I have the "early" system that uses smaller diameter hose for injectors return line. Would it behoove me to change to "later" system which is larger hose? If so then how? If changed will the connection from hose to metal line behind intake be the only issue? TIA
JASTECH
I would probably use a good dose of diesel fuel before using silicon based products.
Answered on my iPhone.
Answered on my iPhone.
Seconded, I wouldn't use anything with silicone. You shouldn't even use silicone O-Rings or other deals with diesel, it will degrade them. (Makes me wonder about the wisdom of using RTV for the oil pan, since the oil gets contaminated by blow-by.)
Ok, will buy some vasoline. I went ahead and tried to start the truck 3 times, ether, WD-40
and nothing. Looked at intake and took pic of right front injector.
and nothing. Looked at intake and took pic of right front injector.
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Just recieved notice, type4 will package a custom kit for my old girl with over 200k miles on factory injection lines and caps. I am feeling better now! You guys ROCK!
They are for drain back only, then why increase size? Maybe as said that the larger line is cheaper. I need to look it up as I can't grasp the line being under the supply and not assist in some way. Is there a valve that opens after engine is off that allows the drainback?
Like any diesel engine only a small amount of fuel is injected by the injectors compared to the fuel volume that is bypassed past them and returned to the fuel tanks. It's continually recirculating while the engine is running. To give you an idea, the drainback hose on a big diesel is something like #12 AeroQuip hose (3/4" I.D.). In icy cold weather you get your thighs warmed up leaning against a saddle tank while fueling up. There's a LOT of fuel circulated through the pump, heads, etc, then returned to the tanks and it's plenty warm. And with all that which is recirculated, a big Cummins NTC 855 Cu.In. engine will only use one measly gallon of fuel per 45 minutes of idling.
LMJD, Thanks! I need schooled on this diesel stuff, alot different then my old gasers. So is the same high pressure of our injectors (1850psi) the same as the IP needs to out put? So there is a "volume" of fuel supplied to a cavity in the IP by the uplift pump? Then via the engine cranking/running the IP then increases the fuel pressure to 1850 per line to cylinder in proper order? The excess flow that doees not go to IP is returned to tank? This all makes sence except why the need for return lines on the injectors? Sence the T's sit on top of the injectors, how is there no hi-pressure in return lines?
The fuel pump (which is a classic pump used since back in the days of carburetion) pumps fuel into the filter at somewhere between 6 and 12 psi which then passes through another line to the Injection Pump. The IP contains a transfer pump which pulls fuel from the inlet and feeds it to the cylinder inside of the IP. If this pump pulls fuel as fast as the lift pump can provide it, then the pressure in the filter head becomes low. If the lift pump provides it faster than it can use it, that passes out of the line on the filter head that connects to the return system. The IP pumps the fuel at high pressure through the hard lines to the injectors. The IP is cooled only by fuel so it is necessary to have excess fuel passing through the IP and being returned to the tank for cooling via radiation and contact with air passing over its surfaces.
Note that this diagram is funny because the fuel tank is placed in front of the vehicle instead of behind it, and it omits the tank selector valve in the process for simplicity's sake.
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The uninjected fuel is released through two holes on the sides of the upper part of the injector. An O-ring seals the cap above and below these holes. As long as the fuel is not impeded from this point to the tank, the pressure remains low because pressure is caused by resistance to flow. There is some resistance to flow caused by turbulence while passing through the return lines, but there is nothing else of note to restrict the flow.
The pickup unit (which also holds the fuel level sender) has two hard lines on it, one for pickup and one for return - the pickup line has a rubber foot with a bypass valve on the side in case it gets clogged, while the return line is terminated with an anti-siphon nipple, which is a little piece of rubber with a sort of slit in it that opens up when fuel flows through and more or less closes off when it stops. This is less effective than an actual check valve, but also introduces far less restriction as there is no spring to work against.
When we discuss the pressure induced by turbulence in a hydraulic system (and this is one, of course, as it depends on a working fluid to transmit force to do work, namely opening the injectors and spraying fuel, which is also the working fluid) we refer to it as pressure drop as it affects the pressure coming out of the other end. However, there is no need for pressure in the return, because no work is done there. Increasing the size of the lines in the return system decreases the pressure drop, which is another way of saying that it decreases the back pressure, or the resistance to flow. Fuel delivery was increased for the 7.3 engine and it is increased still more for turbocharged models, so it would make sense to increase the size of the lines.
Note that this diagram is funny because the fuel tank is placed in front of the vehicle instead of behind it, and it omits the tank selector valve in the process for simplicity's sake.
The uninjected fuel is released through two holes on the sides of the upper part of the injector. An O-ring seals the cap above and below these holes. As long as the fuel is not impeded from this point to the tank, the pressure remains low because pressure is caused by resistance to flow. There is some resistance to flow caused by turbulence while passing through the return lines, but there is nothing else of note to restrict the flow.
The pickup unit (which also holds the fuel level sender) has two hard lines on it, one for pickup and one for return - the pickup line has a rubber foot with a bypass valve on the side in case it gets clogged, while the return line is terminated with an anti-siphon nipple, which is a little piece of rubber with a sort of slit in it that opens up when fuel flows through and more or less closes off when it stops. This is less effective than an actual check valve, but also introduces far less restriction as there is no spring to work against.
