Stuck injector, clogged return line?

[bleucrew6.2]

Hello All.

The old boy has been running down the road quite well since the front end/steering/stub shaft rebuild. Recently I went out for a dump run, and smelled fuel on the ride home. The culprit turned out to be the rubber cap at the end of the fuel return system on the driver's side. It was missing...and fuel was running out of the open nipple on the injector.
I had no idea why this could have happened. I haven't had to mess with the injectors, supply lines, return lines, etc. at all before this. The dealer sold me a new rubber cap and clamp (generously accepting my first born in payment). I installed these parts and all was well until now.
Today I smelled fuel again. Popped the hood again. Leaking at the same location. Rubber cap/clamp is still in place on the nipple, but fuel is spraying from under the cap.
Is it possible that this injector is stuck? Maybe the fuel return line is clogged and creating backpressure? Truck now has about 110K miles on it. Is it time to replace the injectors?

Thanks in advance for your help and suggestions.

John Sullivan

[Robyn]

The issue is a plugged return line somewhwere either on the engine or the return to the tank.

You will most likely need to check the return flow through the whole return system to see where it is plugged up at. Remove the return line where it runs from the engine to the frame steel line and blow into it and see if it is free to the tank.
If all is ok there you need to systematically check back through the return line that crosses the front of the engine and then down the individual injectors to see where the obstruction is. Be sure to keep things clean.

You can try unhooking the one thats leaking at the nipple oposite the cap and see if fuel is coming out. If no fuel comes out the open end then there is your gremlin.

Replace the injector with a known good one and the issue is resolved.

The hoses that connect the nipples between the injectors can over time sweel internally and stop up.

The return lines on the injectors are in series and the fuel flows from one to the next and so on up to the front and then back to the tank.
The IP also has a return flow into this same system.

Good luck and keep us posted

[bleucrew6.2]

Thanks Robyn. You mentioned replacing the injector with a known good one. Does that mean that the existing one may be bad? If I need to replace it, I might as well get a complete set to keep things consistent. I've seen return line kits that contain all the lines and clamps too. Considering the age of the truck (nineteen years), would it be prudent for me to just change out all of them in addition to checking the metal lines? I think the problem is isolated to the driver's side, since I haven't had any issues with the opposite side. I don't drive this truck daily, but when I need it... I need it to run well and dependably.
I've seen lots of rebuilt injectors on ebay. Do you have any suggestions for a reliable source.

Always a pleasure hearing from you!

John

[Robyn]

Might not hurt to just get a fresh set of injectors then and the hose/clamp kit and do it up right.

best and good luck

Robyn

[Subzilla]

Got mine from Tim Wagner at accuratediesel.com. Always been treated "right" by him.

[bleucrew6.2]

Thanks. I see they have an ebay site too. I'll let you all know how it comes out!

John

[bleucrew6.2]

Okay. Here's an update.

I discovered that the recently installed rubber cap had a tear in it (?). Which was allowing the fuel to spray out onto the exhaust manifold. (What a fun way to prevent tailgators! Fog them with diesel fuel!)

I was able to trim the cap slightly and reinstall it. Next I removed the return hose from the next injector, but left it attached to the problematic injector to see if it would pass fuel with the engine running. It didn't, so I removed the hose from the engine and blew through it with no problem. Then I started the engine with this hose removed and noticed that no fuel was coming from the nipple on the injector that the hose had been attached to. The rubber cap was still installed. I was beginning to suspect an internal problem with the injector so....

I removed the injector, and took it to my friendly neighborhood diesel injector and pump rebuilder. They put it on the test bench and it passed with flying colors (good spray pattern too!). About this time, one of the mechanics came in from lunch and overheard me describing my problem. He feels very strongly that the problem is in the return fuel circuit in the injector pump. Apparently when there's a problem like this with the pump, the injector's fuel return system becomes over-pressurized and starts popping off these rubber caps.

