Head Gasket Failure Diagnosis - Misfire code P0300 (P0301, P0302, P0303, P0304, P0305, P0306)

Did our video help you? If so, consider buying us a beer: bit.ly/3feE6tJ
In this video, we show you how to use a Cylinder Leak Down Tester in conjunction with a Cooling System Pressure Tester on a 3rd generation Toyota 4Runner to verify either a bad head gasket or cracked head. The 5vz-fe engine shown in this video is also used in the 1st generation Tacoma, Tundra and T100 pickup trucks. Cylinder pressure can be lost through several means. It could be getting past worn or cracked piston rings. It could be getting past a worn valve seat or a burnt valve. It could be getting past a bad head gasket into a coolant jacket, oil gallery, or to a neighboring cylinder. It could be escaping through a crack in the head.
Using a cooling system pressure tester in conjunction with a cylinder leak down tester is for when you suspect the integrity of the cylinder has been compromised and cylinder pressure is leaking into a cooling jacket.
Telltale Signs Are:
*Excessive Exhaust Smoke upon a cold start (smoke smells sweet)
*You're losing coolant but there's no obvious leak (engine is consuming the coolant)
*Engine is misfiring
Sean was getting a General Misfire P0300 Check Engine trouble code on his 2002 4runner. You may experience a specific cylinder engine code i.e. P0303 would point to the number 3 cylinder, a P0304 would point to the number 4 cylinder etc.
An alternative method to verifying you have failed head gasket or cracked head allowing combustion pressure to escape into a coolant jacket is by using a Combustion Leak Test Kit. The kit works by detecting the presence of exhaust gases in the engine's cooling system. Here's a link to a kit I own: amzn.to/3lQauT8 This kit can verify a head gasket or cracked head issue, but it can't tell you which cylinder is compromised like the method we use in the video does.
HELPFUL TOOLS
If you're looking for other tools not used in this video, check out Timmy's Master Tool List.
www.amazon.com...
*1/4" and 3/8" Flex Head Ratchet Set - (Great functional ratchets. Flex head with 120 engagement points is a serious game changer) amzn.to/2ql8nNA
*5/8” Magnetic Swivel Spark Plug Sockets w/ Extension Set - (Nice magnetic socket set with built-in swivels and extensions of different lengths) amzn.to/2HRUmQx
*OTC 5605 Deluxe Compression Tester - (Used to perform an initial compression test of all cylinders) amzn.to/2vNRRbu
*OTC 5609 Cylinder Leak Down Tester - (Used with the Harbor Freight 21 gallon air compressor) amzn.to/36WrQnb
*Digital Borescope Camera - (Used to view inside the cylinder)
amzn.to/2R8NwH0
*Harbor Freight 21 Gallon 175 PSI Air Compressor - (Used with Cylinder Leak Down Tester)
www.harborfrei...
*Cooling System Pressure Tester - (The Matco one I own looks just like this one sold by Harbor Freight. Is it the same quality? Who knows.)
www.harborfrei...
**As Amazon Associates, we earn from qualifying purchases.
**As Ebay Partner Network Members, we earn commissions from qualifying purchases.

[@ronkuhlmeier6414]

Perfect timing, Timmy! Almost... I just finished replacing both HGs (and everything on the way down, injectors, Timing belt, water pump, etc.). I used your timing belt and valve cover gasket videos to get part of the way down into the engine and the shop manual for the rest. Your videos are a master class on 5vz-fe maintenance and repair. Thank you so much. Beer is on the way!!!

[@TimmyTheToolman]

Better late than never I reckon. We appreciate the beer money donation.

[@howabouthetruth2157]

I went through that with my 2000 Tacoma 4x4 with 3RZ-FE motor: I bought the truck brand new, and nearly 22 yrs later @ 374,000 miles, it began running rough/misfire upon starting first thing in the morning. After about 20 to 30 seconds, it would smooth right out & run fine. We detected large air bubbles coming up in the radiator & knew we either had a blown head gasket, cracked head, or both. It was both. The head was barely cracked at the spark plug hole of the 3rd cylinder from the front, plus the bad gasket. I opted to rebuild the entire engine along with a brand new, genuine Toyota head. I bought the new head & over 90% of the parts from LCE. We included many upgrades to the new head and the engine, including balance shafts deleted and all-new stainless header & 2.5" exhaust with a new free-flowing CAT too. Got it all finished last August ( 2022 ) and to date, it runs stronger than ever before.

