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Discussion Starter #1
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?
 

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Discussion Starter #2
Maybe my understanding of the injectors is not right, and my hypothesis is off. I don't know what else it could be though.
 

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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.
 

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Have you checked the turbo?
 

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Discussion Starter #5
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.
 

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

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Oh then yes. Same thing.

How many miles do you have on the injectors.
 

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Discussion Starter #9
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.
 

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Discussion Starter #10
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?!?
 

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CAT lover
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I have a hard time believing that 7 out of 8 cylinders are just plumb worn out and dump 3qts into your cylinders. Especially with 80k on a stock engine
 

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CAT lover
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But in Michigan like Massachusetts the trucks rot out before the engine is junk so you could probably find a junk yard 7.3 for about $500 or craigslist parts truck.
 

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I've been told that a good OBS 7.3 engine should net at least between 380-400 psi, and that anything below about 375 or so indicates a tired engine. Of course, there are several ways to check compression, so it depends.

Bad compression from worn rings and cylinder walls and/or valves can cause oil burning.

The quality of remanufactured engines can vary widely.
 

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Discussion Starter #14
Ok, so they're probably a bit lower compression than they should be.

What kind of boggles me is why don't I have a bunch of blowby if 7 cylinders are bad enough to use that much oil?
To me (and it's very possible I just don't there to be an issue with the cylinders) it just doesn't add up.

I think I may try replacing the 420 cylinder injector.
 

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Discussion Starter #15
Update of sorts. Finally got the oil changed and some archoil added to the oil.

1. Opened the fuel bowl to change the filter and found out it was a Wix cap and filter unit so I put it back in to wait until I get something besides my Motorcraft filter. The fuel in the bowl wasn't exactly clean green. Not dark but advice is needed (see pic)

2. Runs smoother with EBP tube cleaned! However! Still very low on power, like no difference between 1/4 throttle and full throttle. Unplugged the ebp sensor: no change except for a little rougher idle.
Replugged in ebp sensor and unplugged newly installed MAP sensor: CEL comes on and plenty of power, how it should be. Replugged MAP sensor in and CEL goes away and back to no power still smooth. Advice please there also!
 

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CAT lover
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What did the side of the filter look like? If it was black/brown then I'd look into injector O-rings. As far as the map sensor, you could check to see if the sensor is bad by replacing it, or you might have boost issues, turbo worn? Compressor side dusted? Pop off the air duct and check the turbo for play. The stock filters are known to be insufficient and full of leak points in the stock filter housing.
 

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Would be nice to put a boost gauge on it. I’d get a new map sensor too. Maybe I missed it but this truck throws no codes and has no visible oil drips or leaks? When my ccv gets a kink in it, the truck will puff blue smoke. Maybe your ccv filter is clogged. If unplugging your map gives it power then it’s defaulting to the preprogrammed fueling tables. Wouldn’t this imply that the injectors can perform properly when given the correct load calculation?
 

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Discussion Starter #19
The filter was dark in some areas. It's yellow to start with so I'm not sure if it was just dirty or also oil stain.

The lower power issue is not a turbo issue.
Plenty of power with MAP sensor unplugged. Plug it in, low power, still runs smooth.
Feels like the torque of my Civic. Again, no issues with the turbo.
 

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I would blow air through the map line and make sure it’s not plugged. As for the oil. I have not idea. You said you already replace the orings. What brand did you use.
 
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