2.4MFI Q's....I'm confused

[collier]

Dear List,

I have been gone for a while, and now that I am re-opening my 911 project, I naturally have some questions.

The 911 sat most of the summer in the garage, and I periodically started her....not as often as I should have I am sure.

This weekend I was undertaking the following:

Removal

-defroster/heater blowers
-radio and wiring
-defrost and wiring
-foglight switch and wiring
-factory Clock
-etc.

I am trying to clean her up so that she will be my autocross, track day car, hence the removal of the unnecessary items.

Anyway, I was also unplugging some of the wiring harness for lights and things, so that I can get in and clean/repair some item.

First thing I found out is that the car will still run with all the wiring for lights etc. unplugged

The batteries were dead, so after charging them, and still no turnover, I jumped the 911 with my Camry....she started up...but was running rich.....

I turned her off did some other things, and then came back to start her again...

When I turned the key, I could her "buzzing" like a fuel pump, then turned the key, but she didn't start; I repeated this several times, with the same results.

I then rehooked the jumpers, and tried to turn her over....by this time, it would turn over, but I smelled ALLOT of gas, in fact I looked at my megaphones, and there was standing gas in them ! ! !

QUESTION 1

Was the standing gas there, b/c everytime I turned the key, and hear 'buzzing' the fuel was being pumped to the cylinder???

Does this mean, when starting a MFI car, you don't want to let it "sit" in the accessory position too long before turning it over??

QUESTION 2

How exactly does the MFI work?

When you turn the key what exactly is happening?
Is there a check valve that might not be closing on mine that would prevent the gas from being pumped into the cylinder?

QUESTION 3

My car has always "smelled" a little rich, but not as rich as it smelled when I started it this time.

Should I let her run for awhile, and see if it levels out? Could this be b/c I have not run her in a while???


QUESTION 4

Should I check some things before running the engine after sitting so long? It is recently rebuilt, and I don't want to potentially screw anything up on it
I thought that maybe some of the seals might have shrunk since they have not seen gasoline in a while, but this might be totally off base.

I would greatly appreciate any/all help regarding this.

I am really excited to get back to my 911 project, after such a long vacation from her.

I am also looking forward to being re-involved with this BBS.

BTW, Hi Wayne and Jack Olsen, if you all remember me???

chris

[BK911]

Sounds like your cold start thingy works! There's a thingy on top of your fuel filter. When your key is in the start position, that thingy gets 12v, which allows fuel to dump down the intakes. You probably just flooded the engine. If your engine doesn't start within a couple of tries, disconnect the 12v's from the thingy so you don't flood the engine again. But remember that wire is hot, so just don't lay in in the engine compartment!

Good luck!
BK

[tmctguer]

lots of Q's........i'll answer the ones i think i know:

the buzzing sound: i assume that is a combination of your CDI unit whirring and your fuel pump buzzing. the fuel is not going into your cylinders at this point, but the MFI system is being pressurized. it is VERY high pressure (the injectors fire at +200 lbs PSI). i've always let my '73 w/ MFI set for a few seconds in the 'on' position before cranking the starter.

how does MFI work -- i would read all the technical articles on this website to find that out. i THINK that some models of MFI have a cold start mechanism that injects a bit of fuel into the stacks. i do not believe mine does (a '73), but earlier models may have it. i will defer to other experts on the board on this one, but you may find the answer in the technical articles.

try this link: http://www.pelicanparts.com/techarticles/911_MFI/TipMFI.htm

rich smell: my MFI has always run a bit rich. it could be that your repeated cranking of the starter seriously flooded the cylinders. i had a similar thing happen to me this weekend. i haven't driven the car in several weeks, and the batteries were very low. i had to jump start it. i cranked for quite some time, hoping it would start, but i ended up flooding the car. when it finally started (after opening up my MFI stack covers to get some air in the mixture), LOTS of gas was blowing out of the muffler for a few seconds. this is not normal, and prior to my flooding.

i am guilty of not driving my cars enough. when i do this, i end up with run down batteries and other issues related to lack of use.

i hope this helps a bit.

