944 S too much fuel.

[Porsche fan]

Hello all,

I bought an 944 S (2.5 L 16V) 1987. When I start the engine it gives too much fuel (black/blue smoke and smell fuel). I replaced the Airflow sensor and computer but that didn't help. I thought it might be the temperature switch on the engine. I disconnected the switch and the problems was over! Bought a new switch replaced it (a lot of work on a 944S) but I still have the problem. Any suggestions??

Regards,

Joep

[mikepellegrini]

Maybe the O2 sensor?

And welcome to the board!

[Jeff Laurence]

You might try the FPR I think when they go bad they go rich.
Jeff

[Jeff Laurence]

When the O2 sensor goes bad the engine still runs OK but it's too rich to pass emmisions.
Jeff

[Dave L]

my S runs a little rich as well, it still passed emissions but when I asked the smog guy he said it was likely the 02 sensor. I havent done it yet but it is on the list of things to do.

[Porsche fan]

Thanks for so much help!

But that isn't the problem. I also replaced the O2sensor. When it gives too much fuel its really too much. The car runs bad and gives a black smoke. When the Temperature switch is disconnected its runs good.

What is the FPR? And where is it located?

Regards,

[svandamme]

check the fuel rail damper, it has a diaphragm ,
if it ruptures, the vacuum line will suck fuel in the intake

easy to tell, pull the vacuum line, smell it
or suck it if you are a real petrol head

Then there is the pressure relief valve... if that one fails, or the vacuum lines to it are plugged or disconnected... then you get to much fuel pressure and the injectors will deliver to much ...

Could also be a leaking injector, dripping in the intake while the engine is turned off...

for all the above... check the residual pressure... if it drops to much, something is a miss in this area...

also check your oil for fuel contamination...if it smells like there's fuel in the sump...
piston rings might be on the way out...

[SolReaver]

Just putting in my 2 cents worth. If the afforementioned suggestions do not do the trick...

check for stuck injector (lots of fuel) and also check to see that there isn't a short between the 1 and 3 or 2 and 4 injectors. The wiring to the injectors is a crimp connect type that sometimes shorts or disconnects further on in the harness, usually behind the engine. Thx to SoCalDeiver for that info.

[Arizona_928]

Originally Posted by Jeff Laurence

You might try the FPR I think when they go bad they go rich.

+1 that would be worth looking into. it's located on the fuel rail.

[Porsche fan]

Hi,

I replaced the complete fuel line with the two valves and the injectors from an other 944S.
Checked the injectors for shorts between them.
That also didn't work€¤€½¤³½³½¾‘’‘’¾²

Now what?

check the residual pressure said Svandamme.
How do I do that?
But I changed the complete fuel line so that shouldn't be the problem?

Cold engine: black blue smoke, unable to make RPM's. Way too much fuel
Hot engine: No problems, no smoke
Cold engine without the temperature switch connected: No smoke no problems
Anyone

HELP ME!!! PLEASE

[svandamme]

Originally Posted by Porsche fan

Hi,

I replaced the complete fuel line with the two valves and the injectors from an other 944S.
Checked the injectors for shorts between them.
That also didn't work€¤€½¤³½³½¾‘’‘’¾²

Now what?

check the residual pressure said Svandamme.
How do I do that?
But I changed the complete fuel line so that shouldn't be the problem?

Cold engine: black blue smoke, unable to make RPM's. Way too much fuel
Hot engine: No problems, no smoke
Cold engine without the temperature switch connected: No smoke no problems
Anyone

HELP ME!!! PLEASE

residual pressure, put a fuel pressure meter on the rail (there's a plug for it)
then check if the pressure drops in short notice after you turn off the engine

Have you tried replacing the temperature switch??

[Porsche fan]

Hi,

First thanx Stijn for the many replies. I replaced the temperature switch in the beginning.

I'll try to measure the fuel pressure. First buy the meter, ore is there a trick?
But is it necessary? I already changed the complete fuel-line witch the injectors?

Gr,

[svandamme]

borrow a meter


necessary, well yeah, you have to much fuel and you need to troubleshoot systematically
residual pressure will tell you if anything is wrong with that

You have to know what fuel pressure you have under running conditions
and then check if it looses pressure to fast after shutdown

i believe it's 2.5 Bar running (36psi)

and should not drop below 1 BAR after 20 minutes (14.5 psi)

[gtroth]

Yes, you must know the fuel pressure and leak-down, I'm afraid. Clark's garage has the numbers. This meter screws right on to the rail without adapters if you are interested:

http://www.jcwhitney.com/autoparts/Product/Pr-p_Product.CATENTRY_ID:2008126/c-10101/Nty-1/p-2008126/Ntx-mode+matchallpartial/N-10101/tf-Browse/s-10101/Ntk-AllTextSearchGroup?Ntt=star+hoffman

Any other signs of fuel pressure issues (takes a little to long to start when car is warm, fuel pump groans after running a while)?

[Porsche fan]

Bought a meter!
pressure is 4 bar / 55 psi when I run the car..

Is that alright? It can't be the fuel rails or injectors because I changed them. Suggestions?

[svandamme]

that's to much pressure on the rail

[gtroth]

55psi at idle? That would be a bit high for the S/16V (should be 48psi at idle, 55psi is the engine stopped, relay jumpered spec). Also, after stopping engine (or after stopping pump if it's jumpered), does pressure drop to <29psi before 20 minutes?

From Clark's Garage:

Fuel Pressure Specifications

All 8V 944s and 944 Turbos
Engine Stopped - Relay Jumpered 2.5 bar +/- 0.2 bar (36 psig +/- 3 psig)
Engine Running at Idle 2 bar +/- 0.2 bar (29 psig +/- 3 psig)
20 Minute Leakdown Pressure : 1 bar (14.5 psig)


All 16V 944s
Engine Stopped - Relay Jumpered :3 .8 bar +/- 0.2 bar (55 psig +/- 3 psig)
Engine Running at Idle : 3.3 bar +/- 0.2 bar (48 psig +/- 3 psig)
20 Minute Leakdown Pressure : 2 bar (29 psig)

[rmcdonnell]

So this should be your FPR.
I think mine needs changing as well.
Poor start, grumbling until well warm, running rich, sooty exhaust, poor mpg etc.
Aftermarket FPR plus gauge recomendations anyone..?
cheers
Russell

[Jeff Laurence]

I know you changed your temp sensor, but it says in your post that with it disconnected it runs properly?
Check maybe for connections to the DME?
Good luck,
Jeff

[Dean924s]

Just because the temp sensor is new does not meant hat ti is working. I would re visit that. Especially if unplugging it makes it run correctly.