Sound familiar? Sound like BS? Let me know what you all think.

Thanks!

John

[JohnC]

I'm not sure I followed all your troubleshooting logic, but...

The injectors are all manifolded together, along with the pump bypass. Any one of then could be casuing a problem, not necessarily the one nearest the leak, which would occur at the weakest point in the system.

The amount of fuel bypassed by an individual injector is pretty slight, so I'm not surprised you didn't see fuel coming out (right away). What does surprise me is you didn't see fuel leaking out of the other end of the hose still connected to the manifold. Could there be a blockage further up the line? any break in the system should leak a lot of the fuel being bypassed by the pump.

Or, you could be really unlucky...

[bleucrew6.2]

John, I'm not sure I understand your description of the fuel return system. My engine doesn't have a manifold that the injectors connect to. The injectors are connected by hoses that link each one to the other as the return system moves toward the front of the engine.
Last night I installed the injector that was tested, and hooked up the return line. The rubber cap/clamp escaped me and fell down in the gravel below the truck. After crawling around with a flashlight with no luck, I decided to move the truck back in hopes of finding the cap. The ammount of fuel running out of the uncapped nipple on the injector seemed to be substantial. An uninterupted stream.
I'm hoping to probe a little deeper this weekend. I have a replacement return line kit (without clamps), and a few new fuel filter.

What was that comment about being really unlucky? Injector pump?

John

[DmaxMaverick]

By "manifold", I think he meant all the returns route to a common line. The "manifold", would be the main return line, where all the injector returns and the pump return meet. If your tank return line were to be blocked, or significantly obstructed, the fuel in the return will seek a path of least resistance (soft rubber cap). While testing the system, try it with the fuel filler cap on and off. If the cap vent has failed, it will allow excessive pressure to develop, obstructing the return. Expansion due to higher temps will do the same. A collapsed/kinked hose, or kinked/dented line would also cause issues with the return. If you have been using bio or VO, it could have dislodged debris in the system, blocking a bottleneck, or deteriorated a rubber line internally.

[bleucrew6.2]

Interesting about the fuel tank cap. Whenever I fill up and remove the cap, there is a release of pressure. I'm not sure if it's pressure or vacuum. The truck has always done this at fill up. Incedentally, my other vehicles do the same. I haven't changed fuels, although I do add a bit of ATF and fuel conditioner to the tank when I fill up. I can't imagine how one of the metal lines has gotten kinked, I haven't disturbed any of them. The rubber lines all seem to be in good condition as well. I struck out at two auto parts stores last night searching for some new clamps. Hopefully NAPA will have some on my way home from work. I hope to have some time this weekend to investigate this further.

Thanks for the suggestions!

John

[DmaxMaverick]

New clamps can be had with a new complete injector return line kit from JK and others. About $25, IIRC.

The Diesel fuel cap is different than gasser caps. It vents both ways, pressure and vacuum. Having a little pressure behind the cap when fueling is normal. The more empty the tank is, the more pressure it will seem to have. Actually, it isn't more pressure, but more volume.

[bleucrew6.2]

Dmax,
If the fuel cap is suspect, how should I go about testing it? I'm assuming that it is supposed to vent excessive pressure or vacuum, but what are the acceptable parameters, and how can I judge if the cap(s) are compliant? The truck has two twenty gallon tanks.
In testing the return line back to the tank, should I try compressed air and listen for bubbles at the fuel filler? Or is there a better way? I'll be going through the injector lines and the metal line that connects them with the I.P. bypass circuit and the return line to the tank this morning.

