Scan master RPM?

[10 sec TTa]

Driving to work today I had the scan master set on RPM and I notice at 80 mph on the highway it starts jumping from 2650 to 4000 to 1650 and up and down all over the place. It started to feel a little funny too so I slowed down a little and it seemed fine the rest of the way I kept it under 2200 rpm with no issues. I plan to look at the crank sensor when I get home. I just thought maybe someone else has had this issue?

 

[Nick Micale]

The first thing I would check is the ground wire for the Scanmaster?

It is usually grounded to the dash which provides a poor path back to the battery negative side.

A very common indicator of this is when the SM is reading battery voltage and it shows .2-3 volts less than at the battery.

The engine is a good ground plane as the negative battery cable is connected there, and cast iron is a relatively good conductor, unlike the body and chassis which are composed of many different pieces which provides a difficult path for the current to return to the battery which is a MUST in a DC circuit.

 

[TurboBob]

if it really was the data changing like that, it will run really strange. since the crank sensor is a major factor in both the fueling and spark control.

so certainly check the crank sensor and also perhaps the crank hub bolt.

but it also could be data issues, with the scanmaster ground or something similar, (in which case, other data will be goofy also)

Bob

 

[10 sec TTa]

Thanks for the replies. The ground wire is small and connected to the dash so I will run a better one as suggested tomorrow. Driving home the knock retard went crazy reading blips of 40 plus then nothing then other numbers bouncing around. I have a Caspers knock gauge on the pillar and it showed nothing. I stopped and looked at the wire connections and the white wire in the data port wasn't all the way in. I pushed it back in and didn't get any more goofy readings in the 30 mile trip home. I hope that's all it was but I'm going to take a look at the crank sensor tomorrow as well. Thanks again.