When we discuss the pressure induced by turbulence in a hydraulic system (and this is one, of course, as it depends on a working fluid to transmit force to do work, namely opening the injectors and spraying fuel, which is also the working fluid) we refer to it as pressure drop as it affects the pressure coming out of the other end. However, there is no need for pressure in the return, because no work is done there. Increasing the size of the lines in the return system decreases the pressure drop, which is another way of saying that it decreases the back pressure, or the resistance to flow. Fuel delivery was increased for the 7.3 engine and it is increased still more for turbocharged models, so it would make sense to increase the size of the lines.
Wow! (looks for apple to give) So when ypu turned up you IP 2 flats, this is a screw on the IP it's self? This increases the fuel pressure to the injectors I assume? If so the injectors pop at 1850psi and not turn upable, how does this work?
JASTECH, trying to stick to what you asked (what time is it?, not how do I build a watch? :jester
, first IIRC our resident pump guy who rebuilds them for a living, has said the pump actually puts out way more than the 1850 PSI that the injectors fire at. Thought he said something like 20,000 PSI. Although the drainback caps and lines are directly on top of the injectors they are isolated from the high pressure side. The injector orfices in the injectors are such that the extreme high pressure remains on the inlet (pump side) of the injectors and the excess fuel is bled off on the drainback side (caps) at very low pressure and it returns to the tank with some recirculating back through the filter. As far as turning up the pump, years ago when these engines were fairly new the injection shop owner who our truck shop dealt with told me it increases the fuel rate (not the 1850PSI) and only at wide open throttle.
![Image]()
, first IIRC our resident pump guy who rebuilds them for a living, has said the pump actually puts out way more than the 1850 PSI that the injectors fire at. Thought he said something like 20,000 PSI. Although the drainback caps and lines are directly on top of the injectors they are isolated from the high pressure side. The injector orfices in the injectors are such that the extreme high pressure remains on the inlet (pump side) of the injectors and the excess fuel is bled off on the drainback side (caps) at very low pressure and it returns to the tank with some recirculating back through the filter. As far as turning up the pump, years ago when these engines were fairly new the injection shop owner who our truck shop dealt with told me it increases the fuel rate (not the 1850PSI) and only at wide open throttle.All diesels have one type or another, fuel has to recirculate so the pump doesn't stall out, here's an injector from a Detroit, inlet and outlet:
LMJD, that explains it very well. So then the IP puts out 20kpsi and injectors pop/open at 1850psi, so the 20kpsi is to keep up with the 8 injectors at 1500rpm. So there must be a pulse of fuel timed to each injector via the camshaft some how? How does the injector open up at the correct time as there are no wires?
The injectors are mechanical, so they "pop" when the line pressure reaches the correct pressure. The IP is timed via gears to the crankshaft. the Cam shaft is timed via a gear to the crankshaft. Everything is pretty much set and doesn't change while your running the engine. the "pump" inside the IP has a rotary set of passages, and the plunger will charge (pressurize) the right line based on the order of the lines. This is a very simple explanation of the IP and how it works.
Old school gassers used either vacum or weights to advance the spark timing, computer controlled gassers use a series of sensors to set the timing. The computer controlled diesels use sensors to alter the timing of the injectors.
Old school gassers used either vacum or weights to advance the spark timing, computer controlled gassers use a series of sensors to set the timing. The computer controlled diesels use sensors to alter the timing of the injectors.
I am so use to the "old gasser) way, was a mech for years on them. So other then a battery for GP's and starter, electric is not needed on these older diesels? Can I use Simple Green to clean engine before I start the R&R of fuel return line kit?
It's perzactly (love that word) as Chuckster posted, on the IDI's the pump gear is timed correctly with the cam gear which in turn is timed with the crank gear. The injectors on the old 2 stroke Detroit and Cummins diesels were each triggered by a camshaft lobe but that's same principle but a different system.
You can use Simple Green, I always cover the alternator, etc, but a better one that Chuckster put me on to is Super Clean, comes in a purple jug.
You can use Simple Green, I always cover the alternator, etc, but a better one that Chuckster put me on to is Super Clean, comes in a purple jug.
Ahh yes, Super Clean. I have what's left over a gallon jug from over 10 years ago, lol..So mix it or spray consentrated?
Works best on a warm engine, not hot!! I use a old spray bottle and mist the engine, let it sit for no more than about 5 minutes and hose it off. DO NOT let any water enter the intake.
Ok, can't start engine to warm it but can leave the hood up so the 106+ temps. will warm it up. I will put bag over alternator or just remove it. I am ordering a large case 200amp one wire alt. so that should take care of my electrical demands?
Alot of good info, but be cautious. My 89 7.3 had the small diameter and, due to emergency circumstance, is using both diameters. I believe the part 69120 is the small and the 73120 is the larger. Nipples on caps of small feed into center of cap, the larger is offset. Also clamp color is critical and revealing. Green = small: Red = larger. There is also a variance in path of return line from top of IP on mine, it enters a hard tube immediately that feeds to the tank, the larger goes to the front drivers-side injector
I always assumed the drainback 1/4" size started with the first 7.3 engines but I was in the Stanadyne pump shop in Montana a while back and he gave me the smaller end cap, then he talked like some of the early 7.3's had 3/16". I didn't know if he was right or wrong, with all the modern systems he has to stay on top of, can't expect him to remember 100% everything on 22+ year old fuel lines.
Yep, the drainback hose routing is quit a bit different if you install an ATS turbo.
My "research" via part fitment guides and forum posts indicates the same thing, early 7.3s had the smaller lines.
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