1999 F-350, XLT 2 WD 7.2 diesel
Recently I replaced all the injectors. 7 of the "normal and one special type for cylinder 8.
The truck got 19MPG at 70 -75 MPH which is as good if not slightly better than usual.
It starts up immediately and seems to have all the power that it ever did. Current mileage is 237,000

After the truck is up to operating temperature and at an idle II feel a single 1-1 engine revolution vibration. The engine just sort of "throbs".

Thoughts on trouble shooting?

Thank you in advance.
Regards,
Eric

 

 

Had two fault lights indicating 3 and #8 injectors were not contributing to power. 237,000 i figured if i have to do one from each side then i'l do them all.Injectors were from Ruxer and Reman Auto Electric.
Above Idle the vibration seems to go away but that may be because the rest of the engine is masking the effect?

Eric

 

 

Haypower,
Thank you. I'm going to do that this evening.
Eric

 

So I did a cylinder contribution test last night. Now it says 4 and 8 are malfunctioning. I plan on removing the valve cover to see if one of the wires is pinched or otherwise goofed up.
This is getting a bit odd.
Eric

 

Did you buzz test the injectors?
Give the UVC harness/s and cover gasket connectors a good inspection as well,.
If it all looks good, passes buzz, injector health sometimes will show up in the oil amounts being expelled from the injectors exhaust manifold. Since the injectors can fail two ways, solenoid end or hyd/mechanical side, generally one or the other will show up... Truck hasn’t had any prior fuel quality issues?

 

Passes buzz test. Ran it several times over a couple of weeks. I am going to look for the oil output from the injectors oil "dump tube".
I did have both the screens totally clogged a month ago and drained cleaned them and put in a new mail fuel filter. After that is when I replaced all 8 injectors based on #3 and 8 failure code.
Thanks for the help and input., More to follow later this weekend.
Eric

 

Follow up report. I removed the driver side valve cover and examined the wires and connectors to each injector and glow plug. Everything looks fine with no damage or pinching of the wires.
BUT... I did notice the following Part number problem.
#8 has an AE injector
#6 has an AB injector
the rest are AD injectors
Would this cause an issue with smooth running/idling after warm up or cause "confusion" in the mind of the Injector control module?
Thanks in advance.
Regards,
Eric

 

The AE identifies the Long Lead ‘ LL’ injector.
After installing the LL injector the PCM (if not done prior) should be reprogrammed so that it doesn’t flag #8 in future balance tests, or as an invalid code/performer..
The difference between AB and AD is generally the amount of fuel they can flow. AB being slightly less than its counterpart, but depending on builder etc , they can can equal on a flow test. That said, if a mismatch, the potential for balance to be off slightly exists..
Being you had fuel quality issues before, the potential the new injectors got a taste is there. Especially if it was H20 in any concentration.
The reason the LL was used was because of its location,, last in the food chain for fuel availability causing cackle. If your truck was prior reprogrammed, and #8 still fails balance, check for a minimum 55lbs of pressure. If fuel pressure/volume is the culprit normallly drivability will be affected though..
As a test to back up diagnostic results, you can also ‘carefully’ disconnect the injector connector under idle conditions and tell weather or how much the cylinder is contributing. The difference should be a decent thump. Again,, high voltage so if manually disconnecting, use care and caution...