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Cold Engine Start-up Routine MFI

I am curious about how everyone starts there early 911 - especially the 2.4 MFI.

Myself, I raise the throttle lever and the car starts quite fast. However, this causes the engine to "idle" at apporx 2000 rpm. If I udjust the throttle lever to soon, the engine will begin a mild, intermittant backfire/popping.

It just seems excessice to let the car idle while cold at such a high rpm. Or is it? What has your experience been

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David

1972 911T/S MFI Survivor

Last edited by daepp; 10-12-2005 at 02:28 PM..
Old 10-11-2005, 07:23 AM
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Man - my spelling is horrible. Replace "there" with "their" and "to" with "too."

Maybe I should preview these posts, eh?
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David

1972 911T/S MFI Survivor
Old 10-11-2005, 07:26 AM
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Do the revs pick up after you've been on the hand throttle a spell?
That's the signal that the car is warm enough to back off the hand throttle. I'd suggest checking the small heat riser tube, the hose leading into the MFI pump...be sure it's not torn or loose.
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Old 10-11-2005, 07:58 AM
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"It just seems excessice to let the car idle while cold at such a high rpm."

I have the same question regarding my 73 1/2 with CIS. My experience is exactly the same. Anything less than "all the way up" on the hand throttle, and the engine will stumble. But 2000 rpm on a cold engine? Makes me cringe.
Old 10-12-2005, 10:09 AM
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Cringe is right.

However, judging from the blue smoke I get for the first 30-60 seconds makes me hopeful that there's lot of oil down there!
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David

1972 911T/S MFI Survivor
Old 10-12-2005, 10:14 AM
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Start'er up, get some oil pressure, and get going (staying between 2000-3000).
I don't think letting the 2.4 warm up in the driveway is good for anything.
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Old 10-12-2005, 11:31 AM
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Quote:
Originally posted by daepp
Man - my spelling is horrible. Replace "there" with "their" and "to" with "too."

Maybe I should preview these posts, eh?
Hey Daepp,
You can always click on the little "edit" button in the lower right corner of your post, and get another try at your spelling..
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Bill

69 911 T Targa, 2.4E w/carbs (1985-2001)
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73 911 T Targa, 3.2 Motronic (2001- )
Old 10-12-2005, 01:02 PM
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On my 2.2 MFI, with NO cold start gas piping connected, and NO hand throttle connected, I do the following:

From very cold start, push gas pedal to the floor and hold while cranking, after letting pump run for 30 seconds.
Once it fires, lift pedal to around half or so until all 6 cylinders catch, then let it idle for a minute before setting off.

From warm, push pedal to half throttle, hold until engine fires, then slowly release to idle.

That's what I do. My car is only started/driven infrequently, so the first method is used quite a lot..
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Bill

69 911 T Targa, 2.4E w/carbs (1985-2001)
70 911 S Coupe, 2nd owner (1989- 2015)
73 911 T Targa, 3.2 Motronic (2001- )
Old 10-12-2005, 01:07 PM
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It is refreshing to see a MFI being operated properly.

With everything working properly the best sequence is:
Pull on the properly adjusted hand throttle.
Turn the key to “on” (not “crank”) for 1-3 seconds to clear any bubbles from the fuel circuit.
Crank to start.
When it fires give a quick rap to 3-4000 or so to clear out unburned fuel from the cold start.
Drive it immediately, briskly uphill is preferable. You want it to warm up as fast as possible.
With the proper weight oil 4500 is just fine on a stone cold engine.
If you parked it very hot you will notice some chain noise when very cold. It doesn’t matter if it is at idle or being loaded, the chains get lube soon.

The only reason I would let it run for 30 seconds or so is if the temperature were below say -10F. This will put gas in the oil.

The big issue is diluting the oil with gasoline. Don’t expect it to run perfectly when cold. If it does then you probably are too rich and diluting the oil with gas. Change the oil regularly in cold weather. Get the engine hot and use full power to redline every chance you have.

If the oil is becoming diluted with gas rapidly, you may see the oil level actually rise over time. This is a very insidious and dangerous problem. The engines normally use oil; say at the rate of 1Q/600 mi. If the oil isn’t allowed to get hot and vaporize the gasoline, then you can be replacing one quart of oil with one quart of gasoline every 600 mi. Of course the rate of consumption of the mixture is higher than for pure oil. It doesn’t take long to have mostly gasoline in the oil tank. One trip on the freeway on a warm winter day will evaporate all the gas leaving nothing to lubricate the engine – immediate disaster. Of course the mixture of gas & oil doesn’t lubricate properly and accelerates wear.

