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LT1 running rich....and shooting out black spray

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  • #1

    LT1 running rich....and shooting out black spray

    I noticed a couple time recently that when I start my car it would shoot black spray out the exhaust. This last for about 15 seconds.
    Recently the car was in the shop for clutch work and it would not start, they pulled some plugs and they were badly fouled and black. They put some new NGK plugs in and it fired right up.
    The plugs I had in it were the regular Bosch plats that were put in in 98 at about 40K. The car now has 72K and has always run well.
    I replaced the two O2 sensors and noticed that the driver side sensor was big time fouled and the passenger side was more normal looking.
    My question is were the crappy Bosch plats the reason for this problem and should I check or replace anyhting else. I do have the MAF screen out, does that also cause this problem. Again right now the engine is running strong.
    Thanks
    1995 Z28 Convertible, 350ci LT1 73K miles M6.
    Dyno results: 301.5 RWHP 326.7 RWTQ
    Performance Mods 4.10 gears, AS&M CAI, MADZ28 tune, Borla catback, RK Sport mid-length headers, LT4 valve springs, CC pro mag 1.6 RR's, LT4 KM, MSD OVC wires, TB bypass, 160 t-stat, SLP clutch plate w/Kevlar dual friction disk, 52MM TB, TB air foil, 1LE aluminum driveshaft, ASP UD pulley, LS1 brakes w/ Hawk HPS pads, LCA's and PHB.
    Tags: None
  • #2
    I would be the most suspicious of the MAF. I've heard that de-screening the MAF isn't the best thing since contamination can occur if debris gets past the air filter onto the MAF ribbon.
    Darrin C
    '97 Z28 LT1 157K (((S O L D ))) A4, C/I Cold Air Induction, Flomaster Exhaust, SLP Fan Control Mod, Eibach Springs w/1" Drop, Racing Dynamics Shock Tower Brace, Lakewood LCA's.
    07 Ford F150 - Daily Driver. I went from f-body to f-series. I think I'm out of my f'in mind.....

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    • #3
      Is there a way to clean the MAF. Im going to clean the throttle body also. That must be gas that was spraying out the exhaust pipe.
      1995 Z28 Convertible, 350ci LT1 73K miles M6.
      Dyno results: 301.5 RWHP 326.7 RWTQ
      Performance Mods 4.10 gears, AS&M CAI, MADZ28 tune, Borla catback, RK Sport mid-length headers, LT4 valve springs, CC pro mag 1.6 RR's, LT4 KM, MSD OVC wires, TB bypass, 160 t-stat, SLP clutch plate w/Kevlar dual friction disk, 52MM TB, TB air foil, 1LE aluminum driveshaft, ASP UD pulley, LS1 brakes w/ Hawk HPS pads, LCA's and PHB.

      Comment

      • #4
        You could try to blow some air (gently) where the ribbon is. But I'd be very careful because it's very sensitive. If debris such as bug parts or dust got on the unit, it would skew the readings causing a rich condition in the motor. That's why they put the screens on there. There are a couple of ways to test if your MAF sensor is intermittantly faulty . . . .Idle your engine until warm. With the engine running, tap the flat portion of the MAF sensor with a screwdriver. If the engine stumbles or stalls, the sensor is toast. If this doesn't work, use a SCAN tool - they should have a "MAF mode" to diagnose MAF problems quite easily. Here in San Antonio, Autozone loans them out for free with their Loan-a-Tool program. Hope this helps and as they say in China . . . ."Good Ruck."
        Darrin C
        '97 Z28 LT1 157K (((S O L D ))) A4, C/I Cold Air Induction, Flomaster Exhaust, SLP Fan Control Mod, Eibach Springs w/1" Drop, Racing Dynamics Shock Tower Brace, Lakewood LCA's.
        07 Ford F150 - Daily Driver. I went from f-body to f-series. I think I'm out of my f'in mind.....

        Comment

        • #5
          The problem with removing the screen is that it alters the calibration of the meter. It's there to provide "smoothing" of the air flow distribution across the open area of the meter. If you have particles in the airstream big enough for that course "screen" to catch, you have bigger problems.

          When cleaning it, I wouldn't use any sort of compressed air. Some people have tried "electronics parts cleaner" and it seems to work. Do not use any sort of solvent. Who knows what they coat those riboons with. I believe there may be a thin-film deposition on there for conductivity.

          Put it on a data logging scanner. Look at the critical sensors, and in particular the long term fuel corrections (aka "block learn multipliers", BLM's). If you run a log, there are a few of us that will help you out by reviewing it. I also have an online guide to interpreting scanner data.

          You can download "FreeScan" for "free".... and you can download TTS DataMaster and use it 20 times before you have to license it. All you need is a laptop and a cable from AKM Electronics.
          Fred

          381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

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          • #6
            Thanks, the MAF screen is going back in. I wonder why the left O2 sensor was so much more fouled than the right one. Could it be just those crappy plugs.
            1995 Z28 Convertible, 350ci LT1 73K miles M6.
            Dyno results: 301.5 RWHP 326.7 RWTQ
            Performance Mods 4.10 gears, AS&M CAI, MADZ28 tune, Borla catback, RK Sport mid-length headers, LT4 valve springs, CC pro mag 1.6 RR's, LT4 KM, MSD OVC wires, TB bypass, 160 t-stat, SLP clutch plate w/Kevlar dual friction disk, 52MM TB, TB air foil, 1LE aluminum driveshaft, ASP UD pulley, LS1 brakes w/ Hawk HPS pads, LCA's and PHB.

            Comment

            • #7
              The MAF is not going to cause an imbalance between banks, the MAF affects the system as a whole. If one bank is fouling, look to items that affect that bank. You could have bad plugs, wires, distributer, injectors, 02 sensors, etc. A scanner would help greatly. Reading sensors beats guesswork any day.

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