2.4 mfi running problem

lebrunseven · 08-23-2008, 01:09 PM

we have a 2.4 's' w/ mfi. all stock. car developed a hard-starting condition, as well as 'surging' through out the rpm range. seems like it is lean or something. car seems to be low on power & it is freshly rebuilt. any ideas?

356RS · 356RS's Garage

Did you replace the fuel filter?

911 tweaks · 08-26-2008, 02:41 PM

what is the age and octane of the gas ??? Has the car been sitting for a while ???
with todays' ethanol gas, if you have it where you are, it is a hyroscopic fluid = it absorbs water = it will monkey with ALL of your engine components and operational conditions.
Bob

Robert Karow · Robert Karow's Garage

I just finished a rebuild on a 1972 T, and it's a bear to get started. I have to sit there letting the electric pump prime for probably 10 - 15 sec, then start cranking with the accelerator depressed for 15 sec before it will start sputtering and then it's another minute before the engine is running well enough to stop sputtering and popping. Once cranked it runs well accept for what fells like a little stumble around 4500 or 5000 rpm, but it seems to only really do it the first time you run it up that high then its pretty clean. Another strange symptom is that it makes a very muffled back-fire sound when I come to a stop light. I am thinking that it could possibly be a mixture of bad injectors and faulty mid-range mixture on the mfi.

Some history.
I recently had the fuel tank cleaned and lined. Replaced all fuel lines, fuel filter and made a stab at cleaning the injectors out on a stand.

Fast Corners · 08-29-2008, 06:22 AM

Robert,

Not sure how familiar you are with the MFI system but here are a few things that may help.

1). Check to see if your cold start enrichment is hooked up and functioning.
2). Have you read the starting proceedure for MFI. The hand throttle should be used and will help keep the engine running smoother until it warms up.
3). The muffled backfire is a symptom of either: an incorrectly adjusted or non-functioning throttle position micro switch or the RPM transducer has broken.

There is a wealth of MFI info on this site...try looking up the ultimate MFI thread.