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Solving an idle and revving issue on a GMC Terrain

The idle was very erratic and the oil had a strong smell of gasoline odor in it

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.

Like I said last in my last article, I still go to the city and visit with my old fellow garage owner buddies and see how they are doing. One of them called me about problem on a 2019 GMC Terrain.

It was a 4-cylinder 1.5-liter turbo motor with a direct injection fuel injection system and it would start and idle but wouldn’t rev up. The idle was very erratic and the oil had a strong smell of gasoline odor in it.

Paul Grech

I had my propane dispensing apparatus with me. He asked me what I thought and I replied I wasn’t sure because I had never worked on one like this. It seemed to me like a fuel mixture problem.

So, I added a little propane, the engine and the idle stabilized, but the engine would still not rev up. I told him we needed to start with checking the pressure of the fuel injection system. There was no fitting to attach a pressure gauge to because it was a direct injection system.

The plumbing for the fuel injection system looked very heavy duty. With a new Autel scanner, it said that the fuel pressure was about 500 lbs. I then told him that there must be away to release the pressure in the system, so he scrolled down and found the function to release the pressure.

Then he decided to call it into Identifix, which told him to check the vacuum for the booster. The reading was zero. They instructed him to remove the vacuum pump from the rear of the cylinder head.

The pump, which was driven by the rear of the exhaust camshaft, was broken and jammed. How can a broken power brake vacuum pump cause this drivability problem, you may ask? Well, at the rear of the exhaust camshaft was a reluctor pressed on to the camshaft ahead of the vacuum pump. The reluctor tells the computer when to open the injector.

When the pump jammed, it caused the reluctor to shift its position on the end of the camshaft, which caused the fuel to be injected at the wrong time, so the repair procedure required the removal of the camshaft covers. The fuel line went directly over the valve cover and had to be opened up in order to remove the cam cover, but opening a line with that much pressure can cause a serious injury or much worse — the high pressure can pierce your skin and get into your blood stream.

My buddy is primarily a transmission guy and now has to get involved in other areas of auto repair in order to survive. So, we both learned a new lesson about working on late model cars. We learned it the easy way — not the hard way.

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