Have about 60K on the '85 crew after conversion from gas. Bone stock '89 donor motor of unknown miles. It has been simply fantastic. Had an injector intermittantly sticking open, usually on cold startup. Went to Diesel shop for injector testing and decided to have them do a compression test as long as they were at it. Truck was smooth and getting consistant 20-22 mpg with getrag, 3:55's and 33in tire @ 65-70mph (no tach). Has always blown blue smoke on cold startup none on warm startup. Has always used oil 1qt per 1500mi. Has always had some visible blowby from tube. Mechanic says #1 is 100 psi, all others are 380 psi. He recommends new engine because 1) he strongly feels mileage is much higher than I believe based on injector condition. 2) While it may be a valve issue, he says heads are rarely rebuildable and given the cost of a new head, combined with perceived high mileage on lower end, best to get new motor. Might be good advice but I'm just to ignorant to know. Best way to proceed?

 

I would get the truck outa that shop and do a valve leak test on it. The heads on a non ic motor are known to crack. But they aren't hard to change other than they are heavy. I would have the head checked out first before I give up on the engine.

 

I've seen cracked heads do just fine, cracks a common on the non ic engines. I would tear it down before I got another engine. Find the cause of the low compression, don't guess. And if you are not able to do the work find a different shop. This shop sounds like it wants your money! Was the sticking injectors on the same hole that has low compression?

 

i'd run a wet compression test then if its still low i'd do a cyl. leakage test, which will tell you where its leaking...

 

if everything else checks out that people said to check and it turns out you did drop a cyl. and if it's running good, just run it until it dies...

 

To answer 93flatbed, yes sticky injector was on bad cylinder. Probably drove it 50-100 mi. to get home when injector finally failed. Prior to that it was sticking for half a minute or so on cold startup but was running smooth and starting fine the rest of the day. Sounds like the leak down test, at least on the bad cylinder, could have been performed when the dry compression test was being done rather easily.

 

I'd just run it and see if it comes out of it . If he pulled it in the shop when it was sticking it could have.washed the cyl. Down and is the cause for low compression when he done it. Or the rings could be bad now but like Rick said just run it then worry about it when it fails

 

Would no fuel eat the rings

 

No fuel won't because the rings get lubed by oil but he said.they were sticking open which would wash the cyl down and that could eat the rings.

 

IF there is an issue with the rings or piston eating into the cylinder wall you WILL see metalic flakes on the dipstick when its running. The valve guides have been known to wear out on high mileage diesels and allow the valve to not seat correctly. That could cause leakage past the valve. I wouldnt give up on the motor either, at least if there is no metal flake in the oil, just change the injectors and run it.

 

Replaced the known bad injector on the known bad #1 cyl. All the excess black smoke is gone. Confirmation I believe that injector stuck open and likely washed down the cylinder as some of you have suggested. Truck no longer runs smooth, dead hole is obvious at idle and while driving making it no fun to operate and impossible to use and ignore. So I do believe that I have created the bad cyl. since it was always quite smooth. Have arranged to borrow a borescope to look into cyl. in a few days. Like a gas engine, am I just looking for cyl. wall galling/scrapes? Pulled valve cover off while running in hopes of maybe finding a bent pushrod or flat cam lobe but all seems well other than lots of blowby, enough to lift loose valve cover up and down (funny to watch). Oil is NOT contaminated with fuel as I might expect from excess fuel being pumped into the cylinder and bypassing rings. Is lack of oil contamination cause for hope? Also no metallic flakes on end of dip stick. Given this new info, is leak down test still best diagnostic procedure at this point? Thanks for all your ideas and comments.

 

This to me sounds like a partially melted piston. I think I would inspect the piston top and examine the cylinder wall for a vertical gouge from a loose piston ring end using the bore scope.

 

You've checked the valve trane. It's good. Any repair beyond that means pulling the head. Pull the head and evaluate the engine.

 

I still cant imagine its a dropped piston. I've rebuilt alot of diesels and never seen one loose compression like that and not had metal flake in the oil. I'm more likely to believe the rings are just stuck because of all the gunk and soot from the smokey cylinder.

Pull the injector and pour in some marval mystery oil, let is soak over night. In the morning remove the 12v from the shutoff solenoid so it doesnt start and crank it over a few times. Then put the injector back and try it out. If the rings pop loose it'll clear up and run fine after a minute.



Here are some washed down cylinders......