81 running rough and loosing power after long amount of use

[atv_123]

Ok, I am gonna be honest, I joined this site purely to get help with this machine because this is the first Chevy I have ever owned and know next to nothing about this truck and how it works. I bought it for 500 bucks knowing I was getting myself into a project, but I just want to make sure I get second opinions from people that know way more about these things than me. Anyways, on with the specs...

• I believe that it is a 1981 K10 Truck although on the title it says a K10 Blazer... granted I don't think such a thing exists.
• It is 4WD as you may have already surmised from the fact that it is a K10
• It has the Custom Deluxe Trim package on it according to the badges, not that I think it really matters but the more info the better.
• It does not have A/C not that I think it matters really
• And for the drive line, it has a 3 speed automatic with what looks to be a 250 i6 engine under the hood that appears to have been heavily neglected.

Now the problems I am having are numerous but I know how to fix all of the mechanical problems with the brakes and lights and other nonsense as such... my biggest worry is the engine and am hoping you guys can shed some light on what is going on here.

Now this engine starts just about perfectly (even in sub zero temperatures I have found) every time and will happily idle away as if nothing is wrong at all. Now the idle is rather lumpy, but that becomes extremely noticeable once you stick it in gear.

When you are sitting still at idle with your foot on the brake, the vehicle chugs hard... the whole machine shakes as though it is making tons more power with 2 or 3 cylinders then all the others and can sometimes outdo the brakes each chug (they are bad anyways as I mentioned earlier, but still that's pretty bad)

As you are accelerating or maintaining speed, it doesn't really get better, it just becomes faster and faster till it feels like the truck is being powered by a jack hammer... not comfortable. This shaking is so evident that it has broken off the exhaust at the end of the header down by the cat what looks like 4 or 5 times!!!

To add to the fun... after you get about an hours worth of travel under your belt, it looses all power. It doesn't stall or shut off, it just doesn't have enough to actually pull you anywhere. However if you let it sit for about 10 minutes, it comes back just fine like nothing happened... possibly a sign of overheating.

Which is hard to tell because the temperature gauge is not connected... I think I found the wire, but I have no idea where the sensor is on the engine to actually hook it to.

And last but not least, the entire vacuum system is missing...literally everything is either capped or missing except for the brake booster (thank goodness) and go figure, the vacuum diagram is completely covered over in paint so that I cant read it... oh the joys.

So I guess my first question is... where do I even start?

[Irish_Alley]

you dont need the vacuum lines for anything but pc valve (on the vale cover) timing advance and brake booster. the other stuff is for emissions and heater controls. first thing i would do is a tune up (plugs, wires maybe fuel filter) then check timing order and what degree your set at. sounds like its retarded

[atv_123]

Ok, cool, that at least gives me a place to start at!

As far as plugs and wires and what not, according to the last slip they gave me from the mechanic they took it to, it says that it has new plugs, wires, distributor cap, and rotor... the cap and wires I can confirm are new, but the plugs and rotor I have not checked yet.

As far as timing goes, how much would the missing vacuum line throw it off? Could that be a large part of my problem? If so I will try and get that fixed as soon as possible before screwing with the timing any.

[Irish_Alley]

vacuum line on the timing advance? you unplug and plug the line so there are no vacuum leaks it to set the initial timing to begin with

[atv_123]

Oh ok, I'm sorry if I sound like I don't know what I am doing with this thing but like I said I know nothing about this engine except what I have found out about it from the internet already. Plus I haven't had a vehicle with a vacuum timing advance so I didn't even know what that line did. I knew that it had some roll in adjusting the timing but I wasn't sure as to what it did.

[Irish_Alley]

its ok. i dont know half the stuff some of the guys on here know, we all have to not know sometime to learn. i was clarifying that line you were talking about


read this
and this

here rich talks about it and hes taught a lot of us about it

[atv_123]

Man, I thank you for those reads! I learned a heck of a lot from them! Now that I know what it is supposed to do I should be able to check everything and get the engine perfectly timed out.

Even though all these articles are written for V8's (will be useful for when I start working on my Vett) I can see that the principle still stands no matter the engine as long as the parts are the same which they look to be.

Once it warms up out here a bit (just got 6 inches of snow last night) I am gonna go out there and screw with it and try my best to get it dialed in.

So I'll probably be back... cause I doubt that's all that's wrong with this thing.

[atv_123]

I know this is a huge bump, but this is the thread I started so I don't really see a reason in starting a new one.

