I have a 1972 corvette I went from the carb to sniper system. I changed from pentronix to a CC HEi Distributor. If I put the air cleaner on the sniper system acts up. I have followed all of Holleys Tech Support suggestions. I ran ground from carb to manifold to cylinder head to block . I ten ran a separate ground 1/0 from battery to the block where all the grounds connect. I put a ground strap on from the alternator to the frame to the block. Any other person have this problem or solutions would greatly help.

 

Are you hitting a linkage?

Try just putting the air cleaner base on. Same problem? I can't imagine sucking air through the air filter causes the issue, but it will change the vacuum signal very slightly.

Photos help! Many on this Forum are experts with the Sniper EFI system.

 

First buzzkiller, Welcome to the Corvette Forum! This is THE place to be if you have any issues with a Corvette!

I have a 1968 BB C3 and I too have a Holley Stealth Sniper on my 427. The installation went well and my car went to learning without any issues regarding the Sniper and its system. On my corvette I am using a factory L88 hood setup and it has a lower air cleaner assembly which fits perfectly along with the other parts of the L88 carburetor top parts. My setup works as well with the hood open as it does with the hood closed. Are you pinching any of the wires or touching any of them with a metal air cleaner lid. The Sniper's are very sensitive to noise being generated by other sources in the engine compartment so the placement of every wire is important. You want to isolate the power wires from the sense wires like the coolant temp sense or O2 wires. When wires run parallel they have the potential to pick up noise. I ran the power wires by them selves directly to the battery. Then the wires for the fuel pump activation were isolated fairly easily. Where you have to really watch out is when dealing with spark plug wires and other high current power wires (like alternator Output). It seems that some of the Sniper systems have more trouble with noise in a metal bodied car.

Setting up the Idle Air control circuit can be an issue for some folks. I had to do mine a couple of times. There are many question/Answers for the Holley Sniper Systems at the following website: efisystempro.com. Looking at the website will help you with some of the more detailed issues and how to solve them.

These guys are the experts and they sold me my system (under Budget) but the big difference is they provide 2 years of POST-SALE support and will help insure that your engine is running properly. Their website is amazing and has so many questions and answers regarding the Holley EFI systems. One of their technicians is a Holley "Tier Three" EFI technician. This is how you get great service helping you pick out the right parts and making them all work. Did you get the data collection cable to connect a laptop to the system? If you had some Data then it would probably help show you the problem. Have you installed the data on your laptop or desktop and looked closely at what this system can do? It is amazing.

I have worked with electrical systems a lot and one thing I do know is that you CAN have too many grounds on an engine. Before going to the effort of running all the ground wires I would have taken my multi-meter and checked the grounds and if needed record them. I am a Big believer in having the engine block grounded to the frame but that is where I generally stop. An ungrounded engine will have issues so to keep them all happy I check to be sure that they have a good solid ground.

 

Thanks for the info. Holley Tech support was who told me to run all the ground wires. How did you run the wires to the battery. The + and - were wrapped in a loom and run over the transmission next to the main positive wire. The additional ground wire 1/0 is ran through the same location. I am not hitting any wires or linkage with the air cleaner. I will start going through the other wires to see what might be touching. I know a few run down the passenger side. Also do you have the big cap HEI distributor on yours or do you have the points distributor. Again thanks for all your help

 

what do you mean acts up? doesnt idle, floods, poor gas mileage?

 

Welcome to the forum. There are a bunch of users on the CF that have installed the Sniper on their corvettes. There is a lengthy thread that discusses many of the known issues with the Sniper including the grounding issues. See this LINK.
What are the symptoms of your "issues"? Most of the Snipers that I've dealt with don't like EMI, but based upon my experience, those users who are having to run extra ordinary amount of grounds usually indicates either a bad Sniper ECU (overly susceptible to EMI) or bad electrical interference in a 50 year old car. The problem is, neither of these things are an easy fix. Usually, if you suspect the Sniper is bad, users send it back only to have Holley return it and say nothing is wrong. That leaves you with your car's electrical system. I've talked to people who have gone as far as use shielding for their spark plug wires to get it to work. That may have worked, but THAT IS NOT NORMAL. Most Sniper installations on older cars do not require grounding spark plug wire looms, nor wearing a tin foil hat to get it to work. The Sniper system should work with NORMAL EMI precautions, and anything beyond that is ABNORMAL. I know that this advice doesn't get your system to work, but most Sniper's don't require all the grounds that you have added already. So, you are already in an area considered rare - but known to happen.