This is also the reason why it is necessary to do CMA with fresh oil. The vapors vent to the air cleaner assembly and tail pipe CO changes.

The key is having everything working properly and get it fully warmed up fast.

Best,
Grady

PS, I write everything in my word processor and then copy & paste to the Forum. I’m on my 9th 700 page Word.doc. This lets me use the Find function to search my own files.
You can also edit your thread title and add “MFI.” (hint)
G.
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Old 10-12-2005, 01:59 PM
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Grady - thanks for the great info with respect to the cold start AND tips on using the forum.

It's funny - of all the reasearch I did prior to buying an "early" 911, I never thought I'd spend so much time worrying about starting the damn thing. Sure is fun to drive though - lots of smiles to the mile. And I love that early engine - just don't want to blow it - so to speak!

The Forum's pretty cool, too!
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Old 10-12-2005, 02:32 PM
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I have a 1973 CSI and basically follow Grady's proceedure although I do turn the key "on " for a little longer. In any event the engine starts readily. What I have noticed though, is that I can close the hand throttle almost immediately with no ill effect, it seems to idle well even when cold. I should say that that the CIS system was overhauled an adjusted with the remainder of the engine and the car is garaged so it starts at "room temperature" so to speak. Is this okay or may the mixture be marginally too rich as suggested? The engine does run slightly on the rough side on the go, which previously has been caused by the points closing, may be it is a combination of both? By the way, is it wothwhile changing the points to that other system suggested by Pelican, the name of which escapes me?!
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Old 10-12-2005, 02:58 PM
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Have any of you found a good way to get a carbed car to start cold? I have a RS clone 2.7 and it never starts well cold. Usually requires constantly pumping the accelerator while cranking the starter. Once it does start it runs rough for several seconds until the engine burns the unused fuel. That is after letting the fuel pump run for 10 - 15 seconds.
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Old 10-12-2005, 04:09 PM
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Quote:
Originally posted by rrichar
Have any of you found a good way to get a carbed car to start cold? I have a RS clone 2.7 and it never starts well cold. Usually requires constantly pumping the accelerator while cranking the starter. Once it does start it runs rough for several seconds until the engine burns the unused fuel. That is after letting the fuel pump run for 10 - 15 seconds.
If your accelerator pumps are working properly, a few quick jabs of the pedal BEFORE you crank the engine should do it. My Webers always started well that way, actually easier than the MFI, for me.

Flooding Webers can be dangerous - be careful
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Bill

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Old 10-12-2005, 04:37 PM
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Sean,

Welcome to the Forum. It’s good to see an early 911 alive and well in WARSAW, POLAND! I haven’t seen that location yet. Nice stable.

CIS is dramatically different than MFI although the starting procedures are somewhat similar.


Daepp, your next challenge is to post images of your car. Let us know if you need help.

You will find this Forum the best resource in the world thanks to Wayne and PelicanParts. One key is learning the art of using the search function. Keywords are the name of the game. That is the reason I suggested adding MFI to the title of your thread and I included it and CMA in my post.

You will have a great time with your 911. One issue is for you to learn how to deal with the MFI. You can do it; all it takes is knowledge and willingness. Even if you don’t turn the wrenches yourself (but it’s encouraged) you need to know as much about the system as the best techs. That way you can explain symptoms and evaluate adjustments. This Forum can help.

It is good that your engine “pops & backfires” when cold. That is an indication that it isn’t too rich.

Start yourself a resource binder to do with the MFI. The CMA procedures should be your first chapter.



Bill, One of the “tricks” to starting cars cold is to have the throttles almost closed. This creates maximum vacuum. The low pressure forces liquid fuel to vaporize, which it is not inclined to do at low temperatures. The combustion process only works with an air-fuel vapor mixture, not liquid. Liquid fuel can “flood” the engine. I think the original idea behind the hand throttle was to discourage fully opening the throttles.

The MFI pump is dumb enough to give sufficient fuel at full throttle and cranking RPM. It certainly is off in a corner of the mechanical “map”.

