3 replies to this topic

[stu & morpar]

I need some help fixing my 2003 Dodge neon sxt 135k miles. It will sometimes backfire in the intake on take off. It also has a miss on idel. It is not showing any error codes. I am thinking maybe sparkplugs, coli pack or wires.
Thanks

[Rick Anderson]

If you are overdue for a plug change or wire change, then by all means, try that first.  I'm assuming you know the spark plug cables deteriorate with age and use, if you've got more than 60k miles on them, I'd replace them.  You can check their resistance, spec might be in the FSM or a google search might reveal some good gouge on general figures to use for a check.  Same for Coil Pack, if you find carbon tracks or cracks, replace it.

Don't rule out leaking injectors.  I've "heard" the Chevron Fuel Injector with "Techron" additive is the best fuel injector cleaner.  I can't really tell myself and have no evidence, other than a few people I have found very credible in magazines and in forums say the "Techron" additive is a patented, real thing that is better than the others.

A bad cam position sensor can cause the PCM to guess phasing wrong, its got a 50/50 shot, and 180° out of phase on the injectors can make fuel pool in the manifold.  You should have gotten a code for this though.

Don't rule out a bad PCV either, clogged or stuck open could mess up pressures in the manifold, get oil and fumes in the manifold as well.

One last one, really bad exhaust leaks anywhere in the exhaust manifold or pipes by the O2 sensor, usually anything upstream of the Catalytic Converter.  At this point in the exhaust, it pulsing and reversion will create moments of vacuum, that will suck air in through a bad leak in the exhaust.  That will cause the O2 sensor to erroneously sense the A/F mixture is extremely lean and the PCM will respond by making the fuel mixture extremely rich.  Excessively rich can cause backfires in the intake.

Edited by Rick Anderson, January 24, 2012 at 08:55 pm.

[ImperialCrown]

I'm thinking that if you find the reason for the miss at idle, you may also cure the intake backfire. They may be related.
Look at each spark plug when you remove them and keep them in order. You may see one that looks different than the other 3 if the misfire is in one particular cylinder and not a 'random' cylinder misfire.
A lean mixture or leaky intake valve can also cause an intake pop-back and misfire.
The OBD II system should be able to detect misfire and lean mixtures. Interrogation with a scan tool may reveal more information.

[Rick Anderson]

I think they got rid of the EGR by 2003, but I have had the EGR cause idle problems, rougher running and surging up and down a bit. Pulled the vacuum line to the EGR transducer (capped the vacuum leak of course) and the idle got all better. I also never got a code for a bad EGR, but I have the Mopar Performance PCM that doesn't test the EGR. BUT, how I understand the stock PCM tests the EGR, a bad EGR like I had, could still pass the stock test.

The valve head to the exhaust erodes away and lets the exhaust gas pass by it when it should have it capped it off. That is why it messed up my idle, when the EGR should be off at idle. The test is just to open the EGR at idle and look to see if it changed the idle rpm and mixture at the O2 sensor. So this bad EGR stil metered the exhaust gas somewhat and could produce a change during the test and thus pass the test, even though it was leaking exhaust into the intake when it shouldn't and mess up the idle.

I never got backfires in the intake, but I did get a gummed up TB and intake manifold, and an idle that felt like it was missing and surging. Pulling the vacuum line to the EGR improved the idle, but doesn't fix the problem, you have to replace the EGR.

Having said all that, your 2003 probably doesn't have an EGR, but check and if it is there, pull the vacuum line, cork the vacuum leak and see if the idle improves.

Edited by Rick Anderson, January 25, 2012 at 10:17 am.