well, I finally got a compression tester on my 92 NA 7.3 resurrection project, and was VERY pleasantly surprised at all eight cylinders testing out between 490 and 520. It's a cheapie, so I wouldn't be surprised if it's not all that calibrated, but it repeated itself ok on the same cylinders.

But, I still get more white smoke (smells like diesel) from the RDT and out of the oil cap (when off) than I would expect given the compression. Mostly at idle. After stopping, it takes 20-30 sec to kick in. Smoke is partway between the YouTube videos where people respond with "that's normal" and "jeez, thats a lot."

How likely is it that there's an actual problem? What should I be looking at next? Mess with timing? Get a CDR and hope it hides itself?

Thanks.

 

I'm not an expert. But I would go out on a limb and say that timing may cause smoke out the exhaust, but has nothing to do with blowby.

The CDR could easily be the problem. If the CDR is allowing excess blowby into the intake, it will burn and produce smoke.

-Matt

 

You can try cleaning the cdr before replacing it

 

I appreciate the responses.

That's the thing- I don't have a CDR, the truck had a road draft tube when I got it. Is an RDT going to necessarily produce smoke at idle regardless, and getting a CDR would clean it up a little, or is a smoky RDT something I should worry about as a symptom?

I did some searching, but I haven't found an answer yet.

 

we had a very similar problem with my cousins newer diesel p/u. ended up being the injectors, the orings were shot and they were not sealing up correctly. Basically allowing combustion pressure into the valve covers. He was smoking all the time and pushing tons of pressure out the crankcase breather and oil cap. He also had great compression in all 8 cylinders.

not sure if that helps.

 

Well with the IDI design, this can't be an issue, because the injectors are not inside the valve covers. If there's combustion pressure inside the valve covers, then there's a problem with the valves, not the injectors.

As far as the road draft tube goes - This isn't your problem. CDRs cause smoking by allowing oil into the intake, when they are only suppose to allow blowby in. If you have a roaddraft tube, then any oil and blowby is going on the ground, not through the intake.

So it is absolutely impossible for a road draft tube to cause your exhaust to smoke, which is quite the opposite for a CDR. Installing a CDR may help you cut back on oil leakage because a properly functioning valve should hold the oil in. But it won't help your exhaust smoke.

-Matt

 

Right- all the smoke is from the RDT, not from the exhaust at all.

 

Oh. Well in that case... buy a CDR.

It would be quite normal for a RDT to smoke.

-Matt

 

Thanks, that's mostly what I was looking for, plus whether I have anything to worry about with 1) really good compression numbers, but 2) moderate blowby from the oil cap and 3) white smoke at idle after half a minute or so.

I am assuming I'm going to end up on the timing path.

Jon

 

1) Good
2) Probably normal. These engines wear out their rings. It's just a fact of life. Even with slightly worn out rings, you can have good compression. Your engine might have blowby but still be good for another 200,000 miles. It's not unheard of. At all.
3) That's probably timing.

-Matt

 

My truck has blow by too. Then gain it seems to hold in while the engine is running. But if you shut it off you'll get tons of blow by smoke coming out of the filler (if you take it off of course). It's got 345,000 miles so what can you expect?

 

My truck does this as well. I don't get tons of smoke, just a bit but I always wondered if that was normal