My 99 F350 has a rough idle and very low power until the engine warms up, and I'm thinking it might be an injector problem.

This past weekend I pulled the valve covers, inspected and cleaned the UVCH connectors, resistance checked the injectors and glow plugs and re-torqued the injector bolts. I checked for wiring harness chafing, removed, cleaned and re-installed the IPR (with new o-rings) and installed a new ICP sensor. That work improved the idle somewhat and quieted things down a lot, but she's still got problems from a cold start.

I would like to try a few injector tests next but I need some help understanding what I see and hear.

If I buzz test the injectors cold, how will I know if one is having trouble? I have read that the sound will be different but how? quieter? different tone?

If I look at the oil discharge from the injectors while the engine is warming up I know they should all be pretty much the same. How much discharge pressure and volume should I expect?

Are there any tests I can do with AE that will check injectors with the engine cold? I believe the EOT has to be around 130 to do a cylinder contribution test, is that correct? Any other tests I'm missing?

Is the rotational velocity test of any value?

While I had the valve covers off I noticed that injectors 1,3 and 8 were marked with the letter R. Does that mean remanufactured? Why would only those 3 have been replaced ? Might the other 5 be on their way?

A few other observations: All injector coils were 3.3 ohms, all glow plugs were 0.9 ohms. The GPR checks good and the engine never blows any smoke, starting or running. Injection pressure is around 700 psi w/ 12% duty cycle at cold idle and drops to around 500 psi w/8% when warm. Fuel bowl is clean and was recently o-ringed. Fuel pressure is steady at around 60 psi. Oil is full and clean, there was no gunk at all under valve covers (IPR was clean too). Engine has an exhaust leak at turbo exhaust clamp and possibly up pipes as well.

Chris

 

This is how a good (cold) buzz test should sound (in stereo).

Stinky Injectors.MP4 - YouTube

This is what a bad injector can do, so two of mine were replaced with remans to get rid of the noise.

7.3L Injector Noise - YouTube

I'd get those exaust leaks fixed as soon as possible, I know from experience that exhaust leaks make a huge difference in performance.

 

Thanks for the videos Tugly, reps sent. They were really helpful as a comparison when I did a cold buzz test today.

Now for the bad news : 2, 6 and 7 sound muted (quiet, not crisp) when buzzed cold. They improve somewhat after the engine warms up, but not loud and sharp like 1 and 8.

So I guess my next job is to search the fuel injector threads looking for a good rebuilder.

Chris

 

I think that identifying worn injectors is about the hardest thing for me to do with these engines. From what I gather, the best way is to take them out and have them flow and pressure tested but if you are going that far then rebuilding them makes sense while they are out. I have my injectors built by Jim at Rosewood Diesel (Rosewood Diesel Shop) He does a really nice job. I highly recommend brand new nozzles....even if your originals are flowing to spec. It's just something that I feel should be changed as a part of every rebuild....(just my $0.02..)

In response to some of your questions in your original post...
The buzz test while cold is more likely to highlight possible injector issues. I am not sure why exactly....maybe has something to do with oil temp? Sometimes a suspect injector will have a muted or soft sound when the buzz cycle comes around to that cylinder. Keep in mind what actually happens during a buzz test....
There is a long initial buzz command sent out to all 8 injectors. This is a hard buzz for all 8 at once. Then the IDM will buzz each injector in order (1, 2, 3, etc). However, the individual buzz is still all 8 injectors at once but the difference is that the specified injector is hard buzzed while the remaining 7 are soft. So, this means a totally dead injector will still produce a buzz...but it will be muted or soft, which is really the OTHER 7 injectors soft buzzing. (I hope this makes sense...)

Looks like about a table spoon of oil is discharged during each injection event at idle.

Each vehicle is slightly different but the oil temp needs to be in the 130-140 range before AE will run the CCT.

Rotational Velocity and Cylinder Contribution Test is essentially the same thing. The CCT test is more effective if preformed while in gear, idling and foot on the brake (A/C off)

I have no idea what "R" means on the injectors but it's not uncommon to only replace a faulty injector. There is no reason to replace all 8 injectors when only one is bad.

If you use Rosewood for injector rebuild....get ready for a super smooth idle.

 

Thanks for the info Greg. I didn't know about the way buzz test works, but I do understand your explaination. My next move will be to compare oil discharge from the injectors with the valve covers off and the engine cold. While I'm at it I might do a compression test too (after the engine warms up).

Chris

 

I'm glad that buzz test video was helpful. One other piece of info - 3 and 7 were replaced with remans last summer, and I've listened to that video a gajillion times with the hi-def audio on the PC. I can't hear any difference between 3, 7, or any of the other injectors - except for distance from the microphone. I'd say my injector solenoids are doing their bit, but that doesn't tell me if my o-rings or nozzles are still good. I am on the fence about replacing them with stage 1s, so I will likely wait until I have an issue. I am also likely to pull them, inspect them, and put new o-rings in there.

If you have a bad buzz test, your scenario is more "digital" (yes/no). At least your situation is not as amibiguous as mine... and that is not entirely a bad thing. You have an answer and you need to spend money soon, but you can budget for it and you'll be good to go for a very long time after that. Without the AE, you'd be in the dark until a failure - and no option to plan/budget for it.

 

That's pretty much why AE was one of my first purchases. It's an essential tool for troubleshooting, but I don't always have the experience to understand what I'm seeing. That's what makes this forum so amazing, the knowledge and insight on here are priceless.