1986 6.2L K5 Blazer - won’t start

[wmako]

I was handed down a 1986 6.2L K5 Blazer that’s been sitting in storage for a long time, but started regularly. My son has been using it for about three weeks, and last night it stopped running and would not restart. My first thought is clogged fuel filter.



I had it towed home. This morning it struggled to start, but did start eventually, but only with me holding my foot to the floor. It idled for about 30 seconds and stalled. I did not try to restart it. This again seems like the fuel filter to me, and enough fuel worked its way past the clog over night to get it to start, but it is still clogged.


I have never owned a diesel before but do have experience with gasoline engines. My understanding is that because there is no ignition system, the only thing that could stop a running diesel from running is lack of fuel. Could someone please explain to me a little bit about how the fuel delivery works in these engines, and how to trouble shoot it? Any help or info is greatly appreciated.

[crashz]

The fuel is drawn from the tank by a mechanical lift pump on the passengers side of the engine (looks similar to the typical Chevy fuel pump on a gas V8) and then pushed through the fuel filter on the fire wall (I think its sometimes called a fuel manger as it houses the filter, water separator, drain and fuel heater), then to the fuel injection pump, injectors and finally the excess is returned to the tank.

If the truck has been sitting, and now driven, with no change in the filter, then I highly suspect the filter. Even if you put a fresh filter on three weeks ago, my guess is that the fresh fuel would have flushed all the rust, water and junk built up in the tank into the filter.

Hard starting can also be caused by air leaks in the fuel system, but it usually is less of a dramatic stop. And once running, they run (a bit stumbly) until the leak fairly large.

If I were you, I'd start with a fresh filter. Actually keep a few handy.

Search this forum for threads on how to change the filter properly though. Its easy to get these air-bound, then a pain to get the air out of the injection system. Being a noobie to diesels, it may feel imposing, but the gurus here have helped countless people with these rigs.

My method is to simply remove the square filter, replace and use a hand operated vacuum pump with container to daw fuel from the tank and fill the filter, prior to trying to start. Pull fuel until a good stream of clean, bubble free fuel is in the vac pump hoses. The port is on the pass side of the fuel filter housing, and you need to open the vent at the top. I've been able to crack it open and pull fuel, but sometimes I need to remove the plug entirely and then cover the hole with my thumb before I can pull the fuel through. I get a bit of air in the system, but it typically starts, runs with a bit a of a stumble, then smooths out.

[wmako]

The fuel is drawn from the tank by a mechanical lift pump on the passengers side of the engine (looks similar to the typical Chevy fuel pump on a gas V8) and then pushed through the fuel filter on the fire wall (I think its sometimes called a fuel manger as it houses the filter, water separator, drain and fuel heater), then to the fuel injection pump, injectors and finally the excess is returned to the tank.

If the truck has been sitting, and now driven, with no change in the filter, then I highly suspect the filter. Even if you put a fresh filter on three weeks ago, my guess is that the fresh fuel would have flushed all the rust, water and junk built up in the tank into the filter.

Hard starting can also be caused by air leaks in the fuel system, but it usually is less of a dramatic stop. And once running, they run (a bit stumbly) until the leak fairly large.

If I were you, I'd start with a fresh filter. Actually keep a few handy.

crashz, thanks for the reply. I'm going to pick up a fuel filter today. was just wondering what the next steps would be, if that doesn't resolve my problem. It wasn't hard to start before this. I have pressure at the filter on the firewall. When I open the bleeder screw, there is pressure, but I don't know if that is actually before or after the filter, and was also wondering how the check for fuel further down stream.

[DmaxMaverick]

With engine idling, there should be fuel pressure at the bleed valve, and at the drain valve (mechanical fuel pump is pumping). You can loosen the fuel line into the fuel injector pump, or at any coupling between the IP and filter, to verify flow and help bleeding. As said, start with a fresh filter (and have others handy), and perhaps some fresh fuel. #2 Diesel fuel has a remarkable shelf life if kept dry. I've used some decades old in tractors and my '85 with no problems.

Also, with the engine idling, you can drain some fuel from the filter assy via the water drain. Catch some in a clear container, let it settle and see what you have in there. Both the bleeder and water drain are on the "dirty" side of the filter element.

[mrwilecoyote]

If you have the means, cut the old fuel filter open and look. I'm betting algae.

[wmako]

If you have the means, cut the old fuel filter open and look. I'm betting algae.

Good Idea. I will most definitely do that.

[wmako]

I got a new fuel filter. I noticed the four holes were labeled inlet, outlet, sensor, and drain. I blew some air into the inlet, and it easily came out the other three holes. I put my fingers over the sensor and drain holes, and air still easily came out of the outlet hole. I wanted make sure it worked like any other inline fuel filter, so when I removed the other filter, I could test it in the same manner to confirm it was clogged.


Before I replaced the filter, I opened the drain on the fuel filter housing and caught the fuel that came out. Absolutely no water. I removed the filter, drained out the fuel, and tried to blow through it. It seemed completely clogged, as I was hoping.


I installed the new filter. I hooked jumper cables from my car to the blazer to try to keep the batteries fresh. I turned on the ignition and waited for the glow plug light to go off. I cranked the engine over for about 10 seconds. I opened the bleeder valve on the top of the fuel filter housing to bleed out some air. I got nothing but air. I repeated this procedure four more times. I started getting fuel from the bleeder screw. I cranked the engine over again, and it sputtered. The next time I held my foot to the floor, and it started, but stalled as soon as I let of the gas pedal. I started it again, with my foot to the floor, and this time kept on partial throttle to keep it running. After a few seconds I let it idle, and was very happy it was running and only had a clogged fuel filter. I removed the jumper cables, and a few seconds later the alternator starting squealing. My son told me it had also done that to him the other day. I went back inside to look at the voltmeter. It was clearly not charging. It was sitting at 8-9 volts. A few seconds later it stalled. I hooked the jumper cables back up, and was able to get it to sputter a few times, but never able to get it to start and stay running. At first there was clearly fuel coming from the tail pipes, but after a while it didn’t seem like fuel was coming through again. The batteries were not holding up well, even with the jumper cables, so I decided to call it a night.


