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Thread: ZZ502 '68 Camaro fouling plugs?

  1. #1

    Default ZZ502 '68 Camaro fouling plugs?

    OK, guys let me start off by saying I wanted to exhaust every mechanical issue and read some posts and input I could think of before posting another crumby idle post. LOL.

    '68 Camaro ZZ502 Tanks Inc. fuel tank -6AN supply & return
    (fuel psi good) spark is still GM HEI (new rotor, Coil, Cap, Plug wires, plugs, timing verified good) and battery voltage, compression test good, no oiling issues. It has the Fast EFI throttle bracket and I also have the cable for my PC connection.

    Problem is I can't get this thing to idle or fire off without 7-15% TPS which holds the IAC at 20% when it does drop and the IAC goes to 100 and slowly dies still. (Yes I waited until 160°F - even though it takes a bit to get there.) So first first fire it seems to do decent for a small period until it starts fouling the heck out of plugs (soot, not oil), then it's completely shot. I'm somewhat familiar with EFI so I leaned the idle out from 13.5 to 14.1 and backed the Coolant Temperature Enrichment % out 10% with the same result. I even tried covering the IAC hole to dial it in. Where else do I start? This can't be good for the WBO2 sensor and changing plugs is starting to become worrysome. I'll pay someone to modify my calibration and dial it in with me if needed.

    I was planning on paying someone for a custom calibration for my car, but I can't even get this thing to quit fouling plugs to do a proper datalog. I've attached the Config File. Thanks again for all your help! And for a good custom tune I was looking into Chris at I was hoping for someone with some big block Chevy experience.
    Attached Files Attached Files
    Last edited by Pearl68; 04-08-2021 at 11:38 AM.

  2. #2


    Based on your Learn Table, I'd say you have a massive vacuum leak. The leak is so bad that you won't be able to get that engine to idle. Good news is that when the leak is that bad, you should be able to find it fairly quickly.

  3. #3


    OK, I'll dig into it. Only thing changed was the 4150 from carb to Holley really. I know the cam is pretty decent sized from GM too. Thank you.

  4. #4


    You should watch your vacuum gauge (or MAP sensor) next time you try to start the engine. The Learn Table shows that the engine is idling with 100 kPa, which is basically impossible. Do you know how to start a datalog? If not, you should read the instructions. Knowing how to datalog will help you solve problems.

  5. #5


    The time I have to get that going before it fouls the plugs and chasing the leak will be pretty task oriented. I'll read up and get a datalog going

  6. #6
    Join Date
    Dec 2009


    Originally Posted by Danny Cabral
    For further assistance, post your Config File and a short datalog of this occurrence for us to analyze.
    Also, review the datalog and inform us of exactly where in the datalog (time/seconds) the problem occurs.
    Datalog & Global Files can be linked to a document hosting website. I use
    Files can also be "zipped" (compressed zipped folder) & attached directly to a forum post ("Go Advanced" & "Attachments").
    Your Config File is in the "Documents", "Holley" folder, "Sniper" folder, "Config Files" folder (.hefi file).
    Your Datalogs are in the "Documents", "Holley" folder, "Sniper" folder, "Data Logs" folder (.dl file).
    Someone will analyze/troubleshoot the problem & offer advice. (How To Record & Email A Datalog)
    Overlay the datalog onto your Config File, and pay special attention to the center paragraph in blue print:
    Originally Posted by Danny Cabral
    Quick Datalogger Information:
    Always provide data, not just symptoms. Is the AFR & ignition timing optimized? Overlay the datalog onto your Config File.
    Ensure the Target A/F Ratio table is properly programmed for your engine. Ensure the ECU is "Learning" (Learn Table LINK).
    Scroll through the datalog to the problem area. Then look exactly where this happens on the Base Fuel & Timing Tables. Scrutinize:
    RPM, MAP, MAT, TPS, CTS, IAC, Target AFR, AFR Left, CL Comp, Ignition Timing, Duty Cycle, Fuel Flow, Fuel Pressure & Battery. When the engine is tuned & running well, you should decrease the Closed Loop & Learned Compensation Limits % to lock in a good tune.

    Using the Holley Sniper EFI software (LINK), look at where the live cursor moves to during this occurrence, and
    manually tune that area of the Base Fuel Table (enrich or lean) & Base Timing Table (optimize ignition timing).

    I find the most helpful datalog function, is overlaying the datalog on your Config File.
    I'm in the habit of using the datalog Overlay feature every time I review a datalog.
    Click on "Datalog" (on the top Toolbar), "Activate Overlay", then "Open Data Log".
    You can literally "playback" a recorded event, and watch it as it happened on any screen.
    Minimize (shrink) the datalog window, and move it to the bottom of any Config File screen.
    Then click & scroll anywhere on the datalog, and watch it playback on your Config File (EFI software). (Holley EFI Datalogger Instructions) (Datalog Information - Read "NOTES") (How To Record & Email A Datalog) (Closed Loop Datalog Tuning - Posts #2, #4 & #6) (Holley Sniper EFI Datalogging Tech Video)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, 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, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, 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 M/T Street Comp tires.

  7. #7


    Initial checks the driver side PCV hose that was hooked to carb base previously was unhooked. I'm hoping that was the issue. I removed base plug on front of Sniper and routed it there. I'll check back in. I didn't think the PCV would cause major a vacuum leak, but well see.

    UPDATE: Not much change. Got a datalog in before the plugs fouled again. Datalog attached.
    Attached Files Attached Files
    Last edited by Pearl68; 04-08-2021 at 03:38 PM.

  8. #8


    Your Sniper is dumping a ton of fuel into the engine (70 lbs/hr at idle) which is about 10 times more than it needs, but the Sniper still thinks the engine is lean. It has maxed out Learn & Closed Loop, but still thinks the engine is lean. What that means is that either your wideband sensor is dead, or that you have a very large exhaust leak, or that you are running open headers.

    If you have a laptop hooked up then go to the Learn Table and clear it. Turn off Closed Loop and Learn. Fire the engine up and see how it runs in Open Loop. Manually adjust the Base Fuel Table if you want. If that works then figure out if you have an exhaust leak or if your wideband O2 sensor is shot.

  9. #9


    OK, did that now it won't fire. I'll have to wait on my spark plugs to get here. To try again. This is the 4th fouled set, LOL. Thank you. I'll update with a datalog after I get them changed.

  10. #10


    You need to Clear the Learn Table. I'm not sure how, but it's filled with super high numbers. If you need tuning assistance, send me an email: projectgattago at gmail dot com. Andrew

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