Major Issues After Install

[MrSinister55]

OK, so we got everything installed and fired up. Initial fire went great, everything where it should be.
Until the first drive. It runs well enough, until I get this popping sound, the IAC reading spikes to 50-70%, and it sounds like a massive vacuum leak. If I shut the car down, it will sometimes restart easily and idle correctly. If I pull the air cleaner and put my finger over the IAC hole, the idle comes down. The IAC is definitely the issue, I would think. All the other parameters on the handheld are within spec. After couple more quick drives (that's all I can get it to stay running now), the same thing will happen, except now it will die and is difficult to restart. It will blow black smoke when it does restart. It will stay running in gear so long as my foot is on the throttle. When I take my foot off to stop, it dies again. The IAC reading is always above 50% when it's acting up.

Let it cool down, decided to rerun the initial setup wizard. Got everything dialed. IAC reading 6% at hot idle, TPS reading 0%. Idling like a champ. Took it around the block. Stalled twice while stopped in gear. Fired right back up. Ran OK, but had a couple minor IAC spikes (rush of air, handheld reading goes up) that showed on the handheld, but it would settle right down. Brought it home, let it idle some more, everything looking good. Decide to head up the road a little, and it all went to hell. Backfiring through the exhaust, cutting out, handheld going crazy, IAC reading zero at idle in park, have to pump it to keep it running, then it all clears right up for a minute, then goes back to running like hell. Was able to limp it home. Put it in park, idling perfectly. I guess I should try some datalogging, but I'm so angry right now, I think it's best I let it sit for a while.

[ChevyC10]

What is your ignition setup? I had a bad ignition coil and every time it would get warm it would have similar symptoms.

[MrSinister55]

MSD Blaster 2 coil and Holley Dual Sync. Was using a Summit CDI box, but decided to let the Sniper coil driver handle that task. Coil was fine before install.
I'm thinking ignition interference at least, since the handheld likes to freak out going down the road, and not at idle.

[MrSinister55]

First things first. My battery is in the trunk, and is only grounded to the body back there. I'm going to correct that by grounding to the frame AND body, and adding a ground strap from the engine to the frame. I have had some issues with the shift light on my tach flashing occasionally in the past, which I thought I had licked. We'll see if adding grounds does anything to help. Should be a few days before the UPS dude brings my stuff.

[81 TransAm]

I also have my battery in the trunk. I ran a ground from the battery to the chassis and then I went and got the heaviest welding cable I could find (not cheap stuff), and ran it from the battery to the engine block. Then there's another ground cable from the engine block to the chassis in the front. Then I also added a ground from the alternator case to the engine block. Everyone forgets that the negative side of the alternator output grounds through the alternator case, and a poor ground at the alternator case can cause problems.

[MrSinister55]

Good info, thanks! I have one of those 1-wire alternators. What can be done to help ground it?

[Danny Cabral]

I have one of those 1-wire alternators. What can be done to help ground it?

Then I also added a ground from the alternator case to the engine block.

See above, 81 TransAm answered this. But if the engine/cylinder head is well grounded, you should be fine.
https://www.youtube.com/watch?v=MdGX...9AF17&index=18 (Holley EFI - Proper Grounding)

[MrSinister55]

You're right, I missed the CASE part when I first read it.
So what I'll do is ground the battery to the engine, then run a strap from the engine to the frame, and a ground from the alternator case to the block. I think I'll also keep my existing ground from battery to body for good measure, unless that's a bad idea. Are there any spots on the block that are better than others? I'm running an aluminum headed Vortec block if it matters.

[MrSinister55]

PROGRESS!!
So for grounding, I have a 2 gauge cable from the top post on the battery to the body. I have a 2 gauge cable from the side post to the engine block. I have a copper strap from that same point on the block to the frame, and I have a 10 gauge wire from the alternator case to the same spot on the frame. I use a Battery Tender, so I made sure it's connected to the top posts, while the Sniper hot and ground are connected to the side posts.
It fired right up and idled like a champ. Got the guts up to take it for a spin, and it ran flawlessly. The handheld did jump menus a few times, but it never lost sensor input. It was also damp as hell last night, so could that cause the touchscreen to register false touches? Or maybe a little dirt/grease on the screen?
I only ran it a couple miles down the road, but that's a lot further than I could go the last time I drove it. The importance of proper grounding for these units is readily apparent now.

So, not calling it a win yet, not until I can run it all day with no issues. Forecast is looking pretty wet, so I don't know when that will be.

Question: Should I re-run the setup Wizard since it was trying to learn initial parameters while all screwed up?

Observations: IAC was much more stable, but tended to be higher than I thought. At a cold start, it was around 50%. It did drop to around 40%. Driving it, it will settle on that 30% number a lot, but I also see 0% while coasting in gear. Stopping and putting it in park would be around 25%, and it would slowly drop. I never did see the 6% I had it set at the other day, hence my question about re-running the setup wizard. I also definitely think I need that throttle arm extension. Yikes!! Thanks for the help so far!!

[Dr_Grip]

The IAC is "held" at 30% while you are off-idle, so you will see that figure all the time while driving. I don't think you'll have to re-run the setup Wizard. Just reset the idle screw to 6%-ish hot in neutral and be done with it.

[MrSinister55]

I'll do that then, thanks. That makes sense, as it requires very little throttle input to maintain speed now. I should mention that my car runs very cool. So much so that it will drop below 160° (on a 180° thermostat) at cruise on a 70° night. I'm going to have to lower that Learning threshold temperature.

[81 TransAm]

If all goes well and you feel brave you could try the progressive linkage modification: https://forums.holley.com/showthread...I-WAAAY-Better

[MrSinister55]

I may. I ordered the Demon throttle linkage extender, so I'll see how that does first. But due to a large cam (Comp XR294HR) & 350 cubic inches (and 3.70 gears, 2400 stall), it's always been lazy down low. The added punch the Sniper gives off the line may actually be beneficial in my case. I see heavy traffic situations being white knuckle the way it is now. It really wants to go.

[RPnova]

Here's the best way in my opinion to get the IAC perfect. Start your car and warm it up as it is.

Then turn the engine off and cover the IAC hole with a strong piece of tape make sure it doesn't get sucked in.
Then start your car, now you may need to open the throttle blades via the screw to get it to idle,
and that's fine, turn the screw in until it will idle on its own with the tape still attached.

Next, set the idle screw until the RPM are roughly about 50 RPM less than what you have set in your handheld.
Very important, once you do this turn the car off then remove the tape while the car is turned off.
Now start the car and when you do the RPM will go up like your starting a new car, then will drop to the appropriate 2% to 8% IAC range.

If the IAC is a little high still then lower 60 RPM or if the IAC is too low try 40 RPM below the target idle speed set in the handheld.
This method works great because you want the throttle blades controlling most of the idle that's why we tape it off.
I used this information from Chris at EFISystemPro.com: Solving Holley Sniper High Idle Issues

I have a carb extension lever on my Sniper and it's a night & day difference. I had a sore calf muscle from the Sniper, but not any more.

[MrSinister55]

Pretty interesting trick! I may have to try that, thanks. For what it's worth, it doesn't idle high. I'm just seeing higher IAC readings than expected. My pedal was rock hard with the same return spring I had on my carb, so I just removed it and rely on the Sniper's return spring. It's the tip-in that way too antsy. TPS always returns to 0% at idle.