The engine cranks over but does not start. What do I check first? Well I am going to start out by saying that you should always check to see that you have a good spark (Ignition) first. Most no start conditions are related to ignition not fuel. That being said, you do need to insure that you have fuel. This article is focused on Propane or LP powered Forklift trucks. The procedure is similar for gasoline power and I will try to point out the differences.
One of the most common problems found on a no start service call is that the propane tank fitting is improperly fitted to the LP fuel supply hose. The cause is often that when the operator changes the LP tank the sealing ring that is in the tank fitting becomes dislodged or breaks. The seal often comes out of the tank fitting and becomes lodged in the hose fitting. This prevents the fitting from being fully seated on the new tank and prevents tank from filling the fuel system. You can identify this problem by looking in the end of the hose fitting. If you find a black square cut seal around the center of the fitting you will need to remove it. You will want to check the tank you took off to see if it is missing a seal. Occasionally you will find that the seal has broken and causing the fitting not to fully seat. In this case just replace the seal and you are in luck. I recommend keeping a few of these seals in stock as they are very inexpensive and service calls are not.
Once you’ve determined that your tank has fuel and that the fuel connection is secure it is time to turn your attention to spark. I have seen many a professional technician spend hours working on the fuel system only to find that the problem was weak or no spark. Don’t overlook your battery. Just because your starter works it doesn’t mean your battery has enough reserve voltage left to properly supply the ignition system. If you have a spark tester you can start by checking spark at the coil wire. Attach the spark tester to a plug wire. You are looking for a good solid blue spark that jumps at least a 1/2 gap. A weak yellow spark will often not be enough to ignite the fuel especially in a cold engine. Also check at coil wire If you have no spark, you should first check to see that you have BV (battery voltage) available at the positive post of the ignition coil with key in on position. Check this with a 12v test light or a VOM. If you do not have voltage at this point check the ignition circuit thru the ignition switch, fuses, and wire harness connections. If you have voltage at the positive post of coil move your test probe to the negative side of the coil. Now crank the engine over. You should see your test light blink on and off as the engine turns over. This indicates that your igniter or ignition points are functioning correctly. If light does not illuminate remove wire from negative post of coil and check for voltage. Light should stay on with ignition in on position. If light remains off this indicates a defective ignition coil.
The next step is to remove the distributor cap. Inspect the underside of cap for signs of tracking. These are lines that are burned into the plastic. This will cause a misfire or result in no spark getting to the spark plugs at all. Look for the same thing on the rotor. Also check for excessive dirt or corrosion. If you have traditional mechanical point ignition check the points for proper gap and pitting on point surface.
If at any point in this process you find parts that failed or are in questionable condition, replace the part. I recommend replacing all ignition consumables at this time. This includes points, condenser, cap, rotor, spark plug and coil wires and spark plugs. This is considered an ignition tune-up and is good insurance against future failures.
You’ve checked all of the above and the engine still will not fire. Must be a fuel system problem, right? Not so fast. Assuming that you still have plenty of juice left in your battery and the engine is cranking over good, the next step is to insure that you have good compression. If you do not have a compression tester or don’t know how to use one, now is a good time to call in the professionals. If you choose to skip this step and dive into the fuel system be advised. I have seen many DIY attempts that ended with a lot of new parts only to find out that they needed a valve adjustment, a complete valve job or an engine overhaul.
Ok, so you’re pretty sure that it is a fuel system problem. There are several components that need to be working together in order for the fuel system to work properly. First you have the fuel supply, the tank. Then there will be a fuel filter. To change the fuel filter, disconnect the fuel tank and discharge the line pressure by pressing in on the center pin of the hose fitting. CAUTION; make sure the fitting is facing away from you and there is no ignition source present. You can also crack the line fitting with a wrench to allow pressure to escape. Again use extreme caution as propane gas is very flammable and under pressure. Now you can open the fuel filter canister and replace the fuel filter. Some fuel filters are contained in the vacuum lock-off housing often referred to as a VFF. See below.
The next step is to make sure your safety shut-off valves are working properly. There are several types used depending on the age and make of your forklift. Many older forklifts use an electric solenoid shut-off that is connected to a vacuum switch or an oil pressure switch. This can be identified by an electrical wire attached to the solenoid. Be sure that you have 12 volt positive to the solenoid when the engine is cranking. If you do not detect voltage, trace the wire back to either the vacuum switch or the oil pressure switch. If you have 12 volts at the supply side of switch but not the switched side you most likely have a bad switch. There is the possibility that you do not have vacuum or oil pressure. Vacuum can be checked with a vacuum gauge and oil pressure with an oil pressure gauge. Both of these tools are readily available.
So you’ve determined that you have good spark getting to the spark plugs, you have compression, and fuel thru the tank connector, fuel filter and lock-off valve. The next component in the fuel system is the fuel regulator. The technician has specialized low pressure gauges to check operation of the regulator. If you have checked everything up the line and you have an Impco type fuel system you are in luck. These regulators are easy to rebuild. Kits can be purchased or replacement regulators are also available at reasonable cost. Follow the included manufacturer’s instructions to disassemble clean and rebuild. This normally is the extent of your repair. Most no start problems are not caused by the mixer (commonly but not correctly called the carburetor). It is now time to delve into the fuel mixer.
If you have a diaphragm type mixer it is simply a matter of replacing the diaphragm and cleaning the housing. The most common problem with this type especially when used as an updraft design on many inline engines is oil accumulation in the housing. Repeated problems with oil accumulation can be caused by contaminated fuel. Check with your fuel supplier if this is the case. Be sure to install the new diaphragm correctly. Pay close attention to the direction of the valve slots when disassembling and reassemble in the same fashion. It is rare but the housing can become worn causing the diaphragm to stick and hang up. Inspect and replace the mixer assembly if needed. If you work in cold conditions be sure to ask your parts supplier about diaphragms especially designed for these conditions.
Your mixer may be a sliding valve type. In this case I recommend disassembling and inspecting the mixer for wear. In many cases the housing is worn causing the valve to hang up and not move freely. Replace the assembly. This type of mixer works fairly reliably and is rarely the cause of a no start. They will cause sluggish acceleration, rich or lean mixture and poor fuel economy.
Whenever working with propane fuel systems:
- Work in well ventilated area
- Keep fire extinguisher handy
- Keep ignition sources away
- Clear area with compressed air when done before attempting to start
Hopefully you found this article useful. We will be adding more how to articles soon. – GB