Holley Sniper reliability issues

[Winkz]

So in the fall of 2025, I added the sniper to my build, and it's been a constant battle with reliability and driveability. I don't really trust it for any drive longer than 30 min. Often, I can't make it back from the gas station across the road without nursing it back to the garage.

Most of the issues were pretty simple to diagnose and fix - a few bad grounds, an exhaust leak, and an issue with ignition. Although these fixes solved smaller issues, the overall issue- reliability- remains. When it works, it drives great; then the issue randomly will appear, and it's undriveable again. Basically, the AFR drops to the 9s - not getting enough fuel. I placed a gauge on the fuel line, and it's pinned at 60 psi. When this first started to happen, I found the ground to the fuel pump needed adjustment. Soon the fuel pump itself failed. I replaced the pump, and the issue appeared to have been resolved.

After a few weeks, the AFR was erratic, jumping up to the high 20s then back to the 9s. The fuel pump seemed happy, so I looked at the O2 sensor - cooked. Replaced the O2 sensor and looked for an exhaust leak. Found the leak with soapy water and a leaf blower up the tailpipe. Again, fixed the issue and it ran great for about 3 weeks.

This past week the issue has returned. Erratic AFR; engine is struggling to stay running. Still starts and idles great, but under load, it struggles. I looked for another exhaust leak with the soapy water and smoke this time; didn't see any leaks. Vacuum is at 18-19 Hg. My AFR settings are Idle 13.0, Cruise 14.5, WOT 13.5.

It feels like there is still an exhaust leak, but I do not see any evidence of one. I am not sure what else to look for and am hoping those with some experience troubleshooting these things might chime in. I'm very close to ripping out the Sniper system and putting the carb and original fuel system back.

 

[Lead Head]

So in the fall of 2025, I added the sniper to my build, and it's been a constant battle with reliability and driveability. I don't really trust it for any drive longer than 30 min. Often, I can't make it back from the gas station across the road without nursing it back to the garage.

Most of the issues were pretty simple to diagnose and fix - a few bad grounds, an exhaust leak, and an issue with ignition. Although these fixes solved smaller issues, the overall issue- reliability- remains. When it works, it drives great; then the issue randomly will appear, and it's undriveable again. Basically, the AFR drops to the 9s - not getting enough fuel. I placed a gauge on the fuel line, and it's pinned at 60 psi. When this first started to happen, I found the ground to the fuel pump needed adjustment. Soon the fuel pump itself failed. I replaced the pump, and the issue appeared to have been resolved.

After a few weeks, the AFR was erratic, jumping up to the high 20s then back to the 9s. The fuel pump seemed happy, so I looked at the O2 sensor - cooked. Replaced the O2 sensor and looked for an exhaust leak. Found the leak with soapy water and a leaf blower up the tailpipe. Again, fixed the issue and it ran great for about 3 weeks.

This past week the issue has returned. Erratic AFR; engine is struggling to stay running. Still starts and idles great, but under load, it struggles. I looked for another exhaust leak with the soapy water and smoke this time; didn't see any leaks. Vacuum is at 18-19 Hg. My AFR settings are Idle 13.0, Cruise 14.5, WOT 13.5.

It feels like there is still an exhaust leak, but I do not see any evidence of one. I am not sure what else to look for and am hoping those with some experience troubleshooting these things might chime in. I'm very close to ripping out the Sniper system and putting the carb and original fuel system back.

You said "AFR dropping into the 9s - not enough fuel". That actually means the opposite. An AFR of 9 is very rich.

What does your AFR do under load? Where is your O2 sensor located? Generally exhaust leaks matter less at higher load.

 

[Winkz]

I have aftermarket headers and a Y-pipe collector; the O2 sensor is on the collector as it becomes a single pipe. Under load, the AFR jumps around, 9-20. I disabled closed loop and the engine can barely run.

 

[Lead Head]

If your AFR is jumping around that much open loop, then either your MAP sensor is bad (is it jumping around or reading steady?) or your VE table is just hopelessly corrupt.

I think I would probably start over and reset the Sniper. If you can find someone with a Sniper file for a Jeep 4.2, that will probably run well enough as a starting point.

 

[Winkz]

Ive reset/re-ran the setup Wizard a few times while attempting to resolve the issue. Once under load, it's like its stuggling to match the target AFR, resulting in the engine sputtering and RPM drops.

Is the MAP sensor a serviceable part for these models?

 

[Lead Head]

What's the fuel pressure do under load? Are you sure the engine is mechanically healthy?

 

[Winkz]

I am not sure what the fuel pressure is under load. When it works, I can go WOT; it pulls hard, with no bogging or hesitation. The engine was recently rebuilt due to low compression on 2 cylinders.

 

[Skreddy]

Are you letting it warm up above 160 engine temp before driving it?