[@TimmyTheToolman]

Did you do the rebuild yourself?

[@howabouthetruth2157]

@@TimmyTheToolman Oh Lord no.....lol. Sorry, I should've mentioned that. We are lucky to have a certain shop in my area: Brevard Cylinder Head & Machine Shop, rebuild the engine. They are heralded as one of the very best in all of central Florida. A friend of mine who has been a Toyota tech for over 25 yrs now, referred them. Before that, the owner of the shop actually worked with my buddy at the Toyota dealership garage for nearly 10 yrs. Only a few months before doing mine, they had built an entire 2JZ for serious drag racing, turbo'd of course. I wish I could have seen it, but a couple buddies of mine has, and they said it's a beast. They do all types of race motors in addition to stock/every day driver applications. They also take on work that the other machine shops turn away, such as rare and/or exotic heads/engines from really old stuff, such as old WW I and II era aircraft engines. Every customer reference I've found online gives them a 5 star review.

[@TimmyTheToolman]

@@howabouthetruth2157 That's great. Sounds like you got the right shop to rebuild your engine.

[@howabouthetruth2157]

@@TimmyTheToolman Yeah man! Got quite a bit more power to be naturally aspirated too.

[@johnremus]

I just did a full head gasket job on mine in January. My passenger side gasket failed in cylinder 1. I opted for to pull both heads and do a full gasket job, all the typical seals that go with it, plugs/wires. Also took my injectors in to RC Injection for cleaning since we have them right here in SoCal - and damn were those dirty. Hardest part of it all, really, was having to do it across a couple weekends in my free time rather than a few a days straight through. As much time as Sean has put in to his car, may as well do the driver side while you have everything taken off.

[@TimmyTheToolman]

Yeah, we're definitely going to pull the driver side head and have it pressure tested and resurfaced. It's definitely the smart thing to do. Thanks for the comment.

[@theotherserge]

I had a dead #5 cylinder and brought it in. The exhaust valves on the 1-3-5 side were all blowing by. Burnt valves and or valve seals. My mechanic said he’d seen this on 5vz’s and pointed out an old recall for these cars (and also some GM engines) was an issue with the PCV integrated with the valve cover. The windage tray on the underside collects hard sludge which interferes with proper cooling. It’s been his practice to replace that valve cover at every timing belt interval with the trucks he’s worked on. I had him do that and install new heads and it was pricey but I love my T100 so it was worth it to me. Modern trucks are kinda embarrassing these days.

[@TimmyTheToolman]

Interesting. Thanks for sharing this.

[@theotherserge]

@@TimmyTheToolman thank you for sharing so much more!

[@chrisfort7340]

Excellent video! My 07 FJ has recently misfired on no5. I’ll be doing both head gaskets, timing chain, water pump since it’s 18 years old and 194,000 miles. I’m tempted to pull the engine and do the work on the stand versus bending over. Thank you sir!😎

[@TimmyTheToolman]

You're welcome Chris. Where do you live?

[@chrisfort7340]

@@TimmyTheToolman, West Los Angeles. How about you?

[@TimmyTheToolman]

@@chrisfort7340 I'm in NorCal, San Jose. It would be cool to do a head gasket job on that engine.

[@ckhaira]

Always wanted a Timmy the Toolman (...and Shaun) head gasket video. Looking forward to seeing what you guys decide to do

[@TimmyTheToolman]

It's going to be a multi-part series. Stay tuned!

[@Miles-wy1zr]

You should be a doctor brother. Incredible diagnostics and very informative.

[@TimmyTheToolman]

Thanks for the nice compliment. We appreciate it!

[@hlubmoon8211]

Yes, I love to get a tutorial video. Thanks!

