Sniper EFI flat spot at ~2200 RPM

desmocruiser

SILVER Star
Joined
Dec 17, 2005
Messages
1,622
Location
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?
 

Skreddy

SILVER Star
Joined
Feb 3, 2020
Messages
1,780
Location
Stanwood, WA
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?
 

desmocruiser

SILVER Star
Joined
Dec 17, 2005
Messages
1,622
Location
Big Orange Country, TN
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.
 
Joined
Apr 7, 2021
Messages
635
Location
Minnesota
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.
 
Joined
Apr 7, 2021
Messages
635
Location
Minnesota
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.
 

desmocruiser

SILVER Star
Joined
Dec 17, 2005
Messages
1,622
Location
Big Orange Country, TN
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?
 

wngrog

Moderator
SILVER Star
Joined
Feb 10, 2002
Messages
42,660
Location
Canton, Mississippi
Website
www.seeandeatms.com
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
 

desmocruiser

SILVER Star
Joined
Dec 17, 2005
Messages
1,622
Location
Big Orange Country, TN
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 !
 

Users who are viewing this thread

Top Bottom