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Unread 06-03-2013, 11:14 PM   #1
rssxy
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p0304 code, loosing coolant and low oil pressure....crap

im about ready to take the AR15 to my xj. seems like its been one thing after another with this thing lately.

now, on a cold start my 01 xj starts running like garbage and throws the p0304 code at me which is a cylinder 4 misfire. i have also been loosing coolant and i have no clue where its going. i recently changed the water pump, radiator and hoses because the radiator was leaking (rented the gauge at o'smileys to verify, pissed coolant all over me) but its still leaking. i have also had low oil pressure when it warms up. it will start off at 40-50 but when it warms up it will drop to 0 at idle and the check gauge light will come on.

now where i'm stumped is that i hooked up a mechanical gauge to the sending unit and it was perfect. was steady at 40 and dropped down to ~30 at idle.

does this sound like a cracked head? i dont have a milkshake for oil though. i just rented a compression gauge and new plugs for when i get off work tomorrow. is there anything else i should be looking for or can check? clogged injector? bad plugs? also this is has pretty much been the first car ive worked on. just kinda learning as i go, so what should i be looking for when i do the compression test? i read 120+ is good. will the gauge slowly go down if its cracked or will it just be under 120?

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Unread 06-04-2013, 05:59 AM   #2
tjwalker
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If you're losing coolant and you have verified positively that you have no leak (have you?) then the head is a primary suspect. With loss of coolant, you're either leaking it or burning it.

Unfortunately, the compression test is not the best test for troubleshooting a cracked 0331 cylinder head. I've personally seen this test pass with flying colors with a cracked head. And not oil has the "milkshake" appearance either; some do and some don't. Much of the coolant actually is burned off.

Here is something easy that you can start with. Remove the oil fill cap and with a good light, inspect inside near cylinders 3-4. Oftentimes (not always) you can see the coolant seeping through the crack with a pressurized cooling system. Pressurized means either a hot engine turned off or pressurize the system using a cooling system pressure tester (can be rented) which hooks up to your radiator cap and pumps up to pressurize.

Good luck and keep us updated.
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Unread 06-04-2013, 06:42 AM   #3
Kalali
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First things I'd do are replace the oil pressure sending unit and fix the radiator. However, I don't think either of these are causing the poor running condition and/or the misfire. You could also switch the #4 injector to rule out (or in) the injector if you see the code move with the injector. After all these you can concentrate on the head. Keep us posted.
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Unread 06-04-2013, 07:29 PM   #4
rssxy
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i already replaced my sending unit as well. its not looking good though. i got 110, 175, 160, 90, 130, 170. im going to try with a different gauge though because i ran it multiple times and got 150 in cylinder 1 one time and 80 in number 4 the another time. can anyone help me diagnose this? its apparent my rings bad in number 4 but why would the other ones be so high? and what could cause the drastic variation in psi? also, can the misfire in cylinder 4 be caused by the low compression? and could any of this be cause by a cracked head? should i look into a leakdown test next?

ETA: and tjwalker, i cant find it leaking anywhere. ive been underneath it. its not dripping anywhere i can tell. still dont have the milkshake oil everyones talking about.
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Unread 06-04-2013, 10:09 PM   #5
AZ Jeff
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Quote:
Originally Posted by rssxy View Post
ETA: and tjwalker, i cant find it leaking anywhere. ive been underneath it. its not dripping anywhere i can tell. still dont have the milkshake oil everyones talking about.
Milkshake oil only shows up on vehicles whose head crack has advanced for a long time. A subtle early head crack will not have this symptom.

The best sure fire way to confirm a head crack (short of removing the head and having it magnafluxed at a machine shop) is to have a radiator shop "sniff" the coolant for presence of hydrocarbons (oil).

The low pressure on #4 sounds more like a bad valve than anything else. What does a "wet" test with the compression guage show for the cylinders?
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Unread 06-04-2013, 10:59 PM   #6
rssxy
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i didnt do one. ill do it tomorrow after work. ran out of light today and everythings still apart since the nice ppl at o'reilley's gave me the wrong plugs. so looks like im going to be bumming a ride to work tomorrow. how do i do a wet test? just put a cap full of oil down the hole? and repeat? also, i just realized i didnt have it at WOT. will that skew the results at all?
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Unread 06-05-2013, 07:49 AM   #7
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Quote:
Originally Posted by rssxy View Post
i didnt do one. ill do it tomorrow after work. ran out of light today and everythings still apart since the nice ppl at o'reilley's gave me the wrong plugs. so looks like im going to be bumming a ride to work tomorrow. how do i do a wet test? just put a cap full of oil down the hole? and repeat? also, i just realized i didnt have it at WOT. will that skew the results at all?
A few squirts with an old fashioned oil can is all you need in the cylinder (about a teaspoon full).

Not having the engine at WOT has a very small effect.

One key when doing a compression test is to make sure each cylinder gets the same number of compression strokes. YOu can hear each stroke as it pumps the guage, so try to crank the engine an equal number of strokes to get the most consistent readings.
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Unread 06-05-2013, 07:36 PM   #8
rssxy
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just did it again with the same gauge. i got 170-180 on all cylinders except for number 4 which gave me a big fat 0 dry and 30 wet. never got even close to 90. after it got to temp i removed fuel pump relay, removed all of the plugs, put it at WOT and let it let it go for 5 revolutions.. that sound about right? i also noticed oil on the plug from cylinder 4 and when i looked inside i saw oil as well. so im assuming my valve covers leaking and the rings bad?
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Unread 06-05-2013, 09:57 PM   #9
AZ Jeff
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Quote:
Originally Posted by rssxy View Post
just did it again with the same gauge. i got 170-180 on all cylinders except for number 4 which gave me a big fat 0 dry and 30 wet. never got even close to 90. after it got to temp i removed fuel pump relay, removed all of the plugs, put it at WOT and let it let it go for 5 revolutions.. that sound about right? i also noticed oil on the plug from cylinder 4 and when i looked inside i saw oil as well. so im assuming my valve covers leaking and the rings bad?
A "ZERO" when dry means a HUGE leak. That can only come from a MASSIVE head gasket leak or a really bad valve (or a hole in a piston, but that is unlikely).

I thought your previous test showed SOME compression on #4 (90psi is what you reported.) How did the compression go down so low now? I am assuming you are using a "screw-in" type compression tester, and not one of those you have to hold in the cylinder by hand pressure. Is that correct?
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Unread 06-05-2013, 10:32 PM   #10
rssxy
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ya im using the screw in type. i could be doing it wrong, but the only thing i did differently was put it at WOT this time. im going to try and get a different gauge since i rented this one and its obviously been used before. no telling if its working correctly. do you remove all of the plugs or only the one your testing then replace it?
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Unread 06-11-2013, 09:40 PM   #11
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Quote:
Originally Posted by rssxy View Post
ya im using the screw in type. i could be doing it wrong, but the only thing i did differently was put it at WOT this time. im going to try and get a different gauge since i rented this one and its obviously been used before. no telling if its working correctly. do you remove all of the plugs or only the one your testing then replace it?
I normally take out all the plugs
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