[@TimmyTheToolman]

It's coming very soon. Look for Part 1 in a few days. If you're not getting notifications, be sure to click on the Notification Bell so you'll be notified every time we upload a new video. You won't want to miss out on this series. It's going to be a great one!

[@LoneScout1]

Same scenario last year my S/C Taco…..when I got the heads off I no true smoking gun on the H gaskets, however upon inspection found multiple cracks between the valves. Both heads were replaced & valves freshened up. One of the difficulties I had to deal with was the fact of resealing the TRD headers which thankfully I found Remflex 7013…somewhat difficult installing those as the headers do not have a proper flange or boss for each ring to sit in. I went with all new exhaust studs for ease of installation. Also replaced the head stretch bolts. Runs awesome however after all that work I somehow tend to go a little easier on my right foot. The misfire/rough at first startup scenario exactly as described. Pinhead was also helpful as he does a pretty good series on this task. #3 was the worst by far. I didn’t bother with the leak down as my borescope showed antifreeze and obvious wash. Great videos….thanks again.

[@TimmyTheToolman]

I think the TRD headers aren't worth the hassle for any perceived performance gain. When Sean got his Supercharger, my first thought was I bet there's a price to pay for the increase in horsepower and torque. My guess is we're going to find a crack between his valves as well. Yes, the head bolts are torque to yield and should never be reused. Some people go with ARP studs instead of the bolts. We're going to get started on this project soon.

[@LoneScout1]

@@TimmyTheToolman the additional boost def could be a culprit on the head cracks, however I believe it is a possible thing with the 5VZ-FE as Pinheads experience shows. Yes the headers a bit of a pain, but in 250k miles never had to touch them and they sure sound great. As for any gains….I would expect some performance increase, however as you say Timmie not worth the hassle to install. In my case the truck is an early ‘02, and when the dealer installed them when the truck was new they unfortunately ended up altering the front cat flange whereas if I went back to stock manifolds I would need to replace the front cat.

[@TimmyTheToolman]

@@LoneScout1 Who's this Pinhead guy? Is he on KZbin?

[@LoneScout1]

@@TimmyTheToolman PinHead0001…very articulate fellow

[@TimmyTheToolman]

@@LoneScout1 I just looked him up on KZbin. He's got 12 videos and they're mostly about rebuilding an Aisin carburetor. I don't see anything about 5VZ cylinder heads.

[@akinolabusuyi2787]

Hey Timmy I have 09 Toyota Camry that’s over heating replaced radiator, ect sensor, thermostat and housing after those fixes I got 2 more codes p0304 and other codes pertaining to bad spark plugs and ignition coils at this point im not sure what else to do

[@TimmyTheToolman]

Did you perform a compression test or leak down test to see if one of the cylinders is compromised? - Sean

[@atomicdmt8763]

high end head gasket / crack sealant- might work also? thanks

[@TimmyTheToolman]

Are you asking about sealing the cracks in the head with sealant?

[@CharlesGodwin-fg2bs]

Please i have and issue with my 5L diesel engine,number 3 cylinder is misfired i have changed the nozzle still same i have service the injector pump is still same please what is the problem i need help please thanks

[@TimmyTheToolman]

Hey Charles, do a leak down test of the cylinder. You might be losing compression causing the misfire.

[@JB-he1jt]

I would NOT buy an expensive 3rd gen 4Runner with over 200k miles for asking price unless the heads had already been replaced! Learned with my 2000 4Runner that that's their weak point no matter how meticulously you maintained it or how often you replaced the Toyota coolant! Not a bad job if you are a DIY mechanic and watch Timmy the Toolman channel.

[@TimmyTheToolman]

Yeah, it's a fairly common failure. I agree it's pretty crazy what people are paying for these 3rd Gens with a lot of miles on them. I wouldn't pay it.

[@cbdreamer1709]

I would. If you gave to do the heads should be good or swap in a new motor your good forever. Cheaper than buying a new one. Glitchy nightmares

[@heatmyzer9]

Bought two…at 206 and 220. No problems whatsoever. 198 psi across the board. If you can fix it yourself get what you want….ain’t gonna get cheaper/easier to find. Join the club!

