7.3 using alot of oil, compression test decent - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 59 (permalink) Old 12-05-2018, 03:27 PM Thread Starter
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7.3 using alot of oil, compression test decent

I've got a OBS 7.3 with 80k on a reman engine.
However it burns alot of oil, to the tune of 3 quarts/tank of fuel.

I notice that on most starts, hot or cold, and when leaving a stoplight, there is a fresh "puff" of blue smoke, and then a blue haze while running, hot or cold.

I've done a lot of research on the issue so hopefully the common issues are taken care of/checked off already.

-The o-rings on the injectors have already been replaced, no change. Still clean and green fuel in bowl.
-New turbo and delete pedestal installed, dry exhaust soot in downpipe, not excessive at all.
-Blowby cap test results: no blowby "smoke" comes out with CCV line open; CCV line pinched off, some blowby comes out but still not enough to move the cap.
-Actual compression test results on a 40*F (cold, not run in a few days) or so engine:
1: 360
2: 355
3: 395
4: 375
5: 420
6: 365
7: 365
8: 355

Truck starts quickly cold or hot and runs pretty smooth. This is my first experience with an OBS 7.3 so I'm not quite sure how smooth it should run, but for a diesel, seems pretty good.

Performance seems very good. I've heard the 7.3s were dogs, but this one seems to go pretty nicely. That being said, I have been chasing a CEL, just replaced the MAP sensor, and now it's low on power. I haven't run it in a week since I've been doing compression checks, but I did pull the EBP tube and clean it out (about 5 inches of it was completely clogged with soot) so hopefully that will fix my low power issue. No CEL now with MAP sensor replacement.

Back to the compression test. I'm wondering why cylinder #5 is so much higher than the rest. It's pretty much at a compression that would be appropriate for a new engine.
My hypothesis for this thing using oil: Number 5 injector is internally worn and allowing oil into the cylinder to be burned. This is also the reason that is has a higher compression because its essentially a wet compression test (oil in the cylinder).

I understand that if injectors are internally worn that it would start hard due to the thinner oil getting past the intensifier piston easier. But with just one injector worn, would it be possibly to have good starting, yet still burn that much oil?

What do you guys think?

1996 F250 XL 2WD 5speed 287k on truck, 80k on reman engine.
All stock
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post #2 of 59 (permalink) Old 12-05-2018, 09:27 PM Thread Starter
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Maybe my understanding of the injectors is not right, and my hypothesis is off. I don't know what else it could be though.

1996 F250 XL 2WD 5speed 287k on truck, 80k on reman engine.
All stock
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post #3 of 59 (permalink) Old 12-06-2018, 11:26 AM
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Re: 7.3 using alot of oil, compression test decent

I would guess your injectors are worn too. I'm not sure about the compression test. Did you pull the idm relay when you did it? Did you pull all the glow plugs and test one at a time? Having open cylinders makes it easier to spin over and cant get compression from the adjacent cylinders. Usually a bad head gasket but very unlikely on the 7.3.

01 f-250, Standard
Rev tech 4" lift, 37" military wrangler Mt tires
KC diy 66, Full force 160/100 and custom tunes from PHP
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Diy quad feed, Hydra, Isspro boost, pyro, and fuel pressure
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post #4 of 59 (permalink) Old 12-06-2018, 11:27 AM
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Re: 7.3 using alot of oil, compression test decent

Have you checked the turbo?

01 f-250, Standard
Rev tech 4" lift, 37" military wrangler Mt tires
KC diy 66, Full force 160/100 and custom tunes from PHP
Banks intercooler and full 4" exhaust, Diy S&B intake
Diy quad feed, Hydra, Isspro boost, pyro, and fuel pressure
3/0 battery cables with military style terminals
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post #5 of 59 (permalink) Old 12-06-2018, 12:21 PM Thread Starter
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I did not pull the IDM relay when doing the compression test. What would that do?
I DID pull all 8 glow plugs so it could spin freely.
Turbo and pedastal was replaced a couple thousand miles ago as part of trying to fix this. Downpipe is dry.

1996 F250 XL 2WD 5speed 287k on truck, 80k on reman engine.
All stock
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post #6 of 59 (permalink) Old 12-06-2018, 12:52 PM
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Re: 7.3 using alot of oil, compression test decent

It keeps the injectors form firing and pumping fuel into the cylinders. It could skew the numbers.

01 f-250, Standard
Rev tech 4" lift, 37" military wrangler Mt tires
KC diy 66, Full force 160/100 and custom tunes from PHP
Banks intercooler and full 4" exhaust, Diy S&B intake
Diy quad feed, Hydra, Isspro boost, pyro, and fuel pressure
3/0 battery cables with military style terminals
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post #7 of 59 (permalink) Old 12-06-2018, 12:53 PM Thread Starter
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Quote:
Originally Posted by Sbluke55 View Post
Did you pull the idm relay when you did it?
I'm assuming this is so the injectors don't try to fire? I did not have the valve cover harness connected when I did it, so this would essentially do the same thing correct?

1996 F250 XL 2WD 5speed 287k on truck, 80k on reman engine.
All stock
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post #8 of 59 (permalink) Old 12-06-2018, 12:59 PM
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Re: 7.3 using alot of oil, compression test decent

Oh then yes. Same thing.

How many miles do you have on the injectors.

01 f-250, Standard
Rev tech 4" lift, 37" military wrangler Mt tires
KC diy 66, Full force 160/100 and custom tunes from PHP
Banks intercooler and full 4" exhaust, Diy S&B intake
Diy quad feed, Hydra, Isspro boost, pyro, and fuel pressure
3/0 battery cables with military style terminals
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post #9 of 59 (permalink) Old 12-06-2018, 01:07 PM Thread Starter
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Quote:
Originally Posted by Sbluke55 View Post
Oh then yes. Same thing.

How many miles do you have on the injectors.
I'm not sure, that's the thing. I'm taking care of this truck for a friend overseas, and he bought it with reman engine that only has about 80k miles on it. But I don't think the injectors were changed because there is nothing about it on the receipt.
The truck has 280k miles or so.

At least 1 of the injectors has been replaced (not the suspicious cylinder) because it's got a brown top instead of the gold-ish color.

1996 F250 XL 2WD 5speed 287k on truck, 80k on reman engine.
All stock
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post #10 of 59 (permalink) Old 12-07-2018, 02:13 AM Thread Starter
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Well, I presented this situation to a guy I know who works at a diesel shop that does powerstrokes, and apparently all the guys there think that the 420 cylinder is the only good one, and the rest are burning the 3qts/fuel tank.

Does everyone else burn this much oil who has this compression?!?

1996 F250 XL 2WD 5speed 287k on truck, 80k on reman engine.
All stock
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