Track Car issues, power cut out

[txhokie4life]

I'm getting power cut outs on track.

Usually full throttle, seems to be later in the day and later in run sessions.

symptom runs from a stutter,
to a slight momentary RPM drop, and return.
to RPMs dropping to 0 and then back to proper state (almost immediately)
to engine cut out, but will refire with a down shift and/or throttle blips
to (only once) complete stall and had to refire with key (which was immediate)

I'm thinking some heat related issue with the speed or crank sensors?

I'm thinking the engine compartment is not getting adequate cooling.

Car is running warm during tracking, but is not over heating.

I know I need better aero ducting, which is my next plan of attack.

Plug wires look decent, fuel injectors have been rebuilt, ignition rotor is in good shape.

thanks for your thoughts in advance.

mike

[S ECU Repair]

Hi, by the symptoms you mention ,the problem can be referred to the DME , cold solder joints ,Overheated capacitors and other components that they are just too old can generate this symptoms specially on the ignition side of the unit .
We will kindly test your unit for free to rule out any problem.

Jose

[kdjones2000]

Does it only happen during hard right hand turns? If so you may be having fuel starvation issues, which can be fixed by replacing the strainer in the fuel tank.

Good luck, Keith

[txhokie4life]

Happens a lot in straights but could be after coming off right handers

I'll check strainer as well
Mike

Does it only happen during hard right hand turns? If so you may be having fuel starvation issues, which can be fixed by replacing the strainer in the fuel tank.



Good luck, Keith

[924RACR]

Unless you're running low on fuel, then yes, I'd be suspicious of crank sensor wiring or DME...

Are you another one of those guys who just starts with a full tank and runs it down? (really dumb idea in a 944, BTW)

[txhokie4life]

I'm pretty new to the whole racing scene -- but
we are running enduros -- so unless there is some reason
not to run with as much fuel as possible -- that is
what we do to reduce the refueling needs.

I've been to one DE (and will do another this weekend)
to improve my driving skills as well as shake down the car.
For that I try to duplicate the racing setup as much as possible
which means starting with a full tank and running at least until
below 1/2 tank.

Mike

[S ECU Repair]

By your description sound more like you have a Ignition Problem due to the fact on how the car is acting and also the Tach loosing signal , i will let the fuel side alone for now .

[924RACR]

Agreed further with S ECU... sounds ignition then.

Some guys who DE don't realize how much the balance of the car changes with fuel load - but sounds like you're on top of it.

[jerryw]

We had a 944Spec racer DNF when the connector on his ignition switch was loose. It vibrated enough that in the middle of the race his engine just died and refused to crank. I'd agree with the diagnosis of ignition issues - add to the above suggestions a check of the ignition switch and wiring.

[txhokie4life]

Hit the track yesterday
Second session battery gave out.
New battery seemed to have it running better

But hesitation in third @ 5200 rpm
Solid below and above

The running good above is quite confusing.

Not sure if hesitates in 4th by the time I would be in 4th ag those rpms
I would be busy with other issues :-). Like braking and downshifting :-)

Have a race in 2 weeks
Would be nice to figure out.

Thanks

Mike

[VaSteve]

Are you another one of those guys who just starts with a full tank and runs it down? (really dumb idea in a 944, BTW)

Why? I don't understand your logic.

[924RACR]

Originally Posted by VaSteve

Why? I don't understand your logic.

As I mentioned in a previous post - it has a massive impact on the balance of the car... which is a really bad idea when you're at a DE and trying to learn how to drive the car. The idea is to remove variables, not add to them.

Remember, the gas tank sits above the rear axle. This means a very significant change in the weight distribution.

[txhokie4life]

I'm blue solo at best -- so I have a lot to learn.

The DE work I have done has been to just get seat time
for the racing (LeMons/ChumpCars) that I have been doing.
Get comfortable at speed, and learning how to drive a momentum car.

That being said -- to me it is about learning how the car feels,
how to pick my lines, and how to approach the edge
of my limits and how to control the car as both our limits are pushed.

I understand at a DE you are looking for consistency, but as the fuel load gets
tossed around the car will behave differently -- I need to be able to compensate
for that. Not sure I know I actually can tell what is causing the difference
in car -- I'm just at the stage where I'm compensating for my flaws
and the quirks of the car at the time.

Therefore, running with various fuel levels actually helps
me prepare for the races. Who knows how much fuel I will
have when I jump in the car.

But I totally can see how all that fuel sloshing around can change the dynamics.

I just know I'm probably not good enough to even notice :-)

m

[VaSteve]

Originally Posted by 924RACR

As I mentioned in a previous post - it has a massive impact on the balance of the car... which is a really bad idea when you're at a DE and trying to learn how to drive the car. The idea is to remove variables, not add to them.

Remember, the gas tank sits above the rear axle. This means a very significant change in the weight distribution.

Sure for racing I guess I take your point. I did some quicky math. Fuel weighs 8 lbs a gallon. Assume a 15 gallon tank. That's 120 lbs. If you run full to empty over a span of a couple of hours I don't think you'll notice too much. It's more dramatic to have a 200 lbs passenger in the car and then they get out (all at once).

For 5 years I fill up in the morning near my house, drive 60 miles to the track with all my gear and spare tires. I barely notice the difference in weight throughout the day.

[924RACR]

It's not the fuel sloshing around, but rather the weight distribution as VASteve points out. Even an extra gallon will make a difference, though modest.

The main point is to be aware of your fuel loading and its effect on the car's balance. Since most DE'ers are simply trying to get a handle on the car at the limit, they're best off running a consistent fuel load. It's no different than setting your tire pressures before you go out. If you fail to do so, you'll likely be surprised by how the car handles.

I've been shocked to find some of the less-prepared racers, let alone DE'ers, not even keeping tabs on their fuel load.

As you burn off gas, the rear of the car gets light, and the car oversteers more and more (gets looser and looser). For those who run with a full tank, and simply burn it off through the day at a DE, this makes a very evil combination with a tired driver at the end of the day pushing for that last second of lap time. If you're not paying attention to it.

That's why we always set our fuel load (typically 1/2 tank) at the beginning of each race session.

As for how significant: on our ITB cars, going from a full tank to 1/4 is about equivalent to at least a 1psi difference in tire pressure front to rear - if not almost two. For those who may question this, note that we will set our tire pressures down to the tenth of a pound for precise tuning.

[txhokie4life]

Originally Posted by 924RACR

As for how significant: on our ITB cars, going from a full tank to 1/4 is about equivalent to at least a 1psi difference in tire pressure front to rear - if not almost two. For those who may question this, note that we will set our tire pressures down to the tenth of a pound for precise tuning.

Thus the difference between the PROS and us weekend warriors (wannabes) :-)

Thanks for your inputs,

mike

[924RACR]

LOL... we're all weekend warriors! Some of us just take it too seriously...

Cheers...