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Erratic timing

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  • Erratic timing

    When I lock the timing at 12* to set base timing, I'm getting erratic readings. The light is bouncing in the range of 10* +/- but I'm getting a few flashes on 12*. I've tried 2 more timing lights but all are older Sears models with the same results. I took the distributor cap off, checked and nothing loose in there. I'm letting the ProFlo 4 fire the coil which is one of the Summit recommended units. Timing advance at idle (warm) is modulating 17* - 22*, I figured that's normal since this unit using air/fuel and timing to control idle. The ECU is mounted on the driver side inner fender so it shouldn't be experiencing RFI noise. Any ideas, try one of the newer timing lights? Thanks.

  • #2
    To clarify, when you lock the timing at 12° you're seeing timing values on the timing light that range from 2° to 22°? Is that correct? That would be a range of +/-10° from a base of 12°. Or are you seeing 10° on the timing light and some +/- wiggle of a degree or two? Not really clear in your description. What engine? What firmware version?

    You probably don't have a timing light problem. There is definitely some timing accuracy variance to be expected with this type of system. The kit uses a distributor mounted positioning trigger system so all the lash of the crank to cam chain and then cam to distributor mean that there will be a difference between the crank's true position and the "sensed" position coming from the distributor. It's always a good idea to bring the RPM up above idle (2000-3000 or so) to help get some of the lash out which will help stabilize the timing. At the end of the day, it's a bit of a trade off in simplicity vs accuracy but luckily the pent roof combustion chamber design with fairly low-ish compression ratios of most engines that Pro-Flo 4 is being used on means that the engines are very tolerant of some minor timing variance.
    Last edited by Nate S; 07-10-2019, 07:19 AM.


    • #3
      Correct on 2 - 22 degrees. 385cid SBC, Firmware; 53. I'm used to mechanical advance, I'll bring up the rpm's and see where we are. I'm confidant that I'm pretty close. I have total timing at 34* with 8* vacuum, so I'm a bit on the safe side. Thanks Nate.


      • #4
        Hmm that's not normal. The timing should be much more steady than that. The typical range I'd expect to see with the timing locked is no more than +/-3° at idle. Bringing the revs up to check timing should be done with the timing locked. When you lock the timing, are you audibly hearing that the engine's tone changes? You might actually want to try a different timing light. I use an old dial back Snap On MT1241 timing light and it shows steady timing when locked. Also, sometimes the direction the inductive clamp is put around the spark plug wire affects how the light works. And sometimes the proximity of the inductive clamp to other spark plug wires can make a timing light read funky. I'm very confident that you're not actually getting that large of a timing variance.
        Last edited by Nate S; 07-10-2019, 07:29 AM.


        • #5
          Yes, I'm hearing an audible change when I lock/unlock timing. I don't think I'm getting that much timing variation either, I think the inductive clamp is picking up some cross feed. I'll play around with it some more tomorrow. I have new Taylor Thunder Volt 8.2 wires so that shouldn't be an issue. Thanks.


          • #6
            Harmonic balancer outer ring slipping.


            Hall-Effect sensor mounting in the distributor loose.
            At 43,861 MPH Elon Musk now owns the fastest car in this Galaxy


            • #7
              Ahhhh.... Never underestimate the power of tin foil. I put the clamp as close to the plug as I could get, then wrapped it good with tin foil. That knocked out about 90% of the fluctuation, then brought the rpm up ~2K and virtually all gone. Just to double check, I took vacuum advance out, set mechanical advance to be in by 2.5K and checked total timing. It's within a RCH of set point, so I'm a happy camper now. Thanks.

              Just as an afterthought, my plug wires are low resistance spiral wound. I'm wondering if they could be creating their own frequency noise that effects the timing light pickup?
              Last edited by CorkyE; 07-10-2019, 07:29 AM.


              • #8
                Nice. Thanks for the follow up.