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1998 Ford Van shudders and misses at 55-65 mph

We have a 1998 Econoline Ford Van that has 270,000 miles on it. It has worked very well and we have had to do little repairs, we do lots of routine maintenance. Recently, it has started to miss and falter

at 55-65 mph. We have changed the air filter, checked the spark plugs, changed the fuel filter. Our excellent mechanic is

stumped and so are we. Any ideals?

Do you remember when the last time the spark plugs were replaced? How about the spark plug cables, have they been replaced during the course of the 270,000 miles?

I don’t check spark plugs, just rip them out and replace along with the wires.

Your thoughts are in the right place: it could be a fuel system problem. With that many miles, you need to check the fuel pump pressure. To hook up the test fuel hose, you need a Ford test hose, or, screw the valve out of the tire-valve like fitting on the fuel rail, slip a fuel hose onto the nipple, and test. Test the fuel pressure under load. Let the engine run at 2,000 rpm with the automatic transmission in DRIVE for three minuets. If it’s a manual transmission van, attach the fuel test gauge using a long fuel hose, attach the fuel test gauge to the side mirror, and drive the van. Observe the fuel gauge while driving. If the fuel pressure falls below specs, the fuel pump isn’t keeping up.

They were replaced at 202,000 miles. Along with the wires, etc. One of the spark
plugs blew so we replaced wires etc, at that time.

Our mechanic did a fuel pressure check last week. He said the pressure was good.
I’m wondering if he checked it in the way that you are suggesting. Is it smart
to just go ahead and change it out? We are going to be needing the van in the next
month and really need it to be fixed, but it’s a situation that it is not really
"broken" yet…What do you think?

I doubt that your mechanic did a load type fuel pressure check. If you ask, be prepared for smoke. Think of a garden hose which has been laying in the hot sun. You squeeze the nozzle trigger one time and water shoots 20 feet; so, you could assume that there is plenty of pressure in the hose. From experience, you know that is not the case. The same idea applies to fuel pressure. It takes a couple of minuets to release that first surge of pressure.