I was driving down the road and my engine started to run rough like it was running on 3 cylinders. So I stopped to see if I had a spark plug wire come loose or something. I didn't see anything amiss so I started it up and headed for home. Shortly I started getting a very loud knocking sound coming from the engine when it's under any kind of load. Back off the power and it's quiet.

I'm thinking a stuck lifter or broken valve spring or something along that line.

I just moved into an apartment so I don't have anywhere to work on it right now so I'm hoping to narrow the scope a little so I don't waste time when I find a place to work on it.

Any ideas are greatly appreciated?

So I got around to taking a closer look at the truck and I found 2 vacuum lines that were off (one going to the vacuum advance). I thought "Sweet" I found the problem... Well not so much. I hooked them back up and no change.

So question: Is it possible that a vacuum leak could cause an issue like this? As in another leak that I have yet to find.

The engine starts and runs (albeit roughly like it's running on 3 cyl) and doesn't make any noise until you put a load on it.

I'm going to get some carb cleaner tomorrow and do the leak check on the manifold, carb and hoses.

I'm considering pulling and capping all of the vacuum lines. If I do what size are the caps that I need?

I saw a post a while back that had pics of all of the lines capped but I can't find it again, does anyone have the link to the post?

Hello

I Finally got back to work on the truck.

Ignition checked good.
Carb has needed work for a long time, replaced stock with Weber.
Did compression test:
#1 145
#2 150
#3 35
#4 30

Pulled valve cover to see if somthing simple and easy to fix had happened up top. No such luck. Pristine and everything in order.

Then I gave the timing chain a push and on the non tensioner side it's just flopping in the wind.

I tried to look down the hole at the tensioner and see if it broke or just came loose but I really can't see much down there.

So my question is: Could a tenstioner failure/slip be the cause of my issues (rough running with knock and/or low pressure in the back 2 cyl)?
Also is it possible that the tenstioner came loose and allowed the chain to jump a cog?

With this coming on suddenly and no perf degrade prior, I'm supprised to see 2 cyl go flat like that.

Also I just finished moving and my manual for the truck is still packed away somewhere. Is there a link to the FSM or a good tutorial on timing chains?

Thanks for your help

if the timing chain was loose i would check the valves

Are you thinking that they probably contacted the piston and are bent?

How do I check them? Do I need to pull the head or can I use something like compressed air in the plug hole with the piston at TDC and listen for air coming out the exhaust or intake?

Thanks

i don't know how to get to them, but my GTI's chain snapped and bent the valves. with you getting no compression in 2 cylinders, it adds up

as for checking them, you should be able to visually see if they are bent

Put some oil in the cylinders with low compression, if it improves some your rings are bad, if no change valves are the issue.