Still knocking and burning off Glow plug

[83Blzr62]

My engine has been knocking since it has been built about 290 miles ago. I traced it to the #7 cylinder because I found that a glow plug had burned off. I replaced the glowplug thinking that it burned off because of low quality or a long glow time. Then the new one burned off too. I replaced the # 7 injector, retarded the timing a 16th of an inch, and put in a new glowplug. Once again the knock remained and two days 50 miles later, that glow plug was also burned away. What else could cause this? I want to know everything I should check before this kills my engine. I would hate to know what this is doing to my #7 piston. Also, my oil pressure is low but still in spec. It is right on 10 psi at idle. Could the two problems be realated?

[More Power]

If the glow plugs for the other seven cyls are unaffected, you could rule out injection timing. Does the knock go away if you crack the injector fuel line with the engine idling?

If the knock is unaffected by loosening the injector fuel line, then you may have a mechanical issue - assuming #7 has been identifed as the knock source.

What can cause a glow plug to burn off? As you considered, too much timing advance can do it, but it'll affect more/most of the other cyls. Too much fuel can do it, but again, it'll affect more/most other cyls as well. A certain percentage of gasoline can do it, but that too would affect more/most other cyls.

With a mechanical distributor type pump, it would involve a pump defect that I'm not aware of to produce excessive fuel delivery to just one cylinder.

Too high (much higher) compression in just one cylinder..... I dunno...

Jim

[DmaxMaverick]

Like MP said, it has to be something unique to just that one cylinder. Higher compression, perhaps, but I don't know how that would happen. Maybe a compression test is in order? If you've already changed out that injector, well, you can rule that out. The only thing left, really, is the valves and pre-cup. Perhaps the precup is damaged, or some debris is causing the GP contact to ground. The only other thing I can think of is maybe a leaky valve guide??? If engine oil were to be constantly present in one cylinder, well, that would add "fuel", and increase the combustion temp for that cylinder. Engine oil has non-burning properties, which could cause deposits to form on a GP, increasing the heat retention of that plug. More oil in a cylinder can also raise the compression.

Can you post some pics of the GP remains and of a plug that's ran in the cylinder? How about pulling a couple injectors and compare the differences seen in the precups?

Have you tried running with that cylinder's GP disconnected? That could determine if added GP heat is adding to the failure problem, or if it is just a combustion event causing it.

[83Blzr62]

Yes, I have ran it with the glowplug unplugged. Before I pull anything I will get the injection pump tested and do a compression test just to make sure. But if that is not the case, Is there a way to test if there is oil in the cylinder? Would it be best to pull the entire engine and recheck everything again, or should I just try pulling that head?
Thanks for all the replies.

[DmaxMaverick]

If there is oil being dumped into the cylinder, you should be able to see evidence of it by comparing glow plugs and precups. You can see the business end of the precup by removing the injector. The injector and GP are located inside the cup. More oil present will show more grimey deposits and coking. If there is more flakey black stuff in there, that is probably the cause. It shouldn't be too difficult to spot, given the scope of your issue.

[EWC]

Have you checked to see if any injector lines are crossed ?

[redbird2]

I think ECW is on the right track check the injector lines does it seem to miss when running?

[john8662]

This is a stumper for sure...

I like the comment about the injection lines being out of sequence, it's possible to get them mixed up.

I forget which two are the culprits tho.

Do you have an illustration in a manual you have in your posession of where the lines go?

If not, I'll hook you up.

Be good to verify this before continuing.

J

[83Blzr62]

No , I do not have an illustrtation. It does not seem to miss, just tick and knock under load. Please post up the picture john and I will check that out.

[More Power]

I remember a story from a few years ago - told to me by a dealer tech. He said a customer's 6.5 (new at the time) was running rough and made more knocking sounds that other 6.5s he'd worked on. They eventually pulled the heads, and discovered a missing precup.... :( Apparently, it had missed the QC while on the engine line.

Jim

[john8662]

Ironic thing, this scenario did bring the story that Jim just told to mind, I remember the story being told...

Anyways, here is the injection pump firing sequence for your troubleshooting.