The ECU for the Sniper 1 is in the front part of the Sniper throttle body. Therefore, relative to your distributor, it is as far away as it can be. Fords often have more of a EMI problem due to the closer proximity to the ECU with the forward distributor. Chevy's or Corvette's - regardless of the type of distributor should have less susceptibility. Your IAC has a greater chance of being affected by the distributor. I'm not sure what your actual symptoms are, so I'm shooting in the dark a little.

What is your air cleaner made of? Normally an air cleaner gets somewhat isolated from the throttle body via gasket, but is common with the throttle body through the wingnut and the threaded rod to the throttle body. However, that may be electrically isolated from the block via another gasket between the throttle body and the intake manifold. Ground the air cleaner housing? Again, this is abnormal, but I'm trying to think of other things for you to try. Especially if you state that the Sniper works fine until you put the air cleaner on it.

If you get a chance to elaborate on your "issues" we may be able to better help.

KT

 

The Holley units have been prone to acting weird to air disturbances. What type of intake manifold are you running?

 

I don't want to go down a side discussion - in order to help the OP - but I'm curious:
I've run both dual planes and single planes with the Sniper, and they both functioned as expected. Is there another type of manifold to use with the Sniper? What are the "weird air disturbances"? Could you elaborate - perhaps on a side discussion?

 

That's AOK being we are somewhat on topic. In short it's not just the Sniper but just the throttle body style fuel injection units in general. There are scores of threads out there on Holley and FiTech forums talking about driveability problems on dual planes.

I'm not smart enough to know why, but it appears that some engine combos (Fuel injection unit, camshaft, cylinder head, intake manifold etc) have driveability issues with full on dual plane intake manifolds. Why? I have no idea. A somewhat educated guess is that there isn't a consistent and strong enough vacuum signal feeding the fuel injection MAP sensor thus the ECU for the fuel injection unit either cuts fuel, timing, or both. You'll see where guys have cut down the center divider alittle to get past this issue. You'll also see folks put a small carb spacer on to get past this issue. When folks do this it seems to clear up the problem from my reading.

With that said OP, as I was looking for a tech article from Holley about the cutdown thing I'm talking about I ran across this thread on yellowbullet. Basically the same issue you are having. https://www.yellowbullet.com/threads...eaner.2211194/

 

10-4.
I agree that different combinations may yield some different results. I would also typically recommend that any user of an EFI system (throttle body or tuned port) move straight to a single plane manifold if able. However, most Sniper applications will work fine with dual plane manifolds. They do work better with an open plenum and whether that's accomplished with a notched divider or spacer, it will help. There are negligible downsides to running a single-plane manifold with EFI. I discuss that in detail in the Sniper thread linked above.

I hope the OP describes the symptoms in more detail, we've gone from grounds to manifolds to air filter, and so on. I feel like we're shooting a shotgun at a fast moving target with our eyes closed...

We're all just trying to help.

 

Acts up. Isn't really very descriptive.
Runs fine without a airfilter?
Then plays up with airfilter installed?
OP. How are your plug wires routed?
Like factory? Or run across the top?
Spark plug wire noise could be reflected by the airfilter base if wires are run over the top.
Just a thought.
I also run a throttle body EFI system. Not the Holley unit. But none the less throttle body EFI. I run a large cap HEI distributor. My plug wires run through the factory looms. Down the backside of the block. I keep ALL wiring well away from the plug wires.
I run my power and ground wires to the battery along the main positive battery cable over the transmission.
My system runs great and has for years.
Perhaps you can clue us in on exactly what "Acts up" means.

