Weak or bad injectors?

Mark Nixon

Mark Nixon

No Savior among the flesh
Joined
Feb 26, 2009
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A little background information first.

The engine is a basically stone stock 1995 Cummins, backed with a 47RH, and has @ 240,000 miles.
It appears that every external part on the engine is either new or rebuilt, turbo starter, alternator, lift pump, even the injection pump is super clean, the timing cover has been off at one point, as well.
It does not APPEAR that the injectors have ever been removed.

The engine fires right off, 1 turn and it's running, but has a "miss" at anything much above an idle.
I've feel I have ruled out a potential scored cylinder, or bad piston, due to the fact that there is no blow by at the filler or the draft tube.

When I first fired it up cold, it had a series of distinct rattling sounds, ALMOST like a rod knock, but higher pitched, which repeated itself one other time during my examination of the engine.
The engine miss is almost imperceptible at idle and it's not terrible in higher RPMs, no popping, nothing besides a noticeable miss.
In truth, it does seem to miss at idle, but it's not slap-in-the-face noticeable.

Am I right in figuring that it's possibly a faulty injector causing the whole issue?
Are there any other simple tests that I can do to pinpoint the fault?
Crack the lines, maybe?

Mark.
 
I had the same thing on my 94 auto. Thought it was a injector too. the 160 pump was just worn out and scored #5 plunger. I would try injectors first though, if everything else is good... Fuel pressure, timing, ect...
 
Stock injectors can be had fairly cheap, granted they may not be perfect either. I would swap injectors first before anything else just because that's simple
 
Mark, with it idling lightly put your finger on each injector line at the pump and feel for a difference between each, do the same at the injector....try to get a feel for it.....if there is a problem it will tell you. If you find a problem and want to verify it swap holes for the injector....2 to 5 swap ect, if the problem follows there is your issue, if not it is deeper or like adam said might be the pump.

Jim
 
I have heard of some pumps with worn gov assemblies do this. Mine did but under load it was smooth like normal.
 
would cracking each injector one at a time an listen to see if one sounds different than the rest work?
 
I have yet to do much more than unload the truck, but the intent is to check it all over to-morrow or Tuesday.

As I'm understanding it, cracking a line is like pulling the spark plug wire on a gasser, no spark makes a dead cylinder, as would cracking the line on a diesel injector.

Likewise, if a plug is "fouled" and you move it to another cylinder it'll affect that cylinder, but if there's no change, then there's a "distributor" (or injection pump) issue, or something is affecting compression on that cylinder.

At least, that's how I read it anyway.

Mark.
 
Well, I messed with it for a half hour, ran it, cracked the lines and there was a LOT of air in them, it smoothed right out and I was happy....
Until it got to operating temperature and I could hear the rod knock. :(

Looks like another dead truck gets the axe. :bang

Mark.
 
Yes, it's a rod knock, it got worse as it warmed up and I can hear it near the pan when I'm underneath the truck.

Mark.
 
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