"Flat spot" in my engine

#1

Last Sunday, we had planned to dyno cars at Summit Point but the dyno wasn’t working properly, due to heavy rain Saturday night.

I was hoping to see on a dyno chart, where my "flat spot" starts and where it ends, and am hoping someone might shed some light on the cause.

At about 4600 rpm, the engine power seems to flatten-out some. It comes back on at about 5200 and pulls as strongly as any other car, right up to the redline.

This flat spot gave Chris and David a three car-length jump off a couple of the corners at Summit last weekend.

I know the difference in exit speed and how it affects performance and lap times. This is a distinct but mild hesitation in the engine power. It feels as if I had let off the throttle slightly.

Any suggestions?

Carter

#2

the weird part about what you are saying is that it picks back up at 5200. I think we all are familiar with the infamous M20 dip in power around 3500 rpms, but I have never heard about it up in the high 4’s.
try swapping out another ecu and see if you get the same situation.

any idea the last time the injectors were cleaned?

why am I helping you, I need you to lose all the power in the world if I am going to catch up. Disregard above comments and immediately check your headlight switch, I am sure it is the problem.

#3

Is it flat going straight, or only in the turns?

Tom

#4

Carter

I think it sounds like a problem Chris had with his E30 back in May. I cant place my finger on the name of the part. But there is a cable in the engine compartment that can go bad. Sean Thompson knows quite a bit about it, he helped diagx Chris E30, I find the name of the part.

#5

I emailed Sean, so he can give us the source of the problem and see if that releated

#6

When Sean and Chris were diagx the problem they swaped out the ECU and that WASNT the problem. The car hesitated about 5k rpm

#7

I think its the reference sensor, The cable can short out, since it tells the ECU what the crank position is, a faulty one would certainly cause problems

#8

Thanks for the replies. I’ll try to find it, using these messages as a reference.

Carter

#9

Carter:
I had this problem when I built my new engine last summer. I was at Patriot course and experienced the same thing. Guess what it was! mY OxYgen Sensor! I also took my car over to a dyno shop in Raleigh before finding this out, saw the flat DROP on the dyno chart, a friend suggested we unplug the O2 sensor, and POOF! IT was Fixed! The car was running really lean before and after the O2 sensor was unplugged, so we addressed that, then it ran fine! Unplug that O2 sensor and see what happens! --Great, I have just given Carter even more help to walk away from me on track…heh.
Peace,
Forrest

#10

Forrest:

For your first time at Summit, you turned some very respectable times.

And thanks for the tip. I’ll try it at VIR Sunday. If it fixes it, I’ll buy your dinner at the next race weekend.

Carter

#11

Inquiring minds want to know??? What fixed it…

#12

Yes, what was the root cause?