Bike is running on one cylinder, checked spark plugs they are OK, have a new fuel injector on, new stock air cleaner and manifold gasket. Can't figure out what is wrong

If the RPM is high check for a vacuum leak. Examine all vacuum hoses for cracking or disconnections. If no problem is found, spray carburetor cleaner on the intake manifold and any other gasketed areas on the top of the engine. If, when spraying, the engine RPM fluctuates, then suspect a gasket leak where the spray is entering the engine. Also check throttle body for sticking. Clean it with carburetor cleaner.

Low RPM could indicate a clogged fuel filter, low gas, dirty or bad fuel injectors. If engine idle is low because it is running poorly (e.g., a misfire), check engine for misfire. Misfires can be caused by bad spark plugs, bad spark plug wires, bad fuel injectors, a bad coil pack, low compression in a cylinder, etc. Check the obvious cheapest things first.

If RPM is varying up and down, check Idle Air Control Valve (IACV) for sticking or obstructions. You may need professional help at this point.

Intake manifold gasket ,try torqueing intake bolts,or spray carb cleaner around bolts and seem while running see if it rums smoothly while spraying if so new intake manifold gaskets needed. YouTube video check to see.

Sounds like a dirty Throttle Body and dirty IAC (Idle Air Compensator) valve. Get some good Throttle Body cleaner remove the flexible hose at the Throttle Body spray it and wipe it very very clean an old tooth brush works good for getting in there.

Now remove the IAC from the side of the throttle body, careful with the gasket if you want to reuse it. Spray it down good inside moving the valve back and forth as you do let it soak for a few minutes and clean it again. Blow it out with some compressed air and reinstall it. Put some throttle body/injector cleaner in the fuel tank.

Keep us updated.

3.9L, 5.2L, and 5.9L Engines To Remove:
3.9L Engine

1. Before servicing the vehicle, refer to the precautions at the beginning of this section.
2. Remove or disconnect the following:
   • Battery negative cable
   • Coolant
   • Intake manifold-to-alternator bracket support rod
   • Alternator
   • Closed crankcase ventilation system
   • Evaporation control system
   • Air cleaner, air in-let hose and resonator
3. Release fuel system pressure.
4. Remove or disconnect the following:
   • Fuel supply line from the fuel rail
   • Accelerator linkage and, the speed control and transmission kickdown cables (if equipped)
   • Distributor cap and wires
   • Coil wires
   • Coolant temperature sending unit wire
   • Heater hoses and bypass hose
   • Vacuum supply hoses from the intake manifold (3.9L Engine)
   • Fuel injector harness and secure out of the way (3.9L Engine)
   • Cylinder head covers and gaskets
   • Intake manifold and throttle body as an assembly
   • Exhaust manifolds
   • Rocker arm assemblies and push rods, and identify to ensure installation in original locations.
   • Head bolts from each cylinder head and remove cylinder heads
   • Spark plugs

To Install:

1. Install or connect the following:
   • New cylinder head gaskets into position on the cylinder block
   • Cylinder heads onto head gaskets and cylinder block
2. Tighten all cylinder head bolts, starting at top center and in sequence
   1. Torque to: 50 ft. lbs. (68 Nm)
   2. Repeat and Torque to: 105 ft. lbs. (143 Nm)
   CAUTION
   When tightening the rocker arm bolts, ensure that the piston in that cylinder is NOT at TDC.
   
3. Install or connect the following:
   • Push rods and rocker arm assemblies in their original positions.
     1. Torque to: 21 ft. lbs. (28 Nm)
   • Intake manifold and throttle body assembly
   • Exhaust manifolds
   • Spark plugs
     1. Torque to: 30 ft. lbs. (41 Nm)
   • Coil wires
   • Coolant temperature sending unit wire
   • Fuel injector harness (3.9L Engine)
   • Vacuum supply hoses to the intake manifold (3.9L Engine)
   • Heater hoses and bypass hose
   • Distributor cap and wires
   • Accelerator linkage and the speed control and transmission kickdown cables
   • Fuel supply line.
   • Alternator and accessory drive belt.
     1. Alternator bolt - Torque to: 30 ft. lbs. (41 Nm)
   • Intake manifold-to-alternator bracket support rod and bolts
   • Cylinder head covers
   • Closed crankcase ventilation system
   • Evaporation control system
   • Resonator assembly (3.9L Engine), air in-let hose and air cleaner
   • Heat shields
     1. Torque to: 30 ft. lbs. (41 Nm)
   • Coolant
   • Negative battery cable.

