P0300 code along with 3 seperate cylinders Renegade Liberty 2003 3.7

[HoosierJeeper]

Kind of talking out of my ass here, but next step is I'd look at fuel trims. Cylinder one I think would be bank one (driver's side), see if it's running rich or lean. I believe fuel trims should be near 0, but hopefully someone smarter can chime in. If it's running rich or lean on bank one, then you likely have a fuel injector issue. I'm guessing the one misfire could possible trigger others since then it gets all out of balance.

Lot's of "I guess and I think" in my response LOL

 

[Tin Man]

So what should I do? Should I pull the plugs and coils and re-check them?

The check list from easy and cheap to "oh sh*t" is spark plugs, fuel injector, coil packs, compression test. I'd suggest the compression testing now just to make sure you are not wasting your time and money trying to find easy and nice solution.

Coils and and fuel injectors can be tested by switching them between cylinders. If the fault follows them your problem is solved. If not, you are basically screwed.

 

[GitEmSteveDave]

Kind of talking out of my ass here, but next step is I'd look at fuel trims. Cylinder one I think would be bank one (driver's side), see if it's running rich or lean. I believe fuel trims should be near 0, but hopefully someone smarter can chime in. If it's running rich or lean on bank one, then you likely have a fuel injector issue. I'm guessing the one misfire could possible trigger others since then it gets all out of balance.

Lot's of "I guess and I think" in my response LOL

I cleared the code when I got home tonight, and the light cleared, and after 10 minutes of idling, not even a pending code. It seems to only happen at cold start idle. My torque pro app crashed last night and lost all my settings, so I'm trying to remember what protocol I had it on(there are two choices for the 03 Liberty, one that doesn't like it when I stop and turn off the engine, and one that doesn't mind and neither can seem to clear codes via the app and my bluetooth adapter, so I have to break out my harbor freight tool) I can check to see if I can set up a screen showing me Trim banks once I reconnect to the ECU, but according to my app, there are 6 sensors for each bank: long term,short term and sensors 1,2,3 & 4.

I guess I should try to grab the Freeze Frame data next time it's triggered, either pending or actually triggered.

 

[GitEmSteveDave]

Had a solid week of no codes, but Pending P0303 showed up again tonight, about a minute after I started her up after work and had just been idling. Put $20 in on Wednesday, and I'm about a half of a tank.

Got the freeze frame data:

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Should I try swapping 1 & 3 next monday on my day off, or is there some info in the freeze frame?

 

[TomB985]

The first thing that comes to mind with the misfire at idle is a possible vacuum leak. You really need to check your fuel trims before going further in my opinion. If you have have double double-digit positive positive fuel trims, that indicates the PCM has to increase the mixture to compensate for unmetered air entering the manifold.

This unmetered air throws off the mixture and will cause a misfire, but becomes a drop in the bucket once you apply throttle and the engine consumes significantly more fuel and air. This is an easy thing to check without throwing the parts store at, which it looks like has already been done.

 

[GitEmSteveDave]

The first thing that comes to mind with the misfire at idle is a possible vacuum leak. You really need to check your fuel trims before going further in my opinion. If you have have double double-digit positive positive fuel trims, that indicates the PCM has to increase the mixture to compensate for unmetered air entering the manifold.

This unmetered air throws off the mixture and will cause a misfire, but becomes a drop in the bucket once you apply throttle and the engine consumes significantly more fuel and air. This is an easy thing to check without throwing the parts store at, which it looks like has already been done.

Could a cracked breather hose cause enough of a leak?

 

[TomB985]

The crankcase breathers I've seen pipe into the intake before the throttle body, if that is the case then no. Take a good look at every vacuum line going into the intake manifold, particularly elbows and joints. A vacuum leak is anything that lets air into the manifold around the throttle body (and IAC, for that matter).

 

[GitEmSteveDave]

Another code, cleared, and it's been a few cycles since even a pending is showing:

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But.... I've notice the past few cold days, after starting, that there is a hissing sound from the drivers side when I let off the brake and don't hit the gas. When I warm up and hit the gas/brake, no noticeable noise. It seems to be a Brake Booster problem. So, since the brake system operates on a vaccum, could it be related?

 

[TomB985]

But.... I've notice the past few cold days, after starting, that there is a hissing sound from the drivers side when I let off the brake and don't hit the gas. When I warm up and hit the gas/brake, no noticeable noise. It seems to be a Brake Booster problem. So, since the brake system operates on a vaccum, could it be related?

Yes, it certainly could. A leaky brake booster is a vacuum leak, which would cause your misfire at idle. Remove the line to the booster and cap it, then listen for your hissing noise and misfire. If no longer present, that’s your problem.

 

[GitEmSteveDave]

Yes, it certainly could. A leaky brake booster is a vacuum leak, which would cause your misfire at idle. Remove the line to the booster and cap it, then listen for your hissing noise and misfire. If no longer present, that’s your problem.

To be fair, the hissing doesn't correlate to the misfire. The misfire codes happen ONLY at idle/startup, and at that point, I have never hit the brake and don't hear a hiss. It's frustrating because it sometimes clears on it's own, and other times takes me hooking up a scanner to clear the code. So if its the plug, it should throw itself ever time I do a cold start

 

[TomB985]

To be fair, the hissing doesn't correlate to the misfire. The misfire codes happen ONLY at idle/startup, and at that point, I have never hit the brake and don't hear a hiss. It's frustrating because it sometimes clears on it's own, and other times takes me hooking up a scanner to clear the code. So if its the plug, it should throw itself ever time I do a cold start

Only one way to find out, and it costs nothing. Cap the line and see if you still get a misfire code.

 

[GitEmSteveDave]

Only one way to find out, and it costs nothing. Cap the line and see if you still get a misfire code.

Cap what line?

 

[TomB985]

Cap what line?

The vacuum line going from the manifold to the brake booster. You're disconnecting the brake booster and sealing the line, then running the engine to see if anything changes. I wouldn't recommend driving around like this, you won' have power brakes.

 

[GitEmSteveDave]

Just an update, been nearly three weeks since my last pending misfire, which was surprisingly cylinder 2 instead of 3 on 11/9. Only thing I have been doing different is I bought a gallon jug o' Lucas and also a little 4oz bottle, and I put a little bottle in every time I add gas into her.

 

[Somar]

hi, any good news?

 

[GitEmSteveDave]

hi, any good news?

Still no check engine lights, pending or otherwise. I still get nervous every time I start up, but she's been good.

 

[GitEmSteveDave]

SIGH.

So Cylinder 2 is my new misfire central. Already swapped coils from 2 and 3, and still getting a confirmed CEL from cylinder 2. Is my next step replacing the plug on 2? I'll have to wait until next Monday because I work everyday until then, and the engine doesn't get to ambient enough unless it's been like 12+ hours.

Also, when I replaced Coil 2&3, the entire bolt(into the block) came out on both. Is there a way to avoid that, or if it happens again, should I put some red thread lock on when I reinsert it?