 

Another suggestion:

If the unit "acts up" when the air cleaner is not on, then start the car without the air cleaner on, start a data log, then put the air cleaner on while idling. If the Sniper starts "acting up", you'll have a recorded bunch of data while it does. RFI / EMI is generally very easy to spot during a data log. It can show up as Sniper resets - where you miss data due to the ECU rebooting, extremely noisy RPM signals (or other telemetry), battery voltage fluctuations, to name a few. Additionally you can see if other things are causing an issue. The data log will quantitively tell you something is wrong in real time. It is the single biggest reason why aftermarket EFI is superior to a carb. Real time data analysis to both tune your engine better AND troubleshoot problems. There are are users out there that are pretty competent at looking at data logs. Once you get used to seeing what is normal, and what is not, the guessing stops, and the knowing starts... If the data log definitively looks like EMI, the moment you put the cleaner down, then you can do some things to mitigate that. However, I do stress that there are thousands of Sniper units out there on all kinds of older vehicles with various levels of EMI in the engine bay. Many older classics have the over the carb air cleaner housings. Overly sensitive Sniper ECUs (to EMI) do happen, but it is not the norm. Users generally find the right component they need to shield in an extra ordinary way, and the Sniper behaves normally after that.

 

try a jumper wire from the air cleaner to the block - who knows
Also see if the Air cleaner is touching and ignition wires or coil.

 

no linkage is not hitting

 

thanks for all the help I really appreciate it. So last night went home and tried some suggestions. I ended up wrapping the HEI in tin foil and removed the ground from the air cleaner I was running from the carb. The car runs great. I still have one issue and that is I can drive the car all over like normal. Once I come to a stop the RPM stays and 1100 and will not come back down to 650 / 700 where I have it set. I can shut off the car restart and the idle comes down. The linkage is not hitting .

Any suggestions for shielding the RFI from the HEI unit since tin foil doesn't look that good on a car. Reading some of the suggestions I also see not running the hot wire to the fuse block as the instructions stated from holley. Is that a source of trouble.

 

First off, good job on finding the problem. I always hate it when guys end up covering their engine compartment with aluminum foil, but it does happen (and it shouldn't have to happen). There are just some Sniper's that are overly sensitive, or cars that have excessive RFI / EMI out there. I wish I knew why some cars need that excessive precautions and most do not.

If you can, run the hot wire directly from the Sniper to the battery as described in the installation manual. That will be your cleanest source of power. The Sniper is a microprocessor, it doesn't like 50 year old dirty power.

For your idle, what is your IAC doing? What is the IAC hold position setting?
IF the IAC is closed when idling and you are at 1100 RPM, your engine is still receiving enough air to not be able to return to your desired idle RPM. There are several causes for this.

Usually high RPM idle is from excess air flow from somewhere either internal to the Sniper or not. That is normally an obvious statement to make, but most people immediately blame the Sniper unit after an install. Carburetors are less sensitive to vacuum leaks and other sources of air in leakage because the user typically tunes the carb to incorporate the in leakage. The Sniper is fueling your engine based on the total air flow (from all sources) it directly monitors via the O2 sensor.

The position and what the IAC is doing will help you troubleshoot. Keep an eye on the IAC once idling. If you IAC position goes closed while idling, that means you are putting too much air into the engine via some other means (throttle blades or other). If it opens up to 100% and stays there, your not getting enough air.

A high RPM at idle, no matter what your fuel delivery system is, means too much air. The Sniper (1 or 2) only controls air in two ways at idle: The throttle blade screws and the IAC. Your throttle blades should be letting in just enough air to effectively allow you to idle 50 RPM less than your desired idle speed. The IAC actually controls idle air after that. You can block off the IAC air port with something that won't get sucked through and see what your idle does. If you idle doesn't come down with the IAC port blocked, and the throttle blades almost closed, something else outside of the Sniper is letting in too much air.

Make sure your throttle blades are centered and equal with each other. That problem is rare, but it does happen. There is a way to adjust them, but I don't suspect that is your problem - not at first anyway. You won't see this problem as an external linkage hangup. Sometimes the throttle plates simply rub the bore after a heat soak. They usually require a re-centering when that happens.

You mentioned how you got it idling correctly, then it randomly doesn't when you come to a stop or other random driving event. Again, without seeing anything, you know that your air flow to the engine at idle is being altered.

 

You can get some braided stainless steel sleeves to make shielding. I got a roll when I bought my Sniper 2 just in case but didn't need it. Looks a lot better than tin foil and you can solder a wire on it and ground it too. All you need to do is ground one end. You could keep the foil wrapped and put this over it too.


This is a good read:

Understanding Shielding

At work we never mix power cables with signal cables. Keep your sniper cables away from your ignition parts as that is the highest voltages that will cause EMI.