Thanks!
John

[bleucrew6.2]

So far I have removed the metal line that connects drivers side, I.P., and passengers side to the main return line. This metal line checked out fine. I found a niftly little attachment for a bicycle pump used to inflate beach balls, air mattresses, etc., to test the main return line back to the tank(s). I removed both fuel caps. I could hear bubbling as I pumped, so I'm assuming that this line is clear as well.
Does all this mean that the prime suspect is the bypass circuit in the I.P.? I've been quoted $450 for a local rebuild. I think I would rather go that way than with a "deal" from ebay, unless someone has a better idea. Right now, the timing mark on the existing pump is lined up with the one on the front cover, and hopefully having my pump rebuilt would make installation and subsequent timing of the pump easier.
I'll check back later today. If the pump needs to come out, this afternoon would be a good time to tackle it (fair weather out on the driveway, you know?)

Thanks!

[Robyn]

Remove the injector that keeps popping the cap off and be sure the little creature does not have an issue internally thats preventing the fuel from flowing out the nipple thats hooked to the hose.

This system is a series where the rear most flows to the next and to the next and so forth.

Now the problem could be further up the line from the rear on the side that loses the cap.

Hook a small hose to the rear nipple (remove cap) unhook the very front line on the same side and then use your little pump and see if that whole series is clear.

Its possible that one of the other injectors has an issue thats stopping the flow and then the pressure is building and causing the cap to pop off.

Keep us posted.

Robyn

[convert2diesel]

This may seem obvious, but I have been fooled myself. When the return hoses come off, more times then not, they actually break off right at the barb on the fitting, leaving a small section of the old line still on the fitting. Especially hard to see where the dead end hoses attach.

Had the same problem a while ago. Wouldn't let the new hose seat properly.

Just a thought.

Bill

[DmaxMaverick]

I quit "testing" fuel caps long ago. They're cheap. If suspect, they get replaced.

The IP circuit shouldn't be the problem. The outlet can be blocked by debris or a failed check valve, but it wouldn't cause a pressure issue. The return system can handle full bypass, as more fuel is returned than burned, anyway. Pressure is irrelevant. Once the fuel hits the return, the pressure is gone, unless there's a restriction in the return line somewhere (which is what will pop off the cap). Flow can't outrun the lift pump, so unless you are using a high volume/pressure pump (not for Diesels), it's a non issue. The problem lies in the return line, or just a return line cap dilemma. You should be able to pull the end cap and pressurize with air. The air should blow back to the tank. If it isn't, there's blockage. If it does, could be the injector or cap. Try switching the injector with the adjacent injector. If the same cap pops off, it isn't the injector. If it pops the line on the same injector, the injector is the problem, regardless how it tested. test stands are great, but can't duplicate a real environment 100%.

[bleucrew6.2]

I actually did test the return system through the injectors with a long piece of fuel line that I could blow through. Removed the metal crossover line and checked it out too. Blew air back through the metal line back to the tanks, and could hear it bubbling. Considering that everyone is telling me that the amount of fuel returning to the tanks through this system should be minimal, I'm beginning to wonder if the fuel injection mechanic's diagnosis is correct. (He was quite sure that the I.P.'s bypass circuit was at fault). I will find out soon. I removed the I.P. last night, and am taking it in for testing/rebuilding this afternoon.
I'll keep you all informed.

John

[bleucrew6.2]

Okay...

The I.P. pump came back all pretty and clean. Techician said that it was adjusted about 10% lean(?), so he calibrated the pump to factory specs. Pump re-installation went fine. Took a few cranks to bleed the lines, but the truck sounded great after all was tight. Didn't have time or energy to give it a highway test that day, and it has sat waiting until today.
Two miles into the "highway run", I started to smell fuel. I knew d**n well what is was, and took the shortest way home. In the driveway, I have fuel running off the frame rail...AGAIN. The cap had popped off....AGAIN. I checked one of the rubber return lines back near the transfer case by removing it, and had fuel running from both directions. I hooked up the trusty bike pump to the nipple that had blown the cap, and pumped. Bubbling could be heard through the open tank fill tube.
So, I have all new rubber return lines between the injectors, the cross over metal line is clean and clear, the I.P. has been rebuilt, fuel is present in the return line halfway back to the tanks, a bicycle pump can easily blow air ALL THE WAY TO THE TANK, and the problem persists....

