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I'm sure this has been discussed before, just looking for some feedback on my theory. My truck ran great when new. At 800 miles a slight idle knock began. At 6000 miles the cackle began. Now at 11000 miles I have a loud idle knock and the cackle comes and goes. At first I though it was oil related. Now I think it is fuel. Recently truck was sounding really bad, so I changed the oil in hopes it would clear up the random choppy engine noises. It didn't. Then I filled the tank completely up to check for mileage and went on a 400 mile round trip, all highway miles. Truck ran really strong, and engine sounded great. No washers in the can sounds. Quite smooth, the way it should run, except of course for the harsh idle knock. Got back into the city and parked it. I had a little less than 1/2 tank of fuel left. Later that day went for a drive (city driving-lots of turns and sloshing in the tank) and truck again sounded really bad with the choppy engine sounds. Changed oil again with no luck. So I started thinking. Again filled tank to full and went on a 200 mile highway trip. Wierd sounds went away again, except for #8. Have since kept tank above 3/4's full and engine sounds alright. Now my theory: Some trucks exhibit cackle/idle knock while some do not. NONE seem to do it when brand new. What if the knocking and cackling is caused by damage to the injectors by the introduction of air from the fuel tank, and from what I have been reading this is can happen. What exactly happens to the injector to damage it? My truck ran great when new, so the long-lead injector seemed to be doing its job correctly. Then was it damaged by air intrusion? I know I ran my tank low many times to see how far I could go. If I never let my tank get below 3/4s full would I have a knocker now? Or if I replace my #8LL now with another LL, will it run correctly until further damage occurs. Am I way off base here? Sorry for the length, inquiring minds want to know. Thanks, John |
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You pretty much summed it up, except if there is injector damage it can be any injector or several injectors, the LL injector does not help purge air from the system, it was Ford's way of altering the timing in #8. The damage comes from the aerated fuel and lack of lubrication it gives the plunger and barrel assembly, once the plunger or barrel are scored the injector cannot hold pressure properly during the first phase of injection and it will always fire the main fuel load too early until the injector fails completly and will not fire at all. |
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Sounds to me like you have a classic case of Hutch's air being sucked in pre-pump. And a good case for looking in to his tank and line mods. I assume you are familiar with those threads. A plausible explanation would be that your truck is one that did not develop those leaks for a while. The fact that your engine does okay on a full tank argues for air leaks and against significant injector damage, if any. My truck has an aux tank with a hard pickup and still has the stock pickup intact. I have no difference in performance with either, and my motor has always been quiet. From that I conclude my stock setup doesn't leak yet - it may start tomorrow. What I mean by quiet is at 70, all I hear is road noise and turbine whine. I have run Stanadyne from day one, which may or may not have anything to do with it. Maybe I'm just lucky. Hutch's tank and line mods are cheap and easy - I'd look in to that before assuming the worst about injectors. |
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Thanks Hutch, that's what I was afraid of. Just out of morbid curiosity, I think I will do your tank mods, then replace #8 with another long lead. There should be a lot of LL's floating around out there now! Then on to TT's fix. Thanks again, John On edit: Thanks to pine knot too! You have given me some hope. I have done the pre-pump. It's just that the idle knock is really starting to get to me. I can hear #8 knocking at speed too. An engine is not supposed to do this! Edited by JOHNNYDCON (05/27/02 03:34 PM) |
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Kim lux stated they will all do it eventually, I recently asked that question again, Kim confirmed it, but would not elaborate. My truck gave what I consider good mileage when new 16.25/16.5 now with 38000 I lucky to get 15. I don't have a loud idle knock but I have something on both sides that isn't completely even. As far the cackle goes I cannot detect it. I've lugged it in OD on slight inclines trying to hear it but can't. I do not notice full/low tank sound differences. My oil analysis looks good and oil consumption is reasonable about quart every 2500/3000. I've gotten must updates done, new torque converter, new airbox, swaybar, ashtray. Now comes the WAG [Wild Ass Guess] I think the split shots cause some very weird harmonics in the fuel rails, a couple injectors starting getting low fill on the pre shot, this