need help with 911sc

abossana · 02-17-2008, 03:10 PM

hello, filled the gas tank up to full on thursday @ cheveron. drove the car thursday night, friday, parked it saturday and tryed to drive it this morning but i went to start it and it fired right up and the rpm droped suddenly to about 200 rpm and barley runs. if i give it any gas at all the intake starts backfiring and poping like crazy. i checked my POV and it is closed. i drove it down the street and it was nearly impossible to get the car to accelerate without really loud pops and coughfs and no power at all. im lost. please help.

thanks, anthony

sjf911 · sjf911's Garage

Quote:

Originally Posted by abossana

hello, filled the gas tank up to full on thursday @ cheveron. drove the car thursday night, friday, parked it saturday and tryed to drive it this morning but i went to start it and it fired right up and the rpm droped suddenly to about 200 rpm and barley runs. if i give it any gas at all the intake starts backfiring and poping like crazy. i checked my POV and it is closed. i drove it down the street and it was nearly impossible to get the car to accelerate without really loud pops and coughfs and no power at all. im lost. please help.

thanks, anthony

Fuel filter plugged?

DarkSideDe · 04:46 PM

Water in the gas
Dirt clogging the fuel distributor

Get yourself a Mercedes Benz dealer and get yourself a can of Fuel line cleaner - really good stuff, expensive (like 26 bucks for one can) but really, really good...

You could also get a fuel line cleaner at an auto parts store -- much cheaper...

And when was the last time you had the fuel line filter changed?

You may have a fuel injector clogged. After you clean fuel line - check injector.

And coming from left field - one more suggestion: check your distributor cap - make sure it isn't cracked.

Previously owned 1979 911SC -- even a hairline crack could cause disruption of the spark plug.

jjone20 · jjone20's Garage

The first year I had my '79 911SC, I filled it up at the local gas station, and it ran like crap. It was fine before the fill, and I got it home but it was bad the next day. I started doing all kinds of research on CIS, etc. I even bought the testing guages as preparation for serious digging into the fuel system. In the mean time, I kept driving it until the next fuel fill, whereupon, VOILA!, everything was fine. It may be just bad gas. With a full tank, it's a lot of trouble to run it through, but perhaps you could drain it into a less sensitive vehicle and re-fill your Porsche with a top-tier source. I haven't had any trouble since.

fred cook · fred cook's Garage

Sounds like you got gas with a dose of water in it. Go to your local NAPA store and buy a bottle of their gas treatment that eliminates water. If there is no NAPA store nearby, find some of the STP gas treatment in the yellow bottle. Both work well and can "save" a contaminated tank of fuel. One bottle should be enough for a 20 gallon tank. Good luck!

abossana · 02-17-2008, 05:05 PM

thanks for all the help guys, i was leaning toward bad/ contaminated gas due to the fact that it ran great befor the fill-up. ill try some of the recomended cures. fuel filter has about 2k miles on it. changed it about 8 months ago.

anthony

abossana · 02-18-2008, 10:49 AM

update: this morning i added some injector cleaner and water remover. started the car up and it ran perfect and idled for about 1 min with no problem, as i was walking around the car it suddenly droped to 200rpm and sounded like it was choking. i gave it some gas and it started to backfire through the intake and would barley run again.........................

anthony

ramonesfreak · ramonesfreak's Garage

if you had a backfire, check the pop-up valve in the airbox
how is our coil? when mine went bad, the RPMs would drop when i gave it gas

ramonesfreak · ramonesfreak's Garage

i see you checked the POV. check the coil. if its the original, see if its leaking oil onto the distributor cap and regardless, make sure the wire is attached firmly to the coil.

abossana · 02-18-2008, 06:13 PM

the coil is new aswell as the CDI box. and i definatly think this problem is ignition related based on the un-burned fuel smell out of the exhaust(very strong) when running. and from past experiance it seems ignition related. im wondering if my (brand new) permatune CDI box is on its way out?

anthony

Deschodt · 02-19-2008, 01:03 PM

even more left field, replace/clean up contacts for the oxy sensor fuse and interior light (same fuse). Mine ran like crap and the fuse was just corroded.... (now I'm assuming the 79 is like my 83 and has an OXS, if not, ignore me)

cay-ahe · 02-19-2008, 01:49 PM

Check the connection on your oxygen sensor control unit (under the passengers seat) also check that the frequency valve is buzzing (near your throttle on top of the engine.) If all is not well here the car can run terrible and produce lean backfires. That's my .02

abossana · 02-20-2008, 05:07 AM

Quote:

Originally Posted by cay-ahe

Check the connection on your oxygen sensor control unit (under the passengers seat) also check that the frequency valve is buzzing (near your throttle on top of the engine.) If all is not well here the car can run terrible and produce lean backfires. That's my .02

i didn't think the FV is buzzing, so i checked the relay under the pass seat and while the car was running like crap i messed with the relay and it ran great, i unplugged the relay and it ran like crap. i plugged it back in and i didn't hear a click or any noise from the relay and it was still running crappy. so I'm wondering if the relay is on its way out and working intermitintly? opinions?

petrolblue83911 · 02-20-2008, 05:53 AM

sounds like a classic clogged fuel filter. Even though you just changed it, I would first check it and see if it is still clean. In a safe env. pull the filter off the engine side, and run the pump into a safe container for several minutes. if flow is consistent, then move on to next options. Lately I have seen a ton of bad/contaminated gas tanks

cay-ahe · 02-20-2008, 05:55 AM

If you were able to make a noticable change moving or unplugging the relay you are in the right area. It could be the relay going bad it could be a wire shorting or broken (grouding). Replacing the relay is an easy check, I think you can jumper the connection as well. Make sure the connector to the oxygen control unit is good as well. All related to making the FV work properly. When the FV is buzzing it is like a rattle snake very apparent.

willf · 02-20-2008, 08:43 AM

i'm thinking it is the relay under the seat. I have been down this frustrating path of triage of the same symptoms you describe to find that the replacement of the old relay is all I needed. Probably the original metal relay in there... P dealer can get these to you for something like $28 or so; Napa sells these bosch relays for little less. good luck bro.

abossana · 02-20-2008, 10:13 AM

UPDATE: yes it was the original relay under the set. I went to the local independent shop and purchase the bosch relay and just installed it and the problem is fixed. here how I verified myself.

started car without relay: ran like crap

started car with old relay: rand like crap

while the car was running I pulled out the old relay and replaced it with the new one: run perfect. unplugged the new relay: ran like crap. and then put the new one back in and ran perfect again. then I repeated the process a few times and I feel safe saying it was the old relay causing the problems!

thanks for all the help guys, ill post and update in a few days

Anthony

cay-ahe · 02-20-2008, 01:59 PM

Glad it was that simple.

gungadin · 02-22-2008, 06:33 AM

Quote:

Originally Posted by abossana

UPDATE: yes it was the original relay under the set. I went to the local independent shop and purchase the bosch relay and just installed it and the problem is fixed. here how I verified myself.

started car without relay: ran like crap

started car with old relay: rand like crap

while the car was running I pulled out the old relay and replaced it with the new one: run perfect. unplugged the new relay: ran like crap. and then put the new one back in and ran perfect again. then I repeated the process a few times and I feel safe saying it was the old relay causing the problems!

thanks for all the help guys, ill post and update in a few days

Anthony

Anthony/anyone
Is this relay only in SC cars or would a '76 have the same relay?
Thanks.