P0304 Code - 4.0L Head Gasket or Something Else?

B

Baba Booey

New member
A few weeks ago I had a rough idle at start-up and all of the CELs. I took it to a mechanic who got a P0304 code. He replaced the coil with an aftermarket brand, changed the plugs (due anyway), and added some injector cleaner. At that time he warned me of the slight chance that I could be looking at a head gasket issue with this motor.

I drove the vehicle for a few weeks without issue and thought I dodged a bullet. This past weekend, I had a very rough idle at start-up, and the CELs quickly returned.

This time I took it to a well-respected independent shop that specializes in Toyotas. If I need a new head gasket, this is who I want to do the work. I told him what had happened a few weeks ago and that, after reading about the head gasket symptoms on forums like this, was almost certain that I was looking at a bad head gasket.

I dropped the 4Runner off last night. He called today with a P0304 code diagnosis and said that he pressure tested the cooling system and looked in the cylinder with a bore scope. The pressure test turned up nothing and he found absolutely no moisture in cylinder #4 with the borescope.

He moved the plug and coil to another cylinder and will drive it around tomorrow to see if the CEL returns and then determine which cylinder is the culprit. If it's not #4, I guess we can narrow it down to a bad plug or coil. If it is #4 again, I guess it would be narrowed down to injector or head gasket (?).

Because the rough idle occurs only at start-up, I was convinced it was a bad head gasket after reading similar stories here and elsewhere. I would rather get this issue resolved quickly because of the inconvenience of being without the car and the logistics involved in getting to work, running kids around, pending vacation, etc. However, I don't want to pay $3k+ for a head gasket if that is not the issue.

Other than the pressure test/borescope, is there a better way to diagnose a bad head gasket? I know there are tests for hydrocarbons in the coolant, potassium in the oil, etc., but I thought the pressure test/borescope would be the most thorough and accurate test.

Any ideas from people who are familiar with this issue that I and my mechanic may be overlooking?

Thanks.
 
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That sounds about right really in terms of his testing, if I had the stuff availble I'd do a cylinder pressure waveform analysis also, but not everyone has the equipment for that.

How many miles are on your vehicle? On some of the older vehicles cold-start-up rough idle can indicate failing injectors.
 
How's your coolant level? The faulty cyl. won't necessarily have moisture all the time. If when you shut down the engine it stops rotating when cyl. 4 is on its compression stroke then the coolant won't seep it were as if its on its intake stroke then it would suck coolant in.

A little "test" you can do...While its idling rough look at the exhaust tail pipe...If white smoke comes out them you got a bad head gasket, if it's black smoke then you got bad injectors.
 
Thanks for the replies and good advice. My 2006 has 121k miles on it. It has led a fairly easy life to this point and has never been overheated. I tow a boat once in a while, but it's only a small 14 ft. aluminum boat.

The coolant level hasn't changed much if at all since I started to check it. I marked the overflow tank with a black marker, and every morning that I looked at it, it was probably within a millimeter or so of the original mark.

The oil level has remained spot on and doesn't look milky or smell funny. There is nothing funky under the oil fill cap, either.

Regarding the possibility of a bad injector, I wonder if I could ask the mechanic to do an ohm test and/or a drop test. I'm surprised that he didn't mention that, actually. As far as a bad injector goes, would it idle poorly after a cold start and then run fine for the remainder of the day? That's what had me thinking bad head gasket. Once the engine is warm, it runs fine. I figured a bad injector/coil/plug/etc. would cause the vehicle to run poorly at all times.

If nothing turns up tomorrow, I'll ask if he has a scanner for the compression test and whether a hydrocarbon test of the coolant is worthwhile.
 
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Well, there are different ways an injector can fail...

For example another member I helped had a 3rd gen with a 3.4L that was having hot running issues. Vehicle was great cold, but started to run rough and misfire when warmed up.

Unfortunately I didn't get a chance to do an current ramp waveform analysis on them like I wanted (they are a pain to get at and require removal of the intake plenum for bank one and bank two I couldn't get my amp clamp around the cables)

But suffice to say, in my experience the injectors start to fail internally and are not able to physically open the pintle fast/far enough for the duration required. They're fine when cold, but as the injectors get warmed up from a hot engine the resistance in the aging coils causes problems.

Long Story short, poor guy needs new injectors on his 200k+ 3rd gen to fix his issue.

Another possibility is clogged injectors, sometimes even running a fuel additive isn't enough; hell we use pressurized injector cleaner cans we hook directly into the fuel rail and they still don't get cleaned. In that case you can remove the injectors and send them out to a professional shop to be rebuild and bench tested.

Just be thankful you don't have those god awful BMW GDI injectors, they're on their like 20th revision and they STILL crack tips like no other (almost every GDI BMW I get with engine problems is in some way caused by cracked injector tips...), not to mention are like $700 a pop. *cringe*
 
Started my Runner and it had a ruff idle so I connect the OBDII scanner and I got a P0304 code, I let it idle for a little while then I hit the reset button on the scanner and the code was gone. I tried again and again to do a scan and the code never came back.