causes injector wear then the problem gets worse from there. I believe Ford has got another huge liable issue brewing. They will end up pulling the injectors and bore scoping the engines for damage and rebuilding the injectors but that is not a fix. So all the tank mods, regulator mods, cross over are OK but not getting to the root of the problem. Now a good test would be to do all the mods and get your injectors rebuilt. See if engine performance improves. So I'm reading and waiting to see what happens I don't put that many miles on it right now. If Kim can turn up the production of his modified injectors and we start hearing good things about his solution [not his personality]I will consider that route. For now about the most I will do is the pre pump mod, can hurt anything. |
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CKing, I like the way you worded all that. It made sense and gave me a chuckle too. Robert |
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CKing, Based on what I measured HERE and HERE demonstrating the acoustic signature of the same vehicle audibly knocking and not knocking, your WAG of the root problem is what I have made my SWAG - scientific WAG with the only exception being a direct shock/pressure wave and not a harmonic could also be the culprit. Only problem is that simple injector modifications IMHO won't solve the root problem - you have to address these shock/pressure waves or harmonics in some way to break them up. Furthermore, these shock/harmonics could also be releasing entrained air that is not currently addressed by any mods thus far with the exception of the flow thru the heads mods which will change a dead end rail geometry and provide a path for air to not pocket and build up in the fuel rails. Finally, I have to add that significant air intrusion in the pre fuel pump fuel system has to be corrected. Larry |
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Has anyone ever proven that the injectors are being damaged by the air? I've seen one picture in all of these threads with a carbon buildup on the injector tip, I think. |
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Good question I post it as a thread |
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GS, I don't know if you could directly link air to injector damage. What I mean to say is if you pulled an injector and it was bad, could you tell if it was damaged due to air ingestion? I have no clue. |
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Since were on the subject of WAG I thought I'd post mine. I'll try to be short. Has everybody seen the pictures Bob Riley posted of the fuel flow through the heads? http://www.dieselsite.com/miscprod/fueldiagramss.html Now, air will rise to the highest point or points in a system. In the block itself the two high points are the inlet where the cv's are and the test ports. My theory is that air (either Hutches air, pats air or air from combustion back through the injector) is collecting in the aerea of the test port. That air changes the harmonics until the engine will cackle and/or will build up enough to be sucked into the #8 injector causing damage and cackle to occur. Now I know people have set up bleed orifices and such and saw no air there. My though is that it is built up over time. The only logical reaason I could find that Ford changed the feed from the back to the front of the LH head was to avoid the heat of the turbo. Does anybody know why? Ray |
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Although I am not technically inclined I have been trying to search for some research regarding problems with common fuel rails. The link below is to a study that was undertaken to model the pressure oscillations in a common fuel rail. I am not familiar with the engine that was used in the study, albeit it is not a Powerstroke, the genesis of the investigation seems to have been to understand performance issues that were occurring at certain rpm ranges (sounds vaguely familiar). There is an awful lot of pressure testing of this particular fuel rail and discussion of the wave harmonics being produced. I don't know if any of this is applicable to our situation and I hope someone with the technical understanding can comment. www.fs.isy.liu.se/Publications/MSc/00_EX_3081_KA.pdf Thanks Ken |
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Has anyone ever proven that the injectors are being damaged by the air? ------------------------------------------------------------ Yes I have, as a matter of fact TT is performing a test of air and it's effects on injection timing, wear and damage, he is testing 4 sets of 4 or 8 injectors each tested at 1000 hours with the variable being the % of air in the fuel supply, #1 no air in the fuel, #2 10% air #3 20% air and #4 30% air, he has some preliminary data that is very interesting and quite frankly shocking. I will try to get in touch with him to see if he will be able to post the results of his testing. |
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Appearance of knock/cacle theory
