I have a 2005 jeep liberty 3.7L with 60,000 miles on it. The engine light when on 2 weeks ago and gave a p300 code. the dealership replaced coil and plugs, I believe. Then would start rough when cold, the engine light would blink for about 10 seconds then remain on. the car runs just fine except when cold…first minute of starting it. they checked for head gasket problem, and cant seem to find the problem. They told me that this could just be something that happens. I don’t believe that. I have no loss of power, no hesitation. Runs fine 99% of the time
Sounds like you probably have a bad intake gasket that’s leaking when cold and seals up after it warms up. You’d be better off (in my opinion) to find an independent repair facility instead of using a dealership to diagnose and repair this problem.
I fully concur. The odds that this dealership will ever find the real problem is very low. That’s been my experience with most dealerships.
I too agree.
Many dealerships seem uninterested in any vehicle that isn’t easy to diagnose and/or isn’t covered by warranty. Why, I don’t know, but that’s been my observation.
Vacuum leak, intake leak, low fuel pressure, worn plugs, weak battery.
Eek…and how much is intake gasket? Dealership not charging cause under warranty…
p0300 means multiple cylinder misfires. A misfire means the power boost the computer expected to measure when each piston is supposed to be pushing at its allotted time downward on the crankshaft, well, that isn’t happening consistently for some reason. There’s a least a dozen reasons why a cylinder might not fire correctly. But you have an important clue. When the engine is cold it requires a richer mixture to run well, so since this only happens when the coolant is cold, and a too-lean condition can cause multiple cylinder misfires with a cold engine, as others mention, best to start with things that cause an unusually lean condition in all cylinders. Could be too little gas, or too much air. Besides those ideas mentioned above, a PCV valve or brake booster on the fritz, or partially stuck open EGR are also possibilities.
I’m going to go against the grain here . . . BIG TIME
The Jeep Liberty engine is known for having valve train issues
A colleague of mine already ran into this. His Liberty had misfire codes. The codes did NOT move when he swapped plugs, coils, injectors, etc.
Check this out
The OP said the shop tested for a head gasket problem. Wouldn’t part of doing that test be a compression test? If they did a compression test, would that be sufficient to test the condition of the valve train?
Maybe so, but I’m well aware that there are pattern failures. As a mechanic I’ve seen many pattern failures, and knowing the eccentricities and weaknesses of a particular engine has prevented many a headache
Check this out. I realize it’s for “international markets” . . . but I’m willing to bet the US market uses the same 3.7L engine as the one mentioned in the bulletin
http://ww.w.autoelectricpro.com/purchased/images/076000/075917.pdf
This is the exact problem my colleague had with his Liberty. The valves were the problem.
Do a google search for Jeep Liberty 3.7 P0300 . . . I foresee that you’ll get many hits. I also foresee that you’ll find many guys talking about the valvetrain.
They did a compression test and also said no head gasket problem. What, if valve issue, is this going to cost me?
I advise you to make some phone calls
Perhaps you should consider calling some automotive machine shops (engine rebuilders), and ask them what experience they have with those Jeep 3.7L engines. Perhaps they can give you a ball park estimate for the machine shop charges
Mind you, the machine shop will not do the whole job. They will only do the cylinder head repairs, as needed. Someone will still have to take out the heads, deliver them to the machine shop, and reinstall them
Perhaps I’m wrong, but my gut feeling is that somebody will be removing those heads
Try an experiment. Try putting the key in the ON position for 4 or 5 seconds before putting it in the START position. This could be as simple as the fuel line losing pressure when off, and if it is the experiment will pressurize the fuel line before starting the engine. Post back with the results.
I will try it in the morning. My luck isn’t usually that good! 
I will post with what happens.
Well, if you try that, do it on/off/on/off/on/off about a half dozen times. On is where the dash lights all come on but not where it is cranking. If there is insufficient fuel pressure, it will more than likely take more than one priming cycle of the pump to fully pressurize the lines.
I let it stay in “on” position for 5 seconds before turning it on. The engine light did not blink and didnt idle as rough. Dont know if coincidence, so will try again when cold. Should i try off/on or just leave in "on " position?
If it seems to have worked, try it again the same way. Some systems “time-out” and only run the pump for a predetermined amount of time if the engine isn’t started, but it would appear that the time you held the key ON was sufficient for your vehicle. If you’re uncertain, you can always try cycling the trick twice before starting. It is totally, completely, risk-free. It can do absolutely no harm in any way.
If this trick does work, you have two options. (1) have the check valve that keeps the system pressurized replaced, or (2) build this trick into your “start the car” routine. Personally, I’d just build it into my morning routine. I actually had an old truck years ago that I had the same problem with. And I just accepted that this was the way to start the truck.
I wiil try it again and post what happens. Should i get engine light reset and see if it stays off? What does check valve run?
You definitely should get the codes read again before resetting it. Post them here.
The valve only prevents the fuel line from depressurizing when the pump is shut off. That’s all it does. What you’ll be doing by putting the key ON for a few seconds is only pressurizing the fuel line. Today’s cars need typically 40psi or more for the fuel to properly vaporize for proper combustion.
The codes are p0300 and p0302.