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Got a vehicle from another shop they can’t solve? You can fix that.

You could be doing a gravy job instead of a problem that’s not yours in the first place, right? But tackling those ‘projects’ will hone your basic diagnostic skills

Editor’s note: Paul E. Grech owned the former San Franciso shop, Allied Engine & Auto Repair, before retiring. In this column series, Grech shares his experiences as a shop owner.

Every once in a while, no matter how much experience you have, you can get a job that beats you up. How you choose to handle it will determine finding the solution. Case in point was a 1996 Ford pickup truck and, of course, it came from another shop, as usual.

Paul Grech

The real problem is not with the vehicle, the issue is not being able to come up with the answers. And then the pressure builds up, because you know that you’re losing time and money on a job like this. You could be doing a gravy job instead of this problem that’s not yours in the first place, right?

But I have learned from past experiences that in the long run solving problem vehicles will hone your diagnostic skills. So, what I do in a situation like this is to go do a routine moneymaking job while I think about it. (This is also the time when a long commute time comes in handy.) I can concentrate on the problem and usually come up with answer.

This particular truck had a severe lack of power under all driving conditions. The vehicle had two rebuilt engines installed, and the fuel pumps and the catalytic converters replaced. So where do you start?

“I noticed a strange looking part on the left side of the frame just ahead of the rear tires — it was black plastic and looked like another fuel filter.”

With the basics of course. In cases like this, I like to check for exhaust system back pressure first. It was OK — little or no back pressure under a load. The reason I check for back pressure is if the substrate brakes off the catalytic convertor, it can plug up the muffler.

Since then, I heard about another way to check for a plugged up/restricted exhaust. You do a cranking vacuum test. First, disable the ignition or fuel pump (whichever is easier to do), so the vehicle won’t start. While cranking, a good engine should be able to develop three to four inches of vacuum. 

I used this recently on a 2005 Ford truck with a no-start condition, found no vacuum and traced the cause to a stuck cam advancer. Next step, fuel pressure test. Luckily the cause showed up here.

The pressure was 32 pounds at idle and would rise up under a load, only a little bit, but not enough when lugged down in the shop. I then tested it with gauge attached to the windshield. Under actual operating condition the pressure went down from 32 pounds at idle.

Now I knew what the problem was, but not actual cause. The vehicle had the fuel pumps changed, all three of them. So now, I went back to the basics. I checked the routing of the fuel lines along the frame, looking for a possible crushed fuel line or anything that could cause a low pressure while under a load.

I noticed a strange looking part on the left side of the frame just ahead of the rear tires — it was black plastic and looked like another fuel filter. It had two fuel lines going in and two lines going out. I called the dealer to try to find out what it was.

The person didn’t know what it was based on my description. He said to take it off and give him the part number. I did, and he said it was not a filter, but an accumulator. So I found out how it works in my shop manual.

The fuel from the tank goes through it on the way up to fuel rail. It is mounted before the high-pressure pump. It was a return fuel injection type system. The return fuel went back through it on its way back to the tank. It went through a valve system inside the accumulator on its way back.

Under an extreme load the returning fuel is rerouted to fuel going to the rail instead of returning to the fuel tank. The valve had fallen out of place, allowing some of the fuel that is supposed to go to the rail to go right back to the tank instead.

Thus, the high-pressure pump couldn’t get enough volume of fuel to build up the needed pressure. So I figured I paid my dues on this problem, would be set the next time I ran into it and even bought an extra one. I never saw another one.

It sat on the parts shelf for 20 years. But the experience has sat with me, too, and knowing that when you set your mind to it, you can fix anything.

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