Johnv

Hi,
I'm helping a guy out who has transplanted an LS1 into a boat.
He has had the loom proffesionally lengthened buy 25 feet so the PCM can be located in the cabin (I personally would not have gone that route).

Anyway, got it fired up and noticed MAP at ldle is reading low (30 kpa) as is the idle RPM (target is 800rpm , only reads 550 rpm)in EFIlives scan tool.
but is definatly idleing around 800rpm just reading low in the scan tool.

So would all that extra loom length possibly cause lower readings at the PCM ?

Will check MAP Kpa key on engine off, tomorrow .

slammed240wagon

I'm new to the SBC crowd, so I don't know the PCM logic. However, 25' is a very long wire, and I'm sure has a pretty high resistance. I would check for voltage drop between the sensor and the PCM.

LSX Power Tuning

iTrader: (4)

I have tuned several old ls swap cars with the pcm all the way in the trunk and they ran normal. However they all had new harness made that long and didn't have a factory harness extended and none were 25ft long.

2xLS1

iTrader: (25)

Wire length shouldn't change the frequency of the signal the crank sensor is sending to the pcm that determines rpm. How can you say it is definitely idling at 800 rpm if you don't believe what the scanner is showing.