[@cbdreamer1709]

@@heatmyzer9 so funny so did I both manual. I like them. Nice trucks

[@juancornejo4502]

Hey Timmy do you have a video for wheel spacers for 3rd gen 4Runner

[@TimmyTheToolman]

No, we don't. But, there's really nothing to them. Remove your wheels, and install the spacers with the supplied lug nuts. Use loctite on the threads if you want, or not. I think loctite isn't necessary. Have someone help you by applying the brakes so you can torque the spacer lug nuts to spec. Then put your wheel back on with your regular lug nuts and torque them to spec. I torque both sets of lug nuts to 85 foot pounds.

[@TheLeachMan97]

Unfortunately I’m going to call that’s it’s a cracked head. They always crack between the valves, especially when boosted. I’ve had 3 5vz engines do it

[@TimmyTheToolman]

Yeah, I tend to agree with you. I've seen the same thing with them cracking between the valves.

[@dqyle]

Thanks!

[@TimmyTheToolman]

Thanks Steve!

[@gzumbana]

Good video

[@TimmyTheToolman]

Thanks

[@adrianmendez8912]

Was there coolant mixing with engine oil "milkshake" ?

[@TimmyTheToolman]

I'm guessing at some level there was. We didn't analyze the engine oil for this diagnosis.

[@adrianmendez8912]

@Timmy The Toolman I had the same thing with my 04 tacoma. I had a cylinder 3 misfire , rough could start. I replaced spark plugs, spark plug wires, coils and fuel injectors, next thing you know i have milkshake in the engine oil, had Yota1 performance take a look , confirmed bad head gasket and now they are saying not worth to replaced the heads and to go with new motor

[@TimmyTheToolman]

@@adrianmendez8912 How many miles on your engine?

[@connorm1600]

@@TimmyTheToolman I had the same issue at 259k miles. I replaced both heads. Its a pretty straight forward job once you get the timing belt off. The Cam gear is spring loaded, remember to put a bolt in the threaded hole before you remove it.

[@adrianmendez8912]

@@TimmyTheToolman I'm at 233k miles

[@noejimenez3]

You guys probably have seen this already but this might be of some help (even though you guys dont need it, especially with the FSM in hand!) kzbin.info/www/bejne/rKCvc4V6j7FsnKc Excited that there is now going to be a Timmy the Toolman and Sean version coming soon!! 😁

[@TimmyTheToolman]

Yeah, we've seen it and the guy did a great job. Since he did such a complete job, it's going to be hard to really improve upon it, but we're going to make our own series anyway. Some things will be different because we will be taking all the timing belt components off and doing a full timing belt job as well as pulling off the driver side head and showing how they are tested and resurfaced.

[@noejimenez3]

@@TimmyTheToolman Cant wait! :D

[@TimmyTheToolman]

@@noejimenez3 Neither can we!

[@oneclickandclosed]

How many miles you get to the gallon with a super charger ? You must be rich !

[@TimmyTheToolman]

It kind of depends on how you drive but I get approximately 230 miles per tank. - Sean

[@Amraam23]

Hi Timmy, It's been a long time since there was a good car mechanic on your channel. Give Shawn my condolences. I hope if it turns out to be just a head gasket, you'll go to the original parts. Will Shawn tell us what he thinks led to this glitch? Greetings from Poland

[@TimmyTheToolman]

Sean does have a supercharger so that could have contributed to the problem.

[@tylaroverturf]

This is perfect timing. I think I have the very beginnings of a head gasket failure or cracked head. It'll run a little rough for a few seconds on cold start after it's been sitting for a few days and then run fine after. If it only sits for one night then it doesn't run rough so it must be a really slow leak for now. Looking forward to your teardown video for getting the head off as I see myself having to do it in the future. Also looking forward to where you get a head if you do end up replacing one or both. If I end up having to replace a head i'd probably just spend the money and do both so I don't have to think about when the other one might fail.

