Blueprint 347 w Holley Sniper runs rough for a while Fixed?

[Caddy Dad]

I have a BP 347 with Holley sniper that has been starting and running great. I have about 5k+ miles on it. Lately an issue has slowly developed where the engine will start and idle just fine but when I drive off it starts to stumble and run rough between 2k-4k RPM. After about 15-20 minutes of driving the engine smooths out and all is good. Could this be an Oxygen sensor issue? Fuel pressure is good, timing seems to be good. I haven't pulled the O2 sensor yet but not exactly what a bad O2 sensor looks like.

Thanks in advance for any insight before I fire the parts cannon.

[Papa]

Have you captured any data logs?

[Papa]

Something you can check would be if you have any fouled plugs. My 347 would tend to foul plugs and not fire on all cylinders. I used a temperature gun to measure the header temp on each cylinder to see which ones were missing. The Sniper wants to run rich when you first fire up the engine and will lean out as temps come up. If you don't let the temps come up, usually from short run times, the plugs will foul.

[Mike.Bray]

My first guess, and that's pretty much all I do, is the O2 sensor.

As Papa Dave said if you have a temp gun checking the header temps for foul plugs is easy.

[weendoggy]

If you have the 3.5LCD, it'll show what the O2 is doing. I usually see them go bad and stay that way. The engine will run o.k. at idle until you put a load on it. Another good test is take it out of Closed Loop (if your tune is good) it should run fair if it's tuned good.

[Caddy Dad]

<<Have you captured any data logs? >>



Good point. No, not yet. That will be my next step before I pull the O2 sensor or remove the spark plugs. After I log the data and bring it up on my laptop, what data stream or responses should I be looking for when it runs rough?

Thanks!

[JMD]

I'm guessing the plugs as well. If it's the O2 it probably wouldn't get better after driving. People tend to run these Snipers rich and plugs foul over time. What's your cruising AFR? I bet they have trouble arcing when cold but work better with some heat. I'm 90% sure it's the plugs or something similar. Easy and cheap fix.

Also the Holley Sniper forum is a great resource for Sniper specific troubleshooting.

[JMJ]

Another thing to look at...check that all 4 injectors are firing. I had the identical symptoms and it turned out 1 of the injector wires had come loose. 10 minute fix and it was back to running strong.

[Caddy Dad]

Have you captured any data logs?

Here is a snip from the data log where the engine is really running rough 217571

Looks like the AFR is about 15 or so until warms up then drops to 13 when I blip the throttle then slowly (or hardly) recovers to 15?

[weendoggy]

Screenshot doesn't tell the whole story. You need to include a tune and datalog to really see what's going on. 15 is lean with 13 rich. So dropping is really going rich not lean.

[bobl]

There are several of us on here that are pretty good with tuning Holley EFI. As Weendoggiy said you can't tell much from a screen shot. I wonder if there's a way to attach the logs and GCF files so they can be downloaded? From looking at this screen shot I think the 02 sensor is working correctly. It stays within a realistic range. When they fail they usually show really lean. A screenshot that included Map sensor and CL % along with showing the values on the left may make it more meaningful. Also a description of how you were driving during the log period.

Bob

[Caddy Dad]

There are several of us on here that are pretty good with tuning Holley EFI. As Weendoggiy said you can't tell much from a screen shot. I wonder if there's a way to attach the logs and GCF files so they can be downloaded? From looking at this screen shot I think the 02 sensor is working correctly. It stays within a realistic range. When they fail they usually show really lean. A screenshot that included Map sensor and CL % along with showing the values on the left may make it more meaningful. Also a description of how you were driving during the log period.

Bob

Hi Bob,
Thanks for the feedback. I've hardly ever even looked at any of the data and parameters that are available with the Sniper. Now I'm intrigued. Is there an on line class that I can take to learn more about tuning the Sniper? Or maybe an in person class?

Thanks!

[Caddy Dad]

Something you can check would be if you have any fouled plugs. My 347 would tend to foul plugs and not fire on all cylinders. I used a temperature gun to measure the header temp on each cylinder to see which ones were missing. The Sniper wants to run rich when you first fire up the engine and will lean out as temps come up. If you don't let the temps come up, usually from short run times, the plugs will foul.

I think you're the winner! I just pulled all the plugs and cleaned them up. They were heavily coated in soot (I've seen worse on plugs from the junker cars I used to drive as a kid). I cleaned them up with a wire brush, checked the gap and re-installed. I also pulled out the O2 sensor and it was caked over with soot! I clean that up with a rag and some elbow grease. I re-installed the sensor and started her up and logged some more data. I then took her for a rip around the town. Drives a lot better now! So hopefully that was it. On the down side I found a big puddle of AF on the floor of my garage while I was cleaning the plugs. I've got to find out where that is coming from now. It's always something to keep me busy!

[Papa]

Good deal! Hope you can enjoy the car again.

Dave

[Theshandman]

Another thing to look at...check that all 4 injectors are firing. I had the identical symptoms and it turned out 1 of the injector wires had come loose. 10 minute fix and it was back to running strong.

Same! I tie-wrapped all 4 wire-plugs.

[Papa]

I think you're the winner! I just pulled all the plugs and cleaned them up. They were heavily coated in soot (I've seen worse on plugs from the junker cars I used to drive as a kid). I cleaned them up with a wire brush, checked the gap and re-installed. I also pulled out the O2 sensor and it was caked over with soot! I clean that up with a rag and some elbow grease. I re-installed the sensor and started her up and logged some more data. I then took her for a rip around the town. Drives a lot better now! So hopefully that was it. On the down side I found a big puddle of AF on the floor of my garage while I was cleaning the plugs. I've got to find out where that is coming from now. It's always something to keep me busy!

On the anti-freeze puddle, it could just be that the overflow tank filled up and dumped fluid out of the overflow tube.

[bobl]

Hi Bob,
Thanks for the feedback. I've hardly ever even looked at any of the data and parameters that are available with the Sniper. Now I'm intrigued. Is there an on line class that I can take to learn more about tuning the Sniper? Or maybe an in person class?

Thanks!

There are numerous efi training courses available. However, the key to EFI is having a very good understanding of engine operation and tuning in general. EFI is not magic, it's just a very powerful tool. A good way to learn what it can do is to go through the various parameters and click on the help menu. It gives a brief explanation of what each one does. Then it's up to the tuner to understand how that parameter integrates into the overall tune.

Bob

[CraigS]

Glad you found the problem but what to do so it doesn't happen again? How to make it run leaner, that will be your question. I think you will enjoy learning about tuning your Sniper. Best wishes.

[Mike.Bray]

Did the OP mention if this was a Sniper 1 or a Sniper 2? There's a world of difference between the two.

[Caddy Dad]

Did the OP mention if this was a Sniper 1 or a Sniper 2? There's a world of difference between the two.

I think it is a Sniper 1 I purchased the engine from BPE in 2020. My understanding is the the Sniper 2 didn't come out until 2023?

[TrackDay17]

I think it is a Sniper 1 I purchased the engine from BPE in 2020. My understanding is the the Sniper 2 didn't come out until 2023?

I went to the build school last weekend and the 302 engine we installed had the Sniper 1 on it.
According to Jim our instructor on the Sniper 2 they moved the electronics from the front to the left side of the Sniper to eliminate electrical interference with the distributor.
I'd say if your electronics are on the front it's a Sniper 1.

[David Ferguson]

If your plugs are fouling, then consider running hotter heat range spark plugs. Often cold plugs are fitted to high-performance engines in anticipation of significant time at high load. Unless you are racing, this is unlikely to happen with a street car.