Borrow the battery out of your other vehicle just long enough to complete the compression test.

 

After my dunce hat moment with the battery I fed the battery from another vehicle. I believe I have found my problem. My dry compression test results are as follows.

Dry Compression Test:
Cylinder 1- 175, 177, 177 psi
Cylinder 2- 160, 163, 164 psi
Cylinder 3- 170, 165, 165 psi
Cylinder 4- 142, 145, 146 psi

So after those readings I went to my guide I found online on how to do the test. Part 2 -How to Test Engine Compression (Ford 4.6L, 5.4L)

To interpret my results I had to take my highest reading, 177, and multiply it by 15 percent. This would allow me to find the lowest psi my engine would run properly and not misfire. I took 26.55 from the multiplication problem and subtracted it from 177. I got 150.45. 150 psi is the lowest reading my engine can have to successfully run. According to my findings anything under the 150psi mark will cause a misfire. That goes hand in hand with the P0304 code and a cylinder 4 misfire. Cylinder 4 is the only cylinder consistently under 150 psi. The only two outcomes now are either worn out piston compression rings located in the bottom block of the engine, or cylinder head valve damage.

The way to distinct the two is to do a wet compression test with 1-2 tablespoons of motor oil in the cylinder with the misfire psi readings. I took a little medical syringe filled with the correct amount of oil, and squirted it into cylinder number 4. I then proceeded with the wet compression test. The results changed by a big amount.

Wet compression test results:
Cylinder 4- 175, 171, 170 psi

So, at this point its safe to say the problem child is a worn out compression ring located at the bottom block of the engine. It took a bit of work, but it was a fun learning experinece with my father. I can't imagine how much this would have cost at a mechnaic.

I just want to check and see if my findings to you guys seem right. From this point its safe to say I will need an engine rebuild, correct?

 

It definitely seems like you found enough evidence for a bad piston ring by interpreting the results from the compression test on cylinder #4. Given that you also have good spark at the ignition coil and fuel at the injector further supports this idea.

It really sucks that there couldn't be an easier fix for this misfire, like a coil or injector, now the problem is much more involving. As far as how much it would've cost to diagnose this at a shop depends a little bit, many shops charge $99 diagnostic fee. An engine misfire is a very common issue and technicians usually check for compression during misfire diagnosis. You did really well on diagnosing the problem, being able to find the cause of a misfire can be very tricky and you were able to test spark, fuel, and compression. These are fundamental in identifying any misfire and what you learned will apply in the future whenever you encounter a misfire again.

Now the real decision begins; there are a few options out there depending on which course of action you decide to take, and if you feel it is necessary to get it running again. The 4.6L V8 engine is very common and parts are very readily available; you could purchase a rebuild kit and rebuild the engine. Likewise you could try to find a good running used engine at a salvage yard to replace. Or you could find a long block and transfer the parts from your engine onto it.

 

The one thing that really confuses me is that even technicians missed this at the Ford dealership. They looked for the p0304 code and claimed I needed a new coil pack. I swapped the coil pack to position one, and the coil worked just fine. The same p0304 code popped up. I am very leery to trust a person who cant do a simple thing like I did, when I had no experience doing any of this at 19 years old. If I can do it, and he can't... theres a major problem in my opinion. I could be entirely wrong though.

I ship out for the military in 6 weeks and I'll be gone for 6 months. I was planning on getting rid of the vehicle, because I wouldnt be using it, I wanted something a tad bit smaller, and it would be money in my pocket I didnt have. I planned on getter a newer, used vehicle after basic.

So, the way I'm currently looking at it with my situation, wouldn't it be better to just sell the vehicle as is, and list the current problems? Should I have a professional shop confirm my findings to find the true value and condition?

My Expy is worth about 2-2.5k according to my area, but with the engine needing a rebuild... The value is less. Fair condition on kbb is 1800, but for me it could be lower. Luckily the vehicle was a hand- me- down from my parents. They know I have wanted to sell it.

 

Wow, if you took the vehicle to a shop to diagnose a misfire code and the technician didn't check for spark at the coil, fuel at the injector, and compression, that is very concerning! Especially considering how the parts and labor are such a high expense to the customer makes it even worse. I think you did a good job in trying to diagnose the problem yourself and learned something very useful that you can apply on basically any vehicle with a misfire.

