Ok, see if you can figure this tuning problem out

[Cornpanzer]

So, when I bought my 1970S it was missing the paper tubes running fromj teh fan shroud down to the heat exchangers. On my last Pelican parts order I ordered two new ones. Well, after installing them tonight the car ran like an absolute turd. It had a horrible midrange flat spot and wouldnt cruise at a steady speed. Upon returning home, I took the tubes loose and thecar ran perfectly again. I have suspected an exhaust leak since the car backfires upon decelleration (no it isnt the fuel switch). Could it actually be leaking into the heat exchanger and screwing something up when I put the tubes on? Any ideas why this would make the car run poorly? Im at a loss......little help please

[HawgRyder]

Did you route hot air to the MFI ?
Perhaps the MFI was getting it's shot of air from the surounding air in the engine compartment....and when you re-routed this with the new tubes...you upset the status.
This would make the engine run in the rich condition all the time.
Bob

[Early_S_Man]

The MFI engine is uniquie in that the left fan shroud air tube is ESSENTIAL for proper engine operation, because it pressurizes the left heat exchanger ... whose hot air supply is required CONTINUOUSLY by the MFI injection pump thermostat, which is supplied by two 25 mm hoses in series ... a heavy, reinforced rubber one to the sheet metal elbow, and a twin-layer foil and plastic one to the thermostat assembly.

If you haven't already familiarized yourself with the MFI documents at Pelican's 'tips' page, I suggest that all documents be saved on your computer, and printed in a large reference binder. http://www.pelicanparts.com/techarticles/911_MFI/TipMFI.htm

I can't even imagine that a mentally competent previous owner or mechanic would leave those hoses off and maladjust the MFI pump to compensate for the lack of an operational thermostat!

The bottom line is that you need to go to square one in the Porsche document Check, Measure, Adjust! A Gunston Gas Tester (do a search) will simplify getting the system properly running again, but it may take a few days to get things straight!

[jluetjen]

I can't even imagine that a mentally competent previous owner or mechanic would leave those hoses off and maladjust the MFI pump to compensate for the lack of an operational thermostat!

Warren - I agree with you. I am SHOCKED - I repeat SHOCKED, that anyone would do this. Certainly in all of the thousands of posts on this BBS this would be the first time that anyone has reported such a travesty!

[Cornpanzer]

Thanks Warren......looks like I need to do some homework. It is the left side tube that seems to affect the performance when hooked up. Thanks for your input,

[NYSCAR]

Hee Hee - welcome to the world of Early MFI

[pwd72s]

Yep! But once you finally get it running the way it was designed to? You're going to love MFI! Warren, as usual, came through well....

[Cornpanzer]

Im in the process of downloading the check/measure/adjust information. Looks pretty intemidating. Have any of you actually performed this entire process before? Thanks, Dave C

[Superman]

"Rick, I'm shocked, shocked to find that gambling is going on in here."
From Casablanca

[michel richard]

Two things about the check measure and adjust: It is not as intimidating as it may appear, but it is not quite complete either.
For example, there are reports that you don't need the protractors to adjust the pump rod: simply set it to the prescribed length. The rest is easy but do make sure you check compression and leakdown.
Also, checking the injectors probably means sending them out to a specialized shop. I understand that diesel-engine shops can do this. The pump does the metering in this system, so the injectors, even if they are obviously important, are not as central as they are in other systems; they just open and close to let the juice flow.
The stuff this manual does not cover is idling, but there are other things in the Pelican material that give instructions on how to set that.
Finally, I find that if the system is way off, you need to run through the steps a couple of times: the final mixture adjustment, for example, can have an impact on idling speed, which can have on the reading you get of timing.
Anyway, these are just my findings from having worked on my system a bit. I don't qualify as an expert.

Michel Richard

[Rot 911]

Originally posted by Cornpanzer
Im in the process of downloading the check/measure/adjust information. Looks pretty intemidating. Have any of you actually performed this entire process before? Thanks, Dave C

You want to see the long painful process of me going from MFI intimidation to psuedo MFI zen master just do a search under my screen name and "MFI"

[Early_S_Man]

Like the factory service manuals ... many people make the mistake of assuming the Porsche pubs are training materials ... which they aren't! They are merely the OUTLINE, and are expected to be used by factory trained technicians!!!

You need to read ALL of the artcles in the 'MFI TIPS' page before starting through the ' MFI Blue Book' ... as the Check, Measure, Adjust is often called, because the originals have a blue cover. And, yes, a few details are missing, or out of date, like the CO percentages ... most people use 5.5% to 6.5% to get good driveability.

I suggest getting a gallon can of B-12 Chemtool, and start by removing and cleaning the thermostat assembly. It may not have been working correctly, and that may be why the hoses were missing. It needs to be cleaned annually, and don't be surprised to find bugs, twigs, leaves, and dirt clogging up the assembly! The corrugated plastic/foil hose is also very important, and must not be allowed to get crushed, cracked, or torn. If damaged, it should be replaced!

[kwikt 911]

I agree 100% with Early S Man. I tried disconnecting the 2 hoses on the fan shroud and plugging them, thinking I would get more cooling to the engine. Boy was I wrong. The car ran so bad I was afraid to take it around the block. Hooked the hoses back up again and it ran like a smooooth as silk.


Kevin
72 911T/E