I have an 06 2500 with 125,000. I have been suspecting a bad injector for a while. Rough idle and can tell its slightly missing. I did an injector kill test. The only injector that made a major difference in idle when it was killed was #6. #1,2,3 made a noticeable difference but nowhere near as much as #6. #4 and 5 you really had to listen hard to hear a difference in idle. So my question, does this lead to all injectors being bad or do I need to look elsewhere before dropping that much money on injectors. By the way all 6 injectors ohm tested at .3. Any help is greatly appreciated.

 

get the exhaust manifold completely wet and start it. see where it doesn't evaporate the water.

they should all should evaporate at the exact same time.

the ends of the manifold, the center will be slightly faster but 1 and 6, 2 and 5, 3 and 4 should match if the turbo is in the center.

you can do this several times is a row, it is more accurate then the kill test IMO.

 

The ohm test just tells you if the coil is good at rest, not the performance as it is activated. You could till have a bad coil.

Neither the kill test or ohm test will tell you anything about the actual injection event and the inside pieces of the injector.

Running a cylinder contribution test MAY help point out a bad injector. That will still only tell you there is a problem not the overall health of the injector.

Next step would be a return flow test to see if it is obviously high.

Even with all that done and you find 1 or 2 injectors that are bad, the rest are probably on the cusp of going. Your mileage is rather low for injector problems but so much depends on the fuel and additives you have been using that its not unusual.

You get away with replacing the bad injector and maybe not have anymore problems but the odds are not good. A set of injectors is the only way to know they are good then start adding better filtration.

 

Interesting test. I like that one. I usually use an infrared therometer, but not everybody has one.

I just did this on an 05. #6 failed the cutout test, #4 was iffy. Guy got me to replace only #6 against my recommendation to do them all. I understand that though, they are pricey injectors.
Anyhow, it helped start better and removed most of the miss, but in the end he wound up ordering the other 5 injectors too.
These trucks wear out injectors rather quickly although as mentioned your mileage is pretty low for it.
Anyhow, based on my limited experience and knowing the injector issues, I'd say to do the water test or infrared thermometer test (all cylinders should be within 5 or less degrees of each other, a bad injector generally be around 20 degrees out or more) and if you see a notable difference - replace them all. It doesn't matter if it's the injector itself or the electrical side of it - if it's not working properly it needs to be replaced. Period. And if one's toast - the rest are close.

 

Neither a water test or an IR gun is going to tell much once the engine is up to temp, which is where the test should be run. A kill test and cylinder contribution test is way more accurrate than anything else. Aside from a totally dead cylinder, its just a guess.

Intermittent misfies, a rolling misfire, or a worn but not totally bad injector will NOT show with an IR gun or water. Once the engine is up to temp a 100 degree difference between cylinders will never ne noticed due to the heat soak.

Coil problems rarely show cold, unless they are totally dead. More often than not you have issues warm and no codes to indicate a problem. The coils are available seperately and are simple to replace if the injector body is good.

 

I beg to differ. This truck was taken to 2 different places for the injector cut out test with symptoms of hard starting especially when cold, slight miss at times and black haze of smoke when driving down the road. The first place wasn't sure but figured there might be an issue with the injectors, particularly #6. Second place said #6 was shot, #4 was marginal and the rest were ok.
Here's the test I did.
I've thrown out the paper where I wrote the first couple test results before replacing #6 injector, but here's the results after I had already replaced #6:

Truck was started cold and driven 22 miles to town. Some running around town, then drove back to the guys yard - 22 miles. Engine is toasty warm and fuel system completely free of air after the 44 mile round trip plus running around town. Pulled into the yard and let the truck idle for 3-4 minutes to let temps even out, then checked temps. After replacing #6:
#1 - 94.8
#2 - 99
#3 - 101.3
#4 - 125
#5 - 98.3
#6 - 107.5

Remember how #4 was said to be weak via the cutout test? Notice how #4 is 17.5 degrees higher in temp than the next hottest, which is the already replaced #6. 1,2,3 and 5 are all within 6.5 degrees of each other. Before replacing #6, it was running at 132 degrees, but I can't remember what the others were. These numbers all fluctuate slightly as the engine is running with the thermometer in place - I wrote down the average of each cylinder. Heat soak happens VERY quickly at these temps. How else do the Exhaust valves cool themselves for example? Absolute miliseconds that they are seated - at idle. What about running down the road ate 75mph pulling a load of hay bales when the EGT's are much higher yet?

Measurements must all be taken from the same distance away from the manifold and be taken from the same place on the manifold for each cylinder as the infrared beam spreads out with distance.

I interpret the numbers like this:
#1,2,3,5 are just worn - There's you weak injectors
#4 is very weak - There's your intermittent miss
#6 was obviously shot (highest temp) - There's your shot injector

I don't know what a cylinder contribution test is. The cut-out test does not tell you if it's the injector or the coil that's bad either.

