When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have been struggling with my air fuel ratio numbers on my Holley Sniper for a few months. I have put in a new O2 sensor, sent the Sniper back to Holley for a rebuild, moved the O2 bung forward and back on my exhaust to try to find the best spot and nothing helps. Today I hooked a shop vac to the end of the pipe to see if I had any leaks at the headers using soapy water and it all seemed tight. I cant seem to solve this problem. Any ideas?
The only thing I noticed is that my side pipes leak alot of air where the headers and the exhaust connect with the slip connection but since this is after the O2 sensor and after the collector I dont think it is the problem.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
They will always jump around unless you put it in a single tube. The mixture itself is going to vary in a carb style deliver as you have different pulses from the front to the back of the manifold. Unless it direct injection, you will just have to average it out. Carb or Sniper, its always going to jump a lot at low rpm, less at higher rpm but it will always be moving
They will always jump around unless you put it in a single tube. The mixture itself is going to vary in a carb style deliver as you have different pulses from the front to the back of the manifold. Unless it direct injection, you will just have to average it out. Carb or Sniper, its always going to jump a lot at low rpm, less at higher rpm but it will always be moving
I actually just put it in a single tube to see if that made a difference and it did not. It still jumps around.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
thats odd. I would blame it on the sensor and not the Sniper.....I have an AEM wideband and it was usually pretty close to my sniper readings....are you sure the manifold/ header flange is tight so its not sucking in air there?
thats odd. I would blame it on the sensor and not the Sniper.....I have an AEM wideband and it was usually pretty close to my sniper readings....are you sure the manifold/ header flange is tight so its not sucking in air there?
I'm pretty sure it is. I've hunted around the engine for a leak using starting fluid and cant find anything. This is my second brand new Bosch sensor and I get the same results. I have no idea what it could be.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
If you can find a shop with an emissions sniffer they can stuff up your tailpipe, maybe they can tell you if its jumping around or if its fairly stable before you start throwing money at it
How about some pictures of your sensor mounting? who welded in the bung for it? How much is it jumping? In my experience O2 sensors never read steady as the computer is always chasing adjustments.
Do you have this mounted on a dual plane intake? If so....you need some kind of open spacer.......you see, the MAP vacuum signal on these is only on one side, one throttle bore......indifferent pulses can cause that guy to go wonky......
I have been using a 1/4" open spacer gasket from Edelbrock and it does the trick.......
This may not be what it is....but I am willing to bet it is......
How about some pictures of your sensor mounting? who welded in the bung for it? How much is it jumping? In my experience O2 sensors never read steady as the computer is always chasing adjustments.
I'll add, how about some pictures of the engine, too? Single or dual plane intake? Any chance you have a sporadic ignition miss somewhere?
I just checked my clamp on O2 sensor that I just recently moved to one pipe and it is leaking so I just ordered a better style clamp on sensor. I am using the clamp on style as opposed to the weld on just until I find a good spot for the O2 and then I will weld in a bung.
How much is it jumping around? 13.8 to 14.2 or 11 to 16? I went though some erratic AFR readings initially as well. It went away when I replaced the Holley sensor AND added the HBX-1 bung heat sink with flow port.
What about electrical noise being picked up by the wires that connect the O2 sensor to the Sniper?
I took time and routed all the sensor wires as far away from Ignition (Spark Plug Wires) and the power wires and the O2 gives me a fairly stable signal even when going slow. Try moving the wires going to the O2 around while the engine is running and see if that has any effect. We used "sensitive" sensors in my work and they had to be routed in a very different path than any wires with power running through them. The Coolant Temperature Sensor wires are also tricky as I had to relocate my sending unit back to in between #1 and #3 and route the wires so the spark plug wires were clear. You also need to clear the wires feeding power to the electric cooling fans and the blower motor just to be safe. Long wires can act like great antenna's in many applications.
With the Long tube headers I decided to install the O2 about 10-12" behind the joint where the headers meet my Chambered exhaust. The exhaust flow needs to be well mixed and there can't be any air leaks in front of or behind the O2 sensor.
Not sure your leaky header to side pipe connection is not part of the problem. I had erratic AFR, especially at idle, until I sealed the leaky joint. If the O2 sensor was in a straight pipe you would need 18 inches or pipe behind it or fresh air will make it back to the sensor. Your leaky exhaust is also sucking fresh air in. You may have another problem but I’d fix that one first.
After seeing Halfnium’s post below I remembered something else that helped mine. I went to a fixed orifice PCV valve. The vacuum leak remained constant so the Sniper didn’t have to compensate so much to keep the AFR constant.
IF the 9.6 AFR is due to the unit chasing an overly lean condition (and overcompensating) => that is pointing toward a O2 problem. IF you've changed sensors and are still getting the same erratic AFR AND the ECU is assumed good, it still points to an exhaust issue. EMI is always a concern, but if you find yourself taking extraordinary measures to combat possible EMI, it's usually another problem. The dual plane manifold without a "notch" or "cutout" will mess up the MAP sample cutting off half of the cylinders. All of these things need to be ruled out the best you can. I too had some issues when I first installed the Sniper. I found some small vacuum leaks (PCV) and even a small one on my vacuum / boost gauge connection! They collectively added up, but once addressed my idle / AFR got more stable. I guess what I'm trying to say, sometimes it's not just one thing.
My EMI had been addressed by moving my coil to the fender well and swapping out the air filter screw rod for a delrin rod. Still no change
10-4. In my experience, normal EFI measures were enough for my Sniper to function properly. Others that I have read about, have taken extreme measures to alleviate problems. Like I said, if you are having to wear a tinfoil hat, run 350 mcm cables to chassis ground, wrap all of your wires in shielding, and wear ferrite beads - something else is wrong with your Sniper. They are sensitive, but not that sensitive...
I don't run a Sniper. But none the less a similar throttle body wide band EFI system. The most important things are good clean power and a very good clean ground. Next is a perfectly sealed exhaust system.
one shouldn't need to experiment with a good place to put a O2 sensor. It should be as close to the collector as possible. Done.
constant variation in O2 readings is normal, but the wide swings reported by the OP is not.
even a miss fire on one cylinder wouldn't cause such wide swings.
I agree with the above advice of going to a exhaust testing facility and see how there meter reads.
This really sounds like a ECM issue to me. If the power and ground is correctly wired. And 2 different O2 sensors act the same. One would think that the computer reading the inputs is faulty.
An O2 isn't going to cause a 7 wide spread of A/F.....it can't.....the MAP is the main A/F source for the computer and the O2 is a fine tune window that checks the MAP.......
04-21-2023, 11:29 AM
A/FR for Sniper jumps all over
