[Whatwarranty]

Ok so I just purchased this car and put headers and full exhaust on it.when I’m driving the car and alternator is charging (hair over 14volts) I have no issues. Once alternator cuts off (12-13 volts) tach begins to jump on decel and around 3800 rpms. Now since it works when alternator is on I know it’s not a bad ground. My question is how can I make the alternator continuesly charge. Or what will resolve my issue?

[rjacobs]

did you get a tune?

[Whatwarranty]

Not yet. But I don’t see how exhaust would cause my issue. I bought the car and it went straight into garage for exhaust so the issue was probably pre existing.

[Whatwarranty]

I am going to be putting the car on e85 and throwing a tsp vvt3 in I’m just waiting for the phaser limiter that’s on backorder.

[Whatwarranty]

Any ideas?

[iPODFAN11]

Haveth a read below good sir.

PIC6299A: Intermittent Tachometer Fluctuation While Driving

Some customers may complain that the tachometer has erratic operation or that it flares between 1,000 - 7,000 rpm. The engine RPM's will remain constant and drivability is not affected during this concern. This is strictly a gauge issue and is in no way related to engine performance. This condition is not dependent on engine speed, vehicle speed, or the current gear in which the vehicle is operated in. Technicians will also notice that with the scan tool, the Engine RPM parameter in the Instrument Panel Cluster (IPC) and Head Up Display (HUD) will remain constant, even when the concern is happening.

The tach signal that is displayed by the IPC / HUD on these cars originates from the Camshaft Position Sensor (CMP). This sensor reports to the Engine Control Module (ECM). The ECM then sends a signal out on a dedicated Replicated Camshaft Signal circuit, directly to the IPC. The IPC interprets this signal and displays an accurate engine speed signal. A problem may arise when Electromagnetic Interference (EMI) makes its way into this circuit. This will cause the IPC to interpret phantom engine speed counts that are not actually present. As a result, the IPC / HUD tachometer reading may appear to be jumping wildly or acting very erratic. The interference can be caused by any aftermarket accessories, depending on what it may be, and where the wiring harness is installed in the vehicle. Some other known sources of interference are the anti lock brake solenoids and the engine active fuel management actuators. If this Replicated Camshaft Signal circuit has been routed incorrectly and now passes by one of these components, this may induce interference into the circuit and cause the concern. Another common cause of this symptom would be any number of poor grounds on the vehicle.

Depending on previous service work, some technicians may notice that the concern is no longer present after a new IPC has been installed into the vehicle. This will be true as long as the new cluster had not been SPS programmed yet. The base software in these clusters allows the IPC to read the tachometer signal from the ECM over serial data. Not until the cluster is SPS programmed does it look to the Replicated Camshaft Signal for the tach signal. In similar fashion, the scan tool is NOT obtaining the engine RPM signal from this Replicated Camshaft Signal circuit. It takes the information from serial data. This is why the concern may be present and the scan tool reads a consistent, accurate, engine RPM reading. This may lead a technician to believe that the IPC is faulty and require replacement.

For CAMARO models ONLY:

If this concern is encountered, dealership technicians are to inspect the following areas on the vehicle

Important: Just because a ground connection is "tight" or the ground cable will not rotate under the fastener, this does not mean the ground is making a good connection. There may paint under the cable eyelet, glue from the cable manufacturing process, etc., that may still be preventing the circuit from making a good connection to ground.

 1. Closely inspect the large ground cable that runs from G103 to the engine block. This cable attaches to the core support underneath the negative jump post stud on the right hand side of the vehicle. It attaches at the engine near the generator. This fastener may be loose on the engine block, causing a poor system ground.

 2. G201 - IPC Ground - This is located inside the passenger compartment, underneath the RH kick panel trim.

 3. G102 - This ground is located in the engine compartment, on the RH side of the radiator support.

 4. G103 - This ground is located in the engine compartment on the radiator support, near the under hood fuse block.

 5. G130 - This is the ECM ground located on the rear side of the LH cylinder head (V8), the RH cylinder head (V6), or the rear of the cylinder head (I4).

 6. If no obvious ground issues have been found, inspect circuit 121 that runs from the ECM to the IPC for any connection issues. This circuit has several inline connectors. Make any repairs as needed.

IIf the previous locations have been inspected and the concern remains, dealership technicians are advised to call the GM Technical Assistance Center (TAC) for additional direction.

[Whatwarranty]

Thank you. I’ll give that stuff a shot. It’s just weird that it doesn’t do it when car has 14 volts.

[camaro5]

Important: Just because a ground connection is "tight" or the ground cable will not rotate under the fastener, this does not mean the ground is making a good connection.

There may paint under the cable eyelet, glue from the cable manufacturing process, etc., that may still be preventing the circuit from making a good connection to ground.



They have been doing this for forty plus years - paint under ground terminal. Discouraging.

More than one have found the engine ground mentioned here to be the root cause.

n

[vergil]

I have the same issue rpm gauge goes crazy without revving the engine going to take it to a dealer asap. Thanks for the info guys.

[Camaroguy555]

My car had this, it was just a bad ground covered under warranty.

[Whatwarranty]

So update.... issue still exists and now fuel gauge is reading empty or half a tank.

[Whatwarranty]

And solved issue. While checking out my cars fine back side I discovered a 1” strip of mangled rubber. I took wheel off and found chewed up wires they were fuel pump wires. Fixed connections and rerouted the harness. All issues are now gone. Lowering the car I guess caused a slight rub.

[SnakeEyeSS]

Originally Posted by Whatwarranty

And solved issue. While checking out my cars fine back side I discovered a 1” strip of mangled rubber. I took wheel off and found chewed up wires they were fuel pump wires. Fixed connections and rerouted the harness. All issues are now gone. Lowering the car I guess caused a slight rub.

That or bored vermin.

[DatBrotato]

sorry to bring this back from the dead. But i'm having a very similar issue.
Were those mangled wires lining or near the fender wells somewhere?
All my problems started after I put some slicks on(they do rub a bit).