I noticed this evening my tachometer has a delay....I rev, 1/2 second later the tach reacts. Just noticed it today. An ideas would be appreciated.

 

Mine does it too, immediately after I had my stage 2 installed. I didn't remember it doing it before, but it was the first thing I noticed when I left.

 

have you had it back and questioned the dealer (I assume hey reflashed your car)? I have had the stage 1 for about 2 yrs now...hmmmm

 

no haven't taken it back, I thought I was crazy but it's done it ever since....and I hardly notice it now so I just let it go, it's acurate other than that initial blip

 

its an electric gauge not mechanical so maybe thats why?. . .

 

Thanks for the input...Keep the ideas coming, that's what makes this site great.

 

is the car stock?

 

gm stage tune, pulley,airbox mod, mag.muffler,3922 auto lites..nothing major

 

I believe the tach is ahead of the engine in 1st and 2nd gear...meaning redline is 7000 but in those gears the tach travels past that 200 rpm or so. At least that's what I've noticed and heard. It's a redline but I guess the cobalt ss/sc is the same.

 

If I am idling and just blib the throttle the tach will read idle for 1/2 , maybe more, then it will move. I guess you could call it a rubber band effect. It has been fine up until I noticed it today. I would like to see a wiring schematic for our cars someday.

 

It's a known issue , GM has a tsb out for it . I'll see if i can find it .

Here it is




Service Information 2006 Chevrolet Cobalt | Cobalt, Pursuit (VIN A) Service Manual | Document ID: 1887694
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#PIP4023: Inaccurate Tachometer At High RPM with GM Performance Parts Stage 1 Or 2 Kit - keywords accuracy cut cutoff early engine fuel high I II kit limit limiter no off rev RPM stage superch17801947 17803229 - (Jan 15, 2007)


Subject: Inaccurate Tachometer at High RPM with GM Performance Parts Stage 1 or 2 Kit


Models: 2005-2007 Chevrolet Cobalt SS

2004-2007 Saturn Ion Redline

with 2.0L Engine (VIN P - RPO LSJ)

and a GM Performance Parts Stage 1/2/3 Kit




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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
The tachometer used in the Ion Redline is Class 2 based and the one used in the Cobalt SS is LAN based. As a result, the tachometer display rate is slower than the engine acceleration rate during hard acceleration. This may cause an approximate tachometer delay of 500-600 RPM in first gear and 250-300 RPM in second gear. As a result, some customers may advise that their engine reaches fuel cut off before the tachometer displays 7,000 RPM even though the actual engine RPM is actually at 7,000 RPM. Once the vehicle is shifted to third gear, the engine acceleration and tachometer display rates are similar so the tachometer should display actual engine RPM on hard acceleration.

Recommendation/Instructions:
If this concern is encountered, it should be considered a normal operating characteristic of the tachometer when the vehicle is equipped with a GM Performance Parts Stage 1/2/3 Kit. As a result, do not attempt any repairs to try altering this characteristic.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION


Š 2008 General Motors Corporation. All rights reserved.

 

thanks for the write up Rukkee. that is interesting how they advise that no repair be attemted. I have always noticed the innacuracy of the 1st, 2nd gear tach swing. Mine is now VERY noticebly any where in the tach range. It will not respond to the engine immediately but if held at a certain rpm it will catch up and I assume read accurately...it even delays on the decell of the engine. Thanks again everyone for their input.

 

What your having sounds like a different issue then , the only problem with that is trying to get GM to fix it. They will look at this TSB and automatically dismiss the problem. Good luck with the car .

 

tach inacuracy is something we gotta live with. being electronic and having the signal sent through a lan network its going to have lag, nothing that can be done. its not noticed untill you start upping the power, the tach just doesnt respond fast enough for free-rev or 1st and 2nd gear pulls.

if you continually hit the rev limiter because of this problem, id recomend an aftermarket tach, or even just a shift light. i set my areoforce up for a shift light, i have it set at 6400, i shift 2nd as soon as the light comes on and 3rd 1 second after the light comes on. the interceptor reads the rpm signal through the obdII system so it has the lag on the interceptor aswell.

 

I've done something similar with my interceptor, set it way down at like 6500. This way, it lights up at you with a split second to spare before you bounce the rev limiter. I agree here though, the only real fix would be a mechanical tach or a shift light that doesnt rely on the odbii port.