Hello
Here is what to check let me know if you need help checking this out
most common misfire causes on the cars I've worked on have been:

1. Spark plugs
2. Spark plug wires
3. Ignition coil
4. Fuel injector
5. Wiring to fuel injector
6. Timing Belt
7. Vacuum leak or stuck open EGR
8. Contaminated fuel or bad fuel pump
9. Weak compression
10. Blown head gasket

Bonneville, LeSabre, Park Avenue 2000-2005 Intake Manifold - Removal & Installation

3.8L Engine
VIN 1 Engine

1. Before servicing the vehicle, refer to the Precautions section.
2. Relieve the fuel system pressure.
3. Drain the cooling system.
4. Remove or disconnect the following:
   Negative battery cable Supercharger Thermostat housing Exhaust Gas Recirculation (EGR) tube at the intake manifold Engine Control Temperature (ECT) sensor Intake manifold

To install:

1. Install or connect the following:
   Intake manifold with new gaskets. Torque the bolts, working from the center out, to 11 ft. lbs. (15 Nm). ECT sensor connector EGR tube to the intake manifold Thermostat housing Supercharger Negative battery cable
2. Refill and bleed the cooling system.
3. Run the engine and check for leaks and proper engine operation.

VIN K Engine

1. Before servicing the vehicle, refer to the Precautions section.
2. Disconnect the negative battery cable.
3. Drain the cooling system.
4. Relieve the fuel system pressure.
5. Remove or disconnect the following:
   Fuel injector sight shield Air inlet duct Spark plug wires from the right side Manifold Absolute Pressure (MAP) sensor Vacuum lines from the intake manifold Fuel lines Fuel injector electrical connectors Fuel regulator vacuum line Fuel rail from the intake manifold Exhaust Gas Recirculation (EGR) heat shield Throttle cable bracket from the cylinder head mounting bracket and the throttle body cables Throttle body support bracket Upper intake plenum and gasket Thermostat housing Electrical connector from the Engine Coolant Temperature (ECT) sensor Drive belt tensioner assembly EGR valve outlet pipe Lower intake manifold
   
   
   Fig. Exploded view of the intake manifold and related components-3.8L (VIN K) engine
   

To install:



Fig. Upper intake manifold torque sequence-3.8L (VIN K) engine



Fig. Lower intake manifold torque sequence-3.8L (VIN K) engine

1. Install or connect the following:
   Intake manifold using new manifold gaskets. Torque the bolts in sequence to 11 ft. lbs. (15 Nm); then, re-torque to 11 ft. lbs. (15 Nm). EGR valve outlet pipe Drive belt tensioner assembly. Torque the tensioner bolts to 37 ft. lbs. (50 Nm). Electrical connector to the ECT sensor Thermostat housing Upper intake plenum. Torque the intake plenum bolts to 88 inch. lbs. (10 Nm). Throttle body support bracket Throttle cable bracket to the cylinder head mounting bracket and the cables to the throttle body lever EGR heat shield Fuel rail. Torque the fuel rail bolts to 88 inch. lbs. (10 Nm). Fuel lines Fuel regulator vacuum line Fuel injector electrical connectors Vacuum lines to the intake manifold MAP sensor Spark plug wires Fuel injector sight shield and air inlet duct Negative battery cable
2. Refill and bleed the cooling system.
3. Run the engine and check for leaks and proper engine operation.

Hope this help (remember rated this).

Hi there,
You will need to do some diagnosing of the problem. Some things to check

• compression check across all cylinders. Low compression(less than 100 lbs in a cylinder will prevent it from firing. They should all be with 20 pounds of each other.
• carby to that cylinder may have a clogged air passage or jet.
• try a new plug in that cylinder.
• check for air leaks about the problem cylinder air intake. Use aerosol carb cleaner to spray about the manifold gaskets and carb mount. The revs will change if there is an air leak.

MOst probably you will need to strip and clean down the carbs if you have good compression and spark. Fuel is the only thing left :) Sometimes running some fuel system cleaner additive will also resolve the issue for you without tearing down the carbies. Goodluck regards robotek

Blown head gasket for sure if its a petrol engine.

If its diesel then its overfuelling.

spray carb cleaner on the intake manifold near cylinder 1... common problem is the intake manifold gasket leaks vacuum causing a misfire...the not starting could be due to a faulty crank sensor

check for frozen calipers,e-brake sticking. clogged cat/or ****.