Any and all comments greatly appreciated

John

[Yukon6.2]

Hi Read through all the post's,and was woundering if you ever changed the injector that is popping of the cap with a different one?

[bleucrew6.2]

I haven't replaced that injector. I did take it to the shop and had it tested. It passed wonderfully. What I'm beginning to wonder is if there is just enough restriction in the rubber sections of the main return line to cause some back pressure. Also wondering if the solenoid that switches my fuel tanks has some problem. But why can I blow air through the system all the way from the nipple the cap blew off to the tank?

[DmaxMaverick]

You have a real head-scratcher for sure. Try swapping the suspect injector with another on the same bank. If the problem continues as-is, the problem is the return circuit. If it stops, or follows the injector, then the injector is suspect, regardless of how it "tests".

Your tank valve could be suspect. Air is much less dense than fuel, and there could be enough restriction there to prevent a free flowing return, but allow air to blow freely to the tank. The tank switching valves have been the gremlin in many cases. Also, verify you don't have lines crossed somewhere.

[Robyn]

Something is happening when the thing is running rather than in a static mode (Shut off)

Try pulling the return line off that injector and running it to a can, plug the rear most nipple on the next injector and then see if the issue is present.

Something is happening either in the injector with the cap on the rear nipple or one farther upstream.

You are going to have to find where the stoppage is at during run time.

Best

Robyn

[bleucrew6.2]

When I got home today, I went out to dig in to the beast some more. I removed one return line from each injector, as well as the line that connects each set of injectors to the crossover tube. I left the crossover tube connected to the I.P. I started the truck, and observed.

I could barely detect any fuel dripping from any of the injector's return nipples. Maybe even none at all. The fuel was running out of both sides of the crossover tube still connected to the I.P. If I covered the ends of the tube tightly with my finger tips, I could feel a rapid pulsing.

So maybe the problem is STILL with the I.P. How much fuel is this thing supposed to bypass? I think I've eliminated the injectors as the source of the problem at this point.

I'll be calling the shop that rebuilt the pump tomorrow, and maybe chat with the diesel mechanic that helped me out with the "truck steers itself" chapter in recent Diesel Page history.

I'll let y'all know what happens...

John

[bleucrew6.2]

I had a chance to talk with the diesel mechanic today. He was wondering aloud if the lift pump had a return line on it. It just doesnt' make sense for the crossover tube to have any fuel coming out of it if it's not connected to the injectors. The I.P. doesn't directly tie into it. So....maybe the pressure in the system is coming from the lift pump? I don't know if the lift pump has two, or three lines coming off it. I will find out tonight.

[DmaxMaverick]

This points right back to the tank valve. It is the only other common connection (after the injectors and IP). The lift pump does not have a return line. One in, one out.

Does it happen with either tank selected? Not that it matters, though. If it's failed internally, it could be either way, one tank or both.

[bleucrew6.2]

The mechanic and I discussed that possibility, but couldn't understand how the fuel tank could provide constant pressure back through the return line. Especially enough pressure to blow off that return fitting cap when the truck is on the highway.

[bleucrew6.2]

Home from work now. All these hoses...

I disconnected the crossover tube from the return line that goes to the tank, and started the truck. Fuel still running out of the crossover tube. Somehow, in all of this,(even though I'm the one who removed and re-installed the pump) I wasn't paying attention to the hose that comes out of the top of the pump and connects to the crossover tube. I'm quite sure if I disconnected that hose, I wouldn't have fuel running out of the crossover tube anymore.
I've thought about seeing how long it would take to fill a beer bottle with fuel from the discharge from the crossover tube. Maybe a minute...not much more. I can't imagine the flow at highway speed.
At this point I'm thinking that I'm going to end up pulling the pump again and taking it in..etc..etc... Not sure when I'll get to this. "Hurricane" Hanna will be coming down on my driveway tonight and tomorrow. Lord! to have a garage!