What would cause the scanner to give me a p0304 code then reset and disappear? So far it has not come day in the days after.
 
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The conditions for the code to trigger have not returned yet. If this is your head gasket failing they will return. Usually after it has sat for a while. Good luck.
 
Baba Booey said:
Thanks for the replies and good advice. My 2006 has 121k miles on it. It has led a fairly easy life to this point and has never been overheated. I tow a boat once in a while, but it's only a small 14 ft. aluminum boat.

The coolant level hasn't changed much if at all since I started to check it. I marked the overflow tank with a black marker, and every morning that I looked at it, it was probably within a millimeter or so of the original mark.

The oil level has remained spot on and doesn't look milky or smell funny. There is nothing funky under the oil fill cap, either.

Regarding the possibility of a bad injector, I wonder if I could ask the mechanic to do an ohm test and/or a drop test. I'm surprised that he didn't mention that, actually. As far as a bad injector goes, would it idle poorly after a cold start and then run fine for the remainder of the day? That's what had me thinking bad head gasket. Once the engine is warm, it runs fine. I figured a bad injector/coil/plug/etc. would cause the vehicle to run poorly at all times.

If nothing turns up tomorrow, I'll ask if he has a scanner for the compression test and whether a hydrocarbon test of the coolant is worthwhile.
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How did this turn out for you Booey? was it the HG or injector problems?
 
Bummer, same issue here after 3 weeks(500 miles) of owning the thing. good thing I have the ability to wrench on my own stuff. Im thinking this HG will only cost me around $500 with doing the water pump while im in there!
 
Johnson51 said:
Bummer, same issue here after 3 weeks(500 miles) of owning the thing. good thing I have the ability to wrench on my own stuff. Im thinking this HG will only cost me around $500 with doing the water pump while im in there!
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That sucks. It is a very labor intensive job.
 
Johnson51 said:
Bummer, same issue here after 3 weeks(500 miles) of owning the thing. good thing I have the ability to wrench on my own stuff. Im thinking this HG will only cost me around $500 with doing the water pump while im in there!
Click to expand...

Have you kicked in the teeth of the person who unloaded their problem on you yet?
 
YotaDriver said:
Have you kicked in the teeth of the person who unloaded their problem on you yet?
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Ha I wish! I look at as a chance to get to know my new runner in a very intimate way... Blood, sweat, and hopefully not tears! But I can totally tell that they did some cover up work to make it run well for the first few miles. They changes the one plug that was causing the issue and Im guessing they put some Fix-a-fluid in it also.
 
Johnson51 said:
Ha I wish! I look at as a chance to get to know my new runner in a very intimate way... Blood, sweat, and hopefully not tears! But I can totally tell that they did some cover up work to make it run well for the first few miles. They changes the one plug that was causing the issue and Im guessing they put some Fix-a-fluid in it also.
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Was it priced to reflect the fact that they were aware of the problem? I mean, the fact that they changed one plug, and if I understand correctly only the plug on the problem cylinder, is proof positive that they knew something was wrong. If they didn't mention it, then it's not a good faith transaction.

You've got a good attitude about it regardless, but situations like this are probably why I fantasize about weighing people down with chains and tossing them in the drink so often.
 
YotaDriver said:
Was it priced to reflect the fact that they were aware of the problem? I mean, the fact that they changed one plug, and if I understand correctly only the plug on the problem cylinder, is proof positive that they knew something was wrong. If they didn't mention it, then it's not a good faith transaction.

You've got a good attitude about it regardless, but situations like this are probably why I fantasize about weighing people down with chains and tossing them in the drink so often.
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HA your crackin me up. I did get it at a pretty good deal; 10k with 100,066 miles and it was in need of a set of tires. My lady is a lawyer and we went through the papers, but it is what it is. The damn thing runs GREAT aside from the minor hickup on startup. Ive had my buddy run the oil samples at his shop and there isnt any coolant in the oil; major positive! I dont really feel the need to do a leak down test since I've looked inside the pistons and can tell that the #6 cyl is the only one with moisture in it. Oh well looks like a few days of fun are in the future! :dammit:
 
Johnson51 said:
HA your crackin me up. I did get it at a pretty good deal; 10k with 100,066 miles and it was in need of a set of tires. My lady is a lawyer and we went through the papers, but it is what it is. The damn thing runs GREAT aside from the minor hickup on startup. Ive had my buddy run the oil samples at his shop and there isnt any coolant in the oil; major positive! I dont really feel the need to do a leak down test since I've looked inside the pistons and can tell that the #6 cyl is the only one with moisture in it. Oh well looks like a few days of fun are in the future! :dammit:
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Best of luck with the job man, I hope it goes well!
 
Johnson51 said:
... Oh well looks like a few days of fun are in the future! :dammit:
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Sorry to hear this.
I know there is a partial writeup on one of the other forums but there isn't much detail. Would it be possible for you to do a how-to with pics for the benefit of others who may try this since you are doing the wrenching yourself? Include any tricks or time savers.
 
did you replace your head gaskets? i have a 2004 4r my husband replaced the HG after #6 misfire. now its idel high my husband does not no what to do from here. Any idea??
 
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