Questions and Answers

Explorer Hesitates

Q. 1992 Ford Explorer 4.0 FI, well maintained, 92,000 miles. On first start and acceleration a very bad hesitation occurs no power for a split second then picks up. Driving with fuel pressure gauge hooked up shows no fuel pressure drop when problem occurs. Scan tool showed 211 code-changed crank sensor no code but still same problem. Changed plugs, water misted wires and distributor with scope hooked up all checked out ok. This problem will last for a few minutes and almost disappear. This problem just started out of a clear blue sky . If you preload engine after it sets a while stumble can be duplicated, after two or three hits on the accelerator it goes away. any ideas?

Thanks,
Al

A. I think you probably have a bad fuel pressure regulator Al. You said there was no drop in pressure, which is okay, but was there an increase in fuel pressure? The fuel pressure regulator is controlled by engine vacuum. When you are at idle with high vacuum, fuel pressure is decreased. On acceleration or cruising speeds, vacuum decreases causing an increase in fuel pressure. This compensates for the added fuel requirements of an engine under load.

You can check it easy enough. With your fuel pressure gauge hooked up and the engine running, unplug the vacuum line from the regulator. There should be a sharp increase in fuel pressure. If not, replace it.