Mark Brook

Well it's back, this time worse than ever.

After new caps and rotors, the last misfire was traced to a leaking high intensity washer bottle dripping onto the earh strap conection under the hood. I cleaned up all connections and replaced the neg cable and all was well until a recent track day.

My misfire started when I was down to 1/4 tank of fuel, so I brimmed it and seemed to cure the problem for a while until the tank got back below half full. Now I'm not sure if there is any relationship between the misfire and tank level, but but it wasn't purely happening on bends, suggesting it wasn't a fuel serge problem.

Now, driving on the roads I have the misfire most of the time. It feels like I'm on half power then clears, other times it's like hitting a wall, before stuttering and coming back to life. Approaching junctions it will frequently die completely.
It's worse hot than cold, although still present. Blipping the throttle will sometimes make no difference for 10 seconds. Hot idle is fluctuating between 700 and 1200 RPM, then will stumble and die on it's own.

I can see the dist belt spinning through the inspection hole.

Where do I start?

Mark 90C2

Indycam

DME relay ?

warmfuzzies

Fuel starvation? rather than misfiring......any sparks around the engine bay in the dark? Disconnect the fuel filter, see if it runs clear, maybe your problem, when was it last changed?

Kevin.

Jerry Garwick

Mark

I did not see any previous messages on what you may have previously done to try to solve the problem. I tried the DME and fuel filter approach with no change of missing. From my own troubling experiences I would (1) buy one new coil and change out one at a time to see of that helps; (2) closely examine the lower ignition wires to see if they are oil contaminated. Both problems with my '91 gave similar indications as yours.

jimq

if power is down what about the distributer belt ??

911addict

First thing to check is moisture. Was the car standing in rain overnight? A spray of WD40 can work wonders.

964rh

Dodgy fuel filter, coils on the way out, faulty spark plug?

Just a few thing I needed to sort my misfire out. May be worth checking

Rob

Indycam

Cloged up fuel filters flow ok at low rpm / hp and then can not flow ok at high rpm / hp .
So the motor feels fine at low speeds and then feels down on power the faster you go .

brookewebb

Check Airflow Meter, or O2 sensor.

warmfuzzies

Mark, did you want to meet up sometime, maybe I can lend another perspective....You never know I may be of some use...

Kevin.

Oh, thats if you're still in Essex that is...

Richard Curtis

before you buy a new coil, try this simple test: disconnect a plug wire at the plug; stick in a spare plug and ground it against the engine. have someone crank the engine just a few revolutions while you observe the color of the spark (if you push the accelerator all the way to the floor while cranking,the car will not start). If the spark color is anything other than blue, you've got a bad coil. Of course, with 964s, you'll have to do this with twice to test both coils.

BGLeduc

Mark,

It sounds very similar to the issue with the airflow meter wiring harness. There is a TSB about that (sorry I don't have the number handy), and it is not a hard fix, if it is in fact the problem.

I had a very similar situation. At times the idle would be almost violent in its instability. And then like that, it would stabilize. It took my wrench a bit of effort to understand the problem, since at times it ran fine. But, the bottom line was that, once he carried out the mod as outlined in the TSB, its been solid, and that was close to 4 years ago.

Unfortunately for us, it seems that there can be several different problems that produce similar symptoms. Part of the charm of the 964, I suppose.


Brian

springer3

There is a suction strainer inside the fuel tank. That can cause intermittent problems as the trash can wash off, and you run fine for a while. It is not difficult to clean it except for draining the fuel.

On any car this age, gra-doo build-up at the bottom of the fuel tank is a common problem.

BP

I have the exact same problem with my 90C2, last week it drove perfect, went to take it for a drive today and it didn't want to stay running in the garage then after about three starts it will idle then when you step on the gas you get very little response then all of a sudden the the rpm's jump way up take your foot off the pedal and it will go back to idle but not a very stable idle, almost like it is starving for fuel. The tank is around a quarter full so I will try and get it to the station about 6 blocks away and top it off and see if that helps otherwise I will start checking everything everyone has mentioned. This site is so much help for the do-it-yourselfer everyone keep up the great work and when I get my problem figured out I will let you know what was wrong. Thanks Brian

Mark Brook

Guys,

Thanks for all your pointers, I shall certainly be trying them all, methodically, as soon as possible.

Unfortunately, last Thursday I was advised that I have cancer of the lymph glands in my throat/neck, and I go in to hospital for an operation on Tue 29th. Somehow the misfire doesn't bother me too much right now!

I just want to say that these horrible things can hit any of us (I'm just 40), so please, please, make sure you have critical illness cover, unlike me........

I look forward to tracking down my cars faults, with your help, shortly.

Best regards,

Mark 90C2.