Hello everybody anyones input will be greatly appreciated. So i have a 1992 Pickup 3.0 V6. Went to the smog shop and the guy informed me that the truck was misfiring, I never noticed because i have a exhaust and never really just paid enough attention. Anyway My #3 cylinder only has 30 psi and all others are in between 175-180 psi. Anyone have this same problem and no the solution or
know the next step to find the problem?? Here is a picture of newer spark plugs (20 miles) and the cylinder number with the compression PSI.

 

I read on another thread to put oil in the spark plug hole and re-test the compression? Should i do this? also here is another picture

 

Okay so i pulled my valve cover and put cylinder 3 to TDC and checked the clearances the Intake was in spec. But the exhaust was super tight. I couldn't fit my smallest feeler gauge(.002) the spec is between .007 and .011. Would this make my truck miss fire? ANy input would be great.

 

Well i just rotated the engine to Cylinder #1 TDC and the exhaust valve is just as tight as the number 3 cylinder!But i wasnt having any problems with it, It was firing perfectly fine. Im so stuck in this rut.. Please someone help.

 

I'm not so sure you have a misfire. Sounds like your #3 cylinder has little to no fire. I had/have a similar issue and its common for these V6's.

See my thread. Then search for how to adjust your valves. I've done it a couple times, so ask if you're confused.

 

Adjust the valves. No matter what your problem is, you need to get that done.

Too-tight exhaust valve will a) reduce compression to 30psi and b) that will cause a misfire which will c) cause you to fail smog with too-high HC (I assume that's why "the guy" thinks it's misfiring). So fix the valve adjustment, and re-do the compression test. If No. 3 comes up to something reasonable, I'll bet you'll pass smog.

Incidentally, the "oil in the cylinder" advice is to check the rings. If adding oil makes the compression come up to normal (or close), you have a ring problem. In your case, it will probably make no difference. (Do it if you want, but no matter what you do you need to fix the valve clearance, which will be obscuring any other problems.)

 

Thanks for your guys input. I'll get the valves adjusted hopefully by the end of next week hopefully earlier. Does the distributor coil help in firing all cylinders individually or if the coil was bad would it not fire any cylinders? Now comes the hard part of getting the right shims in without knowing how far off it really is.

 

well i checked all the valves. all exhaust valves except one are out of spec. All intake are good. Unfortunately while trying to pull the cam i broke my only 1/2" 17MM socket. waayyyy to damn tight. What a pain in the A$$. once i get those off i will go down to toyota and order the needed shims.

 

I assume you're pulling the cam sprockets off to remove timing belt and camshafts. That's not really necessary to adjust the valves, although some do it that way. They make a tool to depress and hold the bucket down while popping the shim out with a screwdriver and magnet. It's a little tedious but very doable.

Hers's the tool
http://www.redlandssupplies.com.au/p...1201155628.JPG

Well, I bet your truck will run 10 times better once you get those valves in spec. There is no guarantee that you don't have a burnt valve on your #3 but test compression afterward and that should tell you. I was unlucky when my #6 exh valve had no clearance with 35 psi in the cylinder. Good luck and post your results.

 

Well i ended up pulling the cams completely out. Got new shims ordered and on there way. Those cam sprocket bolts were a pain... 30" breaker bar and a wrench on the cam, didn't mess anything up too bad . But i have a very strange feeling that the reason my cylinder wasn't firing in the first place was a bad line from the distributor to the plug. I'm going to check in the AM with an OHM meter.

 

Okay Little update. I got 11 out of 12 valves properly adjusted. The Exhaust valve on Cylinder#3 Is still to tight after putting a 2.55 shim in. So im going to get a 2.2 ordered up and HOPEfully that does the trick. I'm also going to have my injector for that cylinder checked.

 

Little update. I got all the valves adjusted and retested the compression on Cylinder #3 Its now at 120 psi. All the others are at 180psi. So what else could be going on that its still 60 psi away from the others?

 

The valve is probably burnt from being out of adjustment too long. If the valve has little to no clearance it doesn't seat fully, which is how the valve cools itself, by transferring the heat to the cylinder head.

What was the valve clearance on that cylinder? Any at all?

Add some oil to that cylinder and test the compression. If it goes up then your rings are bad. If it doesn't change much and your valves are in adjustment, you have a burnt valve. Time for a valve job.

 

I had to adjust the #3 exhaust valve about .6mm for it to be in spec. It was a 2.86mm shim and i have a 2.2mm shim in it now. and it is in spec. It was WAYY out. Now, is all i gotta replace is the valve? and clean the bottom of the head where it seats? or is there more to it than that??? I really didn't want to pull the head. Ill try putting more oil in the cylinder tomorrow. I tried that with the original 30psi comp and it didnt change anything.

 

Sounds like the valvve had crud build up on it from being open. You'll need to reseat it at minimum.l