Lean Versus Rich Symptoms
 

In the race last weekend, my car ran great except for the fact that above 3/4 throttle opening it would fall flat on its face and if I reduced the throttle opening it would instantly pick back up and pull hard all the way to redline. It wasn't a one time thing, but consistent, repeatable and demonstrated no other effects other than the flattening of power pull.

So I know that the car was either going full rich or going full lean and I couldn't tell on my wideband as it would just show "---" on the gauge so the ratio was out of the range that the gauge could read. As I was driving the car for most of the race and was getting great flame balls out of the tail pipe on overrun, the pipes look very clean and the plugs look fine as well.

So the question I have is how from the drivers seat to you determine if its a lean condition or a rich condition? I would believe that a lean condition would manifest itself as an abrupt drop off in power or a stall. A rich condition would manifest itself as a gurgleing and a few coughs as it cleaned itself out. The car did neither, it would just go "blaaahhhh" when I exceeded 3/4 throttle opening and instantly come back as I reduced the opening and would still rev cleanly and relatively hard all the way to 8500 rpm. The TPS still shows a reading on its complete sweep, so that looks good still.

The timing is set at a constant 20 degrees at all rpm.

Ideas?

Eric

my P port did that when i ran the butt plug for sound, it just didn't work anymore.

weather you can feel if its rich or lean depends HOW rich or lean it is. if its a little teeny bit, it can feel different, but if you're way off, then they feel the same.

What size is the stock fuel lines. I am wondering if I am running out of fuel flow capability from the fuel pump. I am running stock lines with a 255 lph pump and I wonder if they are too small or if I have a restriction in my fuel system somewhere? It doesn't do this at smaller tracks with shorter straights, only at Mosport with the long long straights.

Eric

stock fuel lines are 8mm, which should be more than enough. you should probably change the filters and put a fuel pressure gauge on it. fuel pump should be enough, but maybe its worn out, or if it was cheap a chinese copy

Thats exactly what I am going to do. Gives me something intersting to do this weekend and get all gas smelling again! whoo hoo........

Eric

Are you carb'd or efi?


(I know your running a 255lph pump, but you could be regulating it down for carb use like I used to)

EFI setup.

What kind of engine management are you running? By the way you describe it I would almost assume a bad tps. Maybe you could data log while its happening. Earlier this year I was having fuel starvation issue due to a kinked hose going to my fuel pumps inlet, and when I would lose pressure during longer straits , the power would start to fall off or flatten out, and would start leaning out according to my wideband, and suddenly it would buck violently when the pressure was too low to to actualy spray out of the injector

between the plugs and pipes, i would tend to lean toward a situation where it's leaning out for whatever reason. i'm not sure if a rich condition could cover it's tracks as well as a lean one - even if the plugs got clean with time and use, i doubt the pipes would. the fuel pump idea is probably BEST right now. look into it.

that said, i would also look a little closer at the TPS even though you said your initial finding is that it's detecting the full sweep. the post above mine asked about logs. do you have any feature that gives you access to a timing log? it might shine more light on what is happening since it seems like something you would be able to recreate BEFORE making any changes.

I am running a Megasquirt, but have left that whole side of it up to my missing crewchief. I will need to learn about how to capture the data logs off the Megasquirt first before I can show them.

Eric

i thought of your thread while i was reading this one:
https://www.rx7club.com/2nd-generati...pikes-1046982/

i don't know if it will provide any insights or not, but i figured it couldn't hurt. hope all goes well with your issues.

1

Your post got me thinking, so I checked the sweep of the TPS again and it was fine. I checked the MAP again and it was fine up to 9500 rpm and the Megasquirt extrapolates from there. So I was stumped. Then I decided to check where the throttle position was where I felt the car falling flat on its face and it was reading 230 mv's or something. Then I checked where the idle was and it was reading 60 mv's or something. So I then decided to check the fuel MAP to see what was happening and "BING" the max TPS reading on the left side was 230 at 9500 rpm....., but the tps went to 255 at full throttle so it was a mismatch on the settings. I changed the top bin to reflect a TPS reading of 255, moved the next one down to 220 and the one below I left the way it was.

Duh.... I finally had to figure out how to setup the Megasquirt as I am doing it myself now and now I know how to set it up and I am going out testing on Sunday to see if that was the problem. I think it is.

Eric

an afr guage would help you a lot with tuning.. takes the guesswork out of it

Rotaries will run remarkably well extremely rich, and they'll also run decently when running too lean.

I used to notice a kind of light misfire under full throttle on the finish straight that we tend to end our courses with. Full throttle 7000-9000rpm pull after a minute or two of constant cornering. I would notice it more by the audio in the GoPro helmetcam more than I'd notice it in the car, given that I tend to be rather busy in the moment.

After I installed my surge tank system, that went away entirely. So, it was fuel starving after the pump would suck air. Because I'm using a rattlebox pump to keep the surge tank fed, one can tell immediately when the tank pickup is sucking air - the pump gets very loud and fast. Turns out, my fuel pickup will suck air at anything under 1/2 tank under certain conditions. The fuel pump is mounted in the stock location under the driver's seat, so there is a large area for air to get stuck in that line. Now, I have a ~700ml tank of fuel and a gravity feed from it directly to the high pressure pump, so I can go for most a run with no problem while the feed pump is sucking air.

For an example, this is me with 1/4 tank. There is a slight banking to the right at the starting line, and you can hear that the feed pump is rattling away sucking air...

i didn't hear your noise, but that looks like huge fun

An A/F gauge is a good tool, but can lie and actually imply the opposite of whats really happening. The gauge only really reads oxygen content, so regardless if you are running lean, or misfiring (can be a rich mis, lean mis, or an ignition failure) the sensor will see an abundance of oxygen and tell you that its running lean. When everything is operating within a certain margin, the sensor will be very valuable , but when running outside of the margin or when there is a severe fault/failure, the sensor will be a hinderence and counter porductive until you find the root cause of the problem