1986 Porsche 911 Targa misfiring

ddiaz 396 · 11-16-2016, 09:10 AM

hi, Im new in this forum and I need help!! My car was running ok, but, yesterday, when I started it up (start and idle fine) the car was running erratic, misfired could not accelerate it. Ordered a new fuel filter. removed the air filter and spray some carburetor cleaner but no changes....still erratic. How can start to find the problem ? DME relay?fuel pump?. Thanks in advance
PS sorry about my writing English...it's not my first language. Daniel

Barrpete · 11-16-2016, 09:16 AM

First thing to check would be the DME relay. Before you do anything else replace it with a new one and see if the problem goes away.

RSTarga · 11-16-2016, 12:12 PM

Heat sensor or crank position sensor.

ddiaz 396 · 11-16-2016, 12:17 PM

I replaced the DME relay 8 months ago.......also replace both sensors

darrin · 11-16-2016, 12:19 PM

what about the head temperature sensor? - my '86 came with a single wire unit that catastrophically failed -- this was superseded by a two wire version -- if you have a single wire head temp sensor, you might want to replace it regardless. Inaccurate temp readings could cause your issue

Casey at Pelican Parts · 11-16-2016, 01:19 PM

Could be a fuel delivery issue, start by checking the basics, fuel pressure, spark plugs, distributor cap and rotor etc. If all this looks good, try to isolate the bad cylinders by removing the spark plug wire and listening for the idle to drop. If you remove a wire, and the idle does not change, that is a faulty cylinder. Once you know that, THEN you can target your troubleshooting more accurately. If all ignition looks good, try swapping the fuel injector from a known good cylinder to the faulty cylinder. If the misfire follows, you have a bad fuel injector.

From memory I believe the fuel pressure should be 3.5 bar at idle...

RSTarga · 11-16-2016, 04:59 PM

Agree with Darrin. Head temp sensor. Frequent failure. I couldn't remember earlier which temp sensor. Car will barely run.

ddiaz 396 · 11-17-2016, 08:01 AM

I think it's a fuel delivery issue as Casey suggested......yesterday a poured some Sea Foam in the gas and make the car run for a little be(car start and idle fine). Today I started the car and the problem was gone!! I was so happy!! Take for a ride and after 2 minutes( probably after carburetor used the gas reserved inside) the problem come back

....I have to come back home very slow(in second gear)and every time that I try to accelerate the car stall....like as not getting gas....so little by little I made it back home. Maybe the fuel pump is not working properly?can cylinder heat sensor get warm and stop working? What should I try to do?(other that take it to the mechanic$$$$$$$$$!!!!). Any suggestion will be appreciated, thanks, Daniel.

ddiaz 396 · 11-17-2016, 08:37 AM

should the fuel pump make noise when I turn the key?my doesn't make any noise......check the fuse (#6) and it's ok. Thanks Daniel

DRACO A5OG · DRACO A5OG's Garage

No, it does not, 3.2's only run when trying to start.

When was the last time fuel filter was changed and which brand of relay did you get?

ddiaz 396 · 11-17-2016, 02:29 PM

the filter will be change first (already order one) and the relay brand (I assume you asking about the DME relay) is URO.

stlrj · 11-17-2016, 03:55 PM

Quote:

Originally Posted by ddiaz 396

...but, yesterday, when I started it up (start and idle fine) the car was running erratic, misfired could not accelerate it...

Need more information. Was it parked outside? Anyone see where I'm going?

Cheers,

Joe

DRACO A5OG · DRACO A5OG's Garage

Quote:

Originally Posted by ddiaz 396

the filter will be change first (already order one) and the relay brand (I assume you asking about the DME relay) is URO.

Good on the fuel filter.

Uro, is notorious for failing out of the box. Do you have the old one to put back in?

RSTarga · 11-17-2016, 05:53 PM

Check the strainer at the bottom of your tank to see if it is clear. I still think it is the Cylinder head temp sensor.

ddiaz 396 · 11-18-2016, 07:29 AM

Yes ,the car is outside under a carport...... once again, today I start the car and is running fine!!(only started and let it idle) I didn't ride it yet.....is like I said before.....during the night the carburetor filled up and the soon the carburetor use the gas in the floating area, can not get extra gas to keep the carburetor working properly then will starve of gas and the car start misfiring.....before I do anything , I will wait to change the fuel filter, then I will try(test) the MDE relay and the last will be the fuel pump.....I hope is only a fuel blockage. Did I mentioned than everything start happening after I filled the tank with Wawa gasoline(no alcohol)? using regular gas, never experience any problems....I dont think so, but.....anybody see a connection?? Thanks a lot to everybody to try to help!!! you people are great!! very helpful forum

RSTarga · 11-18-2016, 08:20 AM

You really need to check the fuel strainer under the tank before you go to all the expensive stuff. If clogged it allows some gas to get by, but once more fuel starts getting sucked it will clog and starve the car.

ddiaz 396 · 11-18-2016, 01:04 PM

Yes, that is a good idea RSTarga......make sense. How do I access the tank filter? under the car? will have to drain the tank? how difficult will be? Thanks in advance, Daniel

ddiaz 396 · 11-18-2016, 03:11 PM

is this the filter that you are talking about??

ddiaz 396 · 11-18-2016, 08:04 PM

this is the one!

PcarMav · 11-20-2016, 02:30 PM

Having similar issue on my 84 with at 95odb1.

Car is track prepped and sits very low in front. Was on a spirited drive and "bottomed out" front on a hump in the road.

Immediately the idle became eratic, and exhaust note is completely off.

At start up it jumps up over 3500 down to 400 back up high then struggles to stay on.

Sure i jolted something loose. Any teouble shooting ideas would be appreciated