• Vishnu Procede N54 misfire mystery solved? CPS offsetting to blame?


      With all the discussion on the CPS offsetting lately, I have been delving deeper into this topic and contacting various tuners to get to the bottom of it. Now, we all know the Procede has had and still has misfire problems and the JB has not had this problem. As I have learned more about the impact of this system I have spoken to a couple tuners who pointed me in the right direction.

      What is the major difference between the two? CPS offsetting.

      Why would CPS offsetting cause misfires? Well, if the CPS offsetting is based on load and not static it will wreak havoc with the misfire detection of the DME. Here is how the Procede does CPS offsetting:

      So, the more load the more offset. Why is this a problem? The ECU uses the CPS signal to mesaure the acceleration of the crankshaft. If the acceleration value is outside what the DME expects, it is interpreted as a misfire. So when the ECU goes to measure the crank speed and this signal is changed, boom, misfire.

      Why has this been difficult to pin down? Because the Procede varies the offset and it isn't static. CPS offsetting isn't the right way to reduce ignition timing but the only option the Procede really has, as do all N54 piggybacks. Since the number isn't static misfires will happen based on a ton of variables that affect the ECU, load, weather, rpm, VANOS, etc. This is why there is no rhyme or reason to it only the constant of CPS offset.

      Further evidence that supports this theory is that Terry of BMS has recently been doing CPS Offset Testing and has been able to induce misfires with the CPS offsetting. So, hopefully this clears things up for people and to be noted a static offset may be best to prevent misfires. Ideally though, tuners we have contacted stated they believe such a vital part of the way the factory DME functions should not be messed with due to its impact on VANOS and the knock detection system.
      This article was originally published in forum thread: Procede misfire mystery solved? CPS offsetting to blame? started by Sticky View original post
      Comments 188 Comments
      1. dzenno@PTF's Avatar
        dzenno@PTF -
        Running meth at 20F doesn't do anything for cooling the charge as its already cooled with IATs very close to 20-30F as well...you could only pull off more octane but not much with meth

        When very low IATs are detected by the procede additional CPS offset is applied instead of reducing boost...same effect on AFRs in the end (either reduce boost or reduce timing) but done differently...
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by dzenno Click here to enlarge

        You will not gain power by adding timing retard obviously but you will prevent timing dropouts which do cost power. Procede attempts to make for an optimum timing curve by adjust this offset run to run.
        The DME already adjusts for the optimum timing curve and does so with no sacrifices.

        Hence why if the DME is left alone it makes more power with all the safetyguards in place.

        Surprised people don't refer to CPS offsetting as a band-aid.
      1. dzenno@PTF's Avatar
        dzenno@PTF -
        Click here to enlarge Originally Posted by Sticky Click here to enlarge
        The DME already adjusts for the optimum timing curve and does so with no sacrifices.

        Hence why if the DME is left alone it makes more power with all the safetyguards in place.
        That's one school of thought, yes
      1. Vertigo's Avatar
        Vertigo -
        Click here to enlarge Originally Posted by dzenno Click here to enlarge
        Does the JB4 still apply a boost decay with IAT? Pretty important...if it just keeps the same boost that you set it could get very dangerous, running say 16psi on pump 94 gas at 50F is like 18psi at 20F, would definitely cause a VERY lean condition and potential catastrophe
        Can you expand on this please? I understand the air would be denser at cooler temps but why would it be dangerous when the DME is trying to maintain a targeted AFR? Wouldn't the DME add more fuel to prevent a lean condition?
      1. themyst's Avatar
        themyst -
        Click here to enlarge Originally Posted by Vertigo Click here to enlarge
        Can you expand on this please? I understand the air would be denser at cooler temps but why would it be dangerous when the DME is trying to maintain a targeted AFR? Wouldn't the DME add more fuel to prevent a lean condition?

        This is a very outdated thread. Vishnu has fixed their tune related misfire issues and there is no fuel limit as Cobb showed us. With piggybacks, fueling still proves to be a challenge.
      1. nafoo's Avatar
        nafoo -
        Click here to enlarge Originally Posted by themyst Click here to enlarge
        This is a very outdated thread. Vishnu has fixed their tune related misfire issues and there is no fuel limit as Cobb showed us. With piggybacks, fueling still proves to be a challenge.
        Weird. Vertigo joined in Feb. 2011 but this is his first post.
      1. scott_uw's Avatar
        scott_uw -
        Click here to enlarge Originally Posted by nafoo Click here to enlarge
        Weird. Vertigo joined in Feb. 2011 but this is his first post.
        Gotta register to lurk remember? 5 thread viewing limit before the nag screen comes up iirc.
      1. nafoo's Avatar
        nafoo -
        Click here to enlarge Originally Posted by scott_uw Click here to enlarge
        Gotta register to lurk remember? 5 thread viewing limit before the nag screen comes up iirc.
        Yeah, but why lurk for so long and then revive a thread over a year old?