Major issues with my car

[bpopham22]

Ok so a month ago i had my car tuned,it was good for a few days and now ive got some major problems. My voltage is really low,i put i volt meter on the battery in park at idle and im getting 13.4-5,once i put the car in drive at idle it drops into the yellow on the gauge and about 12.5-6 at the battery under load. I have a 2 month old optima red top and i just installed a power bastards 220 amp alternator thursday hoping it would fix the problem. It didnt. While in drive at a stop when the voltage gets low it sometimes dies and throws a crankshaft position sensor code. But then it starts right up with no problem. Also with the volts this low i cant go WOT because it acts like im hitting a rev limiter at 4k and above. Whenever it throws the crankshaft code i also notice that my rpm gauge just drops off completely while the car is running. Could my pcm be bad? A short behind the cluster? I know that doesnt explain the voltage,whenever my voltage is 14.4-5 the car is issue free. Ive checked all four grounds on top and the battery cables,also had the dealership install the alternator for me so im sure it was done right,ive never EVER had a problem there before.

[99WickedSS]

If your crank position code comes up and your voltage is low under load I would seriously verify a belt isn't slipping or a harmonic balancer hasn't gone out.

The crank position would only fault if the sensor was bad, the sensor to PCM signal wire is damaged, or the crank position is truely off.

Battery charging is a function of the alternator and engine speed (idle minimum). If the alternator isn't at the correct speed the battery charge would be below normal.

Typical battery voltage should be 12V with ignition off and between 14V and 15V while the engine is running regardless of idle or under load.

[bpopham22]

no my voltage is just above 13 while im cruising at highway speeds. I dont believe the belt is slipping car will run fine when im just cruising around. Any kind of aggresive driving is where the issues are. How could i check to see if the harmonic balancer isnt going out?

[99WickedSS]

The car can appear to be fine. If you continue to drive the car for a while the battery will eventually drain. The 13V is too low, should be more than 15V. The only way to check the balancer is to relieve the belt tension of the balancer. The balancer should not have any axial play in it. Check the tensioner too.

[bpopham22]

well last night once i got back to my car after it had been sitting for about 6 hrs the voltage was up in the 14's on the gauge. however, it was still acting like i was hitting the rev limiter at 4k and above

[importhater81]

I'd address the crank sensor code before doing anything else.

Why not take it back to the tuner...maybe he set the rev limiter too low or forgot to relearn the crank sensor after he tuned it?

[bpopham22]

No thats not the case it ran AMAZING for 3 days after i got it back,i only recently started having problems when my voltage started jumping around. So if my battery is good and my alternator is good,what else causes voltage issues?

[99WickedSS]

The rev limiter is set in the PCM and won't change unless the PCM detects a problem. If the PCM detects a fault it may derate or reduce engine speed, depending on the severity of the fault. The PCM may also go into a "limp home" mode if a severe fault is detected. In this mode the PCM defaults to a programed set of conditions including engine speed, air/fuel mixture, and gearing (for automatic trans ).

The PCM/ECU monitors a set of inputs (sensors), calculates the appropriate air/fuel parameters, and drives the outputs (injectors, ignition, etc). Problems that arise in the overal vehicle powertrain system are the fault of the input (sensors), harnessing, or outputs (ignition, injectors, etc) and not the PCM/ECU.

[bpopham22]

ok but what about my rpm gauge dropping off for no reason while the car is running? and its not really like im hitting a rev limiter but more like im not getting fuel,like its cutting out and sputtering

[importhater81]

No thats not the case it ran AMAZING for 3 days after i got it back,i only recently started having problems when my voltage started jumping around. So if my battery is good and my alternator is good,what else causes voltage issues?

Under-drive pulleys can cause lower voltage at idle.

[99WickedSS]

RPM gauge receives it's data from the PCM. The PCM receives it's data from a vehicle speed sensor. The RPM dropping out could be a result of the vehicle spped sensor failing or the ECU cuts the engine speed due to a detected system issue.

Do you notice anything else wrong when this happens? What are all the fault codes observed?

How many miles did you drive after the tune?

For most faults the PCM utilizes a persistance counter which counts the number of times a particular potential fault occurs before actually setting a fault code. This is why you can clear a fault code and drive around for a while before it appears again. There are some faults which may be higher priority (safety critical) which may not utilize a counter so if a fault is detected a code is set immediately.

[importhater81]

The rev limiter is set in the PCM and won't change unless the PCM detects a problem. If the PCM detects a fault it may derate or reduce engine speed, depending on the severity of the fault. The PCM may also go into a "limp home" mode if a severe fault is detected. In this mode the PCM defaults to a programed set of conditions including engine speed, air/fuel mixture, and gearing (for automatic trans ).

The PCM/ECU monitors a set of inputs (sensors), calculates the appropriate air/fuel parameters, and drives the outputs (injectors, ignition, etc). Problems that arise in the overal vehicle powertrain system are the fault of the input (sensors), harnessing, or outputs (ignition, injectors, etc) and not the PCM/ECU.

He said he had it tuned,the rev limiter is set by the tuner.

[bpopham22]

well i dont have an UDP and ive gone probably 500 miles or so with the tune. Its weird after the tune it was great, then it ran like shit,then 2 days b4 i took it back to the shop it was running great,left the tuner and ran fine,that not started to act up again. I really dont think my voltage should be dropping into the yellow,that doesnt seem right. I just checked my battery with the car off i got 12.6 volts. Im debating on ordering a new pcm from frost,just a blank one and putting my handheld tune back on it to see if the problem persists.

[importhater81]

What is the specific code your car is throwing p0???

[bpopham22]

once in a while its the crankshaft position sensor perfomance range,forgot the number. other than that no code just low voltage

[whitetrashbird]

As stated above, I'd address the crank position sensor code first. As already stated, check the balancer, the position sensor and the wiring. Maybe the dealership pinched a wire from the crank shaft sensor when they installed the alternator.

Dan

[Cutlass]

The "rev limiter" feeling you are getting and the tach rpm dropping off are both related to the crankshaft position sensor problem you are having. If the wiring and connector look ok at the crank sensor, then go ahead and replace the sensor.

The low voltage problem might be a separate issue. Carefully inspect the wiring and red cable. pull on the wires a bit to see if they are tight and in good shape.

[bpopham22]

ok i have no idea where that sensor is. I read behind the starter on the passenger side of the block. Honestly would that be easier to do from under the car cuz there is no way i can fit my arms in there.

[importhater81]

ok i have no idea where that sensor is. I read behind the starter on the passenger side of the block. Honestly would that be easier to do from under the car cuz there is no way i can fit my arms in there.

It's behind the starter on the passenger side.Raise the car up ,remove the starter and it's right there.

[bpopham22]

once i replace the sensor im gonna have to have the re-learn procedure done right?