I have a 2005 Grand Caravan 3.3L with 188,000 miles. I never had a check engine light until about 3 weeks ago. P0301 misfire in cylinder 1. The weather has been very cold, so I planned to look at it when it gets a bit warmer next week. It’s been running just fine and at times the light goes out on its own for a day but eventually comes back on and is always P0301.

The other day we were driving into town when we noticed there was no heat even though the temperature gauge was rising. Then suddenly, the gauge climbed and went over the halfway mark. It never goes that high. Then the temperature gauge dropped pretty quickly, and we had heat. The thermostat must have opened. And there must have been an air gap in the heater core. I stopped to look under the hood and found the coolant a bit high in the overflow tank and there was no pressure in the upper radiator hose. But it wasn’t completely warmed up yet and it was only 3 degrees outside.

After getting home and letting it cool, I checked the coolant level in the radiator, and it was down a bit. Maybe about ½ inch below the inside top of the radiator. I topped it off then later that day we drove a 25 mile round trip out in the country and it ran and heated just fine. The next day I checked the coolant level in the radiator, and it was down again about the same amount, so I topped it off. Drove a few times yesterday and it ran fine and heated but seemed to struggle to reach its peak (inside heating) temperature. Today I checked it, and it was low again and I noticed the tank level was even higher. And there are no exterior coolant leaks.

It seems it’s warming up and pushing the coolant into the tank like it should but it’s not sucking it back into the engine as it cools. I replaced the radiator cap, and it didn’t help. My thoughts all along have been a head gasket leak around cylinder one, but I don’t really know. Every time it was fully warmed up it kept pressure in the upper radiator hose for a long time after shutting it off. Today after driving about 35 miles it sat in the garage about 45 minutes and there was still pressure in the upper hose.

A theory is that the head gasket has a very, very slight leak. And the leak acts like a check valve only allowing a small amount of exhaust gases into the cooling system and allowing little if any coolant back into cylinder 1 after the engine is off and there’s still pressure in said system. And because eventually there’s too much air/gas in the radiator it struggles to suck coolant from the tank back into the engine. And that’s the reason the radiator always ends up low and the overflow tank level gets higher.

I plan to get a combustion leak detector kit to test the radiator coolant.

Any thoughts on my findings? Thanks.

 

I just did the radiator test for combustion gases and it was negative. The fluid remained the same blue color after at least 2 minutes of testing. I then tested at the tail pipe, engine running, and it turned yellowish green instantly.

This next week it's supposed to be nice weather so I'm going to do a swap of the cylinder 1 spark plug and wire with cylinders in the front of the engine.

 

Well I just moved the number 1 spark plug to the number 6 cylinder and swapped the number 1 wire for cylinder 2 (same length wire) hoping the misfire would move to one of those cylinders. Took it for a 15 minute ride and no check engine light. But did a scan and there is already a pending code for Cylinder 1 P0301 (again). So there is something specifically a miss (pun intended) with that cylinder. By the way, my spark plugs and wires were replaced only 2 years ago when I did the valve cover gaskets.

The thing is it runs just fine. The only time I can sense misfires is at a cold start up. It shakes a bit for 5 or so seconds then smooths out. It accelerates smooth and there's no loss of power. And I've been watching the coolant level and it's remained stable.

I hate throwing parts at it but have considered picking up a new coil assembly. They are inexpensive. But I have no level of confidence this will fix it.

Any thoughts are welcome, thanks.

 

It's not as devastating as it is made to sound. It just means the seal for the head gasket is broken, people say "blown head gasket". It's a costly repair but not the end of the vehicle. It can be fixed. Find an honest mechanic.

 

Yeah I've already dealt with head gaskets on a Venture Van. This was in the early 2000's and cost about $1600 in repairs. I'm sure for this van it will be all that and more. The thing is almost 21 years old now (built in April of 2004). Has almost 190,000 miles and rust is taking its toll pretty bad. Was hoping this would be a quick simple fix. If it wasn't for the rust I might think of repairing it but the repairs would likely cost more than it's worth $$. We've been looking to replace it for a while now but haven't settled on what to buy. I hate buying vehicles. Been driving this van for over 14 years and diving my 25 year old Saturn for over 20 years. I've gotten my moneys worth out of both.

