MFI thermostat spacers

[ed martin]

Maybe my explanations are a bit simplistic, but I did have a few years of engineering school. Got through statics and dynamics. One thing I learned there is anytime you have a problem, you need to isolate that problem and break it down into its simplest componant. It helps to write it down on paper and make a diagram. This thing with the thermostat isn't that complicated. Furthermore, even if it's an old car if all the fundamentals are in place there's no reason it shouldn't run good as new. I had this same argument with my mechanic . I would tell him my car had a problem , "Well it's an old car!". Not a satisfactory answer. Thats why I took it increasingly upon myself to understand and work on the car- with much thanks to this Pelican site. If all the elements of the engine are as they should be, as stated in Check, Measure Adjust, starting with the engine compression then there's no reason it shouldn't perform properly.

[Grady Clay]

David,
Yes, for all the reasons you list and some more.

1) Sparkplugs – In order to lessen fouling you tend to run slightly hotter plugs. When you get them hot under full power you are likely to overheat the plugs, damage them, and increase the propensity for detonation.

2) Air filter – Wouldn’t it be nice to NOT have to clean the filter as often?

3) Gas leaking past the rings and into the oil – This is a biggie. The oil lubricates your rings, piston skirts, and cylinder walls. Excess gas washes that oil off and takes it (mostly) out the exhaust. Some also goes past the rings and into the crankcase. The oil on the cylinder also helps seal the rings. Less sealing allows more combustion gasses past the rings; less power and more water and junk in the crankcase.

4) Lousy gas mileage – Not considering the emissions laws, the environmental effects or the reaction of the driver behind you to a stinky Porsche exhaust, there is the economic factor.
If you drive 5000 miles/year and pay 2$/gal getting 10 mi/gal that is $1000. If you get 20 mi/gal that is $500. You can take your significant other out a couple of more times a year with an extra $500.
If you drive 10K miles per year and pay 3$/gal getting 5 mi/gal that is $6000 per year.
You see the point.

5) Gas dilution of the oil – There many very expensive wear parts in a 911 engine. The first that comes to mind is the cams and rockers. Even with the best lubrication these need TLC. Of course there are the rod and main bearings. How much is a set of pistons and cylinders? There are all these “other” parts like chains, sprockets, jackshaft, rocker arm shafts that require proper lubrication. Oh yes, there is this other thing: the MFI pump.

My post above “If left unfixed, the residual gasoline replaces the engine oil. The engine is constantly using the mixture. The mixture gets thinner and thinner and can become almost all gasoline. One stint on the freeway at operating temperature will evaporate all the gasoline, leaving no lubricant for the engine. I have seen too many engines blown up from this situation.”
I should have added that some of those blow-ups had almost nothing salvageable because of the extreme wear from “gasoline lubrication.”

Gasoline diluted oil does not lubricate as well as clean fresh pure oil. When you do an oil change you put in 10 or so quarts of the best oil possible. Would you consider changing to 8 quarts of oil, two of gasoline, and some combustion products?

6) MFI tuning – It is difficult enough to properly adjust your MFI. With slightly fouled plugs it is even more difficult. With gasoline fumes going to the air filter depending on temperature of the oil it is like a thermostat in reverse; rich hot, lean cold. How do you CMA with that situation?

7) Performance – The reason we own these cars is high performance. With plugs fouled and carboned up combustion chambers, exhaust pipes, and muffler; how well does it perform when you call on it with your right foot?
A proper running MFI has a real “snap” to it when not too rich. When slightly rich it runs fine, it just doesn’t perform well.


So, how do you get the engine to do this?

Keep the entire engine system in as good a condition as you can. Replace worn parts. When something malfunctions, fix it. Don’t wait for an accumulation of defects.
These weren’t perfect when new but with 30 years of accumulated knowledge they can be at least as good if not better.
A little leaner can restore that “snap” and avoid a plethora of problems.


We all know how important the condition of the engine, the proper functioning on the MFI pump, and the condition of throttle bodies are to good overall performance. A commonly neglected item is the nozzles. Just because they squirt doesn’t mean they are functioning properly.
The nozzle has to do several things:
It has to suddenly open at the appropriate pressure (213-256 psi.)
It has to perfectly seal at lower pressures.
It has to give a perfect spray cone even at idle fuel flow rate.
The original nozzles were a matched set. I will speculate they were matched for opening pressure.
If one or more nozzles are defective the usual “fix” is to set the mixture rich to cover up the problem. Even the worst of nozzles work OK at full throttle and high RPM.

I used to have a sign in the engine dyno room: “We lean to perfection.”

Best,
Grady

[michel richard]

Took my thermoastat apart, and I found 25 pairs of disks, plus two very washers or spacers, plus one thick one, and the spring retainer.

