Low compression on #3 - '92 Pathfinder V6

[Bozer1991]

I just bought this truck with the intention of bringing it back to life. It has 222,000 miles on it and is mostly original.

 

White smoke coming out the tailpipe led me to a compression test and the results were all over the place. Cylinder number three is at 30 PSI and everything else is above 150. I'm assuming head gasket, which I will start on soon, but does anyone else have any input I should consider? I'm hoping it's not a piston ring or something else in the lower end.

 

Gaskets are cheap and I can probably have the head resurfaced for not too much money. I need to get in there for the timing belt job anyway. I'd love to save this thing, unless someone thinks it's a bad idea? Let me know. Thank you!

[adamzan]

Drop a bit of oil in that cylinder and re test. If it is a gasket or some other failure it'll be the same, but if it is bad rings it should pump the numbers up. You can also do a leak down test to see where the compression is going. That will definitely tell you what is happening.

[gamellott]

I did this job a couple of years ago because I was getting coolant into the cylinders after sitting for more than a day. All in all, doing all of the things you discussed and what I am listing, I think I spent $500 in parts alone. Well worth it if you're inclined to do it. Resurfacing the heads, I think was like $250. I can't remember that exact value.

 

Don't cinch out on the Head Gasket set. You'll need all of the gaskets in that set, including the the gaskets on the back of the heads where the cams go into the head.

 

I almost F'd up my heads. There is an elusive 10mm headed bolt on the back of the passenger side head (Front Drivers side) that will need to be removed in order to take off the heads. I missed that on mine on the passenger side because it's pretty well hidden on the back.

 

You pretty much have to replace the timing belt if you're removing the heads. Or... well... it has to come off, so you might as well do it. I also recommend doing the water pump, and timing belt tensioner, since it's right there as well... There's probably a kit for that. And then there is the crank seal. That can be problematic. I had to get a new crank pulley.

 

It's recommended that you replace the head bolts.

 

I found several exhaust manifold studs broken. They were easy to take out once the heads were off. The manifold to pipe nuts... good luck with those. Hopefully someone along the way has replaced the factory steel nuts with brass ones.

 

+1 on the leak down test. If you're losing your compression into the oil and engine block, that makes plenty of sense. If you're losing coolant, that's a different story, but you might not have that long term information.

 

Good Luck and have fun!!!

[Slartibartfast]

 

White smoke and one dead hole sure sounds like a head gasket issue to me. +1 on the leakdown test to tell you for sure. And +1 for doing the timing belt etc while you're in there. Cam seals, crank seal, bypass hose, belt, tensioner, pump. I skipped the crank seal the first time I did mine, and naturally it started leaking the moment I had it back together.

[Bozer1991]

Thx All!  Ok, I'm going all in on upper end rebuild, just started breakdown yesterday.  Got a full gasket set from Fel Pro on the way and already bought Timing Belt kit including water pump, Tensioner and thermostat.

 

*I didn't get to the leak down test before starting the breakdown and think I missed my window...  I'll check how cylinders look once i have her opened up.

 

Hoping I can find a machine shop around here to resurface Heads, if needed.

 

I appreciate the input!

[Bozer1991]

Removing the EGR tube will be the hardest part of this job, i can already tell. The connector bolts look rusted solid! Weird, because I don't see rust anywhere else. I need to re-up my PB Blaster supply

[gamellott]

3 hours ago, Bozer1991 said:

Removing the EGR tube will be the hardest part of this job, i can already tell. The connector bolts look rusted solid! Weird, because I don't see rust anywhere else. I need to re-up my PB Blaster supply

IF you can get away with it in California, it would be a perfect time to defeat the EGR, Otherwise, YES. That is going to be a giant PITA!!!

[Slartibartfast]

Heat is your friend for that EGR tube nut. Heat, lube, beat on it, repeat. I've had some luck with candle wax for stubborn threads. Heat, melt wax into the threads, try again. Seems to stick around better than PB.

 

I tried just brute-forcing the nut in my '95, and it took some of the threads off the valve, so, yeah, don't do that.

 

If it's a California-emissions truck, an EGR delete will trigger the check engine light.

[Bozer1991]

Got the EGR off!  Only the top nut, actually, but that was enough to spin the tube away from the plenum and remove it. I'll deal with the lower nut later.  *No way I'm getting by without the EGR in CA.

 

I'm down to the block, next up is valve covers and heads.  I also need to buy a 27mm socket for that crank bolt. that thing is huge.

 

*My wiring loom and connectors are disintegrating pretty badly...any thoughts on replacement connectors?  I can rewire the loom myself, but need all the correct female connectors to get that done.  a quick google search didn't help much.  Any suggestions appreciated!

 

 

[gamellott]

Yes, that bolt is giant on the crankshaft. I find it usefull if I have to turn the engine over by hand.

 

https://www.summitracing.com/search/year/1992/make/nissan/model/pathfinder?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=connector

 

Someone who sells Standard Motor Products. You'll have to figure out how they're keyed differently. I bought a set for the fuel injectors some time ago and I still haven't used them.

[Slartibartfast]

Good work! Hopefully the bottom one plays ball.

 

Also check Rockauto for connectors. I got a MAF sensor connector from them a while ago.

 

If you have trouble finding a 27mm socket, try 1-1/16".

[Bozer1991]

Thank you, @Slartibartfast and @gamellott!  I will source those connectors, once I take inventory of what I need.

 

Disassembly is complete as of this AM, taking Heads to the machine shop for pressure test today.  No obvious blown gasket, but the PS Head between #3 and #5 smells like burnt oil.  I also found a bunch of coolant in #6 which makes no sense to me...need to figure that out.  Good news is that all cylinder walls look cherry and only minimal carbon on pistons.  She definitely deserves a refresh, I'm happy with what I'm seeing so far.  Also, almost no rust anywhere - other than EGR and exhaust manifold heat shield screws - I broke 2 off.

 

I got lower EGR tube nut off after a bottle of penetrating fluid, 60 secs of heating the manifold and sledge hammering a wrench connected to the nut. And 3 beers.

 

 

 

 

[gamellott]

My head gaskets were cracked along the inner bead and leaking in from the water jacket. I had one REALLY clean piston. The rest looked normal. When I peeled the gasket off, I discovered that the only cylinders that didn't have cracks in the gasket was 3 & 4, just leaking really bad on 1.