I have a Holley Sniper system on my 1968 with a 383 Stroker and it has been running good. I took it out today for the first time in about 4 days and I noticed the car had an intermittent stumble where it would seem to cut out about every 30 seconds or so and this would last for like maybe 1 second and then the car would run fine again. While sitting at idle I could not notice the cutting out and it seems seemed to happen more often when I left off the gas and then pressed the gas again it would seem to take a second to react. I have the Holey intank fuel pump so I dont think it a fuel issue.

 

check your voltage...They dont like running at 12 volts. Make sure your system is charging. I had those symptoms whne my alternator was crapping out


if that isnt it your tps setting or the IAC settings may have changed as they are want to do for no good reason if you lost power intermittently..
https://www.efisystempro.com/efi-pro...ing-procedures

 

When you take it out again, drive it around and take a data log. See if it recreates the issue, that way you'll be able to look at what the sniper is "seeing" and how it is reacting to what it senses. Also, look at your learning curve. If you have learned a bad set of cells due to an unknown reason, the "bad" learning will keep causing you issues.

Ultimately, you need to figure out if it's the sniper causing the problem, or the sniper reacting to a problem. Was the base fuel table really dialed in? If so, are your closed loop parameters and learn parameters limited or narrowed down? A bad O2 sensor can wreak havoc on your fuel curves - especially if you have large closed loop and learn percentages still allowed.

KT

 

So Im running side pipes so my O2 sensor is at about a 90 degree angle as opposed to like 45 degrees. How do I diagnose a bad O2 sensor?

 

I too have side pipes. The O2 sensor location isn't the most ideal location, but it will work if put in the collector (for aftermarket side pipes). I bad O2 sensor - if it doesn't completely fail - will be problematic unless you rule out everything else. You can replace it with a new one, and compare the readings. I wouldn't necessarily jump to the "bad O2 sensor" first, but it is a possibility. If your sniper was running great before, and your base fuel map was good and locked in, then something has changed to affect your engine. Have you been transferring your learn tables to the base tables? Is your base fuel table smoothed out or choppy?

Could you have a air leak in the exhaust, or vacuum leak at the manifold?

You mentioned the idle was good, but seem to happen when driving / releasing throttle and reapplying the throttle? Are you going lean in that condition? What is the AFR and closed loop compensation doing during that moment?

If you can, take a data log. The graphs will tell you what is generally happening in your engine down to the millisecond. There is a wealth of knowledge both on this forum, and the web (including EFIsystemspro) on the sniper. I'm not an EFI master, but I've been learning about the Holley products (sniper specifically) for the last 2-3 years on my vette. Everyone here will generally help if they can.

 

The one clue that I do have is that under hard acceleration, which the car seems to do fine, I can hear what sounds like air sucking at the engine similar to a turbo sound.

 

If you started noticing that around the same time the sniper started to perform poorly, I'd start with that. It would have been even better if you had data logs prior to the change, but it is what it is. A comparison would be great in that situation.

 

My coil is sitting eight behind on Holley system on the intake manifold. I was watching a video on Youtube that says it can cause electro magnetic errors if too close. Do I need to move it away?

 

That would probably help, although if it was running fine before and the coil was located there, I would believe it to be something else. You could definitely move it to eliminate that possibility.

 

So I started diagnosing the stumble at the battery and the first thing that I found is that the positive battery cable was loose and the crimp on the connector. I could grab and wiggle it and then with a slight tug I pulled it out of the crimp. I just replaced the entire end and now its snug.

I havent driven it and will tomorrow but I assume I found the issue. The car ran fine when stopped and only stumbled under acceleration which is when the cable was probably vibrating.

Ill verify if its fixed tomorrow.

 

 

I would try and catch the stumble in the data logging on the Laptop when engine is on. Having the data stored makes it easier to find wacky things happening. Having the handheld is great but when you connect the Sniper to the PC software you have so much more control and it gives you. Holley did a great job on their on-line software and it is able to do so much more than the basics. I use it to control my Water/methanol Injection based on engine temperature and then vacuum once the engine is Hot. When I am driving my Corvette with the Holley Stealth Sniper I have a PC inside the car storing the data being generated. The data logging ability is very handy when you have a strange issue happening.

It is critical that the Sniper is connected to a good charge holding battery and healthy charging system. Getting a clean 12 volt connection straight from the battery like Holly Instructs us to do is so important. It appears that you have probably solved your own question fixing the connection.

 

So that did not fix the issue and the car still has a stumble. I took a data log but I'm not sure what I do with it now.

 

Did you see the "stumble" in the data log? What's going on during that moment? What is your AFR doing vs desired AFR? What does your learn table look like? Is it pulling or adding fuel in that area? You need to open that data log up on your current configuration, use the "overlay" feature, click on the area where you are seeing the stumble issue. I'd imagine that you should see a "dip" in your RPM during a throttle increase or something of that nature. It's hard to diagnose without seeing what's gong on. I'm not sure how "savvy" you are with using the data logs / sniper software to tune your vette.

 

Ive never used the data log before. I just recorded it onto the handheld but Im not sure what to do with it now.

 

You need to download the Holley EFI software for the unit you have. It is easily found and downloaded on to a full size PC or even a laptop. Take the memory card from the handheld to your PC and copy it onto the PC. Then open the Holley Software and then point it towards the data and all should be okay. I would suggest you play with it before using your actual data. If you do use your data be sure to have a back up of the original.

Knowing "how to read and make sense" of the volumes of information is not too bad. You are looking for a dip in the RPM's like what Halfnium is telling you to do. I keep a laptop connected while driving but you don't need anything like that. The saved data is incredible when you have it available to see on the charts that the EFI software makes for you.

Here is a link to the Holley Page regarding the Snipers and the downloadable software: https://www.holley.com/support/fuel_...on/sniper_efi/
Be sure to look under the title: SNIPER EFI SOFTWARE and download it to your PC.

Using the EFI software it is possible to custom set up your own engine IF you know how EFI systems work on these modern cars. I have learned plenty having a 1988 C4 with it's fun and games. Holley made their software very capable and powerful.

IF you are not 100% comfortable then you might want to get some help as it is very easy to screw things up in your engine if you start making changes without knowing the outcome.

 

Ok, using your handheld, you need to download your current configuration to the SD card that's in the handheld. The data log is also stored on the SD card as well. If you have a laptop, you can do all this stuff directly on that by plugging it into the CAN bus connection, or you can get everything on the SD card. Either way, you need to run the holley software (available for free) to load your current configuration, then load your freshly made data log. Once that is done, you can graphically look at what your EFI ECU is doing as you drive the car, down to the millisecond.

Have you used the Holley Sniper software on a PC or laptop? I'm just trying to get a feel for how familiar you are with this stuff - in order to best help you. If you haven't used any of the software or data logs for the Sniper EFI, you have TONS of improvements to make that are just some small tweaks in the software. That alone may make your vette run much better.

 

I have never used the Holley software before

 

ctmccloskey,
Ha, beat me to it!

 

The good news - you probably can easily get going on the software, and with some help, diagnose your vette issues. If it's a sniper tuning issue, we can probably fix that. It's possible the sniper learned a bad spot in your tuning learn, and that is what your feeling. Maybe not, but we can figure it out...