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  • Help: Intermittent starting problem

    Gents,

    My 94 Z28 with a rebuilt LT1 has had a peculiar and intermittent starting problem as of late. Here's the symptons:

    - car runs fine and usually starts fine. Periodically (usually at the worst possible time), it won't start. Engine cranks normally, but no ignition. After anywhere from a few minutes to a couple of hours, the car starts fine again. Weird.

    It almost acts as if it's flooded (does have a new non-stock cam), but it didn't start doing this until after I put about 1000 miles on the cam.

    If it was a fuel supply problem, it seems like I'd get inconsistent performance while driving, but this is not the case. I'm wondering if one of the sensors could be fouled (throttle position, crankshaft position sensors for example) and possibly disrupting the starting process due to bad info being sent to the computer...resulting in improper fuel scheduling???

    I'd appreciate any help anyone might be able to provide. Thanks.

    RockF16

  • #2
    Have you checked the fuel pressure?

    Have you scanned it for codes?

    When it won't start, have you checked for spark?

    How old are parts like plugs, wires, coil, IC Module and Opti?

    Who tuned it for the cam? What else has been done beside the cam?

    When you feel its "flooding", will it start quicker if you put the throttle on the floor, to put the PCM into "clear flood" mode?

    A full scan data log would allow you to observe things like TPS voltage, MAP, MAF, IAC counts, coolant temp sensor, inlet air temperature, etc.

    Your engine doesn't have a traditional "crank position sensor". The Opti includes a cam position sensor that allows for full sequential injection. The CKP sensor was added to the 96/97 LT1's to detect misfires. Loss of the pulse signals from the Opti can cause no-start conditions. Intermittent problems can be the result of a corroded or damaged Opti harness connector.

    Can you correlate the hard/no-start to periods of high humidity?
    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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    • #3
      I'm sure it's frustrating. When the car won't start, you need to determine what is missing.... ie either fuel or spark. Here is a diagnostic for a no-start condition (provided that the car is acting up when you try to run this) Note that this is an Ignition diagnostic and not fuel.....

      http://www.f-body.com/forum/showpost...48&postcount=7

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      • #4
        After checking all that, i'd have the battery tested at a parts store...
        -Ryan-


        1997 Pontiac Firerbird Formula LT1/T56
        2006 Pontiac G6 GTP, 3.9L V6, 6-spd

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        • #5
          Originally posted by Injuneer
          Have you checked the fuel pressure?

          Have you scanned it for codes?

          When it won't start, have you checked for spark?

          How old are parts like plugs, wires, coil, IC Module and Opti?

          Who tuned it for the cam? What else has been done beside the cam?

          When you feel its "flooding", will it start quicker if you put the throttle on the floor, to put the PCM into "clear flood" mode?

          A full scan data log would allow you to observe things like TPS voltage, MAP, MAF, IAC counts, coolant temp sensor, inlet air temperature, etc.

          Your engine doesn't have a traditional "crank position sensor". The Opti includes a cam position sensor that allows for full sequential injection. The CKP sensor was added to the 96/97 LT1's to detect misfires. Loss of the pulse signals from the Opti can cause no-start conditions. Intermittent problems can be the result of a corroded or damaged Opti harness connector.

          Can you correlate the hard/no-start to periods of high humidity?
          Thanks for the prompt replies, gents. I've been dealing with a family emergency so I haven't had a lot of time to look into the starting problem. As for your comments:

          First, a simple question: What's the best way to check for spark and/or fuel pressure when I get the no-start?

          More info: I recently had the engine overhauled by a shop in California. Nothing major, but I did have the heads ported/rebuilt and a new cam installed. On the invoice the cam is listed as "266 HR-14." With the overhaul, I have a new optispark, plugs, wires, etc. The engine builder did not reprogram the computer, which I thought was strange but his opinion was that the stock program was fine (he had a good reputation, so I figured he would know better). Overall, the car runs great; it has noticeably more power (and worse gas mileage as might be expected). At times it will backfire midly through the intake when operating in open loop in high gear and under load (like going uphill).
          As for the starting problem, it's completely intermittent. It does seem to happen more often when the car is shut down after short trips (i.e. not up to normal operating temperature...perhaps still in open loop). In every case, after for an undetermined amount of time (sometimes several minutes, sometimes a couple of hours), the car starts fine again. I let Mr. Goodwrench keep it for a week and they could replicate the no-start condition.
          There is no humidity correlation and the battery is fine (engine crank is always strong). No codes. The only parameters I can view are with a simple OBDI scanner. If you have a recommendation for laptop computer software that would enable more thorough analysis that would be great.

          Respectfully,
          RockF16

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          • #6
            Spark indicator: $20 at parts store

            Ghetto method: see if the plugs are wet with gas. with plug
            (#1 or 3 are easy to get to) removed, ground it and have a partner try to start the car. if grounded properly and ignition system is flawless, the plug should spark. It works best in a dark place.

            PS Use Joe's ignition troubleshoot first!
            -Ryan-


            1997 Pontiac Firerbird Formula LT1/T56
            2006 Pontiac G6 GTP, 3.9L V6, 6-spd

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