It's gotten much warmer now and I've been watching the coolant level. It's remained very stable. But the misfiring at startup has gotten worse. Sometimes when cold it will misfire for 10 to 15 seconds or more before smoothing out. After that it runs great.

I've swapped spark plugs and wires for cylinder 1 and misfire stayed on cylinder 1. Did the radiator test for exhaust gasses and it was negative. I purchased some higher end fuel system cleaner to clean injectors and/or carbon off the intake valves, etc and no changes. As mentioned before I've contemplated changing the coil module but we'll see. Just not sure what could go wrong in the coils considering the paired cylinder thing and I'm only getting misfires in cylinder 1.

It seems like something gets in cylinder 1 after sitting for a while then needs time to burn off before it will run smooth. Like coolant or a leaky injector that is fowling it up somehow.

Any other suggestions/comments are welcome. I'm not an auto mechanic, just been fixing my own vehicles for over 50 years.

 

When was the last time you replaced the battery? Sometimes the most obvious simple things make all the difference. My 19 DGC had multiple misfire codes 😱 and just replacing the battery which has a bad cell resolved it. Just be sure to replace it with the same 750 amperage. Previously I made the mistake of replacing it with a premium 900 amp and it shorted O2 sensors. Same with the headlights, only replace with the basic H11 bulbs, otherwise the sockets fry out .

 

The battery, which was 9 years old believe it or not, was replaced Dec 2024. Had to go on a 130 mile trip at night in winter to an airport to pickup holiday visitors and did not want to take any chances. It's a 700 CCA.

I can get new coils for around $40 shipped to my house. I may just try that next. Been binge watching videos and reading articles about bad coils in these vans. It's a bit of a crap shoot but I've read countless comments from people where replacement fixed their single cylinder misfire issues.

 

I have a question. This van uses the waste spark ignition system. If cylinder 1 and 4 are firing at the same time and cylinder 1 is the only one having a misfire could a person swap wires at the coil for spark plugs 1 and 4 to see if the misfire moves to plug 4? Know what I'm trying to say? I would have to get some longer wires to do this as they are not long enough to reach to the other side of the coil.

 

I purchased 2 longer wires from Rockauto and did this test of swapping the wires at the coil pack for cylinders 1 and 4. It worked fine. The outcome was not fine however. I still got the same misfire at cylinder 1. So I'm checking out something else and will reply with the outcome if it is positive.

I was able to figure out the coolant issues I was having. After finding out there was no exhaust gasses in the radiator, but the overflow tank kept filling up slowly, I looked through some totes of saved auto parts. Found an old plastic radiator cap and put it on my van's radiator. It was a 14 pounder instead of 16 lb but I thought a little less is better than more pressure. It will be the tie breaker for my other 2 Stant caps I used recently. Well I'll be darned if the thing didn't start working like it should. The coolant level in the tank rises a bit when hot and lowers when cooled down and has stayed very stable. And it heats the interior like it did many years ago. Recently on colder days it struggled to heat the interior like it used to. Lesson learned. Don't only look at the coolant tank when checking the level. When it's cooled down check the radiator level once and a while as well.

 

First, if anyone is monitoring/moderating this forum you can mark this one as "SOLVED".

I solved the cylinder 1 misfire. As stated earlier I did most of the basic things you should do to test for a misfire. Swapped plugs and wires. Ran several quality brands of fuel system cleaners in the gas tank. Swapped the wires at the coil for shared spark plugs 1 and 4 (the waste spark ignition system thing). Figured if it was the coil pack causing the misfire, the misfire should move to cylinder 4. But it didn't, it stayed on cylinder 1. So I figured it wasn't the coil pack. Recently I started to think about how it could distinguish between a misfire on 1 vs 4. There are not 6 individual wires coming from the engine control module to the coils. There are 3 (one each) for each set of shared plug circuits (there's a 4th wire for continuous 12v to power the coils). I have not been able to verify it but I assume when (in my case) the middle coil goes bad it will cause both cylinders 1 and 4 to misfire but only report it as cylinder 1. Because it doesn't know any better. There are no other sensor circuits to distinguish between 1 and 4.

Anyway, I ordered a new coil pack, installed it and the van is starting and running like new again. At first startup the check engine light was off. It was on full time for over a month.