Sniper timing & stalling problem.

[Danny Cabral]

I ordered a new alternator to start. To the best of my knowledge, this one is 34 years old, so it sounds wise to just change it. It's output seems low to me when I monitored it yesterday. I may also swap the battery.

Those old school alternators (Ford 1G, 2G/GM 10SI, 12SI, etc.) output a lot of electrical noise. Modern type alternators (Ford 3G, 4G/GM CS130, CS144, etc.) are much better designs, and output higher amperage at idle RPM. Also, some alternator 4 AWG premium charge cable kits feature noise suppression (LMR SVE-9902A).
https://forums.holley.com/showthread...1964#post61964 (Related Forum Post)
Read posts #90 & #92: https://forums.holley.com/showthread...783#post104783 (Related Forum Posts)

[Bjohnson75]

I'm having a similar issue, but I haven't been able to drive it yet. One minute is will idle just fine for 20 or 30 seconds and stall, and the other, it will surge and stall. Holley said that it may be a high current EMI problem with my coil. I moved my coil and it seemed to still do it. I unhooked my alternator and it didn't seem to matter. My battery is in the trunk, but I have it grounded to the frame, 2 AWG grounds on each side of the block and on on the back going to the firewall. I have another thread, but I'm waiting for someone to check out my datalog. Good luck!

[ajmuller]

Well, huge progress this weekend. I changed the alternator to a CS style, changed main ground location from the stock position on the alternator bracket to the block, added an extra braided ground from the block to the alternator (just in case), and used tinned braided wire covering to shield the only wire that looked like it could generate interference, the power wire for the coil. I also made sure to route my wires as far from spark plug and power lines as possible (most already were, but there were a couple of places I could do better).

I just drove the car for two hours. Local streets, country roads, interstates, and back again. Car ran really well for 3/4 of the ride. Car ran a little hotter than before the Sniper which is interesting. It is about 85°F outside, car has 180° thermostat, and it got as hot as 230°F. I don't remember this car ever getting above 190°F in the past. Not troublesome temps, but certainly a curiosity.

Then the massive vacuum leak!!! Already diagnosed, I followed the instructions above and put my finger over the IAC air port. The car immediately comes down from 2200 RPM to where it belongs and the screaming whistle stops. Based on what was indicated above, I have a bad IAC. I will be calling tech support tomorrow for a new one.

Thanks All! I'm feeling like I am in the home stretch finally.

[ajmuller]

Just a quick update: Tech support still suspects the possibility of electrical interference. They indicated that the majority of IAC problems are not issues with the IAC, but EMI causing it to behave erratically. They are sending me a new IAC, but indicated I should try putting an aluminum shield between the IAC and the distributor. I have also ordered the MSD spark plug wires, Danny recommends to rule them out too. I have 8mm AC Delco wires on there right now, and want to rule out the wires too. Worst case is that I have a spare set of wires. Really stinks only having time to work on it during the weekends. It sure does drag things out.

[Danny Cabral]

Actually, I've always said, "Ensure the fuel injectors or spark plug wires (or any other high voltage wiring) aren't too close to the IAC motor/wiring. The IAC motor is easily susceptible to electrical interference, and it'll cause strange occurrences and become inoperable."

[ajmuller]

Yes, you most certainly suggested interference. That is what set me on that path in the first place. I routed everything as far from the Sniper wires and unit as possible. Spark plug wires routed behind the heads and under the manifolds to keep them as far as possible. They used to run over the valve covers.

This weekend, I changed the IAC and put in the MSD plug wires. I just drove it for two hours in 95°F degree heat with no issues. Well, the car is running hotter than it did, but before it was running very rich so that is probably why.

I'm scared to declare success, since I always jinx myself, but it seems to work perfectly right now. Thanks for all the help. Oh, and those MSD Super Conductor wires are REALLY nice. I think I'll use them on everything from now on.

[Danny Cabral]

Thanks for all the help.

You're welcome.

Oh, and those MSD Super Conductor wires are REALLY nice. I think I'll use them on everything from now on.

Yes, I'm still using them too.

[ajmuller]

Well, good thing I did not declare success, I would've been premature. Here's the story now. The car was running hot in my last post, at times getting all the way up to around 240°. I upgraded to a three row FrostBite Radiator and that brought the temps down where I wanted them. Never higher than 220° on a 90° day. Yay!

I took the car out for an extended version of my typical run. Close to 1.5 hours of driving every condition I could find, even traffic. Car ran absolutely perfectly with the exception of a couple of times where it seemed to try & stall but self recovered. RPM dropped and it felt like it would stall, but did not.

Brought it home and it sat for about two hours. Took it back out and it stalled about 10 times in my subdivision. It would just simply die with no reason. Now for the good part, I datalogged multiple times this happening and brought the SD card inside to try & copy the datalogs. The directory for datalogs was full of garbage. Completely corrupted files & directory structure. I formatted and rebuilt the drive with the SD Card contents from the website.

Tried again. Car behaved the same with the stalling, said it was recording the datalog, but when I brought the card inside, the directory for the datalogs was empty.

Any ideas? I'm typically a very patient person and this adventure has me questioning my sanity.

[ajmuller]

Just an update in case anyone else encounters similar problems. I've determined I had multiple issues that really did not expose themselves until the Sniper install.
A) I had a bad brake booster. It still seemed to drive the brakes, but if you hit the brakes while watching the Sniper display at idle, the IAC would drop to zero. After changing the booster, this problem went away. I suspect it had a vacuum leak, but not a terribly severe leak. I had another vacuum leak in the heater controls. This one was very minor since the size of the lines is minuscule, but it's fixed now.

B) RFI certainly seemed to have been an issue. Things got much better after shielding, rerouting wires, etc. The last bit was wrapping the IAC and its wiring in tin foil. This has eliminated the occasional high idle/IAC stuck open so far. I will let it go a little longer and if it does not come back, I will fabricate a permanent RFI shield out of some copper sheet attached at the mounting studs.