If you want you can seek other opinions about the misfire, but it is too coincidental to have a cylinder #4 misfire and low compression on cylinder #4 as well. In theory, you could install a brand new coil and injector, clear the check engine light and see if the misfire is still there for less than the cost of diagnosis at the shop. But I don't think that's necessary because that doesn't explain the compression on cylinder 4. I'm curious to see what other members think about the compression test results but I think that cylinder 4 is low with respect to the other 3.

 

Well, the compression on that cylinder is only out of spec because it is more than 15% lower than the other cylinders. If the other cylinders had the same compression number as cyl 4, there would be no concern. It should be enough for it to fire, but might be more difficult for it to fire compared to other cylinders, requiring a different mixture. I bet the Ford technician just hooked up the Ford VCM and did a relative compression test with the computer, which I don't think is able to tell if one cylinder is just slightly out of spec...

 

But the p0304 code IS misfiring. That's the whole point. A vehicle, kept maintained should not have an issue like this. Ignoring the problem will only make it worse I would think.

That's very possible. I don't know what equipment he used or even what they use. That explanation would make perfect sense why it was missed.

 

Yes, I never contested that. My point was that it was a bit surprising that it is misfiring due to low compression, when the compression is just out of spec, but not grossly low, and in fact that an engine with 140-150 psi on all cylinders would not raise any eyebrows and fire all cylinders just fine... My wording might have been a bit awkward on that, English is not my native language..

 

In fact, in my shop manual for the 2005 5.4 3v engine, it says the lowest cylinder should at least be 75% of the highest cylinder. And it has a chart allowing compressions as low as 101 psi on lowest cylinder. Based on that, your highest so far is 177, meaning your lowest can be 133 psi, which actually means that your engine passes the compression test so far. I don't have a shop manual for the 2000 4.6 2v engine, but perhaps someone else here has one. The shop manual for the 1999 4.6 shows exactly the same chart as the '05 5.4, so I suspect it's the same....

 

Well, does engine compression differ from engine to engine?

Also, if the compression truly was fine on cylinder number 4, then why did compression shoot up when I did a wet compression test compared to a dry one? The wet compression test made cylinder number 4 increase by 20+ psi and I did 3 readings for each cylinder.

The Haynes manual I have doesn't even state a percentage on how to analyze the compression test results. However, it does state to do a wet compression test as well. The Haynes manual even states the same thing as the online guide I used. If compression increases after the wet compression test, the piston compression rings are worn. Thats two sources that are confirming the same things according to my test results.

Now, you could be right, but I am at a loss for words. It seems all the evidence does focus on a compression ring on cylinder no. 4.

Should I be driving this vehicle at all as well? I've never had a vehicle with an issue like this and I don't know if its safe. I don't want to cause further damage to the vehicle.

 

The rings might be worn, hence the increase in compression on the wet compression test, but they may not be completely worn out. At least from what I read in the factory shop manual from Ford, your compression test results passes the criteria's which Ford has set, where the lowest value is at least 75% of the highest value. It should be able to fire if it receives the correct fuel mixture and has a spark

 

A perfect textbook analysis!

 

Thanks Alloro! I guess I did everything right then!

I was looking at parts for the 3 avenues of approach. The rebuild kits were 700-800 on average. This would require addiotional labor to take the engine to a machine shop as well on top of a mechanics labor.

For a long block, they were double the cost of a used full 4.6l v8 triton engine I could buy off ebay. They were 1800-2200 dollars new. I couldnt find any used long blocks.

For the full engine swap, the cost would be 900-1k for the engine itself according to ebay. A new engine was more obviously.

I just got off the phone with my local mehcanic my family uses. I told him the different avenues, and asked for his prices and parts sources. For any option besides selling it, it would be minimum 1k for the parts and labor with 1.5k being more realistic for labor and parts. Hell, it could be more with the rebuild kit due to the machine shop, or a long block. I did tell him my other option was to sell it.

He pretty much told me this, " Yea, you're better off pretty much cutting your losses, selling it, and getting a more relibable vehicle."

Now, I guess I just need to figure out how much this Expy is worth in its current condition.

 

I think there's more to it than what the compression test shows. Yes, the rings are starting to wear, that's correct, but if you took the car to a Ford dealer and asked them to do a compression test, based on Ford factory specs this engine would pass that compression test, meaning the cylinder should have enough compression to be able to fire.

 

Skauber, then what is causing the p0304 code then? Can you link these factory specs, because I cant find any. I'm not saying you are wrong, but I cant ignore evidence here and what it implicates. I need to figure this stuff out asap, because I will be gone in 6 weeks for 6 months.