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  1. #1

    Default Jeep Vacuum Advance

    I've installed the Sniper on my 258 inline 6 on my '83 CJ7. I've done a few modifications to the engine, including a HEI ignition with vacuum advance. My problem is when I'm in fourth gear on the highway, I'm not getting the advancement the engine needs and it starts cutting out. I've advanced it as much as I dare, and it helped on the top end, so I know that's my problem (I first thought it was a fuel issue). Do I need to swap the vacuum advance HEI for a magnetic pickup? What would the part number be for say, a MSD? When I look up for a Jeep, they all give me the same vacuum advance. Thanks, Todd

    Attachment 2503

  2. #2


    Are you using the Sniper EFI for timing control? If yes, you should lock out all mechanical and vacuum advance mechanisms. If not, your timing behaves exactly as it did with a carb. So any issue you are facing probably is not directly related to the Sniper EFI. The may be related to installation errors, though. Have you checked for vacuum leaks?

  3. #3


    I have the vacuum port on the Sniper EFI connected to the vacuum on the distributor, so I guess I'm using it for timing control?
    The vacuum port gives one "draw" at WOT, but if you ease into the throttle, nothing happens. I've checked for leaks.

  4. #4
    Join Date
    Dec 2009


    Quote Originally Posted by RTIrvin63 View Post
    I have the vacuum port on the Sniper EFI connected to the vacuum on the distributor, so I guess I'm using it for timing control?
    No, ECU timing control doesn't use the distributor's centrifugal or vacuum advance mechanism. A locked out distributor distributor is used for ECU timing control. You'll need someone to help you with this.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  5. #5


    There are three vacuum ports. Are you using the one closest to the Sniper regulator (return line)?

    The vacuum port gives one draw.
    This isn't how the advance port works. It should be constant vacuum when applicable, not a single pulse.
    Last edited by Zmann; 09-03-2017 at 01:49 PM.

  6. #6


    So, from what I can tell, I would need to lock out the vacuum advance, get the MSD rotor cap, set the cap, etc. I think that's my problem, is that I didn't install the required cap. Here's a pic of where I have the vacuum line connected. I have an ACCEL HEI distributor now.
    Attachment 2507
    After studying a little more, I see the adjustable MSD cap won't fit anything but MSD. What do you all suggest? Just get a MSD distributor (part number?), or go full bore with the 6A install? Thanks, Todd
    Last edited by RTIrvin63; 09-03-2017 at 05:47 PM.

  7. #7


    I have an '89 Jeep with 4.2 put a Holley Sniper EFI on it and it runs for a bit, then quits. I was wondering if you used the vacuum advance on the factory manifold or block it off, or use the one on the throttle body?

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