Difficult-to-diagnose problem finally solvedWritten by Nick Shultz | | email@example.com
Recently, I reported on a unique problem with a 41-year-old
1½ ton GMC grain truck that I was working on in my home shop. If you recall, the truck was hesitating badly on acceleration.
While checking the basics, I found that the ignition timing appeared to be adjusted nearly 40 degrees off of the manufacturer’s recommendations. Upon further diagnosis, I realized that the two halves of the harmonic balancer had slipped internally. This caused the ignition timing indicator mark to rotate approximately 40 degrees. The actual ignition timing wasn’t nearly that far off specification. However, the ignition timing appeared to be way off when traditional ignition timing procedures were followed. Once I manually set ignition timing, I realized the problem was with the balancer and was able to resolve that concern.
Nonetheless, this still did not resolve the customer’s initial complaint. I still needed to resolve the hesitation problem.
When I first started diagnosing this hesitation concern, I knew the root cause would most likely be the result of a problem with the fuel system. However, in order to properly adjust the fuel delivery system to the manufacturer specifications I had to resolve the ignition concern first. Now that I had accomplished that task, I could move on to the fuel system.
If you read my last column, you will recall that the vehicle had averaged less than 500 miles a year for the 41 years it has been in service. Obviously, that is not much use. Therefore, the fuel sits in the tank for extended periods of time. The owner, Matt, uses a fuel stabilizer in the tank, which also aids in dissipating water. Nonetheless, as a result of the years of light use, it was very likely the fuel tank had water and rust in it.
I pulled the fuel filter and found that it was contaminated with what appeared to be rust. Although the filter was not completely plugged, it was very nearly so. Obviously, the fuel tank had issues. The tank was removed from the vehicle and drained and flushed. We flushed the tank with kerosene. Once the tank was reinstalled and new rubber fuel lines were installed, we filled it completely with fresh fuel.
Because the vehicle was a 1968 vintage, it was not originally engineered to handle unleaded fuel. The vehicle was designed to burn leaded gasoline. Unleaded gasoline has a detrimental affect on the valve system of an engine designed for operation with leaded gasoline. It is necessary to add a lead substitute to the fuel each time unleaded gasoline is added. There are several lead substitutes on the market today and, depending on the one you use, the amount added will vary. The proper amount must always be used. A plastic measuring cup works great for that purpose.
If the owner of this truck used it more, we would pull the cylinder head and replace the valves and seats with those designed specifically for unleaded gasoline use.
Because of its limited use, redoing the valves is not necessary at this time.
Once the tank and the fuel were in order, I pulled the carburetor and cleaned it. After making all necessary adjustments to the rebuilt carburetor, I installed yet another new fuel filter. I even installed an additional auxiliary fuel filter in the system. Hopefully, the problem won’t resurface for another 41 years.
I would also like to congratulate Ford Motor Company on receiving Motor Trend’s “Car of the Year” award. The 2010 Ford Fusion was voted the best car of the year this week. The Fusion is most deserving of this award. I recently had the occasion to drive one and I believe it may be the finest car I have ever driven. Great job, Ford!
Nick Shultz is an instructor of Automotive Technologies at Owens Community College. He is an arbitrator for the Better Business Bureau who specializes in cases involving the Ohio and Michigan Lemon laws. He is a certified master automotive technician by ASE, General Motors Corp. and Ford Motor Co. Shultz, a Toledo native, will take questions from readers at firstname.lastname@example.org.