p0301 misfire in cylinder 1?

[JgS]

My check engine light keeps coming on after about 20 miles. The code is p0301 (misfire in cylinder 1). I have no noticeable loss of power or extra fuel consumption and the idles is fine. The spark plugs and injectors are about a year old (7k miles). my guess is that it is the coil pack going bad but before I replace it I wanted to get your opinions. The car is a 99 Grand Cherokee with a 4.0 and 170k miles. Thanks.

Topic

[John B Kobberstad]

Check the compression. You have no parts to buy that may or may not actually be needed. you may be able to “borrow” the compression tester from the local parts store. Don’t just start replacing parts. Check the things that you can troubleshoot first and if you can narrow it down to a bad part then buy it. I’ve got a #4 misfire that is due to low compression in the #4 which gives me a constant P0304. Hope this is helpful for you.

[JgS]

Thanks. I don’t really have any signs of low compression. that’s why I’m mot leaning in that direction. But like you said it could,t hurt to check. I have a compression gauge, I’ll give it a try a little later and let you guys know how it goes.

I forgot to mention that the first time this happened I also had the code p1594 (charging system voltage too high)

[John B Kobberstad]

I didn’t think I had low compression either, but when everything else required cash the compression check was free. Now I’m looking at purchasing a leak down tester with the money I saved by not just guessing and throwing parts at it. I tell the wife I needed parts (which I didn’t really need) and spend it on a tool instead.

[EricTheCarGuy]

You might start with a power balance test to see if indeed it’s cylinder #1 that’s the problem. After that the next step is to find out if it’s an issue with spark delivery, fuel delivery, or a mechanical issue.

[JgS]

Thanks Eric and John. I did the compression test and it came out: #1:55 #2:135 #3:130. I ran the test again in cylinder 1 and it came up 0 on both the dry and wet test. So it looks like there is a problem with the compression on cylinder 1.

[JgS]

Anyone think it might be a stuck valve?

[dave]

a leak down test will let you know if you have a valve problem or a cylinder problemo.

[JgS]

I ran the power balance test and it showed cylinder 1 was the problem. I ran the leak down test and it showed I was losing 100% compression. the only place it was leaking was in the crank case so I pulled the crank case cover and noticed that the plunger for the exhaust valve wasn’t seated. I fixed that and ran a compression test it read 100psi (up from 0). No codes right now but it still sounds like it is misfiring. Another power balance test showed there is still a problem with cylinder 1. I am going to run another compression test and leak down to see if anything has changed.

[dave]

you are gathering very good evidence about the misfire without throwing parts at the problem; therefore, i’m going to throw up the rare but prestigious +1 followed closely by me pressing your “thank you” button. banana:

if your leak down is good, then we should look at spark and fuel related issues.

[JgS]

Thank you for all the advise so far. Now that I have somewhat fixed the compression problem I set out to solve the power balance issue. I first tested the injector with a meter and stethoscope. Everything checked out, so aside from making sure the fuel rail is getting fuel to the injector I ruled out a fuel problem.

The next thing I checked is the coil pack. I got the readings
Bank 1: 1.9 ohms
Bank 2: 2.8 ohms
Bank 3: 2.8 ohms
I’m really not good with electrical issues so I don’t know if that means I have a bad bank. I’m hoping someone here can help me with this. Thanks again.

[EricTheCarGuy]

If you still have a valve that’s not sealing it will cause a misfire. It’s possible the valve is bent hence the reason it was sticking. Valves don’t stick without some cause. Don’t waste your time with electrical tests, do a leak down test on #1 to see if it’s sealing, if it’s not you’ll have to remove the head and replace or repair the valve.

[JgS]

Thanks Eric. I worked on it a little more today with a new leak down tester. I had about 90% loss. Most of it through the intake. I took off the rocker arms and ran the leak down test again. the reading came out good, only about 15% loss and I couldn’t hear any air rushing through the engine like I could before. To me that says there is a bad lifter but I cold be wrong. Any advice would be greatly appreciated.

[EricTheCarGuy]

It may be that the valve is bent and is seating in different positions where it will seal sometimes and not others. It would be strange that a lifter would cause an issue like that especially since they’re hydraulic and can only open the valve so much.

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