[@TimmyTheToolman]

Yeah, sounds like you're experiencing the same issue. I'm assuming you're losing coolant as well? We're going to get the heads tested and resurfaced at Yota1 Performance. They usually don't offer this service to just anyone, but since we have a relationship with them, they're going to help us out. If one or both heads need replacing, we're going to buy them from Yota1.

[@tylaroverturf]

@@TimmyTheToolman Yea I seem to be slowly losing coolant. I see Yota1 has heads on their site but they seem to be out of stock for now. New OEM ones would be nice but they're expensive.

[@TimmyTheToolman]

@@tylaroverturf Yeah, it sounds like you've got a head gasket issue or cracked head. Yes, new heads are pretty pricey.

[@efil4kizum]

how many miles are on your rig?

[@tylaroverturf]

@@efil4kizum 221k

[@dylanfischer9056]

Absolutely perfect timing. In the middle of chasing down dame problems thank you 🙏 much appreciated

[@TimmyTheToolman]

You're welcome. Good luck!

[@Wolfgang51501986]

Oh boy… steam out the tailpipe is certainly a telltale sign along with losing coolant without visible leaks. Another great vid Timmy and Sean! Gucci!

[@TimmyTheToolman]

I'm glad you like the video. We'll get Sean's engine all fixed up in no time.

[@jaredt8883]

Nice! I look forward to what you find and do next. I went through all of this just about a year ago, when I was trying to figure out what was wrong with my truck. I ended up with a cracked cylinder head on the same #3 cylinder. Long story short I pulled out the entire engine and overhauled it. Took a lot of time and money, but it is running great now. Stopping is the current issue with the truck, I found that the rear axle was leaking gear oil into the break drums. I did replace the oil seals and breaks, but the bearings are shot and I have neither the tools or the money to repair it at the moment. When I do get around to it, I will definitely be looking up your videos on the process.

[@TimmyTheToolman]

It seems like the #3 cylinder is a common failure point on these engines. Be sure to watch both of our Rear Axle Seal videos before staring the job and read the comments we pinned.

[@mr.rogers5586]

Do I have to do both sides? My dad says you’ll end up with more pressure on one side of the block than the other.

[@TimmyTheToolman]

You should at least pull both heads and have them pressure tested and resurfaced. Now, if one head is bad, do you just replace that one or do you go for both? In a perfect world and you have money to burn, you'd replace both. But, quality heads aren't inexpensive. I can see many people opting to just replace one head and roll the dice the other one doesn't fail in a short amount of time.

[@plowe6751]

How do you keep the piston at top dead center? Isn't that tough to do?

[@TimmyTheToolman]

@plowe6751 It can be tough because sometimes, when you apply air pressure to the cylinder, the piston is driven down. When that happens, you just try again. The key is to get it as close to TDC as possible, and the piston won't move.

[@williamtsol636]

I noticed my radiator fluid dropping lately ! Good timing for the video ! 👍🙏

[@TimmyTheToolman]

If you don't see an obvious leak, you might be in the same boat as Sean.

[@williamtsol636]

@@TimmyTheToolman Did you guys notice any rust on the spark plugs or any other components ? I dont have any codes, as of yet ! Cheers ! 👍🙏

[@TimmyTheToolman]

@@williamtsol636 We didn't really analyze the spark plugs but you can usually notice a difference in how they look if one cylinder has coolant intrusion. You might not get a CEL until the coolant burning off is causing a misfire. The fact you're losing coolant with no obvious leak is troubling. There is a chance you could have coolant pooling in the valley between the heads and that might be something to investigate. But, the intake manifold needs to come off for a good look.

[@larrysciblo3509]

Well. I may late to this video. Just now going through some of these issues. Not sure if I am losing coolant (my bad for not checking it reg.) No white smoke at the TP. Just rough morning idle and then smooths out after warming up. A bit sluggish going up hill and acceleration thou. She has 345K miles and has always run fine...after 22 years..I love the detail in your videos, but may have to take her to a shop...I do not have all these tools to test compression and leak down...But now I won't be surprised when they tell me the news. LOL Thanks again from Borrego Springs, CA

[@TimmyTheToolman]

From the symptoms you described, it does sound like you might have either a bad head gasket or a cracked head. Keep an eye on the coolant level in the reservoir and see if it's going down.

