GM-GMC: 6.5 lt diesel problem, poor fuel economy, diesel machanic

Question
Hi Harry and thank you for your response to the question I posted in January Re: wrong fuel in 6.5 litre diesel. I am still having a problem with the knock in the engine. I have taken it to my local GM dealer and they say that it is a valve and that the engine will have to come out. I also spoke to a diesel machanic at a local garage and he says that it could be back combustion and that the injectors should be changed. I called a machine shop that rebiulds engines and they told me that the 6.5 is a engine that usually 9 out of 10 times has a cracked block or heads and that taking it apart will only increase my problems they have a dozen of them and won't fix them due to the expense. Another tech told me to put lucas additive in my oil to see if this would stop the nock. It did seem to stop knocking a bit but when she warms up the knock is still there. In the cold mornings she is very rough starting and spits and sputters until she warms up. If I change the injectors will this make her run better? This is not an expensive ordeal as I do not want to remove the engine and let them tear it apart. Also, the fuel pump can be rebiult for a reasonable price and the fact that I heard the pump is under warranty for 10 yrs 200000km from GM. is this true?. She is a 1996 GMC 6.5 diesel no turbo injection with 178000 km. I might add that highway driving seems to be ok and that her ability to have power on the highway is good.

Thanks again for the great assistance.

Archie

Answer
Archie,

If you have more than 160,000 km on the injectors (and you do), they can cause the trouble you are describing.

Injectors do not stop working.  They stop atomizing the fuel as efficiently as they did when they were new.  This causes hard staring, rough running, knocking, and poor fuel economy.

You can remove the injectors and have them tested by a reputable diesel injection shop.  They can be rebuilt or you can buy new ones.  Prices range from $8.00 to $35.00, each,in US dollars.

The injection pump does have an extended warranty, but it usually has to fail completely before GM will honor the claim.

I would try the injector test/replacement first.  Be sure and get new coper washers to put on each injector when reinstalling them, the special socket used to remove and replace the injectors, and a return line kit (the return lines tend to get brittle and will likely crack when you try to remove them).

Torque on the injectors is 50 ft-lbs.  The injection line torque is 22 ft-lbs, but "wrench tight" will work.