John

[JohnC]

The cap that blows off is just the weakest link. It has nothing to do with the problem, nor does the injector it is connected to, unless the hose barb is bad.

Originally I didn't reallize you had dual tanks. I'd suspect the valve is not switching the return line correctly or is clogged. Try bypassing the valve but remember that if you bypass to one tank and run off the other all the fuel will end up in the first tank in short order.

The amount of fuel bypassed by the pump can be considerable and will be the most at idle as the pump is not injecting much. If the lift pump is electric you can run it without running the engien and may be able to troubleshoot it that way.

There should be little to no pressure in the return system.

The "manifold" I referred to is constructed of the hoses, tubes, and return collars on the injectors. The purpose is to collect the dribbles from the injectors and the bypass from the pump and allow it to return to the tank. The pressure should be the same everywhere along the manifold, so the cap that blows is just the weak link and not necessarily anywhere near the problem.

[bleucrew6.2]

After disconnecting the main return line from everything the engine contributes, I had no fuel dripping from it. The only fuel running is coming from the injector pump. I understand that the engine would use more fuel when running at highway speed, and that the pump would have some excess to send back to the tank at idle. But why did the truck run fine in the driveway, and even "around the block" without blowing off the cap? I must have let it run for thirty minutes before driving it after re-installing the pump and new return lines. I probably didn't exceed twenty mph driving around my neighborhood, and was happy as a clam when I got home and popped the hood to find the cap still on the injector.
My drive out to the Baltimore beltway involved speeds up to about forty mph. Once on the beltway, it only took about two miles of highway speed to realize that I had that dreaded strong smell of fuel...again.
John, with everything disconnected from the injectors, they aren't even dribbling at idle. And the ammount of fuel coming from the pump is a lot more than a dribble. Are you suggesting that the tank switch is providing enough restriction to back up the fuel in the return system? The only part of the fuel system that I'm really sure about are the tanks, and the hoses that connect them to the metal supply and return lines. I replaced the tanks about a year and a half ago with poly tanks from MTS (very happy with them), as well as the hoses. I guess everything else is suspect, although I'd like to avoid replacing EVERYTHING right now. $$$$$...y'know?

Good God, this has been a long post! I appreciate everyone's help with this. Maybe when all's said and done we'll learn something new.

John

[DmaxMaverick]

After disconnecting the main return line from everything the engine contributes, I had no fuel dripping from it. The only fuel running is coming from the injector pump. I understand that the engine would use more fuel when running at highway speed, and that the pump would have some excess to send back to the tank at idle. But why did the truck run fine in the driveway, and even "around the block" without blowing off the cap? I must have let it run for thirty minutes before driving it after re-installing the pump and new return lines. I probably didn't exceed twenty mph driving around my neighborhood, and was happy as a clam when I got home and popped the hood to find the cap still on the injector.
My drive out to the Baltimore beltway involved speeds up to about forty mph. Once on the beltway, it only took about two miles of highway speed to realize that I had that dreaded strong smell of fuel...again.
John, with everything disconnected from the injectors, they aren't even dribbling at idle. And the ammount of fuel coming from the pump is a lot more than a dribble. Are you suggesting that the tank switch is providing enough restriction to back up the fuel in the return system? The only part of the fuel system that I'm really sure about are the tanks, and the hoses that connect them to the metal supply and return lines. I replaced the tanks about a year and a half ago with poly tanks from MTS (very happy with them), as well as the hoses. I guess everything else is suspect, although I'd like to avoid replacing EVERYTHING right now. $$$$$...y'know?

Good God, this has been a long post! I appreciate everyone's help with this. Maybe when all's said and done we'll learn something new.