[@larrysciblo3509]

@@TimmyTheToolman - OK...Thank you

[@efil4kizum]

? how many miles are on Sean's rig?

[@TimmyTheToolman]

He has right around 200k.

[@johnnyoutwest]

Hey Timmy, thanks so much for the video! I have been dealing with one issue after another with the 3rd gen 4runner I recently purchased (multiple engine misfires, losing coolant, and now a blown radiator). I am wondering if you would be open to a quick phone call for me to ask you a few questions, as you clearly know your way around these cars. I would be happy to pay you for your time.

[@TimmyTheToolman]

Email me your phone number. I'm at a wedding this weekend. I'll call you when I have a chance sometime this coming week. [e-mail]

[@FeistyKev]

Super helpful !!!!

[@TimmyTheToolman]

We're glad you think so. Thanks!

[@akdkdk12]

My car developed exact symptom since December. Mine is showing a code for temperature sensor. But now im gonna do your test and see if my head gasket is cracked.

[@TimmyTheToolman]

Good luck with the diagnosis.

[@djmetropolis]

What battery mount is that?

[@TimmyTheToolman]

This is a billet aluminum battery strap down. We can send you in the right direction if you’re interested in buying one. Let us know! - Sean

[@djmetropolis]

@@TimmyTheToolman yes please!

[@TimmyTheToolman]

Hit up @formidable_4runner on instagram and he will hook you up! instagram.com/s/aGlnaGxpZ2h0OjE3OTQwNjU1NDIwNDYxOTUz?story_media_id=2532414458016181585&igshid=MzRlODBiNWFlZA== - Sean

[@jamesgeorge3900]

Should be an interesting vid. Mine has a slight oil leak on the passenger side.

[@TimmyTheToolman]

It will be a good series. These 3.4 engines are getting up there in mileage. As these engines age, more people will be faced with what Sean is facing and will need a good tutorial to follow.

[@dqyle]

Exact same symptoms on my SC’d 2002: rough start that smooths out in about 5-6 sec after starting and intermittent P0300. Curious what you find exactly and if it’s a cracked head, is there a stronger head option out there?

[@TimmyTheToolman]

We're guessing it's a cracked head. It's not too uncommon of an occurrence. The only country making new heads for these engines is China. Japan doesn't make them and there's no U.S. company either. The only other choice is to buy refurbished OEM heads but that doesn't come without risks because they've gone through thousands of heating and cooling cycles too and could crack on you way sooner than you would have hoped. So, the choices are China or refurbished OEM.

[@dqyle]

Thanks Timmy. What’s the risk of continuing to run the truck this way? I have two of these trucks (the other is a manual ‘00 Highlander edition) and am mulling over taking the ‘02 out of service for a while. Can that coolant damage the cylinder?

[@TimmyTheToolman]

@@dqyle Well, I think the concern is getting coolant into the oil that will mess with the lubricating properties of the oil. I know people run their engines for a while with this condition, but it's probably not a good idea.

[@MarkamisPrime]

Get those heads off takem to a machine shop get them resurfaced ported and polished maybe a valve job. Larger injectors, now is the time to do it.

[@TimmyTheToolman]

We're definitely going to get them pressure tested, vacuum tested and resurfaced. Don't know about the valve job. We might be putting two new heads on. Depends how the testing comes out. Yota1 is going to help us out with it and sell us the heads if we need them. We put new injectors on Sean's rig when we shot the knock sensor video. There's injectors meant for a Supra that supposedly are a higher volume injector for supercharged rigs, but we could never get them. The guy at MotorWest Performance hard difficulty getting them.

[@MarkamisPrime]

@@TimmyTheToolman I have the part number for the Supra injectors, I have them on my rig, and have installed them on several other rigs. Night and day difference from stock injectors. IMO no reason to leave anything stock it’s always time for an upgrade when something breaks.

[@TimmyTheToolman]

@MarkamisPrime I asked Sean about them and he does have a set of Supra injectors he bought a long time ago.