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Discussion Starter #1
Have owned 3 of these in the last 15 years. Currently fighting the common start in morning run for 5 seconds & die problem. Installed new return line kit, didnt fix problem, lift pump yesterday, didnt fix problem. My question now, in what manner does half the fuel leave the filter? does it bleed back thru pump? or back thru return line?

This is my work truck, so I have to run it everyday, if everything works out I should be able to burn up a starter by the end of the week.
 

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Have you checked the line from the filter to the IP? It can drip onto the valley pan and you won't see it. I suppose if you have the cap off the Schrader valve, it might allow air to suck in while the line leaks out.
 

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You've got two rubber compression fittings on each end of the line Chuckster's referring to. If they need tightening or replacing that can be your problem. But you don't want to tighten them real tight like a flare nut fitting. IIRC you've got them on the steel line from the transfer pump to the filter too.
 

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Discussion Starter #4
I'm sure it's something stupid, amazes me how you can buy something that's patched together with different color caps, hoses, clamps & it works fine for about 2 weeks then goes completely to crap. Now the fun part of dumping money & time chasing problems..
 

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If you take a straw and put it in a glass of water then hold your finger on the top, withdraw the straw, the water will stay in the straw, let air in and the staw will empty, same thing as a fuel system, if air gets in, fuel will return to tank. the Olives that seal the steel lines from filter to IP pump get hard and no longer seal, all you have to do is bump that line and the old ones will leak air in. Dieselorings no longer carry them, but an IH dealer might.
 

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Any decent parts house or injection shop, they're commonly used in all sorts of applications.
 

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I will confess my sin:: I used 2 Viton O rings stacked at each end. Been perfect for 3 years now! Statute of limitations is over, right?
 

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Discussion Starter #8
Probably what it is, last night I pinched supply line off behind lift pump & it started this morning. Filled up with fuel today so it will behave till it gets down to 1/2 tank. I can see why people go to an electric pump setup. $25 I could add 12 volt on/off valve on supply line behind lift pump.
 

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Probably what it is, last night I pinched supply line off behind lift pump & it started this morning. Filled up with fuel today so it will behave till it gets down to 1/2 tank. I can see why people go to an electric pump setup. $25 I could add 12 volt on/off valve on supply line behind lift pump.

or just fix the problem correctly and have it last another 20 some odd years?
 

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Discussion Starter #10
Have replaced all the common things including the 70's technology olive seals, this is a good engine with a lousy fuel system. Air intrusion has always been a problem on these, then on top of that the only way to bleed system is with starter. Was looking for more ideas on other ways to repair system. I drive this 25-30k mile a year, fascination about a 20 year repair makes no sense, I'm sure I will have moved on to something else & there will be far fewer of these around.
After all I have read & tried myself, I will be going to the holley red top electric pump setup.
 

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good luck with that, I just did mine properly, now it starts perfect every time and cost less then the electric pump., but as they say your cash!
 

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I have similar problems. I've changed all of my return lines and olives. Installed clear lines in key points. I'm still getting air in the coming off the front of the IIP. I have switch installed for instead of the come temp switch. Here's what happens when i switched it off. Any ideas?
 

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Discussion Starter #15
Follow-up.
Truck went to starting half decent again, so my electric pump just rode around with me. As soon as the cold weather hit 3 weeks ago, the thing went completely to hell. Have been putting battery charger & plugging in at night, the final straw was Sunday, went out to start truck at 9am & finally got it going at 11:30am.
Stayed up late & converted to electric pump, bypassed the mechanical pump. This has made the truck as reliable as my old Mercedes. This week has been awesome, no more battery charger, just plug in at night, in the morning while the glow plugs heat up the electric pump primes everything & starts instantly, no hesitation, just idles perfect. Runs down the road great, best thing I have done to one of these.
 

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Well, I'm on my 2nd 7.3l IDI and I've owned or worked on plenty of GM 6.2l & 6.5l diesels, which have the same fuel system for all intents & purposes, and have never had any undue trouble with either the mechanical lift pump or air in the fuel system. I have had leaks in the return lines, but replacing them took care of that in every case. With the 7.3l it's important not to disturb the return like caps any more than absolutely necessary, which is why the best way to replace them is to remove the system completely and make up the new one on a bench. Then you can install it in 1 shot without having to rotate the caps to connect the lines.
 

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Discussion Starter #17
Well, I'm on my 2nd 7.3l IDI and I've owned or worked on plenty of GM 6.2l & 6.5l diesels, which have the same fuel system for all intents & purposes, and have never had any undue trouble with either the mechanical lift pump or air in the fuel system. I have had leaks in the return lines, but replacing them took care of that in every case. With the 7.3l it's important not to disturb the return like caps any more than absolutely necessary, which is why the best way to replace them is to remove the system completely and make up the new one on a bench. Then you can install it in 1 shot without having to rotate the caps to connect the lines.
I have no idea why you guys jump into threads with 6.2 & 6.5 knowledge, 6.2 is garbage, 6.5 fuel system is worse than 7.3 because they added electronics to it. Point is this is a delicate troublesome fuel system & what I've posted is a alternative way to fix a problem. It's a proven fact with the early duramax that the best way to cure injector failure is adding a electric air dog pump system. IHC finally went to electric pump in late 90's, it's 2014 & there are better ways to fix things now.
Also this is my thread & I'm tickled with my truck now, had a great week financially because the truck started everyday, these are a business not a hobby, the 3 hours I lost Sunday would have paid for electric pump & coffee. I started this thread out of frustration & ending it with a solution.
 

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Because the 6.2 has a nearly identical fuel system as the 7.3l, and the only difference with the 6.5 is the electronics. The IP operates the same way. Same goes for Onan 4L23 and 6A34. But fine, you don't want the point of view of someone who's been operating and working on DB2 systems with flexible return lines for close to 20 years now, and whose idea of how to repair a problem isn't to slap an electric fuel pump bandaid on it, it's no skin off my back. Good luck.
 

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And did you just mention the Duramax after calling me out for mentioning the. 6.5l in a thread about mechanically injected diesels?
 
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