[michel richard]

Meant to attach the following pictures:





Michel Richard

[Grady Clay]

Michel,

Can you measure the thickness of all those parts to the right of the bi-metal discs?
Please include the spring cup and the free-length of the spring.

Thanks

Best,
Grady

[donk]

Michael,
You say you have 2 very thin spacers and one thick one. In the pic, it appears that there are two thick washers. Are they maybe just stuck together? Or do they just look that way? As Grady stated, thicknesses of the spacers would be extremely helpful.

Thanks

[michel richard]

The one thick washer does look like two washers, but it is only one part. I looked at it very carefully.
The thermostat is back in the car, but pulling it is not a real big deal. Maybe tonight, then I'm away for a week.

Michel

[donk]

Sorry to bring this old thread back to life, but I was wondering if Grady or Ed or someone else who has taken several thermostats apart could answer a question for me. Do you recall if the thick spacer looked like the one in Michaels photo above, ie. it looks like 2 spacers but really is only one? The 2 thin ones pictured look like they are similar if not the same as the 3 thin ones I have, but I don't have anything that looks like his thick spacer. Is it possible that different year models used different types of spacers?

At this point, I'm only asking because this is so intriguing. I have already taken Grady's advice and put the thermostat back in as it was and am working on getting the mixture correct with that setting. If I get the mixture correct and it won't run at startup, then I guess I will need to remove some spacers, but otherwise, the spacers will just make it leaner when cold, so I think that's ok.

Thanks to all who have responded to this thread. It has been extremely comprehensive and informative. Hopefully it will be helpful to others who have questions about their MFI thermostat.

[Grady Clay]

John,

One of the reasons I didn’t explicitly answer your original question is because I have seen so many different configurations. Some Factory, some Bosch rebuilds, and some from everyone else (including Rennenhaus.)

The issue is the adjustment, not the actual shim. Your thermostat is in the ball park, abet too rich. See if you can add some shims and still have the 911 run OK cold. They can be hardware store washers – it’s the total dimension that counts. Once you find the “sweet spot”, you can always go shopping for original Factory shims/spacers.

Remember, keep track of where you started.

CMA!

Best,
Grady

[donk]

Grady,
You rock! I suspected I would get an answer like that. I have run through CMA once. I want to go through it again to double check myself. At that point I will try adding shims and get it as lean as possible where it will still run. Thanks for all the help.

By the way, where would one go shopping for "original Factory shims/spacers"?

[Grady Clay]

John,

Try the Porsche salvage/recycle guys first. They probably have thermostats that were broken in a crash or the pump was not rebuildable. The shims/spacers are just that – shims and spacers. I would also get a few spare bi-metal parts.

These parts are also all available new from the Bosch pump rebuilders.

From Porsche you can only buy a complete new thermostat assembly.



Don’t ever feel obliged to apologize for keeping a thread like yours alive. You and others have contributed mightily to the collective knowledge.


What were your CMA results? Cylinder leak, cranking compression, timings, etc? Did you adjust anything?

Best,
Grady

[donk]

Well, don't flame me, but the reason I want to go through it again is because I really didn't check everything. It was sort of just a practice run. I had adjusted the timing recently, and was planning on doing a valve adjust in the near future (did it last weekend). I did make some adjustments to the correlation. I needed to adjust the pump linkage, the air correction screws, and the throttle stops. The other linkage lengths were fine (I think one needed a slight adjustment). Then I hooked up my Gastester mainly to see how it worked. I did turn the part load one click leaner, but I'm sure it still needs some adjustment.

I think I asked this already, but don't remember getting an answer... would any indy Porsche shop have an MFI injector tester? If not, any ideas where I might find one? Is there any way to test these without the proper tester? If it's my only option, where I could send them off to be tested?

Also, this has probably been covered somewhere, but I can't seem to enter the magic key words to find it with a search. What is the proper procedure for CMA item #6: "Fuel Pressure and Flow"? If you know of a thread that already exists, feel free to point me at it.

Thanks

[Grady Clay]

John,

I’m not flaming, just holding your feet to the fire. You are doing all the right stuff.

If you can’t find a local nozzle tester, see if you can find six spare nozzles to use while you send yours to a Bosch test site.

I‘ll post some stuff on #6 tomorrow. I’m fading.

Best,
Grady

[donk]

Thanks Grady. Somebody's gotta keep me in line! Any reccomendations for Bosch test sites? No hurry, I won't be able to get back to work on this until next week anyway.

[ed martin]

HI Donk, But you deserve to be flamed! Check the fundamental simple things first as per Check, Measure Adjust! You have to have all the basics first before you can fine tune! Otherwise your going to waste a lot of time. There is a list - I believe it starts with the air filter and so on. If you don't have a copy, then get one. It is imperative. I think you can download one from the tech site.

