evilmind

I realy hope someone can help me here. i know there are a lot of knowledgable members and hope i can figure this out with help. i have a 98 pre-runner, 2.7 with 182k miles. i took it to a repair shop to have the computer read and all it said was cylinder 4 missing. i knew it was missing and mpg is about 11! idle is low and rough. i have replaced plugs, plug wires, coil packs, both o2's, idle pos sensor, egr, pcv, fuel filter and everything else i could think of. no change. today i checked my valves and am now confused. factory specs are .006 to .009 for int.and .010 to .013 for exh. all my intake valves were within that range. what blows me away is my exhaust valves are as follows, cyl #1 are .006 & less than .005, cyl #2 are both less than .005, Cyl #3 are .005 & less than .005 and cyl #4 are less than .005 & .008 ? my fealers only went as low as .005. i think cyl #4 might explain the miss but what i dont understand is why they are all so tight compaired to the range they are listed by the factory. any help would be great. sorry this was so long. thanks.

Brian R.

Did you check the valves when they are dead cold? Checking them when they are warm is the obvious answer to why they are tight.

If you got those clearances when they were dead cold. I can't explain why they would be so tight except through normal changes possible with that many miles. Since they are all the same, more or less, it seems that it is not a specific problem. It is a general issue that is rearing its head.

Since you can't expect to have your valves stay in adjustment that long. I would forget about worrying why and just get your valve clearances set to the factory specs. What probably happened was over the years, the exhaust valves beat on the seats and caused clearances to tighten up with the cam. I guess this would happen faster if you run lean more often than not. A lean mixture makes everything in the exhaust hotter and softer. What's more, the tighter the clearances on the exhaust valves, the longer they stay open and the hotter everything gets, the tighter they get, etc. - sort of a positive feedback loop.

Just for giggles, I would get a compression check also to test your valves after they are adjusted.

evilmind

brian r, thanks for the response. i spoke to a guy today that was a 24 year toyota master mechanic. he told me the intake tends to shrink and th exhaust tends to expand but not to that extent without added heat. i told him that at one point the exhaust manifold was cracked in 3 places. (ifailed to add that to my question before) at one point the truck belonged to my brother and the manifold was cracked when i got it so im not sure haw long it had been that way. i know have a header. i wasnt able to get the shims i needed today so when i do and get it done i will update you. thanks again for the input, its nice to know you can get info when you need it.

Brian R.

The cracked exhaust manifold sort of makes the hot valve seat theory a little more likely.

TGates81

what are other symptoms that you can tell when to adjust the valve clearances? I have a 95 2.4L taco with 118k and i dont think theyve ever been touched.

Brian R.

If there is alot of ticking noise when the engine is hot is a signal to get them adjusted.

If you are worried about them being off, best thing to do is take off the head cover (engine dead cold) and check some of the clearances yourself. Nothing fancy, just check whatever valves have the cam lobe pointed directly away from the head. Disconnect the high-tension wire from the distributor, briefly crank the engine, and try again when other valves have their lobes pointed up, until you have tested them all. Compare what you observe with the specs.

But

If it ain't broke, don't fix it

TGates81

thanx brian

Brian R.

You're welcome