HansB

Strange things happening:
The other day we tuned my track only car to run 12,2 at WOT (measured with a wide band sensor). Ran just fine and stable for two hours.

In the afternoon the ambient temperature rose with 10 degrees.
Car ran fine again, 12,2 but after a few laps the mixture started getting leaner and leaner, till about 15,5 at which point I stopped. Engine also ran really hot.

I let the car cool down, tried it again, started at 12.7 and after a few laps the same effect. really lean and hot again.

What can cause this effect? And, what can be done about this?

ehall

I can't give you tecnical feedback, but here in Florida, where the temp was 96 F with a humiture of 106F, my car runs like a beetle. I too would like to know more about the science behind this issue, which is why I posted this.

fast951

Hans, check your fuel pressure (if possible) while under load. Your fuel pump might be on its way out.

Peckster

At higher temps air is a lot less dense. Not sure why it would rise after a couple of laps, unless your intake is inside the hood where it gets even hotter as the motor heats up?

HansB

John, we will replace the fuel pump with a stronger one, does not hurt to try. The fuel pump is one of the few origingal parts left on the car.

Peckster, the intake is under the hood, and it certainly gets hot there.
We will get some more cold air in there.
Two Q's:
1. Is not the temperature compensation from the MAF supposed to take care of this?
2. I have read in a couple of threads that direct cold air RAM on the MAF is not advisable?

Thx.

special tool

Hans - I will tell you - This sounds like a melted or disconnected vacuum line from the fuel pressure regulator. This will give these exact symptoms.
Your AFR will look good till about 7 psi or so, then the lack of rising rate will catch up to you.
Those lines are in series, so check those stupid rubber tees under the manifold for cracks.

cpt_koolbeenz

Yeah I agree with ST... Hotter temps would generally make you run richer if your compensating sensors went out... See if your problem changes with boost...

HansB

We thought of that, replaced all vacuum lines recently. To no avail.

Makes sense.

Tried that. At lower boost (12 psi, which is the spring of the Tial WG) the engine runs leaner.

Any additional views?

RobNL

Could it be the other way around that the mixture is getting leaner due to the fact that the engine is getting really hot? Doesn't the DME take into account the signal of the engine temperature sensor or it that only for enrichment when the engine is cold?

Hans, have you checked why your engine is getting really hot?
- Fans not running
- Air inside the hoses
- Waterpump not working properly
- Thermostat

HansB

Yes, Rob, it seems this way. If we limit the stints we drive to 5 laps (20km, 10-15 min) at a time, the temperature and the mixture stays stable.

Question: What thermal effect could cause an engine to run lean? Seems to be something in the fuel delivery path. Fuel pump, AFR, Fuel rail, injectors?

All brand new and working

Theo951

Check that the NTC II is OK. Mesure the resistance at hot engine agains /www.clarks-garage.com/ figures. It makes huge difference in AFR if NTC II became faulty.
Also the NTC I at your MAF should be OK. No contact with hot metals allowed. Need to measure only hot air. Cut one wire ( open circuit) the NTC I when problem occurs and make a run.
I have also notice a minor lean condition when the engine is realy hot in the whole curve, but not the problem you are facing.
Kr
Theo

HansB

Theo, stupid Q: Where do I find this in clarks-garage? Hans

Theo951

Go to http://www.clarks-garage.com/
From there click on: Clark's Garage Shop Manual
From there click on letter "S" for "Sensors and Gauges" > Information, Troubleshooting, and Testing > DME Temperature Sensor Testing
You do not need to go through the whole procedure, because if you had a poor connnection (high ressistance) you go reacher, but your case is lean.
Run the engine exact at 80 °C (176 °F) and remove the connector.
Measure 280-360 ohms via Ohmetter direct at the pins of the sensor. Lower than 280 (worst case short Circuit) indicates a fault NTC II reflecting the problem you have.
BTW: You can get an 360 Ohms resistance and connect it to female connector when engine is warm.
Get some runs and see if AFR is stable. If is AFR stable NTC II is faulty.
If you have MAF check also the NTC I, if you have one. It may be short or contacted to metal causing lean condition thermaly or electricaly. Cut one wire to triger reach condition via DME.
If nothing helps you are facing a mechanical problem.
BTW verify also if the full load singal is delivered to KLR via the test connector under the hood.
If you are so far, let me know how to do this.
Good Luck
Theo