Remember, even cylinders on the passenger's side, odd on the driver's side (physically on the engine)

http://members.cox.net/acmdsl/injection_pump_line_order.jpg

[Scrufdog]

yeah, that looks easy to bone up without a picture

[83Blzr62]

I have an idea of what might be causing it. In the beginning it sounded to me like the knock was coming from the passenger side, so I checked the lifters on that side and ignored the driver side. Now I am pretty sure that the knock is coming from the driver side since that is where the glowplug is burning off at. So could the exhuast lifter be bad enough on that cylinder so that the exhuast cannot flow freely, which would cause that cylinder to run hotter and burn glowplugs?

[Kennedy]

This is a stumper for sure...

I like the comment about the injection lines being out of sequence, it's possible to get them mixed up.

I forget which two are the culprits tho.

Do you have an illustration in a manual you have in your posession of where the lines go?

If not, I'll hook you up.

Be good to verify this before continuing.

J

I think it was 5 and 6 that could be crossed. most easily. It was down low if memory serves. I came across this myself once (not sure if I did it or what, my memory is fuzzy on that one) plud I had another truck driven in like that shortly after pump job. It doesn't really sound all that bad, but a trained ear can tell/feel it.


I don't recall if the injector from the suspect hole was moved or not???

[Robyn]

One thing is for sure, once its all buttoned up its a real nasty one when you figure out you screwed up.

I have one of those line order pix about the size of a 5 gallon pail lid hanking around to refer to when redoing the lines after a pump job or a rebuild.

I dont like tearing stuff back apart.

[83Blzr62]

I figured out what it was a few days ago. I guess I crossed my number 5 and number 7 lines. I thought it would not run at all or at least no where near as well as it was running. Now it is a little smoother and does not knock at higher rpm and under load. I wish I would have got it right the first time. It still ticks slightly, so I think that there is a glow plug tip in the cylinder, so I may need to pull the head. I am going to find a shop with a borescope so I can look in there first. I also left the oil cooler bypass valve out. I found that out when I started taking apart my old block.

[moondoggie]

Good Day!

Thanks for letting us know - many will read this & avoid trouble in the future.

Glad you got it figured out.

Blessings!

[mrbornery21]

:mad: I highly recommend that you have your injectors rebuilt, or taken apart and cleaned, If its not to late. I had the exact same symtoms, Burnt glow plugs and knocking/tapping. The Kid I got my truck from, owed me money for fixing his car, so I told him to give me his 1989 G.M.C jimmy 4x4 6.2 turbo truck he said ok. History about truck, The kid told me that he took it to a diesel shop cause it was leaking oil, when he got the truck back $800. Bill later the truck leaked oil worse and had no power and knocked. he took the truck back and the guy said that he needed a new engine and that he just so happened to have an extra engine that he can purchase for $2,600. bucks. I told the kid that the guy done something to his engine and was trying to scam him. But anyways I towed truck to my house and begun trying too figure out what the guy had done to it to make it run bad. Keep in mind that this is my first diesel truck, and the first diesel I had ever worked on, so it was a learning experiance. After a lot of research I came to the conclusion that the injector lines were crossed. I traced the lines without pulling the intake off and the lines appeared to be hooked up correctly. So I figured that maybe the truck just needed a new set of rebuilt injectors. I purchased a set for $180. and put them in. Truck ran smoother but still knocked and had no power, so the next day I pulled the intake off, ahhh! haHHHH! when I traced the injection lines before, the #5 and #7 lines appeared to be correctly hooked up to injection pump, but i could not see that they twisted under the intake, so the injection lines were crossed at injectors #5 & #7. The injector lines were bent and crossed on purpose at #5 & #7 So I bent them back and hooked them up correctly. This would have been easy to spot with a well trained eye, but I had never worked on one of these engines before. Anyways fired truck up, still had a knock, but had way more power than before. So i took it down the freeway, truck ran good hit the next exit and turned around and started driving the other way and all hell broke loose. Barely got the truck back home engine was trying to sieze screeching, pulled it into my brother inlaws garage. bad news, fine metal mixed in oil. #7 injector tip burned off. Pulled head off, burnt hole in #7 piston and melted prechamber, scared cylinder wall, Because the #7 injector stuck open. Keep in mind that these injectores were freshly rebuilt and only hooked up backwards for a day, but it caused it to get extremely dirty and stick open. Good news is I found out why engine was knocking, #3 piston was hitting the top of the head. Dont know if this was caused buy the injection lines being crossed. Hope this helps, and I hope this doesnt happen to you or anyone else!!!!:mad: