3.2 engine in track car getting lean after 10 min.

[maad914]

Hi all
I have a problem which seems hard to solve.
I'am racing my car in Roadsport track class in Finland.
Last weekend in our 3th and 4th race i had problems with engine as it started to go lean after 10-12min. hard driving. Datalog shows nothing changing but after about 10min. lambda curve starts to drop and it is in a bottom after another minute.
Engine is otherwise stock but the FI is programmable, heads have been worked and headers are homemade.
According to datalog, intake air temp max is 42c and oil max 92c.
Fuel pump capasity is about 120liter/hour and it is measured with back pressure.
Engine was fine in dyno about year ago but now it does this.
I think lambda metering is fine because sparks shows that really goes lean.
There is small differences in spark plug colors but nothing major.

Any idea's and help would be more than wellcome.

Thanks
Mika

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bogeyracing.com

[Steve W]

Let me guess, your fuel tank has no venting?

[maad914]

There is vent which is routed to front wheel well and has air cleaner in it.

[Tyson Schmidt]

Tank venting was my first thought as well.

Maybe the fuel pump is on it's way out. I'd try to moniter fuel pressure when this happens.

[maad914]

Ok. i'll check the venting once again and change fuel pump's just to be sure.
I have a pressure guage in fuel rail and i will add an electric one which i can monitor during driving. I will also add fuel pressure to my data log.

Thanks, i'll let you know how it goes.

-Mika-

[Porsche84]

I agree with fuel tank venting. I lost 2 3.2 engines before I solved this problem on my car. My engine had euro pistons and detonated and sattered the top piston rings. The metal then did more damage. It was not pretty.

Good luck

[maad914]

thanks Jerry. Sorry about your engines. I have had problems with bottom end and 3th crank is now in. What size was your vent line? I have one which is about 8mm inside is that too small?

Regards
Mika

[beepbeep]

Of course, check fuel pressure to begin with.

One more thing to check are EFI maps. You might be running on warmup enrichment. Aircooled engines don't warm up the same way as watercooled ones, so your EFI might be configured to switch to "warm engine" map when sensor says it's hot...what I'm saying is that you might have dynoed it on "cold engine" setting by mistake?

It varies from EFI to EFI but it might be worth checking...

If you have LM1 with AuxBox you can also log injector duty cycle. That way, you can check if it's EFI that is leaning out or if it's fuel-related issue.

[ChrisBennet]

The simplest way to tell if the tank is not venting is to listen for the "whoosh" when you loosen the gas cap...
(Another member of the bad-gas-tank-venting-blow-an-engine-club.)
-Chris

[cstreit]

I cross-drilled my gas tank to avoid these issues... Also the brake lines to prevent gas-build-up.

Seriously though I'd check the tank straightaway. Does it seem to happen more on an empty vs. full tank?

Have you checked your warmup sensor output in your logger? As a test you might temporarily re-map your "hot" setting with your cold map and see if it goes away. Or reset when it makes the map switch...

[maad914]

Tank seems to breath as it does not swoosh when i open the cap even after hard driving.
Warm Up settings were the first one what we suspected. We were actually over the warm-up celcius all the time. All the optio maps, ignition- and fuel maps has been checked, nothing wrong in there. We only have warmup map in use when it's idling and as soon as i hit the gas pedal, it starts to use normal maps.

I changed the fuel pump, did some serious test driving in streets and there wasn't any problem. Next saturday we will get the change to drive it in track and that will show if it's cured.

-Mika-

[maad914]

Hi again
Car does not work. I changed the warm up maps and still it wasn't better.
according to data log it is mostly ok when the engine temp is under 80 and intake air is under 50 but not always.
What do you think, could it be the injectors? Could those loose their power when they get hot? Duty cycle of injectors is max 93%, is that too much? Those are original 231hp 3.2 engines injectors and the engine has 270hp dynoed. I'm running out of ideas. I was leading the the race and the next one was almost half a lap behind when it went lean and i had to pull over.

Thanks
Mika

[Ken911]

mine is doing the same thing it's a euro 3.2 and it runs fine until it gets warm then starts pinging, usually 3rd gear at 3000rpm, lately has been getting a little worse, how do i check the gas vent problem? drive it with the gas cap off and see if any difference? been through the checking for bad gas etc. also did the switch on the computer with all the different timing and erichment settings, and it still pings

[Tyson Schmidt]

Originally posted by maad914
Hi again
Car does not work. I changed the warm up maps and still it wasn't better.
according to data log it is mostly ok when the engine temp is under 80 and intake air is under 50 but not always.
What do you think, could it be the injectors? Could those loose their power when they get hot? Duty cycle of injectors is max 93%, is that too much? Those are original 231hp 3.2 engines injectors and the engine has 270hp dynoed. I'm running out of ideas. I was leading the the race and the next one was almost half a lap behind when it went lean and i had to pull over.

Thanks
Mika

Mika, those injectors should be just fine. If you are at 93% duty cycle, and feel you need more fuel, then up the fuel pressure. That's all Porsche did when they went to the 3.6.

[maad914]

Yeehaa
Engine is working again!
Last weekend we did again some testing and just before time trials we finally changed the coil and o2 sensor, we also took the intake air temp sensor off and now the engine works ok. Next weekend i will try what exatly was the cure.

Mika

[Ken911]

ok so should i try disconnecting the intake air temp sensor , the O2 sensor is already disconnected, ?

[klatinn]

Hi,

You said "Lambda curve is starting to drop"?

Are you reading off the stock Narrowband sensor?
If so, that is fairly normal, as on the rich side of stoich the NBO2 sensor output is much more dependent on sensor temp than on AFR. The output voltage (for constant AFR) drops as the sensor gets hotter. IF you are reading a NBO2 you might just have gotten the sensor warm with some hard driving.

Regards,
Klaus

[WydRyd]

Perhaps check your cylinder head temp sensor is functioning correctly. It's the only thing that affects cold/hot performance I believe.