This test shows the same results as the cut-out test. My way is $60 cheaper and about 4 times faster.

 

Pull the exhaust manifold then start the engine, you'll find which hole is bad.

 

The temps do not indicate worn or any other problem on 1,2,3,5,6, those are pretty normal IR temps. #1 is the coldest and #6 the hottest due to cooling system function. Even a 20-25% variation is normal from front to rear.

Even 4 is not that bad unless there is other corroborative data. The injector is not weak, its over fueling but not that much.

Looks like the kill test was dead on, 4 is going and 6 was gone. You have no idea what the other 4 are like healthwise without further testing.

Like I said, its in the ball park but not close enough to determine if all the injectors have an issue.

 

I beg to differ again. I used the same test to find an intermittant miss on my own 12 valve. #1 was the culprit (verified by repair) and measured in at 105* while the rest were within 3* north or south of 120* - note: 2,3,4,5 and 6 were within 3 degrees. These are original injectors with 235k miles on them. How will you explain that? 20-25% difference in temp is normal? I doubt it. That means I could have one cyl running at 1000* and another at 1250* and this would be normal? Naahhh I don't know about that. Who needs pump barrels calibrated if you can be out as much as 25%? It doesn't take much fuel to make that difference in temperature. Pyro is also useless at that point.

I find it interesting how my actual numbers line up with the "guess and check" cutout test which you have much faith in - and yet you throw my real numbers out the window? Even though they have the same result? Seems a little bias. We established that #6 and #4 were bad. If the others are that close to each other in temperature, I think it's safe to assume something about them is the same. Using the new #6 as a baseline, 1,2,3 and 5 are all noticeably cooler - indicating something is different between them and the new #6 (which I think would be safe to assume is working correctly). Would this not be "wear" after 230k kilimeters? Vs. the shot #4 and the New #6?

I've used this method many times to trouble shoot fueling issues. Although that cooling bit makes sense, I have never seen the temps gradually increase from #1 to #6 - even on a healthy engine.

EDIT: Verification: My 12v has 235k miles, the CR I worked on has 230K killometers

 

Hmmmm..... Yes, I can see the CR temps do increase from #1 to #6, supposing a healthier #4 temp fit in.
You got me there!

Still can't see 25% EGT difference being normal though.

 

Coming from a jerk pump you have a learning curve. No worries, we have all been there.

Consider your observed IR temps and consider actual EGT was around 400-410 degrees. That makes about a 400% difference from IR to actual, more than a little room for error there. An IR is only going to read the heat soak in the manifold not the actual stream temp, it can't. Hence my comment about how accurate it really is. exhaust flow, manidolfd design, etc, will impact the actual temp you see radiating. Doesn't mean if you see the bulk of the cylinders at a close temp an one way off its a bad reading, just not real exact for certain things.

Trying to compare idle temps from a 12V to a CR is again not valid. Too many differences in the fueling control and manifold design. Add the IR variances and its just not going to work. Variances of actual EGT across cylinders can easily be 80 to 100 degrees on either engine.

Now for the biggy, CR injectors fail to hot. Jerk pump injectors fail to cold. Its the fundamental differences in the way they work. A worn CR injector over fuels because the seats are not holding and more fuel is being pushed thru the nozzles and pintle seat. Too worn and you get a miss because the timing is way off, slightly worn and you get a excess grey smoke at higher rpms. The common rail provides a steady supply of fuel so the typical failure is over fueling and excess EGT temp.

A jerk pump typically fails cold because the supply is not constant and runs out too quick. Popping too soon leaves cooler EGT temps because the fuel has all fired early, or, the wear just bypasses too much fuel. On a CR, bypassing too much fuel just gets you hard starts and they run just fine once started.

You can have 6 CR injectors with 5 degrees of each other and they may be good or bad. The temps just mean the pintle seats are holding the same but the internals could still be worn enough to over fuel at rpms. Or they could be good and passs return flow specs at 200k+. You could have all good injectors by spec that will vary 10-15 degrees with IR and be fine. they could vary 60-80 actual EGT temps and be fine.

What an injector contribution test will tell you is how the events are contributing to a constant rpm. The ECU can sense the speed differene in the power stroke base don fueling AND adjust it a bit to compensate for a smoother running engine. When it gets too far out then you get a rough idle and the ECU cannot compensate. The percentage numbers will reflect is cylinder(s) are over\under fueling based on the power stroke speed difference. The typical spread runs 94-99% on a normal engine. When the comparisons go over 100 or under 90 with the bulk in the upper 90's then you can see what is wrong and where.

 

I work on Deere CR's. Very similar to the Cummins system. Learning curve has been in swing for quite a while....

Agreed. What the IR gun is seeing is an average of each cylinder as the heat is lost through the manifold. No, it is not the exact temp as the EGT's, but because it's an average of heat loss over time, it's accurate enough and even enough to pin-point an issue.

