85 Jimmy Air Leak

[crdpoker]

Hi Guys,

I've searched the forum quite a bit, but haven't found anyone with my specific problem. I just purchased an 85 jimmy (identical to K5 Blazer) with the 6.2, and I I'm leaking air somewhere into my fuel system.

With a full tank, the truck fires right up with little cranking, but after a 15 mile drive or so, it starts to surge and sputter eventually dying. Sometimes it will crank right back up and run for a little bit, but then ultimately it won't restart.

The only way I've found to get it to fire back up is to bleed it at the square filter element box on the firewall. If I have someone open the bleed valve while I crank, air spurts out until its bled, then once diesel is shooting out, the valve is closed, and the engine roars back to life (at least for another 10 or 15 miles). I know that air is getting into the system somewhere, and I just discovered a small fuel leak around the lift pump, but can't be certain if it's coming from the pump itself, or higher up.

Whoever installed the last lift pump seemingly did a bad job of it, because it's loaded with permatex sealer around the base. The truck came from up north, and is pretty rusty along the frame, so is it possible that there is a small leak in the metal line, and it's allowing air in? My questions are:

1. Does the air in the filter mean that it's leaking from before the filter (tank side) or after it (IP Side), or is it tough to tell, because it's the high point in the system?

2. I'm really tempted to just rip it all out and put in 1 solid rubber line from tank to filter, with an inline electric pump. It woud really save me a lot of wear and tear on the starter and batteries from trying to get it bled. Has anyone done this recently, and can give me some pointers on line diameter and routing?

Anyone out there with any help would be great, as I'm about to just start ripping everything out due to frustration.

Thanks,

Chris

[DmaxMaverick]

Welcome to the Forums!

A leak near the fuel lift pump is a clue. If it leaks with engine running, it won't likely be the cause of your sputtering/dying. It will leak fuel out, not air in. If you get air after it sits for a while, this leak can cause that. Your air leak will have to be before the lift pump, which is before the filter. It doesn't sound like you have an air leak between the filter and IP. Since you are able to bleed it by cranking, the LP is working. Like you, I'd suspect a rusted line, or a hose/line connection. Pressurize the system with shop air (less than 5 PSI at the LP inlet line) and locate leaks. Fix the fuel leak(s) and you'll likely find your air leak. The fuel system is: Tank -> LP -> Filter -> IP (with tank return) -> Injectors (with tank return) -> Tank. Most of the pumped fuel will actually return back to the tank. While you are at it, replace the LP. They are cheap, and easy to do a correct job. No sealer should be used if the block or cover plate isn't damaged, gaskets are fine.

I would not suggest replacing the steel line with rubber hose. If you replace it, replace what you remove with like materials. It isn't that difficult to do it right, and there's no rule that says it has to be one continuous piece. You can use flare or compression fittings/unions (brass is OK) between difficult bends/obsticles. Use steel or SS tubing, not copper or aluminum, and secure it well to prevent abrasion. Steel tubing can be painted to prevent corrosion, if you have a mind to, but if the truck is pretty rusted, I wouldn't mess with it.

[Robyn]

Two other good posibilities
Bad fuel lift pump and or a leak in the tank pickup unit or surounding connector hoses.

As maverick said these are an easy and cheap fix. Take your time and be thorough with your tests.

Another overlooked issue can be a fill cap that is not venting properly and is allowing the pump to suck a vacuum on the tank

Far too often these little critters will leak air from the tank pickup tube into the system..

If you pull the line off of the pump where is jumps from the frame and cork it up with a new hose and a suitable plug then unhook the line where it connects to the tank and do the same with a fitting that you can add air too. Look for leaks along the frame.

The tank unit is almost easier to just replace than mess with.

If it starts looking like a tank pickup just drop the tank and get a fresh one.

A new fuel pump wont hurt either as the one on there most likely has a zillion miles on it.

Let us know

Robyn

[crdpoker]

Well, after the last couple of days, I think I am proud to report that all of my problems were being caused by an incorrect fuel cap. I had heard the whooshing air noise whenever I had filled up, but just assumed it was positive pressure in the tank blowing out. Now that I've removed the cap, I haven't had so much as a sputter in the last 50 miles.

Some of the lines, both supply and return are leaking, so I still plan on replacing them and swapping for an electric pump. Right now it's a hacked together horror story that the previous owners did, and I think it changes from rubber to steel and back about 8 times between tank and IP.

Question: Where does one go about getting pre-bent lines for an 85 Jimmy. Even in LMC truck, they only have the ones for gassers. Or is it really pretty simple to bend and flange my own together? Also, where do I get the proper fuel cap for this tank, I haven't found one that says its definitively for diesel.

Thanks for the help to everyone, my Jimmy is much happier now.

Chris
Austin, Tx

[Robyn]

Try the bone yards.

You can buy the ready made stuff at the parts house and do your own.

Keep the rubber to a minimum though.

The original had rubber between the tank and the lines at the rear and then steel all the way to the front then rubber to the fuel pump. Then steel up across the engine from the pump and rubber to the fuel filter.
Rubber from the fuel filter to the final pipe down to the IP.

Be sure your return lines are good too and not plugged.

Good luck

Robyn

[mfletch]

Hello all, having air trouble.83 1 ton with dual tanks. Did a search and came up with many threads about air leaks. This seemed like a good one to post to with my problem. I've read several post regarding air leaks and I'm slowly getting and understanding of the problem. I see potential for problems all over. I'm confused on how the fuel lines are routed. I have two fuel filters. One is a smaller one mounted behind the intake manifold for the Banks turbo. The other one is about the size of a typical oil filter and is mounted to the firewall on the passenger side. The fuel line from the tank goes directly to the big filter and then to the lift pump. Then from the lift pump to the small filter. Then to the ip. What confusses me is that I read somewhere that you should open the top bleeder on the big filter to purger air, but this would just suck air wouldn't it? I opened the outlet line on the small filter and it is pushing fuel. I loosened all the injectors but nothing is coming out maybe a little dribble. The other area that I think may be suspect is the switching between tanks. Doesn't seem to be working right and I think the sending unit is screwed up. I guess I should have check to see if there was fuel in the tank. I just assumed that I was empty. Anyway I got air in the system now and having trouble getting it out.
Also I have a third line that comes out of each tank and goes to a petcock mounted on the frame, so sort of bleeder, but its above the level of tank.
Any help is greatly apprieciated. Thanks

[ccatlett1984]

most of the trucks dont have two fuel filters, yours has had a filter added to it.

the factory routing is
fuel tank > lift pump > filter > IP


If you are getting flow to the small filter your lift pump is good. I would then check your fuel cutoff solinoid in the injector pump. There is a large pink wire that goes in the top of the injector pump. turn the key to the "run" position with the vehicle off. then pull the pink wire from the top of the injector pump, you should hear a click, you should hear another click when you pulg the wire back into the pump. if you dont, then your fuel solinoid is bad, its a user replacable part.

[DmaxMaverick]

most of the trucks dont have two fuel filters, yours has had a filter added to it......

1985+ has one filter. 1983 had 2 filters, OEM. One on the firewall, and one at the back of the manifold.

[ccatlett1984]

ok, I stand corrected :o

[mfletch]

1985+ has one filter. 1983 had 2 filters, OEM. One on the firewall, and one at the back of the manifold.

Thanks for the replies. So this is the normal setup. So is the fuel routing correct. tank > big filter > liftpump > small filter > ip

[DmaxMaverick]

Thanks for the replies. So this is the normal setup. So is the fuel routing correct. tank > big filter > liftpump > small filter > ip


Yep. That's the way it came out of the box.