2.7 liter, low compression on 3 cylinders,

Last winter my tacoma didnt want to start at all when it was cold..ran really rich an cranked slow, havent really drove it much since january. I compression tested it yesterday an number 1 read 125 psi, 2-80 ,3-60, 4-60.Two of the spark plugs had a greenish tint where looked like antifreeze has been present. So due to low crankcase pressure I found why it didnt want to start lol But the truck doesnt run hot,or the oil has never been milky.I was thinking could be a head or gasket would answer low compression.But also I know it could need a rebuild.If it would be a rebuild and I wanted to swap motors,can you use a 2.4liter engine in place of a 2.7?Any help an input on this issue is much appreciated thanks.

 

I read somewhere (I think customtacos forum) that you can if its the same year or near. You will need to replace ECU, wiring harness for engine, and possibly the bellhousing.

Hopefully someone who has done this will chime in.

 

did you have the throttle open all the way when you did the test? if not it will skew the numbers. you may want to also do a leak down test to find out where the engine is losing compression could be valves, head, rings. there shouldn't be much pressure in the crankcase to begin with check the PCV to see if it's clogged. should be pretty easy to rebuild the engine there isn't much to it.

 

Did you take out all the plugs when you ran check ? & are you sure the battery is up with good charge ? With no.1 being 125 & 2-80 3-60 4-60 & no oil in water or water in oil kinda leans away from blown gasket or cracked head , I mean it could be but 99% of the time there 'd be over heating issues, maybe internal leak (cracked block ?) leak down test maybe in order, slight chance of warped head... hmmm...

Re do compression check & let engine turn over til the gauge reaches (& maintains) max compression..

Unless I'm missing something or things have changed don't know why you'd have throttle open seeing how compression is determined with valves closed during combusttion stroke...

 

No I didn't have the throttle open..never really knew of doing that during a compression test..yea I pretty well leaned away from the head itself because of none of the normal symptoms an figured more of a bottom end rebuild, or possibly some valve issues.. I took the plugs out one at a time an tested each cylinder that way..I'm going to check it once again an look into doin a leak down test.yes the battery is in good charge, the truck has always ran lil rich an started like that when it's really cold out..it still runs a drive fine..it's not overwhelmed with power but isn't a snail with my four ways on you know..but with only 150 hp turning 31s Idk how much power it should have with hills an stuff lol

 

Yes. Always have the throttle at WOT when doing a compression test. The engine is being tested for compression, AKA how much it can compress the slug of air that it just drew in through the intake. If there's less air due to the throttle being closed, there's less air in the combustion area to compress, so the pressure will be lower. The ideal gas law, people. Same volume, but different mass will ALWAYS net different pressures. PV=NRT.

 

Why not just do it with engine running then ????

 

Ummm, I hope you're being sarcastic! The compression tester threads into the holes for the spark plugs in the cylinder head. You'll always be disabling one cylinder when you test, and firing a (now) unbalanced engine is never good, especially for crankshaft bearings....Plus, since you HAVE to be at WOT (Wide Open Throttle), do you really want your engine screaming and bouncing off the red line?

 

yeah just being a smart ass , i get what your sayin' though...

 

Well, good! I love smart-asses...I am one!

To smart asses everywhere! Thread derailed....

 

well, consider our names brother....

 

Personally I have never had to run a compression test with the throttle open at all. The engine runs fine at idle speed, so why WOT? None of the procedures I have ever read stated to do this. That being said, every procedure I have read says remove all of the spark plugs, and make sure the battery is fully charged. Also allow the engine to complete a minimum of 3 compression strokes on each cylinder you are testing. Low compression on 3 cylinders of 4 could be due to several things as mentioned. Burnt valves, bent valves, worn cams, lower end, head gaskets(low probability, but still possible) bad/worn timing chain (in the case of the 2.7) and other items. As mentioned, a cylinder leakdown test would be helpful. If you do not detect a leakdown into the exhaust or intake, then an easy check is to use a feeler gauge and check valve clearance. If the clearance is excessive, then you can look at the cam...again, there will be a lot of testing to find the root cause. Have you done a "wet" compression test after the initial dry test? A wet test is when you squirt a SMALL amount of oil into the spark plug hole, then retest compression. If compression significantly improves, then you have a ring issue.

Lots of things to check. Let us know what you find out!

 

Ok next chance I get to work on I'll redo the dry an do a wettest..along with the leak down.I would like to isolate it to the upper end the lower end rebuild doesn't bother it's just nicer pulling the head and working vs tearing a engine down I never really considered the timing chain for a cause for the compression.I'm pretty sure it's the original one..thanks for the help!

 

yeah, it is a very commonly overlooked low compression issue. If the chain has worn enough, it can seriously affect compression, and it doesn't always mean that it will affect all cylinders. Again, not a solid cause, just information for you to consider in your diagnosis.

 

Hey BamaToy1997. I just had a (dry) leak down test by a local mechanic. He said I have no compression in cylinder no 3. It sounded like air was leaking out of the intake valve. I've had the same symptoms as the original poster for the whole winter. The mec put a camera into the cylinder and looked around. He didn't see anything wrong with the cylinder, just the valve. He suggested replacing the head and rebuilding the bottom end because the crank case bearings may have some bad wear which may cause the engine to throw a rod later down the road. I'm really skeptible about this and hope to just replace the head. I've looked around at a few forums about people having valve issues, they just replaced their heads and we never hear back from them again. Is it possible to get away with jus the head? Has anyone replaced their head and suffered a problem with the block 1-5 years later?

 

You didn't mention what kind of miles you have on your existing engine. If less than 200k miles, I would say just do the head job and clean the block. If you have 250k miles on it, then sometimes it's not a bad idea to go ahead and do the extra work. Without knowing how many miles, and how hard the truck was driven, it is difficult to give any kind of fair suggestion.