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Thread: Cold start & warm up - rear cylinders excessively lean.

  1. #1

    Default Cold start & warm up - rear cylinders excessively lean.

    390 FE, controlling timing, dual-plane Ford Police Interceptor intake. I’ve spent quite a bit of time tuning and dialing in the tables. I love how it runs, except for the first 3 or 4 minutes from a cold start once the air temp drops below 50°F or so. The rear cylinders are not firing consistently until the engine comes up to temp and coolant is reading 130°F or higher. Once the engine hits 130°F, it purrs beautifully. I’ve chased compression and electrical with everything specing out nicely.

    I have the secondaries adjusted to come in later. Could this be the problem? Until the intake gets some heat in it, it seems like the fuel from the front two barrels just isn’t getting distributed well enough. Any suggestions appreciated.

  2. #2

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    Go back to 1:1 linkage and see if that makes it better. If it does, then you'll have to decide what to do. Another test would be to try a carb spacer. I'd try a one inch open spacer to see what happens. These are just tests. Once you test a few things, then you can decide which solution to use. Another option would be a different intake manifold, but that isn't that easy of a test to make on an FE engine.

  3. #3

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    Are you using a temperature gun?
    Separate WBO2 sensors for each cylinder?
    How lean is lean?
    Which tables have you adjusted and by how much?

  4. #4
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    Quote Originally Posted by Flatlander View Post
    I love how it runs, except for the first 3 or 4 minutes from a cold start once the air temp drops below 50°F or so. The rear cylinders are not firing consistently until the engine comes up to temp and coolant is reading 130°F or higher. Once the engine hits 130°F, it purrs beautifully.
    If this engine ran fine with a carburetor, then check the Coolant Temperature Enrichment % table tuning, and maybe the A/F Ratio Offset table tuning.
    http://forums.holley.com/showthread....6649#post66649 (Coolant Temperature Enrichment % Table Tuning)
    http://forums.holley.com/showthread....6254#post36254 (Good Starting Advice Thread - Especially posts #2, #4 & #6.)

    You don't want Learning to begin until the engine almost reaches normal operating temperature. So the Coolant Temperature Enrichment % Table should be set to 100% (no modification) just before normal operating temperature. The Coolant Temperature Enrichment % Table is a modifier table for the Base Fuel Table, when the engine is cold and warming up. It's the opposite for Closed Loop. You want the ECU in Closed Loop at all times, as soon as the WBO2 sensor completes its initial heating cycle at key-on. Also check your Closed Loop/Learn parameters. "Enable Closed Loop" and "Base Fuel Learn Enabled" are the only parameters that need to be check marked.

    I have the secondaries adjusted to come in later. Could this be the problem? Until the intake gets some heat in it, it seems like the fuel from the front two barrels just isn’t getting distributed well enough. Any suggestions appreciated.
    Yes, first try reinstalling the 1:1 secondary throttle linkage.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 11.8:1 comp, TFS R-Series FTI ported intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 MT tires.

  5. #5

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    Quote Originally Posted by andyf View Post
    Go back to 1:1 linkage and see if that makes it better. If it does, then you'll have to decide what to do. Another test would be to try a carb spacer. I'd try a one inch open spacer to see what happens. These are just tests. Once you test a few things, then you can decide which solution to use. Another option would be a different intake manifold, but that isn't that easy of a test to make on an FE engine.
    Thanks Andy. I was thinking along these lines and posted such on Jay’s FE forum. I currently have a 4 hole spacer and think it may be adding to the preferential feed.

  6. #6

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    1:1 linkage is NOT an option. The driveability just goes to crap. It runs too good when it’s at temp to ignore. I have no problem adding a single-plane if needed, but I’ll check the open spacer first. In response to Danny’s suggestions: I’ll verify the settings you suggested, but I’m not going to fatten the coolant temp compensation back up as a Band-Aid for the distribution issue.

  7. #7
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    Quote Originally Posted by Flatlander View Post
    1:1 linkage is NOT an option. The driveability just goes to crap. It runs too good when it’s at temp to ignore. I have no problem adding a single-plane if needed, but I’ll check the open spacer first.
    The driveability is poor because it's not tuned for it. I've successfully ran 1:1 and progressive secondary throttle linkages on my previous 460" & 508" BBF engines with an Edelbrock Performer RPM Air-Gap dual-plane intake manifolds. A decade ago, Holley TBI throttle bodies were all 1:1. And you don't need a single-plane intake manifold either.

    In response to Danny’s suggestions: I’ll verify the settings you suggested, but I’m not going to fatten the coolant temp compensation back up as a Band-Aid for the distribution issue.
    You can't "verify" the parameters, you have to "tune" them. If the engine ran fine with a carburetor (and I'm sure it did from Ford), then it's not a distribution issue.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 11.8:1 comp, TFS R-Series FTI ported intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 MT tires.

  8. #8

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    For what it's worth, I tried three variations with my 390. At the time it had a iron "S" manifold. The 1" open spacer ran great, but I had the IAC whistle. I put in a 1/2" 4 hole spacer - whistle was gone, but it didn't run nearly as well as the open spacer. Third try was cutting out the middle of the 4-hole. Whistle was gone and it ran as well as it did with the open spacer. Move forward to my new 447 stroker with a single-plane intake - same Sniper. I put in the 1" spacer and it whistled. Ran good, but the whistle is annoying. So, I put the 1/2" spacer with the center cut out and the whistle is gone and it runs great. So, if you have a 1" spacer, try it. If you're willing to "modify" your 4-hole, I would be tempted to start there. Some dual planes work great with a 4-hole spacer, but if you're running progressive, the IAC will open up for high idle, but only the back 4 barrels see that initially. Cutting the center out of the 4-hole will allow some side-to-side and front-to-back flow, which I think is important for any type of progressive.

    If you do cut out the center of the spacer, you can use a open or 4-hole under the Sniper, but you need to run an open gasket between the spacer and the manifold.

  9. #9

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    Quote Originally Posted by Flatlander View Post
    1:1 linkage is NOT an option. The driveability just goes to crap.
    I can see how that stroker is tough to get going from a dead stop with the 1:1 linkage. Throttle extension might be ideal in this scenario.

    I might have misread, but I don't know how you are determining the lean cylinders.

  10. #10
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    GPatrick, good point. We've discussed the benefit open center plenum dividers on this forum before.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 11.8:1 comp, TFS R-Series FTI ported intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 MT tires.

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