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Old 11-11-2009, 04:35 PM
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A challenge to the 7.3 experts

I know that there are over a thousand threads on this topic. However, I think I have tried to read them all and not come across this situation and I know there is an expert out there who knows the solution. Issue: Truck lopes, surges, whatever you want to call it whenever it is below 36 degrees same old story. If truck is plugged in, no matter what the temp, perfect start. I have fought this since I purchased it 3 years ago. Tried so far: Replacing all glow plugs with new Motorcraft plugs and after market plugs and double checked resistances after install, new valve cover gaskets, new glow plug relay and verified length of time it is on and current draw being equal to both sides of motor and mathmatically sound for the measurments taken, removed both batteries and had them load tested and both are new, removed all connections from batterys and glow plug relays including all grounds to the engine block and cleaned-sanded them and re-installed. I have verified the HPOP resevoir is not draining back and has plenty of oil, tried changing brands of oil and filter, checked for poppet valve in oil filter head and it is there and has no issues, and I have tried waiting the full 2 minutes and verifying that the glow plug relay stays on that long and is passing full current to the glow plugs that long with no better result. No matter what I have tried, exactly the same result and I think my wife is ready to kill me. I have no issues with this truck at any other time other than when it is cold and only if I don't plug it in. Ok experts, your turn, I am ready to scream!!!

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Old 11-11-2009, 04:41 PM
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Could be a few injectors dont like to work cold. and how long will this last cuz i think that all of the obs will do this for a few sec. when that cold.
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Old 11-11-2009, 04:44 PM
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It "romps" anywhere from 4-5 times then either dies if it is real cold like around 25 degrees, or it smooths out and idles just fine. Most of the time it "romps" for about 5 times then smooths out, but it really gets me when we're down around 25 all week and it romps then dies, romps then dies, then finally romps and goes into a smooth idle.
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Old 11-11-2009, 04:51 PM
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I would suggest an injector buzz test.
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Old 11-11-2009, 04:52 PM
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What kind of smoke is coming out of it on start up, both cold and warm? Also, what year 7.3, and how many miles?
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Old 11-11-2009, 04:53 PM
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I will try and schedule a buzz test ASAP and let everyone know what they find...
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Old 11-11-2009, 04:54 PM
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hmm maybe be way off but is your glow plugs good? If the oil dont get warmed it will lope like that till little warm.
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Old 11-11-2009, 05:21 PM
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Bought brand-new aftermarket plugs with no change. Removed them, measure them, all were good. Thought maybe it was a mistake to not buy OEM, so I purchased the Motorcraft ZD11's. Measured all of them before I installed them, then verified they were all good after I installed them. Absoultley no change.
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Old 11-11-2009, 05:23 PM
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hmm I guess just check out ur injectors. What kind of oil are you running
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  #10  
Old 11-11-2009, 05:44 PM
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Ok here goes. Mine does it too. When it's cold (depends on the temp for each truck, mine is a wimp so 35-40 and down is hard), the oil is cold, so thick, so doesn't flow fast at all. Like cold molasses. But when you plug in the block heater, it does just that: heats the block. Which contains oil and coolant as well as the cylinders so everything flows nicely and combusts nicely too.
Well on each head there is a high pressure oil rail that feeds the injectors. The rail is only so big so cold oil can only flow down to the end so fast. AND it's a dead head rail, just an end, no loop. Oil enters near the front of the cylinders (#2 on the driver side) from the HPOP and gets pushed to the back (#8). Well in the firing order, #8 is RIGHT AFTER #6. So once 6 fires, it depletes what oil there is in the general area. Since the oil is cold, thick, slow, the HPOP can't push enough oil ALL THE WAY to the back of the rail to the 8 injector fast enough before that one fires, so it gets an incomplete injection. Just a normal engineering hiccup right and just has to be that way right? No.
You can either get some synthetic, an oil with a lower weight for the winter, or both. OR you can get a HPO Xover hose. Just bridges the two oil rails at the #3 to #6 cylinder area. So once #6 fires with that thing installed, you have oil coming from the HPOP AND the passenger oil rail to help replenish the rail before #8 fires. Smooths the idle, ESPECIALLY in cold starts. Makes it quieter. Keeps the RPMs very very steady. Had it on a dyno pre and post HPO Xover install. Pre install the RPMs on the comp were varying by about 50 or so. Post instal, didn't move at all. Ok, maybe 2-3.
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