New injection pump, now hearing low rpm knock.

[MTKirk]

I just installed a rebuilt Injection pump on my '87 6.9, timed it to 8.5 btdc using a ferret meter, cold advance is working correctly. Truck runs fantastic, maybe better than it ever has, BUT; I'm hearing a knock from the rear driver's side bank of cylinders, I hear it at idle and it goes away around 1200rpm. This noise wasn't there with the old pump. The old pump had major issues; fuel pressure dropped out frequently (as it would return excessive fuel most of the time), timing wandered 4 or 5 degrees seemingly randomly. There was however, no knock like I am hearing now. I have a theory that my new pump is pushing fuel harder than the old one and causing an injector (old, unknown history) to pop a little early causing the knock, seem reasonable? Thoughts?

 

[79jasper]

Could.
Loosen one Injector line at a time and see if the knock goes away.

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[MTKirk]

That's one hell of an idea there, jasper! I'm gonna have to give that a try.

 

[Waystro]

Who did you get the pump from?

 

[MTKirk]

I ordered a Delphi reman before I found this forum, if I had it to do over again I might have ordered it from one of the guys on here. Still; so far so good.

 

[OLDBULL8]

Yup, You probably have a leaking or weak popping injector.

 

[icanfixall]

Welcome to the forum where you can get the best help from many well known members. My thoughts are as others and its a bad injector. Its generally felt around 125,000 niles is the useful length of life on injectors or injection pumps. As you appear to already know. An injector that has a weak spring or failed seat leaks fuel into the cylinders causing a fuel knock. Easy to repair compared to an actual engine knock. I suggest reading the Hall of Shame forum above before you spend money of ebay injectors be they are rebuilt or new. Many ebay rebuilt injection pumps and injectors have a rattle can paint rebuild. You get what looks good but is shot from the get go.

 

[Agnem]

The problem with putting new pumps against old injectors is explained here... http://conestogadiesel.com/support/fuelinjectionservicingadvice.html

 

[MTKirk]

So.., I started loosening the injector lines one at a time, like 79jasper suggested. Sure enough when I got to #8 the knock went away. I had tons of rags ready to catch what I was sure would be a deluge of diesel everywhere, turns out it really didn't amount too much. One rag handled it easily. I just placed my order for 8 rebuilt injectors, I'm looking forward to having this thing purr.

 

[79jasper]

Can we ask who/where you ordered them....

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[MTKirk]

I went with R&D IDI performance. I talked with Justin over the phone & felt real comfortable about spending my $ with him. I thought the price was right too. Hopefully they'll work out.

 

[79jasper]

Ah, okay. I think he was back ordered for a little bit or something.
Was just making sure that you didn't get some junk parts.

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[MTKirk]

IT'S FIXED!!!!!!!!!!!!!!!!!!!!!!!

Just to update; I have finally figured out the knock I’ve chasing since I changed my injection pump. It mimicked a faulty injector perfectly. when I loosened the injector line the knock went away, so naturally I assumed new injectors would make the knock go away. You can Imagine how disappointed I was to have the knock still there after installing a new set of injectors. Lately I’ve been reading all the posts I can find about unwanted IDI noises and came across a post by Rick from Memphis member rlphlp

“See if throttle cable is rubbing injector line on driver's side.
Should have the thick rubber covering over the throttle cable touching line at that point.
Will transmit strange sounds to cab area.

Rick”

I read this post and had a eureka moment (remembered what a pain in the shorts the dang accelerator cable was every time I had to work on #8 injector). So I tied back the cable with a cable tie screwed into the firewall, my truck now sounds like 6.9 liters of well tuned diesel perfection, WOHOO!!

This forum is GREAT! Thanks everybody.

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[HammerDown]

That return line looks well, different then the fabric covered hose I'm use to seeing.

 

[Waystro]

Don't you love find simple fixes?

Usually happens to me after I spend a lot on parts then find that I didn't really need them.