I recently found a better ground for my Lindsey Air/Fuel ratio meter and am getting much more accurate readings. One thing of concern though, with my current set-up the car is capable of over 10 psi of boost while still under part throttle operation. The meter shows the system in closed loop function (dithering) under those circumstances to about 10 psi where it then flips to closed and full rich even though the TPS hasn't hit WOT. I'm inclined to believe that might be dangerous, to my headgasket at least. What should kick that to open loop, other than WOT, and should it kick in sooner boost wise?

Thanks for any insight?

 

 

[quote]Originally posted by Andy:
<strong>I recently found a better ground for my Lindsey Air/Fuel ratio meter and am getting much more accurate readings. One thing of concern though, with my current set-up the car is capable of over 10 psi of boost while still under part throttle operation. The meter shows the system in closed loop function (dithering) under those circumstances to about 10 psi where it then flips to closed and full rich even though the TPS hasn't hit WOT. I'm inclined to believe that might be dangerous, to my headgasket at least. What should kick that to open loop, other than WOT, and should it kick in sooner boost wise?

Thanks for any insight?</strong><hr></blockquote>

on your car it may goto full rich or even almost full rich when on 50-80% throttle which is good, the problem occurs when you do get to full throttle, will your air/fuel meter stay rich? that is the area you need to focus on. At the boost max your running will the mater stay rich or does it fall off fast to lean, when your at WOT that is the area you need to look at because that is where fuel becomes an issue, never ever at partial throttle. P.S. i can partially gas it to about 70% of full throttle and hit 18 psi so that is not a concern for you ok

 

Yeah, I'd be careful with the LED air-fuel gauges too. The resolution simply isn't there for super-accurate tuning. These gauges are fine to show when something is seriously out of tune. But the range from too-rich 10:1 to too lean 13:1 mixtures may only be covered by only one to two LEDs, so you never know for sure. Best to calibrate your gauge with the wideband display on a dyno. Then you'll know what the behavior indicates.

 

Yes, my car is marginal at redline right now. I'm planning on running another dyno test since I've changed a few things since the last run. And I agree the meters aren't really accurate enough for fine tuning, but in this case it would be correctly showing closed loop operation and I was wondering if having the ratio go from at least 12:1 to 17:1 and back very rapidly could be a detriment while at 10psi.

 

Andy, I think it depends. If you are really getting to 17:1 then you probably are going to do some damage. If you are running 12:1 then you are probably ok. Do you hear any detonation, sounds like gravel in the hubcap except it comes from under the hood?

If you aren't getting any detonation, you are most likely getting enough fuel to keep the engine happy and well.

I recently went up to 52lb injectors. Had to reduce fuel pressure to get a decent idle, or so I thought at the time. I was getting 10psi or more at partial throttle also. I was getting 10psi before 3000rpm and at about 60% throttle. The car ran great, but I was hearing a bit of detonation. So, I kept increasing the fuel pressure to get the detonation to go away.

Not too long after this episode my headgasket developed a leak in #4.

Haven't taken it off yet to see whether it was caused by detonation or just coincedentally wore out after 16 years.

Dan

 

andy if your only keeping a steady foot on the gas pedal, then yes, the air-fuel meter will dither, this does not mean your rich or lean yet, but basically your o2 sensor is responding well and the car is doing well, and the faster it dithers the better, the meter really only helps when you go 80 percent throttle to full throttle, now it wont dither but rather settle on a specific ratio, either a lean or rich one, now as the rpms rise with boost the light may move 1 place up or down or fall hard off to the lean side of the meter, that is when you need to pay attention. The dithering is a good sign, if it wont dither while on steady driving then your base idle or fuel pressure is set wrong, good luck