Loss of acceleration after changing spark plugs and wires.


Asked by Mar 04, 2015 at 03:00 PM about the 1999 Ford Explorer 4 Dr Limited 4WD SUV

Question type: Maintenance & Repair

I took my 1999 Ford Explorer Limited to the dealer (I know,  mistake #1) but I needed
a loaner.   They "fixed" two CV boots that were leaking and also replaced my spark
plugs, wires, and coil pack.  ( I requested it ) [ should have known better to not fix
what's not broken ]
When I picked up the car and drove away, the engine/car was not the same.  It rides
smooth alright, and there's no shaking or missing, but it lost its power and
acceleration.  It's not like before. It's like they switched engines on me or something.
Also, it's louder during accelerating.  It sounds like a shuttle bus and not a simple
Explorer.   The gas pedal feels tighter/stiffer too.
I get all the noise but no bang for the buck.  I drive decent and hardly ever gun the
engine.  But if I have to get out of my own way I end up having to do that, and all I
hear is a lot of noise, high rpm's but no punch!

It's very frustrating.  Anybody have any ideas based on those symptoms?  I feel like I
gave them a V-6 and they gave me a 4 cylinder car back!

Thanks in advance.


P.S. - Forgot to add.... I took it back to them 5 times.  No difference.  I then found a
trustworthy mechanic.  He said the vehicle has no codes and looks fine.  He doesn't
want to change the plugs because he wants to save me money.
All I know the vehicle is not the same as it used to be.

3 Answers


The only thing I can imagine, and I have not checked if there is any difference, is the replacement parts or plug gap. In 1999 Explorer installed two different 4.0 V6 engines. One was the older pushrod type and the other was the SOHC engine. The pushrod engine had about 25 fewer horses than the SOHC engine. Check to see if the coil pack, plugs, gap, and wires are the same for both. They could have switched something up.


Thank you! Never thought of that. I'll check.


Thank you. Never thought of that. I'll check.

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