Agreed in the fact that the control systems and the actual parts are different, but the events themselves are the same. Both have a begining and ending of injection - the CR's being more precise due to design. Then they both burn the fuel via compression ignition relative to timing. You still have an EGT for each cylinder and you can still read the average heat loss as the exhaust exits the manifold. If any event is altered whether it be 12v or CR, it will show up in the EGT's - even with an IR gun unless it is an extreeeeeeeeeeeeeemely small change.

Agreed again. BUT - It doesn't matter really how they fail - either way, if the timing is advanced on one cylinder, whether it be an electrical malfunction on a CR or a weak spring on a 12V, this can be detected by measuring EGT. If an injector is over fueling - whether it be a worn seat on the CR or 12v, it can once again be detected by measuring EGT's and comparing each cylinder. It shows up because of the fueling differences between them. They do fail in several different ways - I have no issue with that. The point is, reading the cyl temp shows the differences and points out which cylinders have a fault - no, it does not tell you what failed or how. Neither does a cut-out test.

Yes. But ONLY as far as having a high return - like you said, in that specific case, an IR gun probably would not pick it up. However, when you measure all 6 and two of them are radically different from the rest - there is a fueling problem - either in those two or the other 4. If the actual fueling into the cylinder ever changes - it shows up in the individual manifold temps.

You bet. I hook up to the tractors for that test all the time. It does not tell me what's wrong with each injector though, only if #4 for example is not working properly. I can verify that with my IR gun - even though I can't read the exact EGT for that cylinder.

Point is, if the engine is warmed up and then idled for a few minutes to let the temps become stable, the IR gun actually works really well to find the bum cylinder - regardless of manifold design, cooling etc. because it's an average measurement of heat loss.

 

I am never lucky enough to get the obvious stuff.

Every time I have to chase an injector problem the IR was useless. It was too uniform and did not point to an obvious bad injector.

In a couple case even the contribution test did not look that bad, nothing obvious just 2 injectors slightly higher in percentage than the others. What finally convinced us was it moved with the injectors. Even the IR readings were weird because they would move in the bank. Never consistently one cylinder obviously higher\lower than the others.

Then again, the problems we had never showed until loaded or at 2600 plus rpms.

The CR's have 2 events and temps generated are a lot different than a jerk pump. The events are not the same size and the timing is so dynamic that its tough to compare. CR's almost always show higher cylinder temps and larger spread than a 12V because of the retarded timign and the electronic control. Also, having #6 almost totally enclosed makes the temp differences sometimes noticeable.

There is a larger variation on the CR than a 12V with an IR, have seen that first hand and drives a lot of my distrust in it. I have to do 3 more things to be sure.

Yeah, **** as hell but these injectors are expensive and melt pistons easy.

 

Yeah... makes it hard to do an IR test at that point don't it? lol



Do you mean from cyl to cyl? The timing from one to the next can't be that different....?

I'll buy that. Although the temperature differences between a CR and 12V can be/are different, I still maintain a fueling difference due to a bad injector can be picked up with IR on either engine.

Don't get me wrong here, I respect your thorough testing. It's all about efficiency now adays though.... We have to be sure the problem is the problem before throwing parts at a customers unit - the challenge is to find faster ways to diagnose the issues. Now, I don't work on Cummins engines at work for the most part, but that efficiency mentality seems to overflow into every day life somehow.... lol

IR may not work 100% of the time, but it sure works often and it hasn't let me down yet.... knock....knock....knock
Also a great way for the do-it-your-selfer to save some bucks, rather than taking time off work and running down to the local fixit shop.
'Course at work I use it as a quick check, but I still have to do the proper testing in the end. Saves some time though.

 

Ok, from what I gather the kill test, or any other test for that matter is not a fool proof way to diagnose bad injectors. I am not as concerned with finding exactly which injector is bad, I am concerned with making sure it is indeed an injector problem. If it is I will probably replace all 6 as well as add better filtration. Let me try to better describe what is going on.

The idle is terribly rough. It shakes the entire truck. Idle to 1000 rpm is ever rougher. It has a noticeable miss. 1000-1500 rpm it smoothes out. 1600 to 1800 rpm it gets very rough again. 1800 to redline is fairly smooth. The truck is bone stock short of a 5" exhaust and at wot it will black the road out for a second until boost builds. It only started doing this recently. There is also a ticking sound that varies with engine speed. Sounds just like a valve that needs to be adjusted, but I just adjusted them all with no change. I have also noticed a slight drop in fuel mileage.

One more thing. When I did the kill test I also did a contribution test. I did not pay alot of attention as I was really looking at the kill test. Best I can remember there were a couple at 100 or just over. A couple in the mid 90's and a couple in the mid to upper 80's. I wish I could remember the actual numbers. I am just really wanting to narrow it down to an injector problem before I throw that kind of money at it. Thanks for all the help.