[Grady Clay]

OK, on to measuring fuel pressure and fuel flow.

Measure the pressure first.

Here is the Factory P-Tool P233b for measuring fuel pressure at the fuel filter console.
It is also easy to make this gauge locally.
"
"
(C) 1969 Dr. Ing. h.c. F. Porsche A.G.


Note on the left the fitting between the gauge and the banjo.
I made an eight-foot hose with mating fittings so we could monitor
fuel pressure while driving, cold start, etc.
The low-limit spec is: 0.8 bar +/- 0.2 bar (11.8 psi +/- 3.0 psi).
If low, the first thing is to replace the fuel filter.

Here is Porsche’s method of measuring fuel flow using a 1-liter beaker.
"
"
(C) 1969 Dr. Ing. h.c. F. Porsche A.G.

I prefer to extend the hose forward to the fuel filler for the gas tank.
Put a large funnel in the filler and allow the fuel to circulate back to the tank for a while.
All it takes is a calibrated container and a stop watch.



You get better measurements using a large container and longer times.
It is easy to take several measurements and dump the fuel back in the tank.
I always plug the open port on the fuel filter console because there is
usually some residual fuel that can spill.

Always disconnect the CDI ignition box prior to opening the fuel system.
Do these tests out of doors.
Have someone stand-by with a BIG fire extinguisher.
Careful does it!

The low flow limit is 1.8 Liters per minute.
If low, the first place to look is the screen filter in the fuel tank supply fitting.
If screen is OK then the fuel pump is suspect.

This is also a good time to inspect your fuel hoses.
These hoses should be “like new” all the time.
They are inexpensive and easy to replace.
Our host has the hose in bulk quantity.
Always use the Factory hose clamps, not the worm-screw type.

Of course you can use instrumentation quality flow meters and
there are flow meters designed for use with data acquisition systems.


Best,
Grady

[Grady Clay]

OK, MFI nozzles.
"
"
(C) 1969 Dr. Ing. h.c. F. Porsche A.G.

When you have your nozzles tested there are four most important factors:
It must hold pressure
It must have a perfect spray pattern.
It must spray properly and hold pressure at extremely low flow.
All six must do the same thing.


Holding pressure means that after spraying, the nozzle
maintains full pressure by not leaking.
Good nozzles will hold full pressure for several hours.
Bad nozzles won’t hold pressure at all.

A proper spray pattern is a finely atomized conical shape.
Any asymmetric pattern is bad.
Some really bad nozzles just pee off to one side.

Low flow (idle, below idle, and just off idle) is the real “art” of MFI.
The nozzles all must have excellent if not perfect spray
patterns and sealing at very low fuel flow.
The duration of the flow is the determining factor.
This is what gives the characteristic “chirp” from the nozzle.
The ability to still chirp low flow with perfect pattern at
500 engine RPM makes for proper driving.
When you creep up on nozzle opening, it should suddenly chirp with
good pattern. Just leaking is unacceptable.

If the nozzles differ from each other then your setting of the MFI is significantly
more of a compromise. Some cylinders will work better than others.
The poor running cylinders will force you to mal-adjust the system, usually too rich.
Porsche delivered MFI engines with a matched set of
nozzles. They were even matched to each pump outlet.

Most nozzles (even poor ones) work just fine at full flow.

All nozzles work best with the steel pipes, not as well with the plastic RSR hoses.

Nozzles will respond positively to cleaning with aerosol carb cleaner.
Remove the nozzle from the engine, shake out any fuel, fill with cleaner,
let sit upright for an hour or so, shake out cleaner, refill with cleaner,
reinstall in engine with cleaner, and finally run engine.
Repeat as necessary.

Remember, the best way to CMA is just after a long highway trip or DE weekend.

Best,
Grady

[Grady Clay]

More MFI nozzle: Factory test procedure.
"
"
(C) 1969 Dr. Ing. h.c. F. Porsche A.G.

Like many other things Porsche, nozzles need to be "broken-in".
Even a new nozzle may test differently after a few miles of use.
I would not accept or reject a used nozzle without some cleaning and driving.

If you have a set of nozzles from an engine that has been sitting,
swap them into a running engine after cleaning.

With a large enough collection of nozzles, you can make a matched set.
This is where they all have the same opening pressure and are otherwise perfect.

Best,
Grady

[Grady Clay]

John,
If you can’t find a local tester for your nozzles, here is where to go:

Gus Pfister @
Pacific Fuel Injection
153 Utah Ave.
San Francisco, CA 94080
415-588-8880

See if you can find a collection of nozzles your area. I'll bet you can find 50 or more. A worthwhile resourse.

Best,
Grady

[donk]

Grady,
Thanks for all the info. Any tips on where to start looking for extra nozzles?