5.7 Hemi Rebuild

[ramreanimator]

I recently rebuilt my 5.7 hemi on my 06 dodge ram . I installed a Lunati Stage 1 Voodoo camshaft . I am having a problem with the truck idling . When I first start it it will idle for about 3 seconds , then dies . it will start back up if you press on the pedal and will stay running if you keep your foot on it . As soon as you let off it dies . Brand new fuel pump , drained fuel tank and cleaned before I installed . Also new coil packs , throttle body and spark plugs . This was a complete rebuild , with new pistons , rings , rods , rod and main bearings , cam bearings , camshaft and both new ( rebuilt ) heads. all seals o rings and gaskets replaced . pcm checked and flashed to current specs . good compression on all 8 . No codes . Any help greatly appreciated !

 

[HemiLonestar]

When you say "pcm checked and flashed to current specs", this would normally mean on the stock factory tune. Are you saying you're trying to run an aftermarket cam on the stock PCM?

 

[ramreanimator]

Yes, will it need to be tuned for the cam ?

 

[G-Ride990]

Personal attacks are not allowed here gentlemen. Please keep it civil.

 

[ghost03hemi]

Just install a comp cam 260. No tuning required for that cam.

 

[Fast69Mopar]

I was doing my research on here . I had already spoke to a local mechanic who told me the computer would make adjustments for the cam. , obviously he was incorrect . Thank You for your opinions ! And I would believe that someone who tries to make someone else look stupid , when they make a stupid mistake , would be the one with insecurity issues ! I would much rather a humble person answer ! Thanks again Boys !

The local mechanic you spoke to is wrong and gave you incorrect information. The stock PCM calibration is written based on a certain set of engine parameters. The timing map, base start-up fuel map, closed loop fueling, power enrichment and injector pulse width, to name a few, are programmed based on a certain amount of air and fuel entering the cylinder. When you install a larger camshaft, especially a camshaft with a whole lot more duration and overlap, the valves are being held open for a longer period of time which allows more air to enter the cylinder.

The PCM can only compensate for so much. The reason it started and ran okay the first time was probably due to the open loop fuel control and cold start enrichment. If you had a good scan tool you could see your STFT, or Short Term Fuel Trim and the LTFT, or Long Term Fuel Trim. With more air being allowed in to the cylinders the PCM detects a lean condition and the STFT goes positive to add fuel to keep the engine running. But, like I said before, the PCM can only add so much fuel to keep it running.

If you look at the stock cam specs the duration @.050 is only 192°/196° for the intake and exhaust. The camshaft you installed, the Lunatic Voodoo Stage 1, has 215°/221° @.050 for the intake and exhaust. You added 23°/25° to the duration which holds the valves open quite a bit longer. The stock camshaft only has 30.50° of overlap which is the amount of time that both the intake and exhaust valves are off of their seats at the same time. The Lunati Voodoo has 47.5° of overlap which is a big step up in duration compared to the stock camshaft.

 

[ramreanimator]

The local mechanic you spoke to is wrong and gave you incorrect information. The stock PCM calibration is written based on a certain set of engine parameters. The timing map, base start-up fuel map, closed loop fueling, power enrichment and injector pulse width, to name a few, are programmed based on a certain amount of air and fuel entering the cylinder. When you install a larger camshaft, especially a camshaft with a whole lot more duration and overlap, the valves are being held open for a longer period of time which allows more air to enter the cylinder.

The PCM can only compensate for so much. The reason it started and ran okay the first time was probably due to the open loop fuel control and cold start enrichment. If you had a good scan tool you could see your STFT, or Short Term Fuel Trim and the LTFT, or Long Term Fuel Trim. With more air being allowed in to the cylinders the PCM detects a lean condition and the STFT goes positive to add fuel to keep the engine running. But, like I said before, the PCM can only add so much fuel to keep it running.

If you look at the stock cam specs the duration @.050 is only 192°/196° for the intake and exhaust. The camshaft you installed, the Lunatic Voodoo Stage 1, has 215°/221° @.050 for the intake and exhaust. You added 23°/25° to the duration which holds the valves open quite a bit longer. The stock camshaft only has 30.50° of overlap which is the amount of time that both the intake and exhaust valves are off of their seats at the same time. The Lunatic Voodoo has 47.5° of overlap which is a big step compared to the stock camshaft.

Thank You for your intuitive input and for sharing that knowledge with me !

 

[HemiLonestar]

Yes, will it need to be tuned for the cam ?

Yes. A little research goes a LOOOOONNNNGGGGGG way, as this isn't like the old days where you throw a random cam in, rejet the carb and set timing.

 

[ghost03hemi]

You can always get it tuned for the cam.