79jasper
Chickenhawk
The adv(?) Style is a much better design.
Iirc, idioit may have both.
Sent from my SM-G892A using Tapatalk
Iirc, idioit may have both.
Sent from my SM-G892A using Tapatalk
Leaking return lines
- Thread starter Ddizzy77
- Start date
Doesn’t help if you can’t get the whole thing to seal
You can buy my old return lines and try it
Macrobb
Full Access Member
*sigh*. I'm glad some people understand physics around here.
Anyway, to reiterate - the lift pump acts like a supply side check valve... until the rubber valves get crud in them or wear out. It may still push fuel, but doesn't seal well enough to fully stop over-night drainback.
This is why adding a second one helps.
I've done it on several trucks, left the return lines disconnected over night(so air can freely flow into the )and fired it up the next morning without issues.
On the return side, to seal them(because I don't like leaking diesel) I use cheap return line kits from Ebay(I think DCP was the vendor), Viton O-rings, and wheel bearing grease to seal it all together.
I've had excelent luck doing this, and it eliminated issues with "disturbing" the cap causing a leak.
Anyway, to reiterate - the lift pump acts like a supply side check valve... until the rubber valves get crud in them or wear out. It may still push fuel, but doesn't seal well enough to fully stop over-night drainback.
This is why adding a second one helps.
I've done it on several trucks, left the return lines disconnected over night(so air can freely flow into the )and fired it up the next morning without issues.
On the return side, to seal them(because I don't like leaking diesel) I use cheap return line kits from Ebay(I think DCP was the vendor), Viton O-rings, and wheel bearing grease to seal it all together.
I've had excelent luck doing this, and it eliminated issues with "disturbing" the cap causing a leak.
Its happened too many times to me and many other people, to say a simple added check valve in the supply will cure fuel drainback. I am still suspicious. It is getting a little bit over my head, but I am thinking that return line coming out of the injection pump may be where the fuel is draining out when a injector return cap leaks air.
Why hasn't a added check valve solution come up years ago in these forums by very experienced diesel people? I am not saying it won't help, but I am not sure it's a cure-all. Here's a diagram for the 6.9 fuel system from the manual.
Why hasn't a added check valve solution come up years ago in these forums by very experienced diesel people? I am not saying it won't help, but I am not sure it's a cure-all. Here's a diagram for the 6.9 fuel system from the manual.
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diesel fuel flow by D Franklin, on Flickr
Macrobb
Full Access Member
The IP return is never going to drain down. It's got a check valve inside it, holding 5 psi!
Even if if /does/ drain down(say a leaky side plate), it doesn't matter at all. The ip return is for housing pressure, which is simply leaked fuel from various bits of the pump(and a calibrated "vent wire"/leak from the supply side to remove air) - fuel there is never "used" for anything except lubrication and cooling.
Even if if /does/ drain down(say a leaky side plate), it doesn't matter at all. The ip return is for housing pressure, which is simply leaked fuel from various bits of the pump(and a calibrated "vent wire"/leak from the supply side to remove air) - fuel there is never "used" for anything except lubrication and cooling.
No one said it’s a cure all, just something you can do to improve on the stock fuel setup. If you have doubts on its effectiveness try it yourself and resolve that doubt 
tbirdfiend281
Full Access Member
I have never had much issue with my multiple IDI's. They have all had leaky fuel systems to. As long as I had good glow plugs, or the right amount of go juice, they come to life in almost any temperature and 9 times out of 10 don't have too much rough starts.
Even if your lift pump was letting fuel in the supply line between the filter head and the lift pump leak down, your filter would still have enough fuel for starting, it would just run rough after a few seconds. Even if you put the filter in dry it doesn't take a ton of cranking to get the low side system primed. I have a gear reduction starter on my current IDI, if I wanted to I could do every fuel filter replacement without pre filling the filter
Check valves are not needed, you can put one in your fuel system and feel all warm and fuzzy about it, but if an IDI needs a check valve to 'assist' starting and running, there is probably another issue this check valve is band-aiding (or fixing depending on how you look at it)
Besides, the old crowd that use to dominate this forum would almost always swap for a holley pump, an electric lift pump makes all this talk moot. If you are that concerned, spend some cash money and go electric. Running the mechanical pump you run the slight risk of fuel intrusion into the oil pan if the pump does fail that way one day.
Even if your lift pump was letting fuel in the supply line between the filter head and the lift pump leak down, your filter would still have enough fuel for starting, it would just run rough after a few seconds. Even if you put the filter in dry it doesn't take a ton of cranking to get the low side system primed. I have a gear reduction starter on my current IDI, if I wanted to I could do every fuel filter replacement without pre filling the filter
Check valves are not needed, you can put one in your fuel system and feel all warm and fuzzy about it, but if an IDI needs a check valve to 'assist' starting and running, there is probably another issue this check valve is band-aiding (or fixing depending on how you look at it)
Besides, the old crowd that use to dominate this forum would almost always swap for a holley pump, an electric lift pump makes all this talk moot. If you are that concerned, spend some cash money and go electric. Running the mechanical pump you run the slight risk of fuel intrusion into the oil pan if the pump does fail that way one day.
DrCharles
Full Access Member
I got a Facet 40285 (made in USA) electric pump from Aircraft Spruce for $93 plus shipping. For what it's going to save me in batteries and starters, not to mention frustration, it's well worth it!
I always feel warm and fuzzy about upgrades that help my truck, especially when it’s a two dollar part
Works great in combination with my electric fuel pump, another great upgrade for our trucks
Works great in combination with my electric fuel pump, another great upgrade for our trucks
Macrobb
Full Access Member
The only problem I have with an electric pump is varying pressure. If your e-pump will hold a consistant pressure from idle to WOT(within 3 psi), awesome. Unfortunately, I haven't seen that - my Dad's '88 wity facet duralift pushing 7 at idle and 0 at WOT. Really messes with the timing under load.
