all ears here on this thread. My Accel DFI gen VII system shows RPMs quite lower than displayed on the tach gauge.
Tach cluster VS laptop readings
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
Tach cluster VS laptop readings
The past few days I've been logging my car using datamaster. I've always known that my tach was off but I never knew it was this off. My tach is about half off compared to what my laptop is telling me. My tach will say i'm at 5k but the laptop will say 2k. Should I trust my laptop that much? When I was driving today my laptop said I was at 3k and the shift light came up on the dash. I've never seen the light before and I've had the car for 3 years. Does the shift light come on to give me the best fuel economy? Are the Datamaster readings worth trusting? I would assume since it is coming straight from the ECM.
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Yes there is something not right, so here is what id do. Get a decent digital voltmeter with an induction pickup to display RPM, click it over one of your plug leads and see what it tells you compared to the dash and the laptop. It will not lie as long as the plug youve connected the pickup to is firing every time it should 
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
Should I trust my laptop that much? When I was driving today my laptop said I was at 3k and the shift light came up on the dash. I've never seen the light before and I've had the car for 3 years. Does the shift light come on to give me the best fuel economy? Are the Datamaster readings worth trusting? I would assume since it is coming straight from the ECM.
Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
Le Mans Master
Joined: Apr 2005
Posts: 6,413
Likes: 9
From: The Old Dominion
Alright, well when the tach says 5k and the laptop says 2k, what does your gut tell you the motor is doing?
What transmission and rear end ratio do you have? You can get a good idea of the rpm if you know the speed and the gearing.
What transmission and rear end ratio do you have? You can get a good idea of the rpm if you know the speed and the gearing.
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Thread Starter
Safety Car
Joined: Mar 2005
Posts: 4,723
Likes: 11
From: Winnipeg Manitoba, Canada
I tend to trust the laptop more because I know the tach is way off. I can hear that it's off. I'm just scared because the engine has just been rebuilt. It has way more top end power then before and I would like to know where I'm at on the tach. I'm going to fix the cluster after I tune the car properly but would just like to know that I can trust the laptop. It has a ZF 6 speed with the stock rear end of 3.33.