I bought an '86 F150 with a 300 I6 recently. It needed a lot of work and never really ran right. It has always had this knocking/detonation noise at certain RPMs. I am planning on doing the DSII conversion, but for now have the timing locked at 32* with the TFI distributor. I got a non-feedback 1 barrel from an older truck and it works fine. It runs OK, but makes nasty noises once warmed up that sound like a diesel, feels weak in general, and has a rough idle and a consistent "pop" through the exhaust at idle.

I think today I determined that the engine is just very tired. I did a cylinder balance test by unplugging the ignition wire from each plug one at a time and watching the vacuum gauge. Each cylinder makes a noticeable difference in the sound of the engine. But, each dropped the vacuum reading from 19"Hg to about 18.5 when disabled EXCEPT for #1, which made only a couple "Hg difference. Cylinder 5 didn't seem to make quite as much difference either, but #1 was the worst. I did a compression test in #1 and got 90 psi, then I did #2 as well for comparison and got about 120. I added some oil to #1 and retested and got about 120.

It seems to me the engine is tired and weak and needs rebuilt. The rings are probably weak or broken, although it doesn't smoke or burn any oil. None of the push rods are bent, all the rockers are tight, and I didn't see any broken valve springs.

Is there any way to "revive" the rings to get the cylinders to seal a little better?

What are the chances of success in pulling the engine and re-ringing it and maybe replacing the bearings?

Should I just try to find a good used engine and swap it in?

 

Hey 86stepside.

My first question is, what was your procedure for doing a compression test?
19hg of vacuum is quite decent and is a good sign for a (potentially) healthy engine.
Was the engine warmed up? Were all the spark plugs removed? Did you crank the engine a set number of times or did you crank until the PSI stopped climbing?

Either way, if you added oil and the compression didn't go up, that's indicative of your valves, not your rings. If it was your rings, the oil would seal the rings better and raise the compression. But if you have valves that aren't seating and are leaking, the oil won't help with that and the compression will stay the same.

You may simply need to have the head rebuilt and the valves freshened up.

Bad valves could explain the popping and noise.

Otherwise, you might actually be getting "pinging" which is a result of the timing. When you say 32° timing, is that your base timing? What do you mean you have it locked?

 

Just to add to what AB asked. Did you open the throttle while cranking it during the compression test?

 

I let the truck idle in the driveway and revved it occasionally to warm it up. It ran for maybe 20 minutes or so. The temp. gauge was about 1/4 of the way up - not at operating temp halfway, but not stone cold either.

I've had the truck since the summer time and I've just been chipping away at it. The feedback system was not all there or working properly, so I decided to remove it entirely. I got an earlier 1 barrel and removed all the emissions stuff. This obviously put the computer in "limp mode" and would not advance the timing at all. So, temporarily, until I complete the DSII ignition conversion, I have the TFI distributor (no mechanical advance) set to 32* advance with the SPOUT wire disconnected. It's a little harder to start, but since the truck is relatively light it does okay with 32* advance all the time.

I did not have the throttle open during the comp test. I didn't want to flood the cylinders with fuel and wasn't sure how to disable the fuel input. I did the test with all the other plugs still installed. If you re-read my post, #1 made 90 psi dry, then 120 psi with oil. I added maybe two table spoon's worth - kind of a lot. Is it possible that a lot of oil could seal a leaking valve? Maybe I should do a cylinder leakage test to verify where the leak is coming from. Oh, and I tried to watch the gauge while cranking it. The first "puff" barely made any psi, which is usually indicative of bad rings IIRC, and each subsequent puff only added 15 or so psi until it stopped increasing. I cranked it until the gauge stopped climbing, which was maybe six or eight puffs.

I don't have much time during the week, but maybe this weekend I should take the time to do a "proper" compression test at operating temp, with all the plugs removed, the throttle wide open, and somehow disable the fuel. I'll tell ya, the popping thru the exhaust at idle is very reminiscent of how my GTO sounded out of the passenger side pipe when I had a burned valve. But, like you said, it makes 19"Hg which is pretty darn good. The needle vibrates violently, but not even 1"Hg worth. I can't seem to "tune" it out either by removing timing or moving the idle mixture screw. BTW, it's got a new cap, rotor, plugs, and wires.

 

I misread what you said about putting oil in the cylinders. Thought you said #1 was 90, #2 was 120 and was 120 again when you put oil in it. I missed that it was #1 that went up to 120.

Either way, I'd redo your compression test and simply crank until the pressure stops climbing. Don't worry flooding the cylinders with fuel. They're not going to be drawing that much air through the carb. And if they do, it might just stumble a little after starting up. I never worry about the fuel when I do a compression check and it's a non-issue.

However, if it is truly 90 - 120 psi in each cylinder, there are definitely some serious issues. That is LOW. Mine's worn out and I'm still around 120 - 130 in each. 140 - 160 is much more where you want to be. A cylinder leak down test may be in order at that point.


As for the timing, that's a lot of advance for idle and low RPMs and it's definitely going to run poorly. Too much advance at idle will make the vacuum needle vibrate like you mentioned, and hard to start. And too much advance at low RPMs will make it ping and could potentially hurt your engine.

You can always try one of these. It replaces the entire ignition system so you don't have to fuss with the wiring harness, ignition module, etc.

https://www.summitracing.com/parts/s...view/make/ford

I have the DUI version (only one available at the time and about $150 more) on mine and it's a great system.

 

I wish I knew about that distributor before! I am familiar with the GM HEI. I didn't know they made one for the Ford I6. I already have a new DSII distributor and a new Ford ignition module on the way. Darn!

