Vehicle Information: I own a 2006 Dodge Durango Limited with the standard 4.7 V8. The car has 154k miles.
About Me: I am fairly self-reliant with repairing cars. I am, however, not great at diagnostic work. Although, this is something that I am learning with every project. I share this with the community because I am no car repair expert; I am simply good at following instructions. Any advice on the below issue would be appreciate.
Background: About a month ago, the car developed a weird idle, which felt like a periodic and random stumble. I attempted to address the issue by replacing the spark plugs. In the process, I followed the standard protocols for adding diaelectric grease to the coil pack boots. The issue did not improve. I took the car to Firestone, and they completed the diagnostic test. As a remedy, they recommend new oxygen sensors, battery, and purge valve solenoid. All four o2 sensors were replaced along with the battery and purge valve. The periodic stumble continued; however, new codes emerged: P0300 and P0303. The car was running terrible at this point. P0303 isolated an issue on the third cylinder. I identified and replaced a cracked coil pack. I also took the opportunity to clean the intake manifold. Due to error on my part, I had to replace the idle air control valve and the throttle position sensor. (Long story…please don’t ask why.) Subsequently, the P0303 code disappeared and the car started running better as long as the car was warm. The original stumble has been resolved.
Current Issue: Here is the current issue that I cannot seem to resolved. The car has a rough idle at startup, but once warm, it runs beautifully. Computer still shows code P0300, which refers to multiple misfires. The local auto parts store recommends that I replace the remaining (7 total) coils packs. My questions:
Should I replace all of the coil packs? Or, should I test and identify the problem coil packs?
Would the EGR valve have anything to do with this issue?
The rough idle at start up for this engine is usually caused by the fuel pump failing to hold pressure after shut off. Are you experiencing a longer than normal cranking time when starting the engine cold?
allpar,com is my go-to place for tough questions about Chrysler vehicles. You’ll find a forum dedicated to yours. Their minivan forum has helped me several times. Good luck.
When you cleaned the intake manifold . . . did you replace the gaskets?
Misfires and rough idle at startup, but which goes away when warmed up . . . can sometimes be caused by leaking intake and/or exhaust gaskets, which can seal better when the engine is warmed up, because the flat gaskets sometimes swell up as the temperature increases
I’d be hesitant about replacing the 7 remaining coil packs, simply based on the auto parts store’s recommendation. the guys behind the counter are not mechanics, and to be frank, their diagnostic skills are usually pretty weak.
I’m aware the P0300 code states random misfires, but if you hook up a decent scanner and look at live data, sometimes you can see if a particular cylinder is missing very badly, compared to the others.
It might also be a good idea to look at the short-term and long-term fuel trims when the engine is idling, just after a cold start
By the way, when Firestone recommended new oxygen sensors and purge valve . . . if that was due to the rough idle, then that’s a sign that their diagnostic skills are woefully inadequate. I suspect they were not only guessing, but they wanted to sell some parts and make money in the process
I agree with @db4690 in that I wouldn’t replace the coils at this point either.
If all those coils were bad you would have codes for misfires on other cylinders besides just #3 cylinder.
Neither of thee places that have done diagnosis on this engine have very good skills. They seem to only know how to use a code reader and base their parts replacement on the reader alone. Normally a code does not tell you “Which part to replace”. but gives you a direction to go in your next diagnostics.
As @db4690 asked. Did you replace all gaskets involved when you cleaned the intake?
This can be several things unfortunately. The first thing I would be checking is the ignition system and its components. This engine has a coil for each spark plug…it also has a stubby little spark plug wire also. Its not a direct coil on plug system…its a hybrid. It seems the issue got worse after replacing the plugs no? If so…that points to the short plug wires that go from each coil to the plugs…they can degrade and go bad. Also…you need to be certain the spark plug wells are not filled up with oil from a leaking valve plug well seals…this is common. The seals leak oil into the plug wells and nowhere else…submerging spark plugs in oil …and after that the spark shorts out in the oil puddle.
So check your wires and plug wells.
The other monster in the closet is the timing chains… when they stretch you start to throw misfire codes for seemingly no reason at all… New wires, new plugs etc and yet you still get misfires. All can be due to T chain stretching. This was extremely common on the 5.2 V8… but your 4.7 is an entirely different system although no less subject to what happens when the chains stretch or the chain tensioners don’t function properly.
The cheapest route is the ignition system and its components…then you move on to engine ignition timing and vacuume gauges to see if you can ID a stumble in the valve timing. You will need a proper engine diag computer to get a handle on all this to be honest.
Has the vehicle had proper engine oil changes? Do you see gunk inside the valve covers that suggest lax oil change regime ? If so…that heads you in the direction of the chains faster than if there was no evidence of oil change abuse.