I have a few things to say:
a) I am not trying to start a war here, nor poo poo on anyone's efforts at providing information or getting this issue resolved. I think that there is quite a bit of mis information on these forums and even more information that gets repeated again and again, that doesn't need to be.
I originally asked for the forums to be separated as they are now and I thank the powers that be for doing so. I am now requesting a separate FAQ or FAQ item that chronicles a bunch of the known information or theories so that the mis information and repeated information is cut down.
b) For the record, my truck didn't have the knock, then did, then I shimmed up to 100 PSI, then it didn't knock, now it knocks, but my regulator is whining, so... I probably need to check my fuel pressure again.
c) Harry: thanks for the vote of confidence, but I am much too busy with my real life to moderate anything, let alone a forum. I would be happy to contribute *haphazardly*, but not carry any responsibility.
d) JLester: I think that Ford fed you a line:
"First of all, we didn't have a single truck with the fuel cackle (out of 60)."
This is telling in and of itself... this forum seems to indicate that about 45% of the trucks cackle at one time or another and no one has isolated when and why they cackle (or knock) and when they don't... if you had 60 trucks with no knocking, you may have found one of the conditions whereby they don't knock.
Furthermore, you said in your purchase post that you only recently rode in a 99 or new PSD lately... you may have missed the knocking in trucks where it was plainly audible to its owners. Did you query them or did you casually listen to their trucks ?
re:"Aside from that, we did find out what causes the problem. The problem (as we thought) is related to fuel pressure to the #6 and #8 injectors."
OK so far...
re:"They fire sequentially and are right beside each other on the fuel rail. When the #6 injector is sending it's main squirt into the cylinder, the #8 is just beginning the initial squirt (from the split-shot injection)."
I don't buy that. An 8 cylinder engine will fire a cylinder every 90 degrees (720/8 = 90...) Lets say that at idle an injector starts the pilot injection at 10 degrees BEFORE TDC. (This is a Cummins idle spec.)
In order for there to be overlap with the previous cylinder, it would have to be still injecting at 80 degrees after TDC. This would be a phenominally LONG injection cycle, as normally the injection occurs all at once (20 degrees ?), so that maximum power is gotten from the fuel way before 90 degrees. (180 degrees is BDC...) Why way before 90 degrees ? Well, one wants maximum push on the piston before 90 degrees, because when the crankshaft is at 90 degrees, it produces maximum torque from the piston force. If one was injecting fuel at 90 degrees or later, most of its expansive force is lost because it is so late in the piston travel.
Secondly, the knock is most prevalent at idle. On a PSD, the amount of fuel is controlled by the duty cycle of the injection. At idle, the engine is using hardly any fuel and the injection should be the pilot shot followed by a tiny secondary shot. (The time between the pilot and main injection is fixed on a HEUI injector.) At wide open throttle at maximum torque, the fuel injection duration will be MUCH longer. How much longer ? At idle a warm PSD will burn about a gallon an hour. At wide open throttle, a PSD with a BSFC of .4 pounds per HP HR will burn about 14 gallons per hour. Thus, at maximum power, the injection duration should be about 14 times longer than at idle. I say "should be" because the injection pressure will be raised at higher power levels and more fuel will be injected faster, but the ratio should still be 7:1 or so.
One could easily verify this with a Ford scan tool, a hill and a big trailer...
One more thing... as engine RPMS go up, the timing needs to be advanced. I don't know, but I do suspect that at higher RPMS 20 or more degrees before TDC would be the norm.
Now, if the knock was caused by the two injectors' firing patterns colliding at idle, the collision would be 10 degrees worse at higher RPMS. The knocking trucks that I heard tend to smooth out at higher RPMS, but maybe this is a masked effect... I don't know !
re:"Due to manufacturing tolerances, there may not be enough fuel pressure available in the rail to support both injections."
I totally agree with this statement: the number 8 injector is probably starved for fuel. I don't know what or why something knocks. I agree with Harry: lack of fuel at a cylinder shouldn't make it knock.
re:"The recently issued TSB should take care of the problem."
This I don't buy. I don't know what they could have done to the number 8 cylinder to prevent the starvation, especially if it is due to an OVERLAP in injection processes. Futhermore, lets say that the injection process at idle is 80 degrees. The new injector is called a long duration injector and the TSB tells us that the ECM must be reprogrammed to not report a cylinder contribution test failure... if the old duration is 80 degrees, what is the new duration !
Here is my *guess*: the knock is caused by the multiplier plunger striking the injector body when there is not enough fuel in the injector. To get around this problem, Ford put more distance between the pilot injection port on the injector and the real injection port. But why ? However, to get this to work properly they need to reprogram the ECM for a longer injection pulse because there is now a longer wait between the pilot injection and the real injection. The injection period is now going to be longer. If I am correct, this will decrease the power and fuel efficiency of the engine.
re:"All trucks being built now also have the fix."
What these trucks need is a redesigned fuel delivery system, not a new injector.
I really wish that a few Ford engineers would join us for a Chat session for a few hours, so that we could clear this all up. Personally, I think the lack of information, the mis information and Ford's silence have made this whole situation *much* worse than it needed to be.
Kim
