2003 Mustang GT starts but then backfires and stalls

[huh2142]

Engine: 4.6 Liter SOHC
Mileage: approx 60,000

When I start the car it will start up then stall almost immediately. It stalls before I can let go of the key. It also sounds like it backfires. It is sort of a quiet pop more like a burp than an explosion sound.

It was in the shop for the 60K service and I had it diagnosed. Here is what is reported on the Invoice: "EEC Diag. P0340. Pinpoint. Found alternator causing RF Interference to camshaft position sensor circuit."

The recommended service was to replace the alternator, reprogram the PCM, clean the fuel injectors, and clean the carbon out of the throttle body. Since I didn't have ~$500.00 I declined the service.

How soon should I have the recommended service performed? How much damage am I doing to my car by not fixing it immediately? Are any of the services a do it yourself kind? I'm fairly good at following directions but if it is more complicated than tying shoes it may be too difficult. Also if it requires several hours that may not work. I live in an apartment complex so leaving parts on the lawn and sidewalk may be frowned upon.

Can anyone recommend me a good mechanic in the Arlington Texas area? Closer to the 76006 zip code the better.

Thank you for your help.

 

[Bignate603]

I have never heard about that problem before in my life, I'm not saying it couldn't happen but that's really odd. If the alternator is causing issues with it you can replace it yourself for about $150 or less. You'll need an afternoon, a haynes manual, one trip to napa and a set of wrenches.

 

[minendo]

Just clean out the throttle body and see if that helps. Had a similar issue on my Stealth a few years ago and that did the trick.

 

[halik]

Absolute bullshit diagnosis (unless you're using aftermarket ignition wires),
I would bet big money the cam sensor is going bad. The sensor itself is like 20 bucks

PS: Don't ever take your car back to that place, they'll take your money.

 

[alpineranger]

yeah, p0340 is a camshaft position sensor problem. How would they know it's the alternator instead unless they had already replaced the cam pos sensor.

 

[alkemyst]

Originally posted by: minendo
Just clean out the throttle body and see if that helps. Had a similar issue on my Stealth a few years ago and that did the trick.

doubt you were throwing a P0340 code though.

Search P0340 online. There are proper step by step troubleshooting guides out there. Replacing the alternator is not where I'd start nor do I know how the mechanic could determine that was the issue.

It can be your PCM though...don't know how reprogramming it would help that either.

 

[huh2142]

Thank for all the replies.

It was a Ford dealership that performed the service and made the recommendations for what thats worth. The Service Advisor may have had a boat payment due.

I don't know if I have after market wiring. I bought the car second hand from carmax. How would I tell?

I searched for P0340 and found the following. I understand the words but I'm not sure how to do the steps. Would the Haynes manual help in that regard?

http://www.obd-codes.com/p0340

Causes

A code P0340 could mean one or more of the following has happened:

* a wire or connector in the circuit could be grounded/shorted/broken
* the camshaft position sensor may have failed
* the PCM may have failed
* there exists an open circuit
* the crankshaft position sensor may have failed

Possible Solutions

With a P0340 OBD-II trouble code, diagnosis can be tricky at times. Here are some things to try:

* Visually inspect all the wiring and connectors in the circuit
* Check for continuity in the circuit wiring
* Check the operation (voltage) of the camshaft position sensor
* Replace the camshaft position sensor as required
* Check the crankshaft position circuit as well
* Replace circuit wiring and/or connectors as required
* Diagnose/replace the PCM as required

I also found this link http://www.mustangforums.com/m_1224848/tm.htm about a TSB 05-23-17. It talks about a different year model but I'm guessing that there is prior TSB that references my year model. It talks about testing the generator which I assume is part of the alternator. If that is the case then maybe that is why they recommended I replace the alternator.

 

[alkemyst]

That TSB may apply to you. It's pretty specific though as to how you need to test the alternator.

Likewise the above is also pretty specific in how you do it. You are going to need to know how to use a multimeter.

You can ask the mechanic what test did they try and supply the TSB.

Now if it's indeed the alternator and they will replace it and do those other items $500 is not a terrible price. The alternator alone is about $150-200. The reprogram of the PCM I am betting is just a reset. If they are doing a true fuel injector cleaning (direct, not a gas additive) then that's about $100 or so usually for a good job. The TB cleaning is minor, but a value to the rest of the job.

You are looking at about $200 in labor for the alternator plus their cost on the it probably will be a bit higher than what I quoted.

If it were me (I don't have an scope), I'd do all the straight tests and if all passed I'd replace the alternator. With a serpentine belt it's not a bad job should be a 1/2" drive to loosen the belt. Then should be all of disconnecting the battery, a couple bolts, a wiring connection bolt to the back of it usually and a harness that snaps on. May set you back a little under $200 with the core return. The biggest place someone screws up here is either shorting a connection by not disconnecting the battery or overtightening the rear connection.

*edit* being you are in an apartment complex it's going to depend on how much space you have. Most people get really pissed if you are lugging a toolbox and stuff down the side of their cars...this job should not require more than a couple sockets/wrenches, a 1/2" ratchet and thats about it; should only take a couple hours tops probably less than 30 mins for most. I am almost positive that the 4.6L's alternator comes out from the top. You shouldn't have any parts having to lie around.

 

[huh2142]

Thanks for your help. It sounds like the testing routine is beyond my capabilities. I guess I'll let the dealership do the work.

 

[Marlboroford]

Thanks for your help. It sounds like the testing routine is beyond my capabilities. I guess I'll let the dealership do the work.

just want to revive this tread, i have the same, ive seen a lot of pople in forums like this with the problem, but no one says how they fixed it =S. any clues anyone?

 

[DaTT]

Your best bet would be to hit up Mustang forums.

The Mustang Source is a good place to start.

 

[exdeath]

Does sound like crank or cam position sensor. No start and back firing due to completely wrong ignition and fuel injection timing reference.

Ideally you'd back probe those sensor outputs at the computer connector in the passenger foot well and compare the wave forms during cranking to a known good one. Unfortunately unless you are an electronics hobbyist you won't have an oscilloscope in your home. The next best thing for at home DIY is to narrow it down to a couple suspect parts with research and basic tests, then throw parts at it and take advantage of the return policy at the parts store if you guessed wrong.

A noisy alternator (electrical noise) could conceivably cause problems as some sensor outputs are very low voltage and could be "hidden" by noise in the electrical system. One of the diodes in the rectifier being bad would cause this for example. You could rule out the alternator by removing the belt and disconnecting it and trying to start it. Engine should start and run just fine without it.

PS remove the belt completely or make sure its clear of the crank pulley when are testing belt driven accessories, don't just take it off one thing and try to start it , and don't drive it that way as you will have no coolant flow or charging. When working with alternator connectors without disconnecting battery (because you need to start the engine), take precaution with the large battery cable (attached to the alternator with a nut) to not allow your tools to touch anything else while loosening the cable and make sure the loose end if the cable can't touch anything when you set it aside, doing so will cause a direct short across the battery.