[derek murray]

I would recommend downloading a copy of check, measure and adjust... the link is below, in my signature area

[Peterfrans]

Question 1.
No fuel should be pumped into the cylinders with the ignition on (or acces.) without the engine running. The only thing happening should be the electric fuel pump supplying the mechanical high pressure fuel pump with.... fuel. You could leave it in the acc position indefinately. Fuel would be only be recycled from tank to high pressure pump to tank etc. If something went amiss here, like a loose hose, fuel would be dumped in the engine compartement.
Question 2.
The MFI is a timed high pressure fuel injection system (much higher pressure than a jetronic for instance). This high pressure causes the fuel to be sprayed into a very fine mist, which causes the performance gain over carbs. The high pressure pump resides above the left cylinder bank of your engine and is driven of the left camshaft by a belt. Therefore this pump only delivers fuel to the engine when the engine is running or turning on the starter motor. The amount of fuel delivered to the engine is programmed into a "space cam" and subject to throttle position, engine speed, engine temp and altitude.
When you start the engine a thermo time valve earths a relay, which in turn supplies current to a solenoid on top the fuel filter. This dumps fuel directly from the low pressure electric fuel pump into the stacks. If this solenoid would stick open, a lot of fuel would be dumped into the engine, hence no start, and fuel in the exhaust (it happened to me).
Fault may be in the electrical system because of which the solenoid is under current all the time, or just a stuck valve (maybe old gummed up fuel??).

Question 3.
Probably due to the faulty cold start enrichment. Make sure the valve is closed and drive the car and see if it still smells rich.

You could probably leave the cold start off in hot climates. Mine needs some extra fuel on the cold mornings to start right away.

Question 4.
I would change the oil, especially since it probably is saturated with raw fuel now. In my opinion not that much else to be done.


I suspect you probably got a bit over enthousiastic removing all those wires. The relay/wiring for the cold start is very near the rear window heater stuff.

[collier]

[QUOTE]Originally posted by Peterfrans
Question 1.
No fuel should be pumped into the cylinders with the ignition on (or acces.) without the engine running. The only thing happening should be the electric fuel pump supplying the mechanical high pressure fuel pump with.... fuel. You could leave it in the acc position indefinately. Fuel would be only be recycled from tank to high pressure pump to tank etc. If something went amiss here, like a loose hose, fuel would be dumped in the engine compartement.
Question 2.
The MFI is a timed high pressure fuel injection system (much higher pressure than a jetronic for instance). This high pressure causes the fuel to be sprayed into a very fine mist, which causes the performance gain over carbs. The high pressure pump resides above the left cylinder bank of your engine and is driven of the left camshaft by a belt. Therefore this pump only delivers fuel to the engine when the engine is running or turning on the starter motor. The amount of fuel delivered to the engine is programmed into a "space cam" and subject to throttle position, engine speed, engine temp and altitude.
When you start the engine a thermo time valve earths a relay, which in turn supplies current to a solenoid on top the fuel filter. This dumps fuel directly from the low pressure electric fuel pump into the stacks. If this solenoid would stick open, a lot of fuel would be dumped into the engine, hence no start, and fuel in the exhaust (it happened to me).
Fault may be in the electrical system because of which the solenoid is under current all the time, or just a stuck valve (maybe old gummed up fuel??). [/qipte]

That makes perfect sense, and gives me somewhere to start !

Question 3.
Probably due to the faulty cold start enrichment. Make sure the valve is closed and drive the car and see if it still smells rich

You could probably leave the cold start off in hot climates. Mine needs some extra fuel on the cold mornings to start right away..

How would you suggest removing this? Electrically only, or physically removing it as well; this car will only be used in warmer weather.

I suspect you probably got a bit over enthousiastic removing all those wires. The relay/wiring for the cold start is very near the rear window heater stuff.

Most of the wiring that I removed, is up in the trunk area...and mainly cigaretty lighters, etc. although, you are right about the rear defrost, I will have to check.

But wouldn't that be okay, since earlier you state that removing the cold start in a warmer climate would be alright????


chris

I want to thank everyone for taking the time to respond, this gives me a little more info and confidence to continue on.

[Peterfrans]

Electrical only, easy just disconnect and make sure that the loose wire does not short circuit.

I had a look in the wiring diagram and could not find a direct relation to the window heater, so I would focus on the thermo time switch. This has two connectors, one for a yellow wire (this is spliced of the wire powering the starter solenoid, the other is grounding the relay which in turn powers the cold start valve. It is grounded only a short while (few seconds) based on temperature of the engine. If this grounds all the time you might have found the culprit. Otherwise a mechanical problem on the valve itself. See what happens if you supply 12v to it directly, does it click and click again after disconnecting the wire?


Sure it would be ok to remove it and the rest of the stuff.