Giving the engine full throttle while cranking is appropriate to clear the engine & intake of unburned fuel. Very desirable after heat soak.


Best,
Grady
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Old 10-12-2005, 05:11 PM
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Grady says:

Bill, One of the “tricks” to starting cars cold is to have the throttles almost closed. This creates maximum vacuum. The low pressure forces liquid fuel to vaporize, which it is not inclined to do at low temperatures. The combustion process only works with an air-fuel vapor mixture, not liquid. Liquid fuel can “flood” the engine. I think the original idea behind the hand throttle was to discourage fully opening the throttles.

The MFI pump is dumb enough to give sufficient fuel at full throttle and cranking RPM. It certainly is off in a corner of the mechanical “map”.

Giving the engine full throttle while cranking is appropriate to clear the engine & intake of unburned fuel. Very desirable after heat soak.
===============================
Grady,
I guess I understand your description above. What I have always wondered, and hope you can tell me, is what does MFI do when the throttle is closed at cranking speeds? Does any fuel (or enought to start the car) get injected?

Thanks for the lessons...
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69 911 T Targa, 2.4E w/carbs (1985-2001)
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73 911 T Targa, 3.2 Motronic (2001- )
Old 10-12-2005, 05:17 PM
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Bill,

Good question.

When cold and trying to start the MFI has two (or three for ’69) assists. While the pump only knows throttle position and RPM it is adjusted by barometric pressure via the aneroid and the cold running thermostat. While cranking, there is additional fuel added via the cold start system. For all there is a solenoid valve on top of the fuel filter console that sorta sprays raw fuel down the intake stacks. (’69 has an additional enrichment that forces the MFI pump full flow).

In practice the cold running thermostat has the major influence over the mixture while running cold. The cold start circuit(s) only function while cranking. They are temperature dependent and disable themselves with the thermo-time switches if you crank too long.

To answer your question exactly:
Yes, the MFI pump is starting and running in a very rich mode governed by the cold running thermostat. The throttle position probably doesn’t change the mixture other than normal (I have never measured that) but is very influenced toward rich by the thermostat. There is the additional cold start enrichment while cranking.

Best,
Grady
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Old 10-12-2005, 05:48 PM
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and we all thought the Japanese introduced variable valve timing to the assembled masses... (gotta watch my grammer on this thread)

BTW whats CMA?
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Old 10-12-2005, 06:06 PM
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We all need to watch our use of jargon here. CMA stands for Check Measure Adjust, a Porsche Factory booklet 4532.20. It is titled “Porsche Mechanical Fuel Injection, Check, Measure, Adjust.” This is the “bible” we all use. It isn’t complete and is designed for knowledgeable technicians and all new components. I’m working on CMA2 – an extended version – that is understandable by novices, is far more detailed and deals with geriatric MFI.

Here is CMA in pdf format.

The critical issue with MFI (as with many other systems) is to confirm the proper operation of all the engine systems before you adjust anything.


Best,
Grady
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Old 10-12-2005, 07:36 PM
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Quote:
Originally posted by MBecker911
"It just seems excessice to let the car idle while cold at such a high rpm."

I have the same question regarding my 73 1/2 with CIS. My experience is exactly the same. Anything less than "all the way up" on the hand throttle, and the engine will stumble. But 2000 rpm on a cold engine? Makes me cringe.
Hi,

To start my '73.5, I pull the hand throttle all the way up, put the key in the run position and listen to the fuel pump. After a few moments, the sound ever so slightly changes and I turn the key to the start position and get her to fire. I wait for the idle to stabilize 2-3000 rpm and then cut it back to 1500 rpm. Blip the accellerator to verify smooth operation and off I go. Once the temp gauge moves off the peg, I start closing the hand throttle to maintain a 700-1500 rpm idle until it is closed.

Works every time.

Also, I like to let the car idle for a minute or so before moving to be sure all is ok.
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Old 10-12-2005, 07:57 PM
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Thanks Harry,

In fact, I pretty much follow the same procedure. That tell-tale change in the sound of the fuel pump (which I'm guessing means the CIS system is fully pressurized) seems to be the key. I just sort of figured it out by trial and error.

As for the original question (is it OK to have a cold engine immediately go to a 2000 rpm idle), the gist of the thread seems to be that that is normal and OK.

Old 10-13-2005, 10:43 AM
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