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Misfire on all cylinders

I have a 2004 saturn vue 3.5L v6. The honda engine. When I got it, it only had a cel for a bad o2. This winter, it started misfiring on all cylinders. I literally have every misfire code the ecu can throw. I got around to replacing the o2 sensor, hoping that would fix it, but it did nothing for the misfiring. It no longer gives me the o2 code, so it wasn’t a waste. Anyways, it ONLY misfires when the engine is cold-cold. If its been running for any length of time its fine. The guy at the parts store said something about cleaning the injectors. Didnt jive with me. Ive only owned civics and integras my whole life, done multiple engine swaps and rebuilds and have never had dirty injector problems. Not with used imported engines, not with 200k + mile factory engines.
Anybody have any suggestions on where to start looking for issues?

The first things to check on multiple missfires are fuel ,spark, compression, timing. It would be easier to give you direction if you posted all the codes. P0301, etc

Just because you’ve never HAD a problem with injectors doesn’t mean he’s wrong. Tossing a bottle of injector cleaner in the tank can’t hurt. May not fix all the issues, but can’t hurt.

He’s one the right track, though, as it seems like a fuel delivery problem. You didn’t post nearly enough info to narrow anything down.

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The first place I would be looking into with multiple misfires is the ignition system. Your engine has a timing belt as well as sensors for camshaft as well as the crank. If you jump time via the T belt you will see misfires…and same goes for the sensors. However…you would throw codes for that.

What you would not throw codes on is if the exhaust valves were tightening up on this engine…and this engine is known for this. Over time the exhaust valves essentially try to hammer their way up through the cylinder head and in doing so they take up the slack between the cam and the valve stem…which will cause misfires outside the scope of the computer to be able to know about. This sounds like where you might be at this point based on your problem description as well as no ignition or sensor faults…AND the effect temperature has on the issue… All point to this condition.

This is such a common issue that many people have looked for its solution…and there are many resources on the net that follows this theory out… Here is one fellow who knows his stuff explaining the situation…there is also a followup part 2 or 3 as well.

Might want to look into this…

I fought with this for months and once I actually figured it out, it took me 5 minutes to fix!

Basically the car would run like crap and misfire when started cold. It was worse on rainy or damp mornings.

It ended up being the sensor grounding points for all the sensors on the intake. Someone told me to remove these and clean all contact points. That is what I did and the difference was amazing. This is so easy and basically costs you nothing so I suggest doing it before attacking any other possibilities.

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Also check for oil down in the spark plug wells… Bad valve cover gaskets leak oil down into the plug wells and short out the spark…which creates misfires also.

@cwatkin makes a good point to look into because those grounds are a common area to address imho. Any issues with those connections can really make troubleshooting difficult because the items needing ground will function in strange ways while searching for a good connection.

Lots of possible causes, but the one that seems to stump “mechanics” is the valve lash tightening up…no one seems to want to believe that issue exists. I don’t blame them in that, but I don’t need convincing and know that condition rather well, where and when it sprouts up can be surprising, but it is definitely “a thing” for certain.

It also sounds like valve lash tightening up is a common with these and other Honda engines as well. When was the last time you had lash adjustment performed on this engine? This is a scheduled maintenance item and you will burn valves if this isn’t done.

It seems like there are two schools of thought on lash. Some people prefer hydraulic lifters which adjust for wear throughout the life of the engine and do not need adjustment. Other others prefer solid which will not be as impacted by sludge causing them to stick or overpumping due to high RPM. This makes sense for racing applications but not a minivan!

Check the fuel pressure.

Low fuel pressure can cause misfires on all cylinders when the engine is cold, and the demand for fuel is highest.

Check the coolant temp sensor for the computer.

If the coolant temp sensor is telling the computer that the engine is at operating temperature when started cold, the computer will provide the improper air/fuel mixture, causing misfires on all cylinders.

Tester

I’m familiar with the process. Tdc on comp, check/adjust clearance, rinse, repeat. I should probably look to that for my v45s hot start issue as well. Thanks for the suggestions everyone. Ill go ahead and let the car rest till I can check the valve clearances. Crossing my fingers for no burnt valves. Its a recent issue, so hopefully its okay.

Ah Saturn. Home of the mystery/phantom codes. I would say your pcm is not grounding the injector pulse. Or you have several corroded wire crimps in plug assys. I belong to several Saturn forums. Had a 04 v6 for 1 week. Made $1300

Ill check this first just in case. Even if its not what’s causing my problems, its something that’s free to do and generally a good idea. Thanks