Dyno Run / Erratic Air Fuel ratio

[Rusty Heap]

see the attached dyno chart, and help me understand the erratic air fuel ratio bouncing all over the place.

Car engine spec's in my signature line.

The o2 sensor has been disconnected, not even wired up on John Walkers advice, plus he says that at WOT it is bypassed anyways.

SSI's have the o2 sensor hole plugged, but I'm having him re-install the sensor in as we speak to see if this helps.

Other 911's that ran that day had dead flat air/fuel ratios. Walker thinks maybe clogged injectors? It's running pretty lean too.

I was also dissapointed in the "only" 167 h.p, as another 3.0 L in another 1979 911SC that pulled 179 with my same mods but with stock cams and not my web 20/21 cams. That really bummed me out! but I did gain the air/fuel knowledge.

Walker set the idle A/F mixture on the rich side....

Any ideas on fixing the air/fuel ratio at WOT?

[timcantrell]

Are you still running the CIS? CIS does not like a cam that provides a lot of valve overlap.

[Rusty Heap]

Yup, still have the CIS stock unit.

[Steve W]

that looks more like there's something wrong with the dyno's wideband than your air fuel ratio. There's no way your air fuel ratio is running so flat like that.

[Rusty Heap]

Well check out how flat this other 3.0L air fuel ratio is, and we ran back to back on the dyno.

"splain this to me" what do you mean by wideband of the dyno?

[Rusty Heap]

Once again the master John Walker has the answers, I'm fortunate to give him all my money to wrench on my rig.

He's adjusting my valves after the web 20/21 cam break in, and found this out when working on the motor.

"The frequency valve plug was not connected. i know it was on when it left here, that would certainly cause the fuel problem. when the freq valve isn't working, the car feels like it's dragging an anchor." Spoken like the fine master mechanic he is.......

And thanks to our fine host: see part 77 here:

http://www.pelicanparts.com/cgi-bin/PartsLookup/search.cgi?command=show_page&Catalog_Name=911_USA_78_83_KATALOG&Illustration=107-15&Line_Item=77

I'll take it back to the dyno, and see what improves.

THANKS JOHN!

[Steve W]

The wideband is the wideband O2 sensor that is used to sample an measure the oxygen content in the exhaust the determine the AFR. Not to say that that isn't really your AFR curve, but I have never seen an AFR curve on a Dynojet come in at such a flat line of 15.0 with not even a deviation of 0.1(ignoring the noise spikes) unless there was a fault with the wideband pump system. The second dyno you've posted is what is normal and would be expected, as it has a curve that smoothly varies from 13.0, down to about 12.2, and back up to 13.0.

However if you really are running somewhere that lean at 15, connecting the frequency valve so you are getting closer to 12.5-13 would be good for at least 15-20 hp. Good luck.

[Lorenfb]

"The second dyno you've posted is what is normal and would be expected, as it has a curve that smoothly varies from 13.0, down to about 12.2, and back up to 13.0."

Here comes the hyberbole again;

12.2 ????????? PLEASE!

What's the error in printing/reading the graph much less printing/reading it to tenths?

A real joke, but what would you expect?

"The frequency valve plug was not connected."

As has been noted, a disconnected FV will cause the AFR to be on the high side
as will:

1. low overall fuel pressure
2. a mis-adjusted WUR
3. a mis-adjusted fuel distributor mixture screw
4. a bad Lambda control unit
5. a bad O2 sensor (when connected)
6. a bad FV

[Steve W]

WTF is your problem?

Edit: keep editing away - the point of your post is .... ??

[willf]

you are a lucky guy to have Walker spending time with that 911. So now that the FV is hooked up; how does it feel?

[Rusty Heap]

picking the car up tonight, so will post if it feels better, and another dyno run to verify proper air/fuel metering.

[Wavey]

Originally Posted by Lorenfb

12.2 ????????? PLEASE!

Every time you shout "PLEASE!", I can just picture you with one hand on your hip, flipping your head back, and tossing a feather boa over your shoulder with a cigarette holder in your other hand. You know, like Ru Paul.