2001 Mustang V6 Hesitating... Worse on Inclines

jonwb · Mar 14, 2012

My wife's Mustang has a problem. She has to press the accelerator slowly to get to go without hesitating. If she steps on it too hard, the car will hesitate and sometimes backfire. Above 35 MPH, it's ok unless she's on an incline... then it hesitates consistently as it speeds up. Any ideas? Car has low miles despite its age.

Thanks

2001 Mustang Coupe (base model)
3.8L V6
45,000 miles

wmburns · Mar 15, 2012

For a backfire symptom the 1st thing to check is the ignition. Check the spark plug wires. This is IMPORTANT! Are the spark plug wires touching any metal parts? Has the factory routing been followed using the factory looms and stand offs?

Try this old racer's trick. Run the car in a totally dark location. Look for the blue hue of escaping spark. Inspect the spark plug wires for white spots which is evidence of arcing.

I personally don't put much weight on the incline angle until the usual causes of back fire have been ruled out. However, if you believe this to be the cause, look for a clogged fuel filter and water/debris in the gas tank.

jonwb · Mar 18, 2012

Thanks for responding. Checked the vehicle last night in a dark location... no sign of blue arcing. Pulled the wires on three of them and found no white spots either.
My wife took the vehicle to work this morning and on a level surface, the Service Engine Soon light began "flashing". Not a good sign according to the Internet. We'll take it in tomorrow. A friend of ours knows a good Mustang mechanic who'll check it for free, but is overall pricey and only uses OEM parts. I figure for this issue it's better than Pep Boys right?

wmburns · Mar 18, 2012

The flashing check engine light while the motor is running means that a misfire is actively occuring.

A misfire can be caused by a bunch of things. As stated before, ignition should be the 1st thing on the list. Once you are positive the ignition is good, then look at fuel. Possible causes are:

clogged fuel filter
water/debris in the gas tank.
clogged fuel injectors
incorrect fuel pressure. Is the intake vacuum reference line connected and leak free?

While not always possible for a DD, consider a fuel injector cleaning/flow test service such as injectorRX.com if you suspect an injector problem. Once cleaned and tested, the injectors are as good as new. Cheaper than new.

jonwb · Mar 19, 2012

Took it in to a recommended Firestone mechanic ... bad coil pack on cylinder one. They recommend new pack, wires and spark plugs... $290 in parts + 158 labor + 69 diagnostic! I'm pretty mechanical... how easy is it to change these things?

(Their 3-step fuel injection service is $157)

wmburns · Mar 19, 2012

Search the threads and you will find 1000's of cases of ppl replacing their own spark plugs, plug wires, coil packs.

There are also tons of threads where ppl make mistakes. Route wires incorrectly. Plug wires into the wrong holes. ect.

If this is your first rodeo, TAKE PICTURES during disassembly. Follow the factory routing. Use all of the factory looms and stand offs.

jonwb · Mar 20, 2012

Got the car back. Will definitely look into buying a code scanner before I pay $69 again for a tech to read it.

Didn't realize how easy this would be. Coil pack is easy to get to and spark plugs are very accessible (although air intake has to removed on passenger side). Plan to change plugs first and work backwards from there. Code found was a P0301. Would it be a good idea to first change out the spark plug on cylinder 1 and see if that was the problem? Either way I'll change ALL the plugs but her wires look brand new and I'd hate to replace the coil pack if I didn't need to. As mentioned earlier... vehicle has only 45,000 miles.

Thanks for your help BTW!

wmburns · Mar 21, 2012

My recommendation is to change all 6 plugs. I also recommend changing all plug wires at the same time. Inspect the wires for white spots which is evidence of arcing.

Do not let the plug wires touch any metal parts.

Unless I knew for certain that the coil was bad, it's a reasonable plan to wait.

Also have the alternator tested for correct output and excessive AC ripple. Most autoparts stores will do this for free. Don't skip this step as sometimes a bad alternator can mess up the cam sensor. An unstable cam signal can cause misfires on the V6.

jonwb · Mar 21, 2012

Ok, changed out the spark plug on cylinder 1. Noticed white spots on and around the plug. Instantly sounded better when started. Drove around the block and no more hesitating... hooray! I have five more plugs on order and will replace those when they come in. Are the wires really necessary? I'm not kidding, they look and feel brand new.

Checked alternator with my multimeter... 14.5 steady when running. SES light is still on... I'll need to clear the computer code. Is there a "poor man's" method to do this?

Thanks

Killian Korth · Apr 2, 2012

It'd probably be a good idea to do all the plugs a the very least. Wires, you could get away without but it'd be better to do them now instead of having the other 5 go bad eventually and have the one new one working still.

and as far as clearing the code is, you should be able to go to an O'reily's or Advanced Auto and ask to borrow theirs. They'll take your driver's license and you can take the code reader out and do what you need to do and take it back in with no charge to you. I'm pretty sure that's a universal thing, I've done it a few times and haven't paid a cent for it. Just go in and ask if you can use a code reader. They'll probably try to sell you one, which you could do if you wanted to but if you're that hard up for cash just borrow theirs and such.

hope I helped.

wmburns · Apr 10, 2012

jonwb said:
I'll need to clear the computer code. Is there a "poor man's" method to do this?

Either:

disconnect the battery. Expect the car to idle rough while the PCM re-learns new idle trim values.
go to your local autoparts store. Almost all will read/reset the codes for free.

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