change while you are
testing.

Do a search on my extension to CMA. It has several things
in it that weren’t obvious to Porsche when CMA was written
in ’67-’68. I like to call this “geriatric mechanics.”

Please post your LM-1 data and the conditions. That will help.
Are there some known good parts that can be swapped onto
the engine?

To be fair to the artist, here is the original:

(C) 1974 Bob McDonald "McGee"

Best,
Grady

[svandamme]

Originally posted by Grady Clay

Come on guys - - - I want you to solve MFI issues, not become
victims of a traffic “incident.” PLEASE be careful.

Grady , trust me when i say , i wasn't pushing the enveloppe

i just did acceleration runs on open straights, and with close to zero traffic around, my brakes have been thouroughly tested on previous days, and prior to this incident, i slowed down well before the turns

that throttle got stuck well before this particular turn, which meant i had time to overcome my surprise, and deal with it, just didn't have time to coherantly explain it to Peter.

[Peterfrans]

Stijn,

I had some conversations with Grady about this situation. We should probably fix the missing cold start thermostat first.

Grady suggested to do as follows: make a little adjustment plate that replaces the thermostat. You cannot run with no thermostat in place. The critical issue is the screw must turn off the cold running thermostat while not damaging the pump internals. Screw the adjusting screw in by finger until it stops. Back out the screw 1/8 turn. Tighten the locknut. You can check for the thermostat being fully off by removing the little 2-screw triangular plate on top of the pump above the thermostat. With a jeweler's screwdriver push down on the mechanism below the pivot. The mixture should not change (push = lean). It is desirable to have some slight movement when you push.

OK, now the cold running thermostat can be left in the "off" position (except for cold starting).

[svandamme]

i actually had such a replacement thingie when a started off
but with me beeing not so handy with welding and so on , i simply JBwelded an M5 nut to the plate
and then ran a screw in there

obviously ... it fell off not so long ago
i didn't get the idea that while it was on there, it was working
i think the pivot might be "off" because yesterday , lm1 hooked up , engine idling , pushed in where the thermostat should be , but no change whatsoever....

didn't have more time , but was planning the triangular thingie for my next weekend...

for the record, i still haven't figured out what the thermostat does

is it pushing in the pump when hot, or does it push the pivot when cold??
bit confusing with the spring and all, i'm looking at the thermostat now, even tried heating it , but i'm not seeing much movement either way