Thursday, February 11, 2016

Fuel Pump Problem....or Not? (AKA Quits when Hot)

When an engine quits running, it is common for folks to suspect a fuel pump problem. After all, enough LD'ers have had that experience.

But....while a noisy pump often indicates a problem it doesn't necessarily mean you have found the problem. There are other parts that would can cause the engine to stop running that are also heat sensitive, failing only when hot and working again, once cooled. The two most likely items of a ignition system of older LD's are the ignition coil and ignition module.
Heat related failures are very hard to troubleshoot, you need to be able to quickly check for spark, fuel pressure and pulsed power to the injectors, at the time of failure. Without actually checking it when it will not start, it's an educated guess.
Back in the good old days where a lot of parts needed frequent replacement.I carried a spare coil, ignition module and a full tune up kit.

Now to help troubleshoot problem with the LD, I carry a fuel pressure gauge, a wireless spark detector and fuel injector noid lights (used to check the fuel injector circuits).
Many times a faulty part will set a Check Engine light (CEL).  An inexpensive code reader, one capable of erasing codes, is very helpful to have. You need to have a list of what the codes mean or an internet connection to check online. I have found a lot of ScanGauges and UltraGauges that will not erase Check Engine codes, where a code reader will.
Add to the box a 12-volt test light and a decent multimeter, the type with a clamp-on amp meter is useful for a whole range of troubleshooting.
With these basic tools and proper knowledge you have a good chance of finding what part of the equation is missing.
Working with engines, gasoline and electrical can be dangerous so if you do not have the proper training or experience, let a pro do it or find a good teacher. It's cheaper than going to the hospital.

Think your fuel pump isn't working or it suddenly stops, the fuel pressure gauge can let you know if it is providing adequate pressure, which need to be within a few PSI of the set point.
The pump does not require that the engine is running to be tested, only the ignition needs to be turned on.
When attaching the gauge, have the ignition switched off. Hold a rag around the connection point to capture any gas that may still be under pressure and spray out. Safety glasses are a must.
Please stay safe or find an experienced mechanic. Try this at home so you know how it's done before needing to use it on the road. Also find the specified fuel pressure for your engine's fuel pump.
Besides helping to find a defective pump, the fuel pressure gauge can also help find leaking injectors and check valves.

Many newer engine have the coils mounted right on top of the spark plugs, also known as COP, coil on plug. This arrangement makes it impossible to use a conventional inline spark tester.
The LD's V-10 has COPs that cover most of the access to the spark plug. They do have slots where the thin tip of a wireless spark detector can be fitted.
I use one of these. It's sensitivity is adjustable, a handy feature as every engine seems to have a different physical layout requiring more or less sensitivity.
With someone cranking the engine, check for spark at one or more plugs.
Practice at home so you have a good idea where the best spots are to test for spark and how to adjust the sensitivity. Actually, the V-10 is hard to access when checking for a heat related failures, because of the difficulty of removing the doghouse quickly, needed to access the rear eight plugs. It you look and tie things back, you can access the front two plugs and injectors from under the hood.  Coils do fail, so carrying a spare is't a bad idea. A bad coil will usually set a specified code for the cylinder.

If spark and fuel pressure are present, then test the fuel injector circuits for pulsed signals. Use the proper size "noid" light for your injector's plug. Noids are are small lights, that plug into fuel injector plugs, once uncoupled from the injector.  They test the fuel injector circuits for pulsed signals, when the engine is cranked or running. They are useful for finding a dead ignition system, a failed injector or a failed injector circuit.
My fleet contains four different sized fuel injectors plugs so it was cheaper to buy the big set and keep the extras for the future.

If the engine is running but is either making noises or missing, an inexpensive mechanic's stethoscope can be invaluable. You can listen to individual fuel injectors, Comparing them each other. A dead or stuck injector usually makes a much different noise. You can isolate noisy bearings and eliminate changing the wrong part. Be extremely careful to stay far away from the moving belt and pulleys, they remove fingers quickly.
Even good parts can make strange noises, it's good to know what "normal" sounds like.

For all the test tools above, the internet has hundreds of sites and videos that explain how the various tools and systems being inspected work. Above all, work safely.

Contributor: Larry Wade

Published: 11 Feb 2016