Sniper EFI flat spot at ~2200 RPM (1 Viewer)

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desmocruiser

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Dec 17, 2005
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Big Orange Country, TN
I recently purchased a 78’ FJ40 with a Holley Sniper EFI kit and brought the truck from flat New Orleans at 0’ elevation to hilly East TN and 1000’-1500’ elevation.

I love the Sniper (it is a Mosley kit with the inline fuel pump installed by 49 Tire approximately 2000 miles ago) and everything seems to be operating as it should, quick starts after prime, strong throttle response with the exception of climbing decent grades in 3rd gear at about 2200 RPM. At that point it seems to hit a flat spot and slight sputter and the afr dips to yellow 9 or 10 from 13 or 14 and stops making additional power, it also goes into learning mode.

Is there a different setting or other corrective measure needed or is this a somewhat normal adjustment to change in elevation and hilly terrain and will improve with additional time at elevation?
 
My guess is that it just never learned that area of the fuel map? Driving should take care of it if so.

How’s the ignition system? What distributor and advance? Working properly?
 
My guess is that it just never learned that area of the fuel map? Driving should take care of it if so.

How’s the ignition system? What distributor and advance? Working properly?

It had a new HEI installed along with the Sniper, I will check advance, but it seems to be working properly in other driving scenarios.

I will have a chance to drive it on a few different grades and slight elevation changes later this week to see if/where it duplicates.
 
1500' of elevation isn't much of a change. Even if the setting didn't change at all, I wouldn't think you'd be lean enough to matter.

Zero help, I know. I'm just thinking about motorcycles and jetting. I wouldn't have even bothered with that kind of elevation change. Which makes me wonder if it's something else.
 
1500' of elevation isn't much of a change. Even if the setting didn't change at all, I wouldn't think you'd be lean enough to matter.

Zero help, I know. I'm just thinking about motorcycles and jetting. I wouldn't have even bothered with that kind of elevation change. Which makes me wonder if it's something else.
Correction: Rich enough to matter. Higher elevation, less air density, less fuel needed.
 
99% of Sniper issues are input issues.

Check it all before you dick with the settings.

Fuel filter.

Timing.

O2 sensor.
Thank You!

I am going to address in that order, beyond that I willl be seeking far more expertise.

It appears Holley lists the proper micron replacement fuel filters with Napa P/N’s, should be straightforward enough.

Is there a target advance you have found stock 2F’s with Snipers and HEI’s perform best?
 
Thank You!

I am going to address in that order, beyond that I willl be seeking far more expertise.

It appears Holley lists the proper micron replacement fuel filters with Napa P/N’s, should be straightforward enough.

Is there a target advance you have found stock 2F’s with Snipers and HEI’s perform best?

7-10 usually. I also gap the plugs about .040
 
7-10 usually. I also gap the plugs about .040
9* Seems to be the magic number, thanks for the guidance! I am going to address the plugs, some fluid changes along with a couple of underhood cosmetics when some parts arrive.

I really like the power that the Sniper helps discover, this one performs much better than my still smogged and stock 79’!

Now off to search to remedy a newly developed gas smell after being parked overnight and a solution to a rattling/noisy shifter base !
 

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