Are valves all adjusted to spec? Ignition system health?

 

[Winkz]

Are you letting it warm up above 160 engine temp before driving it?

Are valves all adjusted to spec? Ignition system health?

yes and yes. Always let the engine get to operating temps and the valves have been checked several times.

 

[Lead Head]

Why did you disable closed loop control?

 

[Winkz]

Why did you disable closed loop control?

to take the o2 sensor out of the equation for a moment. It has since been re-enabled.

 

[kody472]

Sounds like you and I are in the same boat. Sniper installed this winter after complete rebuild. Runs amazing, but it wants to stumble when coming to a stop, usually when downshifting and pushing in the clutch. Sometimes it even dies if it doesn’t catch itself.

The AFR seems to go into the 9s as well when this happens. My IAC is perfect and I have no other issues with it.

Curious to see what you find out. I’ll be trying to make adjustments as well.

 

[Lead Head]

to take the o2 sensor out of the equation for a moment. It has since been re-enabled.

can you post what your VE table looks like

 

[Winkz]

I took it out twice this evening and could not reproduce the issue. I reran the wizard between runs, and it ran a little more smoothly the second time.

Since I reran the wizard, I'm sure it has some learning to do, but not sure when or if the issue will reappear.

 

[klinetime574]

I have my oxygen sensor mounted a little ways back from where my header pipes merge. I checked with Holley and they state 6-8” away from where the pipes merge, mounted at proper angle, etc.

I’ll be honest I’m not sure exactly the distance mine is mounted from the collector, but I’d recommend checking yours to be sure. Also I feel like eliminating my converter seemed to help it run better. Honestly haven’t driven it much since I did that.

 

[Lead Head]

I took it out twice this evening and could not reproduce the issue. I reran the wizard between runs, and it ran a little more smoothly the second time.
View attachment 4168886

Since I reran the wizard, I'm sure it has some learning to do, but not sure when or if the issue will reappear.

That VE table is crazy out of whack wrong for a 2F. 100%+ VE the kind of VE I would expect for a streetbike engine. I'm guessing the engine runs so rich poorly at those higher load and RPM points that it starts misfiring, which strangely enough will show as a lean condition to an O2 sensor, and the Sniper tries to add even more fuel.

First, triple check you have the engine displacement, fuel pressure and injector settings properly set.

Then, take a look at this Chrysler Slant 6 VE table I found. This is about what I would expect a 2F VE table to look like.

Personally, I would start with this Chrysler VE table. It will be a bit of work, but I suspect it will be a much better starting point for the self-tuning.


You will need to compress it a bit, as the 2F ain't going to 5000 RPM. By that I mean, whatever that Chrysler VE table says for 5,000 RPM, put it your table at the 4,000 RPM line. Whatever it says for 4500, put it on your 3750 RPM line. You get the idea.

Every RPM column after 4000 (so 4250 - 7000) should just be a copy-paste of the 4000 RPM column. You won't be winding a 2F up that high anyways, and you don't want the computer to be doing weird blending towards redline.

Obviously that Chrysler VE table has a lot fewer kPa rows than your table. That's okay. Just input the values that match up, and then interpolate between them. So by that, I mean if the Chrysler table says 50% at 60 kPa and 40% at 70 kPa, and your table has a 65 kPa row, just split the difference and input 45%.

We're not looking for perfection. The Slant 6 is just a similar enough low-HP i6 that it should get the Sniper a lot closer to sucesfully autotune.

 

[dbbowen]

Do you have a dyno tuner available near you? My dad put a 4 bbl sniper on his 383 stroker firstgen camaro and the self learn was essentially useless on it. His car would run super rich no matter what he did. He took the car to the dyno tuner and they put a custom tune on it and it drives and runs perfect now. Its every bit as reliable as my 5.3

 

[DrRock]

I have a Sniper on my 2F and it runs great but I did have some initial issues. Mine was installed on a freshly rebuilt engine. A couple other things to check:
1. How much advance are you running and have you confirmed your advance mechanism on the distributor is working properly?
2. Do you have all vacuum tubes removed save to the critical ones? (Advance, brake booster and dizzy vent).
3. Where are you getting the signal for the RPM’s?
4. What’s the compression numbers for the engine?

For the advance topic, I only run around 9DEG as I have higher compression and was pinging with anything more.

 

[Winkz]

I am running a GM HEI distributor - Tach signal is from the distributor. Timing is set to stock. As for vacuum tubing, it's pretty basic.
Having looked at compression since the rebuild.

I have been driving it some, and it's not throwing fits, but it will, as I can tell, it's running rich. I can smell gas after turning it off.

At this point Im going to find a place to tune it.

 

[cruisermatt]

why not just adjust the VE table and see how to goes? Takes about 2 minutes.