2005 chevrolet 2500 multiple cylinder misfire, engine light on, tach not working and speed odometer works off and on..

Intermittin Engine Stall
Engine No Start
Missfire
MISFIRE IN motor cylinder is more likely the cause to engine stall and hard start.
You will have to fix this problem first,
A misfire, most the time, is caused by, incorrect cylinder firing order (diagram at bottom). Or no or low cylinder compression
no or low compression is the result of A Vacumm leak.
If the timing chain was recently replaced, the valve cover had to be removed, the valve cover gasket could cause a huge vacumm leak which would effect some if not all 6 cylinders,

Symptoms
Lack/loss of power
Hard start
Engine hesitation

For Now
check firing order( coil pack to sparkplug)
check sparkplugs

NISSAN 3.5 V-6 FIRING ORDER
SPARK PLUG GAP 0.050''
SPARK PLUG TORQUE
COIL PACK LAYOUT


I hope this helps for now
If you have any questions, you can email or post back
[email protected]

I'm guessing you have over 100000 miles , definitely replace all the spark plugs and ignition cables and cap and rotor if your motor is such equipped. If you want a better idea of which cylinders are misfiring, go to your local Checker or Autozone and ask them for code retrieval, codes stored will give you an idea of what is failing. Code po300 is multiple misfire, po301 is cyl #1, po302 is cyl #2 and so forth.

PO300 - Random/Multiple Cylinder Misfire Detected

When a misfire occurs, engine speed will fluctuate. If the engine speed fluctuates enough to cause the crankshaft position (CKP) sensor (POS) signal to vary, Powertrain Control Module (PCM) or Electronic Control Module (ECM) can determine that a misfire is occurring.

Causes:
- Improper spark plug
- Insufficient compression
- Incorrect fuel pressure
- The injector circuit is open or shorted
- Fuel injectors may be faulty
- Intake air leak
- The ignition signal circuit is open or shorted

Solutions:
- Perform Injector Service
- Replace Spark Plugs
- Replace Injectors
- Replace Ignition Coils

DO NOT DRIVE IT.....Driving it when the check engine is flashing may cause a simple problem to become a major problem if not fixed right away. Cruise control will always disable when the check engine light is on, when cleared, it will work again. Blinking light means serious malfunction, needs to be repaired right away. This can be many things, from simple multiple cylinder misfire, to something more serious.

The problem with the speedometer is the internal stepper motor. This is a really common issue on these. As far as it not starting, i dont know what to tell ya on that.

cylinder 1 misfire change spark plugs i just had that problem. you can still drive it it wont hurt the engine.

It sounds as if the vehicle speed sensor is malfunctioning.

OBD II 300 Random/Multiple Cylinder Misfire Detected

When the misfire monitor detects a misfire, it will trigger the check engine light with the specific cylinder number as the last digit in the P030X code. For instance cylinder 1 misfire is P0301, cylinder 2 is P0302 etc. In this case we have either multiple cylinders misfiring, or the computer simply can't determine the specific cylinder, and as such we are left with the P0300 in computer memory.

Possible Causes:

Fuel injectors, related wiring, sensors and computer issues
Running out of gas, or poor fuel quality
Evaporative emissions system (EVAP) concerns: fuel vapors leaking into engine
Incorrect Fuel Pressure
EGR system concerns: leaking EGR valve or restricted ports
Base engine concerns: low compression, valve train problems and timing issues
Ignition system concerns including, but not limited to:
Faulty spark plugs
Faulty coil or related wiring
Ignition module or related wiring issues
Ignition related sensor faults or wiring issues

replace the speed idle sensor

I would recommend going back with ac/delco platinum plugs.Some of these "high performance" plugs dont work well in newer gm vehicles.The computer is sensing more than one cylinder misfiring and cant determine the cylinders the style of plug your using could very well be causing this