FI injection mixture problem?

**Richard G.** · October 9, 2010, 12:12 AM

Re: FI injection mixture problem?

I have graphed the air fuel ratios in excel.
See if it makes it any easier to understand.
Rick

Attached Files

fuel inj air fuel mix excel.png (17.9 KB, 49 views)

**Mike R.** · October 9, 2010, 01:11 AM

Re: FI injection mixture problem?

Thanks Richard. I have it in Innovate's Logworks graph format but coverted to tabular because most people won't have Logworks and I wasn't smart enough to do it in Excel

Mike

Originally posted by Richard Geier (7745)

I have graphed the air fuel ratios in excel.
See if it makes it any easier to understand.
Rick

**Joe C.** · October 9, 2010, 06:41 AM

Re: FI injection mixture problem?

WOT A/F ratio for maximum power should be between 12.5:1 and 13.0:1. Your numbers look very good!

**Mike R.** · October 9, 2010, 09:27 AM

Re: FI injection mixture problem?

Thanks for weighing in. The displayed data is about as good as I can get in the current condition. What is not apparant in the excel graph is that the mixture first gets richer then leaner. This occurs on both sides but somewhat less on one than the other. All this is easier to see in the expanded graph in Logworks. The question is why it first gets leaner then richer. One possibility is an intermitant ignition miss. The problem with this idea is that it is occuring on both sides but less on one than the other. My understanding is that the K66 TI system pretty much either works or not.

Mike

Originally posted by Joe Ciaravino (32899)

WOT A/F ratio for maximum power should be between 12.5:1 and 13.0:1. Your numbers look very good!

**Richard G.** · October 9, 2010, 02:05 PM

Re: FI injection mixture problem?

I love to see modern techniques used on the old motors. I am always wondering where we were in terms of emissions and power levels and in this case A/F mixtures. Especially before the feedback loops and computers. I would like to see this same data on a 365 HP motor. How much difference did the injection make? Thanks
Rick

**Joe C.** · October 9, 2010, 04:52 PM

Re: FI injection mixture problem?

Originally posted by Mike Rapoport (50767)

Thanks for weighing in. The displayed data is about as good as I can get in the current condition. What is not apparant in the excel graph is that the mixture first gets richer then leaner. This occurs on both sides but somewhat less on one than the other. All this is easier to see in the expanded graph in Logworks. The question is why it first gets leaner then richer. One possibility is an intermitant ignition miss. The problem with this idea is that it is occuring on both sides but less on one than the other. My understanding is that the K66 TI system pretty much either works or not.

Mike

Oh, yes it is. Throw out those first few lines of data, as the wideband has to stabilize for the first couple seconds. After doing so, you have a perfectly acceptable dataset showing (about)12.5:1 @ 1750, slowly climbing to (about) 13.2 @ 6400. The only anomaly that I see is that last dropoff and erratic section between 6400 and 6600, when you got out of the throttle.

This area might be explained away as a misfire, as you said, but as you might already know, an intermittent misfire will often show up as a LEAN, that's right, lean condition rather than as rich. Why? Because the wideband O2 sensor is not actually measuring air-fuel ratio, per se. What it IS measuring is oxygen content of the exhaust stream. If you have intermittent misfire, you will have a higher concentration of free oxygen molecules in the exhaust stream. Guess what the O2 sensor thinks about that?

I am not familiar with the Rochester fuel unit, so can only speculate on this last 200 RPM worth of data. Try posting your question here:

Page not found – Innovate Motorsports

http://www.innovatemotorsports.com/forums/index.php

although I doubt whether anybody there is familiar with much more than EFI systems. It's worth a try.

One more thought: as you increase RPM @ WOT (WOT implies maximum possible VE for ambient conditions), the maximum cylinder pressures increase, making the charge somewhat harder to ignite. Getting back to the misfire theory: are you working with a fresh set of spark plugs? If the answer is YES, then try short gapping them at .025" instead of .035", as a one shot deal.........a test which will remove misfire due to insufficient voltage from the equation. Do not run the engine for very long like this, because you will foul plugs under normal driving conditions.

**Mike R.** · October 9, 2010, 07:49 PM

Re: FI injection mixture problem?