John

I suggested this earlier, and it's looking more and more like your problem. Even if the valve is cycling, and has a clear return, the return may be restricted. Blowing air through may be a false security. Fuel is considerably more dense than air, and may not be able to pass through unrestricted, building excessive pressure. This could apply to other locations as well, such as the fitting at the tank. Also try testing with the fuel cap loosened or removed (could still be an issue). Lift pump pressure (4-10 PSI) is not enough to pop off the lines/cap. But, IP return pressure can be several hundred PSI if restricted. Your return is restricted, at the tank valve, or between the tank valve and the tank. Try bypassing the tank valve. Choose a tank (one with fuel in it), and make sure the supply and return lines go to the same tank. Also, does this happen with either tank selected, or just one? This could be important if the problem continues with the valve bypassed. If your tank selector valve is original, it could be highly suspect, for other reasons as well.

[Robyn]

Try this.
Hook up a length of return line of any sort thats clean and bypass the lines on the frame.
String it down the side of the truck if need be and run it to the fuel tank you are using. (In the fill spout)

Hook it up to the return line that leads off the engine to the run back down the frame.

Run the truck and see if all is ok.
If this fixes the issue then you are going to have to work through the sections of lines and then the valve all the way to the tank to find the gremlin.

Biggest issue is to be sure its not related to a faulty injector in the series on the side thats losing the cap.

The return system should be free flowing (Easy to blow by mouth/Zero pressure buildup.

A little piece of hose material that has come from the inside of a hose could easily clog the run during actual operation and cause the problem.

Keep beating on it, you will get it.

Robyn

[bleucrew6.2]

Hopefully I'll be able to get into it again before this weekend, and FIX IT. I have purchased a new tank selector valve, new rubber hose, new clamps, etc. Unfortunately I still have at least ten gallons of fuel in each of the two tanks, and no where to put it. What I'm going to try is removing the caps from both tanks, and sealing the openings with a careful application of duct tape. Hopefully this will create enough vacuum that I can get the valve and hoses replaced without getting soaked. Any other creative ideas are much appreciated.
This new selector valve has a sticker on it warning against installing it without "suitable filters between the valve and the two tanks". This will apparently void the warrenty (although I could find no mention of a warrenty period on the unit or the papers that were packed with it). Currently there are not any filters installed on the truck except the one in the engine compartment. Does anyone have any experience with this? It seems like quite a hassle to cut into the metal lines, and install serviceable filters on the frame or crossmember...is it truly worth it?

John

[DmaxMaverick]

To seal your filler cap, use cellophane food "cling" wrap. The old "Saran Wrap" is pretty stout, and will hold up to threading in. Just use a 6" square over the cap and screw it in, slowly, until the cap gasket makes contact. To draw a slight vacuum on the tank, you can use a vacuum pump, or natural thermal contraction. If you are doing it at the end of the day, the fuel will naturally contract as it cools (seal it after you are done running it). If any other time, you can wet the tank with water (the outside!) to cause the cooling effect. If you can't run it (fuel spilling out the return), use a hose connected to the return, and route it to the filler, to circulate warm fuel with the engine idling. If you have 10 gallons of fuel in the tanks, there is enough remaining airspace to cause a significant vacuum on the tank.

[JohnC]

If the fuel lines come out the top of the tank, all you have to do is break the siphon and fuel won't come out. Open the cap and blow air from the line back to the tank.

[bleucrew6.2]

Thanks guys. I figured someone had needed to do something similar to my job, and had gotten creative about it. I'll be in touch.

John

[farmerpatrick]

All-
For me, the little cap on the rearmost injector (driver's side) blows off about every 2000 miles (best guess). It's done this about 3 or 4 times. At first, I just tried different ways of sealing it up and it continues to blow off.

It's been a couple of years and tonight I decided to start diggin into it- of course it's tough to get to that injector.

I'm going to start with an "injector test" or new injector and then go from there. My mechanic (whether he knew what he was talking about or not) - said he thought one cylinder was "missing" so I am going to start with the injector.

Mine is a 91 K5 Blazer (always cranks and runs, but very slow and very little power- won't run 80 on the interstate without downshifting- slows to 65 going up a slight hill).