Back pressure test is best . Ck at upstream o2 sensor or drill a small hole in front of cat and ck with gauge .

 

I was going to suggest a clogged cat but Scotty beat me to it. Loosen the 2 nuts connecting the pipe to the manifold. The O2s are a PITA to get to.

 

According to the pics in post 17 the engine is timed correctly. The vacuum at idle should be around 18-20 in and drop to almost 0 when the throttle is wot then it will go back up. The cams control what stroke the engine is on so the crank cant be 360 out. If both cams are in time with the crank then it is right. On the modulars no pistons are at TDC when timing the cams to prevent any piston to valve contact in case one of the cams has to be turned to get into time. I believe we are finally on the right track with the clogged exhaust. Depending on the amount of meltdown in the converter you may need a muffler too. I have seen chunks get lodged in the muffler and cause an intermittent blockage.

 

Lets say the crank is at 6:00 and the cams are at 90*.....and you take it all apart. You have BOTH heads off. For some reason the crank gets moved....whatever. Can you just set it back at 6:00 with no regards, put the heads on turn the cams to the 90* point drop them in then hook up the chains per the links?

 

Yep, just as long as you align the timing marks on the chains, crank, and cam it does not matter if the crank is turned one revolution.

 

Thanks...that is good to know for in the future.

 

NP, now another scenario would be taking just one head off and for whatever reason turning the crank 360 degrees then the head that was not taken off would be 180 out from the other head. You would still have compression on both sides but the side that doesn't have the cam sensor would be firing the plug at the top of the exhaust stoke and firing the injector during the power stroke. The PCM uses the crank sensor to find TDC #1 and the cam sensor to find what stroke #1 is on then fires the plugs and injectors accordingly.

 

If the chain was off of the head still on, would there be intercourse with the 360* turn?

I don't mean to hi-jack this thread, I shall ask no more.

I hope it is a plugged cat, seems like it is leaning that way.

 

scotty and everyone! It was indeed a clogged CAT! THANKS to all of you for your suggestions! I just loosened the bolts on the exaust from the manifold and that was enough to prove the problem. reved right up like it should. So i fixed the CAT today and its back on the road! Thanks a million to everyone that chimed in. This was sure a puzzler for me and now i've learned alot!

 

 

Glad you got it fixed even though it took tearing it down a few times. I bet you can do it in your sleep now LOL. Spotty one of the valves would have to be open for there to be any contact if the crank was turned with the chain off. If need be you can look at the cam lobes to see which one is open then pop off the rocker.

 

This is unbelievable!

So i fix my freinds truck....only charged him $400 labor+parts which is a steal to replace a head on this engine.

He has the truck for 2 days and is driving down the highway....he says he lost oil pressure and the engine quit.
I go pick it up last night and it doesn't look good. Oil is at the correct level on the dipstick and clean (we just changed it) but from what i can tell the engine is seized.....
Has anyone seen an oilpump completely fail like this?

 

I havent seen many oil pump failures. Take the oil filter off and see if there is metal in it.

 

Man...who in the universe did you **** off...LOL. That is unbelievable... Total failure....doesn't happen very often. Will it turn over at all or is it seized tight? i had an old 400 M that had nylon covered timing gears. A chunk busted off and got into the pump and stopped it dead.....I ruined that motor. Wonder if a piece off one of the chain guides chipped off and got into the pump....I would think the screen would stop that though. Let us know what you guys do....good luck!

 

so far i have all the pulleys and stuff off.....i can't turn the engine over either direction at this point. Next is to pull the timing covers off and look at the chains to see if one broke or something.
I've read that sometime oil slugg or broken timing guides can plug up the pickup tube and cause a loss of pressure.

What gets me is that this guy noticed his oil pressure loss and instead of shutting it down he "punched it" to get the engine to rev up to increase pressure.....ouch....it worked for a few seconds i guess then it dropped to 0

i just can't believe the whole thing. The first thing i asked him was did he notice any oil leaks and what the oil level was on the dipstick.
He said No leaks and checked the dipstick level was fine.
Later he said "i think you just forgot to put oil in the engine"........i live a good 45 minute drive from town and without oil i don't think i would have even made it out my driveway to take it back to him the first day.

So i'm tearing it down to try and find cause and see if there is any hope of life with this engine.