I realize that failure to ignite shows up as lean. I decided to start my winter corvette projects today. I pulled the trans and will be removing the engine this week for some head work and to see what I have for connecting rods.

I recall that the highest cylinder pressures occur at the torque peak and not the HP peak. I suspect that if there is a misfire it is a defect in the TI module or coil. I actually bought some new plugs yesterday to see if it made a difference but didn't try them

Originally posted by Joe Ciaravino (32899)

Oh, yes it is. Throw out those first few lines of data, as the wideband has to stabilize for the first couple seconds. After doing so, you have a perfectly acceptable dataset showing (about)12.5:1 @ 1750, slowly climbing to (about) 13.2 @ 6400. The only anomaly that I see is that last dropoff and erratic section between 6400 and 6600, when you got out of the throttle.

This area might be explained away as a misfire, as you said, but as you might already know, an intermittent misfire will often show up as a LEAN, that's right, lean condition rather than as rich. Why? Because the wideband O2 sensor is not actually measuring air-fuel ratio, per se. What it IS measuring is oxygen content of the exhaust stream. If you have intermittent misfire, you will have a higher concentration of free oxygen molecules in the exhaust stream. Guess what the O2 sensor thinks about that?

I am not familiar with the Rochester fuel unit, so can only speculate on this last 200 RPM worth of data. Try posting your question here:

Page not found – Innovate Motorsports

http://www.innovatemotorsports.com/forums/index.php

although I doubt whether anybody there is familiar with much more than EFI systems. It's worth a try.

One more thought: as you increase RPM @ WOT (WOT implies maximum possible VE for ambient conditions), the maximum cylinder pressures increase, making the charge somewhat harder to ignite. Getting back to the misfire theory: are you working with a fresh set of spark plugs? If the answer is YES, then try short gapping them at .025" instead of .035", as a one shot deal.........a test which will remove misfire due to insufficient voltage from the equation. Do not run the engine for very long like this, because you will foul plugs under normal driving conditions.

**G B.** · October 10, 2010, 08:00 AM

Re: FI injection mixture problem?

I've been calibrating Rochester FI units on a Dyno-Jet chassis dynamometer for the last couple of years. I have print-outs from all those runs.

If you're interested in my comments about your results, you're welcome to call me at (251) 478-4003 between 8 am and 9 pm Central time.

**Dick W.** · October 10, 2010, 08:58 AM

Re: FI injection mixture problem?

Mike, you have an offer from the expert, Jerry Bramlett, take him up and call him. He is recognized as one of the premier experts on FI

**Mike R.** · October 10, 2010, 11:45 AM

Re: FI injection mixture problem?

I agree and it was great to talk to Jerry. I learned a lot. It is always useful when working on vintage mechanical devices to know what is typical and also the limit of what is achievable. After talking to Jerry, I realize that my fuel curve is fairly typical but could be improved somewhat. We always want everything to work as well as possible and we need to know what is possible or we will never get to drive our cars. Even on modern EFI engines AFR vacillates between two points defined by the narrow band O2 sensors.

I also learned some more details about the system and have concluded that some very clever people worked at Rochester 50yrs ago!

I'm off to disassemble my M21 which doesn't like downshifting into second...its easy to see why the synchro sleeve does not want to engage the worn tips on the synchro ring...something I can remedy today

Mike

Originally posted by Dick Whittington (8804)

Mike, you have an offer from the expert, Jerry Bramlett, take him up and call him. He is recognized as one of the premier experts on FI

**Jerry G.** · October 16, 2010, 10:08 PM

Re: FI injection mixture problem?

Originally posted by Richard Geier (7745)

I have graphed the air fuel ratios in excel.
See if it makes it any easier to understand.
Rick

Did you take data from both the right and left exhaust pipes? I have found a significant difference in side to side. I haven't found the reason yet. It's probably a problem in the spider or on nozzle.

**Mike R.** · October 16, 2010, 10:14 PM

Re: FI injection mixture problem?

Yes and both sides are pretty close and follow the same pattern.

Mike

Originally posted by Jerry Gollnick (8575)

Did you take data from both the right and left exhaust pipes? I have found a significant difference in side to side. I haven't found the reason yet. It's probably a problem in the spider or on nozzle.

FI injection mixture problem?

FI injection mixture problem?

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