pcmhacking.net

hey guys iv got a delco 808 running a tb 42 patrol duel fuel i will be needing a 4600 rpm spark cut limiter because there is no limit on lpg and dont want to over rev it how can this be done ?

You'll need 424 PCM and 11P to do this as the 808 lacks the hardware to do this, otherwise VL400 ignition module with the 808 will work but that's an expensive way about it.

I assume it’s the old single ring gas system in the intake tube or at the throttlebody and not the more modern injected vapour system?
F this is the case there is no simple solution as if you cut spark you now fill the exhaust system with air and gas and when spark is turned back on you’ll get a backfire through the exhaust.
If your not going to limit bash and just set all timing above 4600rpm to about 10-15 degrees, this should at least cut power noticeably, if you bash the limiter like this the exhaust valves will get hot.

Totally agree, spark cut wouldnt be ideal for this.

Can use the soft cut rev limit function in 12P to pul X degrees above a certain RPM. Set the RPM limit to 4600RPM, then the scalar "RPM below upper to begin spark reduction" to 0 and set "Spark reduction value" to something like 20 degrees or so. You will feel it as its a sudden reduction.

ok cool thanks guys ill set the limiter and timing reduction. it is running an old school gas ring system