I finally had time to mess with this thing and I have the timing tuned to perfection... or at least as close as it would go with it chugging like it is. I also did some messing around with it and found out some interesting things.

#1. By doing a standard power test (just unplugging spark plugs and listening for a difference) I have found out that the number 2 cylinder is not firing (starting at the front of the engine)... at all... it was what I think is causing the horrible chugging.

#2. When I found that I decided to do a compression test. While all the other cylinders are running at about 85 to 90psi, cylinder 2 was coming in at a sad 60 to 65psi... not looking good.

#3. When the engine is running the exhaust smokes... a lot. At idle its like sitting next to a camp fire, barely noticeable unless you stick your face in the exhaust. When you put your foot on the throttle however, its like a moving burning biulding just bellowing white smoke everywhere. Again, not good.

#4. When held at a constant RPM (or best I can do by ear) probably around 1k to 2ks, you can hear something that sounds like an occasional rattle or perhaps a ping... not real loud... almost like its knocking or perhaps the valve lifters are loose.

#5. When you take off the oil fill cap, you can hear the valve train and it almost sounds like coins clattering around in your pocket. Now I am assuming nothing has fallen off and that something is loose because it is in time with the engine running. Granted, like I said, I am completely new to this engine and maybe an engine with valve lifters always sounds like that. I know you are supposed to adjust them for valve lash when putting them back together... but those are still pretty tight tolerances, so I don't think that it should make that noise.

So I guess what I want to know is... from the sounds of that description... is there any hope in saving this thing with something like a rebuild kit of some sort? Is it a simpler problem then I think? Or should i not even bother and just pick up another engine? I have heard that doing engine swaps in these things are a piece of cake since there are no computers or anything to worry about. Also if I did an engine swap it would be to another 6 cyl... even though this one is new to me it is what I am most familiar with and unless I get some sort of killer deal on a V8, I am gonna stay 6.

Any help would be appreciated, but I am not in a real hurry... I have time to mess with this thing and do more tests if that is required.

[mrnda]

had the same issue with a 250, turned out to be a cracked head.  Rebuilt the engine, mine was a #1 cylinder but yeah would lose power after it warmed up.  You may get away with replacing the head but they are pretty simple to rebuild.

[frotosride]

Cracked head isn't far fetched. You can sometimes take the cap off the radiator while engine is cool then start it and warm it up. I the exhaust gases will force their way into the radiator an you will see a fair amount of bubbels. Before you do this che k the level and fill with water if needed. Also do you remember what the exhaust smelled like. Remember that carbonmonoxide is deadly and you will put off the signs initially so don't sniff the exhaust as if you are huffing it but you will smell a sweet smell...kind of like sweet burning plastic. That's antifreeze.

[OfficialTull]

So I doubt this is the issue but some of your symptoms sound familiar... should probably ask a few questions first though before I toss in my 2 cents.
What Carb are you running?
What do the chambers of the Carb look like? Soot stained or are they clean?
what's your exhaust setup?
If you Turn the engine on at night and shine a flashlight over the Carb do you see fumes?
This is a bit of a split from the direction the other guys are going but maybe it can help.

[atv_123]

Well, the exhaust is just a stock exhaust system, single 2.25in pipe (I think thats what it is... I didn't measure it.)

The Carb is also completely stock, which if my memory serves me correctly should be a single barrel carb. Now I didn't disassemble the carb at all to clean it because of how incredibly well the engine runs (even with these odd problems and missing cylinders) and as the old saying goes... if it aint broke... don't fix it.    So I am not sure if there is any soot in it or not, however, it is tuned so well that it will start and idle without even making more then 2 full revolutions on a cold engine. For me that's pretty amazing for a carburated engine... now since it has an automatic choke, perhaps that's just how they run. I don't really know, everything else I have ever owned was a manual choke.

As for the fumes coming out of the top of the carb... in all the hours that I have been working on it I didn't see any, but I can look again.

I didn't smell anything like burning plastic, it smells like burning oil to me. Also, don't worry, I do know the dangers of exhaust fumes, I was just making the face in the exhaust remark as to drive home how unnoticeable it is at idle 

As for the exhaust gasses coming up through the radiator, I hadn't heard of that one before, but I learn new stuff every day... plus if it is a cracked head it does make sense. The next time I get home I will fire it up and give all these ideas a try and I can go from there and report what I find back here. That may be a little while seeing as I just started up college again but like I said this is no emergency. So when I get results I will report back here and see what you guys think.