I am a big believer in fixing what you know is broken, so the next thing I will do is replace the alternator, but I was looking for peoples input as to what they think might be going on.


Could there simply still be air in the system, and I just need to run it a little more before it starts to go back to normal?


Could the bad alternator and having only 8-9 volts cause the injector pump or something else to not work properly, and that is why it stalled out after I removed the jumper cables? It did exactly the same thing the day before, BEFORE I replaced the fuel filter. Maybe the fuel filter was never the problem? I couldn’t blow any air through the filter I removed. Could I have had two problems at the same time? Seems unlikely.


Any ideas or thought would be greatly appreciated. Thanks.

[JohnC]

There is an electrically operated shutoff solenoid. If you have enough juice to crank the engine over there should also be enough to keep the shutoff open, though.

Sounds like you still have a fuel delivery issue...

[crashz]

I think you may still have some air in the system, and now dead batteries.

Before you replace the alternator, I'd have it tested. It might be OK, just not charging due to slipping belts. Every 6.2L rig I've owned has been a constant battle to keep battery connections clean and V belts tightened enough so that the alternator does not make them squeal.

Sounds like your batteries are run way down as well. Get them on a slow charge for a while (like overnight or something) and then have them tested when you take the alternator in. If run down low and continued demand (such as trying to start over and over) they can be damaged internally.

A fresh set of batteries (if you have not already replaced them) and clean connections never hurt these rigs.

[wmako]

I hate when I find problems on forums and no one ever posts the solution, so here is the rest of the story. The alternator I had gotten was not the right one, so I could not eliminate that as a suspect. I decided I would not disconnect the jumper cables no matter what, so I couldn’t be tempted into thinking that somehow low voltage was causing me problems. Of course I kept forgetting that part of my plan, and would disconnect them when I thought everything was good, only to have the truck stall, and me still be wondering if it was because of that.

I decided I would go through the fuel system as systematically as possible. I made a list (mentally) of the things to check and how to check them from the info I’d read in the forums and from this Youtube video someone posted a link to.

http://www.youtube.com/watch?feature...&v=W5cmL19Fb34

Unfortunately, I will probably not be able to tell you the exact order and results of everything I did at this point because I’ve lost track of some of it.

I checked for 12v at the fuel solenoid and made sure I could hear it clicking open and closed. It seemed ok. I pressurized the gas tank with a wet/dry vac and checked for leaks between the fuel tank and the mechanical pump. Did not find any leaks. I bled all of the air out of the filter housing by turning the engine over 5 times, open the bleeder valve, repeat. After about 3 or 4 times of this, I would get nothing but fuel, and the engine would sputter and sometimes start, but never stay running. I found I could get it to start by holding my foot to the floor, and sometimes I could keep it running, but it didn’t really seem to want to idle. After this I would find air in the fuel filter housing, so it still seemed like air was my problem. I placed a piece of clear tube going from the mechanical fuel pump going into the fuel filter housing. Bled all the air again, and started the truck. It stayed running for a few minutes, but when I shut it off, there was air in the filter housing again. I saw no air coming through my clear tube. I bled the air, and restarted, and even while it was running, I could get air out of the bleeder screw on the filter housing. With no air coming up through my clear tube, I was starting to worry the maybe my filter housing was cracked. Next I was going to fit a piece of clear tube on the fuel line coming out of the filter housing. I figured if I saw air there, I would have it narrowed down pretty well. Unfortunately the line coming out of the filter housing was a smaller diameter, and I could not come up with a fitting that I could connect without leaking. At some point I started to wonder if the fuel filter maybe was somehow not sitting right. I removed it and tried to blow through it and couldn’t. Maybe the other one was never clogged? I blew all the fuel out with compressed air. I did the same thing to the old one. Was the fuel somehow locked in there, and that’s why I couldn’t blow through it? I put the old filter back on. With my clear hose I could see the fuel was coming through, and I could also see it was not completely full of dirt and rust. I bled the air out again, and started the truck. It stayed running. It would idle. No air in my clear hose. I look under the truck and fuel is pouring from the weep hole on the mechanical pump.

Long story short (at least a little shorter), I replaced the mechanical pump, removed my clear line, reconnected everything, bled the air and started the truck. It ran fine, and has been running fine since, over a week. I know the fuel pump was not leaking at the beginning of all this, and I hate not knowing what I fixed, or if I even fixed anything.

Could air have been getting into the system through the weep hole on the mechanical pump as is was starting to fail and it finally let go completely?

Was it just a coincidence the fuel pump failed at that moment, and I inadvertently fixed an air leak somewhere else? Maybe from the new fuel filter not being seated right?

Is nothing fixed, and I am going to have this problem again?

I have no idea, and hate not knowing. I waited to post to see if the truck kept running, and so far it has. My son uses it every day, and last week the temperature was in the single digits.

To add more to my confusion, the night this truck left my son stranded (the very first time it died) on the side of the road, the first thing I did was open the bleeder valve on the fuel filter housing. There was good pressure there at the time so I know it was getting fuel, at least to that point, and there was DEFINTELY NO AIR. We cranked it over a million times, and the batteries held up really well, so I know the alternator had been working.