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Ford Explorer Has A Blocked Exhaust?

Q. I've been having an intermittent, elusive problem in my 1993 Ford Explorer 4WD for about six months in which the engine suddenly loses power. It's not a total power loss, but it is incredibly annoying. The vehicle:

  • 1993 Ford Explorer 4WD
  • 4.0 liter V-6
  • Automatic transmission (A4LD)
  • 118,000
  • Fuel Injected
  • ABS brakes
  • P/S, A/C, Cruise control

Ford Explorer Has A Blocked Exhaust?

At first, I checked all of the regular stuff. Trying to troubleshoot this one problem, I have replaced the air filter, leaned the air filtration system and intake manifold, replaced spark plugs and wires, replaced the fuel pump and filter, run fuel system cleaners through the gas tank and engine, and checked for leaks in the engine vacuum. None of this had any effect and the problem is getting worse and more predictable.

On Saturday (10/29), I hooked a pressure gage to my engine vacuum. I couldn't drive the truck while testing because of the equipment, but just running the engine up showed something funny. While at idle, the vacuum pressure was about 20 in/Hg.

When I accelerated the engine up to 2,000 RPM, it remained around 20 in/Hg. When I opened up the throttle and got the RPM's up to 4,300 it still read 20 in/Hg. But when I let off the gas, the pressure went up to 30-32 in/Hg and stayed up until about 3 seconds after engine RPM's had returned to idle, and the return to idle was a little rough. I repeated the test, and it did the same thing.

In my inexperienced gut, I'm thinking there is some kind of blockage in the exhaust system. Is this diagnosis consistent with the results of the vacuum test I just described or should I be looking elsewhere? I've seen recommended on some web sites that to test for this, I should disconnect and reconnect my exhaust system piece by piece to see if I can isolate the problem. Is this the best way to do it?

If, in fact, my catalytic converter is at the end of it's life, should I replace it with the expensive factory replacement or the cheaper Auto zone version that fits multiple vehicles? The truck is in otherwise great condition.

Please toss a bone to a novice...


A. You can read my article Engine Testing With A Vacuum Gauge on how to check for excessive exhaust back pressure. If the test does indicate excessive exhaust back pressure then drop the exhaust at the exhaust manifold and the redo the test. If the test shows an improvement, then you, quite possibly, have a partially clogged catalytic converter.

If that is the case, My personal preference would be to replace it with one from the Ford Dealer. An exhaust system is calibrated to have a specific amount of back pressure and keeping the exhaust system as original as possible will help the engine perform at peak efficiency.

In addition, if your state requires emission testing it will help insure that your vehicle will pass the test.

Additional Information provided courtesy of AllDATA

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© 2005 Vincent T. Ciulla

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