I warmed up the engine to operating temp and blocked the throttle wide open. I determined that the cylinder pressure stopped increasing after eight cycles, so I cranked it for ten cycles, just to be sure I get a maximal reading.

Dry test:
#1 100, #2 140, #3 130, #4 145, #5 150, #6 150

I tested the two weakest cylinders with about two table spoons of 10w30 added.
Wet test:
#1 195, #3 195

It seems my rings are not sealing well at all. Is it at all possible that it could still be a valve issue (fingers crossed)? I doubt it myself, but I'm all ears.

 

Can you return the components you have coming your way? Sorry I didn't think of posting up that HEI earlier. It's a slick system and it's what I have on mine. I'm really happy with it.

Hrmmm... Well, SOME of your cylinders are okay. I find it strange that you would just have bad rings in one cylinder. Maybe it's just a stuck ring? You could try pouring some Marvel's Mystery Oil down in the spark plug hole and letting it soak overnight and then fire it up the next day and see what that does.

But if the rings are really worn like that, I'm not sure what else you could do besides tearing it down.

Normally, if you have one really low cylinder, it's a bad valve. Two low cylinders next to each other is generally a blown head gasket. But those don't normally bump up with a wet test.

Someone else may have more insight as well.

 

Why? There is nothing wrong with the DSII system.

 

No, there isn't. But was saying he liked the idea of the other, so I was throwing out the option.

 

If he likes the HEI ignition module. He can always run one with the DSII distributor. If he does that just make sure to mount the module on a heat sink of some kind. Otherwise it will melt itself down.

 

That's true fordman 75. I could use the DSII distributor with an HEI module. In fact, I think I have at least one HEI module laying around in the garage somewhere. Although, I really like how the HEI distributor is all one integrated assembly. There are so many options!

I remember reading somewhere a long time ago to dump kerosene in the cylinders on an old engine that's locked up to free up the rings. I wonder if I dumped kerosene in the cylinders for a few days if that would free up the rings if they're stuck. Or like you said, I could try that Marvel Mystery stuff.

I find it strange too that #1 is almost dead while the others are pretty good. #3 is weak but #1 sticks out like a sore thumb. I'll have to do a leak-down test to verify that its leaking into the crankcase. Maybe a piston ring broke.

 

Check this out! https://www.amazon.com/HEI-DISTRIBUT...00+distributor

 

I'm not a fan of the HEI set ups or gm's for that matter. I've owned a few gm products when I was much younger and didn't know any better. And that HEI set up left me stranded more then once ( broken carbon button between coil and rotor, bad coils, bad modules, loose wire at connector ) . Add that to me not being a gm fan. Everytime I see one I think gm and sitting stranded on the side of the road. So seeing one of those on my favorite engine is like seeing a super model with a big hairy wart on the end of her nose. But it's your vehicle not mine. So if it's something that interest you go ahead and run one. The guys that have one seem to like them.


When I was much younger I had a engine that smoked. And this old timer that was a friend of the family said I should add some ATF to the oil. He said the detergent in the ATF would clean things up and free up any stuck rings. I never tried it because I ended up replacing the engine. If it makes you feel better go ahead and try soaking stuff in the cylinder/s or adding something to the oil or trying seafoam or something similar. As long as you don't hydrolock the engine. Or add something to the oil that will damage bearings or plug up oil passages. It isn't going to hurt anything to try. If it helps great, if it doesn't you aren't out a bunch of money or time.

I would do the leak down test to try and narrow down the problem. If it's going into the crankcase I'd be kind of worried about a damaged piston more then the rings.

Does it smoke at all? If it's got an issue with the rings, a piston or the cylinder wall ( damage or wear ) then it should be burning oil too.

 

Wow, I have not seen that one. They're really getting the price down on those. Granted, the lower you get the price, the more likely the parts are made in China.
However, the reviews are good.
It's certainly worth a try. If your budget allows, get two and keep one as a spare...

I've done the ATF a few times. Basically, you swap out an entire quart of oil for a quart of ATF. Just be ready to change your oil in a couple hundred miles because it'll be coming out BLACK (which is good). You repeat the process a few times until it stays nice and clean. ATF has some very strong detergents in it.

 

I've tried the ATF in the oil thing a few times in the past on other engines, but I never tried it to fix a more serious problem like this. In the past I did it just in an effort to cleanse the inside of a neglected engine. I've only put maybe 1,500 miles on this truck since I've had it and I've already changed the oil twice. I did it when I first got it, and then again when I replaced the oil pan gasket because it was leaking like a sieve.

I still need to borrow a leak down tester from someone at work to determine if it is indeed the rings at fault in the #1 hole. In any case, I need to get the ignition resolved. I like the GM HEI system because it is all contained in one unit. Plus, I have spare parts for it already. Here's the thing: I already have a DSII distributor and module. I've done a bunch of research, but still don't know exactly what is involved with wiring it up. I really don't want to go to the junk yard to source a whole new engine harness. I'd rather wire it up myself and I have no problem doing so. Can someone please tell me exactly how to dire up the DSII distributor and module?

It can't be that hard to wire up, but if I have to cut connectors off of these brand new parts to do so, and if it sounds like a big hassle, I might just see if I can send them back and get an HEI instead because they're so clean and easy to hook up. If I knew they were available for this engine I would've gone that route in the first place.

I always thought it was weird when I saw a big HEI cap under a non-GM hood. And I understand how it's a little sacrilegious, but hey, it's a viable, simple system with parts always readily available.