IA_F150

I have a 97 with the 4.6L
I've had issues trying to get my truck running right (misfire in cylinder 8- P0308) and have spent a small fortune doing so. I have now discovered that I have absolutely no compression in cylinder 8. We took the valve cover off and nothing jumps out as being wrong, but none of us have ever been into an engine this new either. What should we look for or test next?

fabfordtech

You likely have a valve problem and you need to check compression on the whole bank on that side. If cylinder #8 is the only one without any compression and the valve cover is off of it rotate the engine so that cylinder #8 is on top dead center and both the intake and exhaust valves are closed. You should be able to take your compression gauge and change the adapter at the end to fit the air hose coupler on your compressor or air tank. You need to do that to the rubber hose end of the compression tester that feeds the gauge. Now instead of hooking the gauge up, attach your air hose to the rubber end screwed into the cylinder with a consistent air pressure supply feeding the cylinder. NOW... Just figure out where the air is going. If it is coming out the tailpipe you have a bad exhaust valve, comes out the throttle body you have a bad intake valve and if it fills the crankcase / oil pan then you have bad rings or a bad piston. It sounds like either case the motor will have to come out. WARNING..... Do not try to pull the head off this truck with the engine in it. You will get it 1/2 torn down only to realize you have a head you dont have room to remove and have a huge mess. In order to pull the head off either the cab has to come off the frame or the engine has to come out. GOOD LUCK

IA_F150

Thanks for all the info so far. I forgot to add that I checked the vacuum and it was reading 15-16, which I believe is acceptable from what I've read.

Good old Bill

Fabfordtech is right on with the leak down procedure, we called it differential pressure test in the aircraft circles, but same results obtained. Thought I have read about the rockers breaking on OHC engines. When the cover was off, did you observe valve action while cranking the engine over? Should be able to see the valves mooving although this won't tell you if a valve is burnt or bent.

IA_F150

UPDATE: We did the leakdown test and there was no leak. It held 130 PSI for a minute or two before we released the pressure. So we started playing around, inspecting springs etc. Upon doing so, on the second valve from the rear (part of #8) the camshaft roller follower fell off. We are assuming this means it is just a bad spring and we'll be replacing all springs on that side tomorrow. Anything else I should be looking at or checking on first?
Also, we checked compression in the other cylinders and they were 130, 129, 130, 130, 132, 130 & 133. Is that good?

Good old Bill

Compression readings look good. All gauges read slightly different, I like to see the readings with in 10% of each other. If the valve spring was not collapsed or broken, look at the cam itself, make sure the lobe is not messed up. Compare it to another lobe. Not sure if second from back is intake or exhaust, just look at another lobe of same function for comparrision.

fabfordtech

Make sure you keep air on the cylinder when you remove the valve spring, if you don't you will drop the valve and habe to pull the engine to pull the engine and then the head.

IA_F150

UPDATE:

When we did our leakdown test it held the air perfectly. However, we had the piston top dead center and I now understand your are supposed to back it off a bit prior to performing the test. So we backed it off and did the test again. Air began gushing through the throttle body.

We're trying to do this in the truck and just have the other valve cover and timing chain cover to remove. Then we should be able to pull the head. If the other valves look okay, is it wise to just replace the one or should I have it shipped off to get the whole head checked over or what?

Also, do you have a good place for me to get all the gaskets, headbolts, valve etc. that I'm going to need?

Thanks again for all the great help!

rickapalooza

before rippin it apart i see you said there was a follower off....that is a known problem with the 97 to 99 modulars and is an upgrade to prevent it, bet ur lash adjusters collapsed.put it back in place and fire it up bet ul be good but at least replace the lash adjuster....

fabfordtech

IN ORDER THE PULL THE HEAD OFF OF THIS ENGINE THE CAB MUST COME OFF THE FRAME OF THE ENGINE MUST COME OUT..... Make sure you are prepared for this before you start.