luizinholeao

Dear Friends,

My original 97 have a misfire under 4-5 k RPM in a high gear...
When the boost raises, in third, or fourth gear, a misfire occurs, sometimes light, sometimes hard, cutting off the engine.
I´ve changed plugs, checked all the ignition system, the car have at time just 1050 kms in odo!
It has been stored in a private colletion since new, and a guy that made a maintenance in museum´s cars, put lots of oil at every change.
When i bought it, and put it to run, a lot of smoke get out of exaust.... lots and lots!
So, i think the oil in excess made something wrong in a sensor, like MAF, Lambda, or similar....
Any ideas?
Regards from Brazil
Luiz Leao

rinlv1

MAF

I had similar issues, went away after a tune up and MAF change.

No HTwo O

Luiz, WE DEMAND PICTURES!

A Porsche MAF sensor is very-very expensive now for our 993 TT.

Do you have any stored codes on your DME from the misfires? They should be there.

Is this the same or different issue you had several months ago, back in November?:

https://rennlist.com/forums/993-turb...eleration.html

TheOtherEric

A misfire like this can happen if you install incorrect plugs. For example, if the gap is too large. Happened to me.

jmayzurk

How's your gas? Could be getting knock, causing the timing to be pulled. How's the octane of your gas in Brazil?

Here in California, I find that when drinking 91 octane swill, knock is most prevalent around peak torque.

993GT2

I would suggest to change the MAF unit and check the N75 valve first.

Regards,

Bergamasco

I would suggest you check the oil level very carefully. It could simply be a problem of too much oil in the system.

luizinholeao

Dear Friends,
thanks in advance for help!
here are the answers:

I had similar issues, went away after a tune up and MAF change.
-I change a MAF, from a friends car.... no way, nothing change!

Do you have any stored codes on your DME from the misfires? They should be there.
-there is a MAF code, any times, but with a perfect MAF, coul be troublesome lecture at misfire time?

A misfire like this can happen if you install incorrect plugs. For example, if the gap is too large. Happened to me.
- i´ve change a new set of NGK´s... checked gaps...

How's your gas? Could be getting knock, causing the timing to be pulled. How's the octane of your gas in Brazil?
- I think there is no problem with gas, i use a premium 93 octane, and with our race cars it works fine.

I would suggest to change the MAF unit and check the N75 valve first.
-Dear GT2... what is the N75 valve?
MAF tested with another one from friend´s car.... same thing...

I would suggest you check the oil level very carefully. It could simply be a problem of too much oil in the system.
- oil level lowest possible at dipstick, new PORSCHE O&M filters, mobil 1 10W40 new...
Intercooler cleaned and dryed, as the hoses.

Any more ideas friends? could be electric/electronic failure?
Thanks once more!
Regards,
Luiz

WingChun

This is a long shot but there may be an overboost condition causing the ecu/dme to take action to stop this?
The N75 (boost control valve) has been mentioned already but have you checked that both turbo wastegate actuators function properly?
If not, carefully remove the air connector tube from actuator, connect a hand pump (mityvac) and apply 0.5 bar pressure, the actuator should move freely to open the wastegate with total movement of around 4mm +-0.5.
Ok car has been in museum for many years so should not be any rust etc but worth checking.

luizinholeao

WingChun,
thanks for new ideas.
I dont belive it is overboost, just because when it acelerates hard from first gear, the problem does not appears!
It comes only when the engine is loaded at 3.5 to 5 k rpm in a high gear.....
cheers,
Luiz

993GT2

Luz,

Give me a call, so we can discuss about the car.

11 5642-0917

Abs,

rcg412

Isn't brazil all ethanol gas?

luizinholeao

Dear Friends,

Today i´ve tried to check lambda signal, and surprise: No Lambdas at all!!!
Is that correct? in a Euro model?
Another question?
Where is located a second fuel pump? i want test flow rate, and think is possible that only a front pump is working. is that possible?
Thanks again!
Luiz

Mike J

One pump, accessible under the car, right hand side just behind the front wheels - there is a panel.

Not sure about the Lambda signal, but you are suspecting fuel pressure? Just curious, why do you suspect that?

Cheers,

Mike

luizinholeao

Dear Mike,

I want try to check the fuel flow rate, because pressure is OK...
Was a big surprise to see that there are NOT lambdas in my car, only plugs in their places.
I have checked all ignition system, changed plugs, cleaned MAF, cleaned injectors, new filters, checked hoses before and after turbos for leaks, and the misfires persist under load at 3,4, 5 gears, aprox at 4-5 k rpm.
Now i want to try another pump, and suspected if there is a second one.
No codes at the scanner any time!
Any sugestion?
thanks in advance,
cheers,
Luiz