A/F reading overly Rich ?

[Buick GSX]

This question is for a Drag race engine, v8 with wide band A/F sensors in each header tube, Motor has a 4500 Carb. GM Cyl numbering. NA single carb, Fuel Q16, making a little north of 1000HP.

How will the sensors read if overly rich and fuel is burning in the header?
Similar to a plug wire pulled?

Next I have some data from last week that is confusing me, over 3 runs I increased jets and the RH side of the motor responded as I would have expected, However the LH side went leaner as I added Jets?????

Run 1
DA 1338

LH jet 133 RH jet 137
Cyl 1 = 0.86 Cyl 2=0.91
Cyl 3 = 0.87 Cyl 4=0.90
Cyl 5 = 0.91 Cyl 6=0.93
Cyl 7 = 0.86 Cyl 8=0.91

Run 2
DA 994

LH jet 135 RH jet 140
Cyl 1 = 0.93 Cyl 2=0.85
Cyl 3 = 0.93 Cyl 4=0.86
Cyl 5 = 1.00 Cyl 6=0.89
Cyl 7 = 0.97 Cyl 8=0.87

Run 3
DA 619

LH jet 138 RH jet 140
Cyl 1 = 0.93 Cyl 2=0.86
Cyl 3 = 0.93 Cyl 4=0.87
Cyl 5 = 1.00 Cyl 6=0.90
Cyl 7 = 0.98 Cyl 8=0.88

Thanks for the help in advance

[rebelrouser]

Where is the O2 located in the header? And do you have any exhaust leaks at the flange? Any extra oxygen introduced into the exhaust stream will really affect your O2 readings. If the O2 is in the collector, it may pull oxygen into the tubes during the overlap period.

[David Redszus]

This question is for a Drag race engine, v8 with wide band A/F sensors in each header tube, Motor has a 4500 Carb. GM Cyl numbering. NA single carb, Fuel Q16, making a little north of 1000HP.

How will the sensors read if overly rich and fuel is burning in the header?
Similar to a plug wire pulled?

Next I have some data from last week that is confusing me, over 3 runs I increased jets and the RH side of the motor responded as I would have expected, However the LH side went leaner as I added Jets?????

Run 1
DA 1338

LH jet 133 RH jet 137
Cyl 1 = 0.86 Cyl 2=0.91
Cyl 3 = 0.87 Cyl 4=0.90
Cyl 5 = 0.91 Cyl 6=0.93
Cyl 7 = 0.86 Cyl 8=0.91

Run 2
DA 994

LH jet 135 RH jet 140
Cyl 1 = 0.93 Cyl 2=0.85
Cyl 3 = 0.93 Cyl 4=0.86
Cyl 5 = 1.00 Cyl 6=0.89
Cyl 7 = 0.97 Cyl 8=0.87

Run 3
DA 619

LH jet 138 RH jet 140
Cyl 1 = 0.93 Cyl 2=0.86
Cyl 3 = 0.93 Cyl 4=0.87
Cyl 5 = 1.00 Cyl 6=0.90
Cyl 7 = 0.98 Cyl 8=0.88

Thanks for the help in advance

Compare runs 2 and 3.
Note that RH readings remain unchanged with 140 jet.
But, LH reading also unchanged in spite of jet change from 135 to 138.
Look for air leak or misfires in LH bank.

[Warp Speed]

I would say the carb needs work. Not able to flow enough Q for the engine. When jet changes stop working, its typically in the carb circuits, as long as supply to the bowls is adequate.

[Dave Koehler]

Just curious. Did your ETs and speed change at all with the jet change?

[Buick GSX]

Where is the O2 located in the header? And do you have any exhaust leaks at the flange? Any extra oxygen introduced into the exhaust stream will really affect your O2 readings. If the O2 is in the collector, it may pull oxygen into the tubes during the overlap period.

They are as close to 18" from the flange as possible. One in each tube.

The readings are the average from just after entering High gear until just before Throttle Closes at the end of the run.

No leaks that I can find. Please look at the data from all 3 runs, the only change was jetting ???

Thanks

[Buick GSX]

Compare runs 2 and 3.
Note that RH readings remain unchanged with 140 jet.
But, LH reading also unchanged in spite of jet change from 135 to 138.
Look for air leak or misfires in LH bank.
[/quote]

With the first jet increase on the LH side the bank got leaner, then the next change it remained the same?

Will misfires, and or fuel burning in the header produce a AF reading that is leaner???



Thanks

[Buick GSX]

I would say the carb needs work. Not able to flow enough Q for the engine. When jet changes stop working, its typically in the carb circuits, as long as supply to the bowls is adequate.

This is a Book 4500 about 3 years old, which I have owned since new. We did clean all the air bleeds every good (removed and carb. cleaner washed, 1 by 1 ensuring nothing was crossed up) a few weeks back looking for a solution to this issue. Cleaning the air bleeds produced no change.


With one LH jet in the front and the other LH jet in the rear, each sharing the bowl with the RH jet which is responding to changes, I will conclude the supply is adequate in the bowls and the issue should be in the internal circuits.

I will take your advice and clean all the internal ports with carb. cleaner before the next time out.

Thanks

Any idea on why from run 1 to run 2 the LH bank went way leaner??? Gaskets are newer and look good

[jmarkaudio]

Misfires will spike off the chart, unless you are doing massive smoothing. What size carb, throttle bore, venturi? What metering blocks?

[Buick GSX]

Just curious. Did your ETs and speed change at all with the jet change?

Yes Run 2 the track was colder and the 60' was 0.040 slower, however all the splits were faster with the overall et being 0.058 faster.

1/8 picked up 1.2 mph, 1/4 picked up 1.3 mph R2 being faster.

R3 had no useful clock data as we spun, after gathering it up, I drove it out just for the AF data

Thanks

[Buick GSX]

Misfires will spike off the chart, unless you are doing massive smoothing. What size carb, throttle bore, venturi? What metering blocks?

Sorry to ask dumb questions, how will misfires spike? lean or rich?? I assume (not a good thing to do) it would spike very Fat due to large amounts of un-burned fuel?

How do they react to fuel burning in the header? from a very over rich condition?

Carb is a 4500 with 2.125 bores, metering blocks and all carb work from Bob Book. carb was built for this engine.

AF circuits have a smoothing of 3 in them

Thanks

[jmarkaudio]

Spikes lean off the chart. If you have too much smoothing it will mask it. The metering block will have a number, 5170, 5120, etc...

[rebelrouser]

Misfires will spike off the chart, unless you are doing massive smoothing. What size carb, throttle bore, venturi? What metering blocks?

Sorry to ask dumb questions, how will misfires spike? lean or rich?? I assume (not a good thing to do) it would spike very Fat due to large amounts of un-burned fuel?

How do they react to fuel burning in the header? from a very over rich condition?

Carb is a 4500 with 2.125 bores, metering blocks and all carb work from Bob Book. carb was built for this engine.

AF circuits have a smoothing of 3 in them

Thanks

O2 sensors make voltage using a chemical reaction with the unburned oxygen in the exhaust stream. If you have a misfire that oxygen did not get burned. leaded racing fuels will also foul sensors and make them read funny as well.

http://www.autotap.com/techlibrary/unde ... ensors.asp