True failure rates of the 6CTA8.3L injector pump?

[LCA078]

I own three M939 series trucks with the NHC250 so I'm familiar with how air leaks in the fuel supply system can cause havoc. I'm hearing the 8.3L isn't too different in that air leaks (along with a bunch of other nit-noid things) cause a lot of no-start headaches that people originally misdiagnose a bad injector pump. My question is what is actual fail rate of the injector pump vs. something else that is simple on the 8.3L when it comes to crank- no start issues?

Here's why I'm asking: I plan to look at a M931A2 this weekend as the truck looks much cleaner in pics than the M931A1 I own and I hope to get better mpg out of the newer engine. The seller bought the truck a few years ago as a toy and is getting tired of the upkeep (sound familiar?). He's having crank-no start issues and says he's out of options to work on it so he's trying to unload it. He thinks the IP failed and doesn't want to deal with it. When I asked how he came to that conclusion he said that he changed all the filters, bled the lines, ensured good prime, and even tied back the cut-off solenoid (not sure on this since I never touched an 8.3L). I asked if he checked the inlet supply pressure and he said he doesn't have a way to do it but he can get fuel flowing freely out of the connection right before the IP...thus the IP must be bad. I asked if he asked anyone for help or used any forums and he said his buddy who is pretty good with a wrench (diesel farm tractors) helped him but didn't fix the problem.

So.....

Based on my reading through SS, this doesn't sound like a robust diagnosis and there are lot of other things to check before condemning the IP. But wanted to ask the experts here how many times is it minor stuff to fix or does the IP on these engines have a high failure rate. Thoughts?

 

[Jbulach]

I can only remember maybe one or two IP failures in the time I’ve been lurking around here, verse’s probably a hundred sucking air and another hundred with bad batteries.

Sounds like he covered most of his bases except fuel pressure due to bad overflow valve, lift pump, sucking air before the lift pump, or blockage in the pickup.

First thing I would do is confirm batteries are charged, zip tie the shut off back, verify the shut off is rotated to the run position, good fuel at the ip outlet with the hand primer. Then with your best battery/charging truck slaved and running to it, crank the 8.3 with the accelerator pedal to floor. Even though these are not know to run away you might want to verify the intake system is buttoned up, the mushroom cap off, and a hard bound book laying on the passenger seat.

If it’s cranking fast and doesn’t start to fire in 15 seconds, I would verify fuel pressure with a gauge.

 

[fuzzytoaster]

The 8.3 suffers from dry rot fuel lines, stuck fuel shutoff, and (if a tractor/dump/wrecker) bad fuel tank selector switch. These are your most common problems. As of the past two years I've seen a large trend in stuck IPs for this engine due to the fuel and lack of operation. There are a few minor tricks you can do to get the pump to free up but so far it's 50/50 on if it works or the pump needs to be rebuilt.

1. Tap a fuel cap and install a Schrader valve to pressurize the fuel system to 5 psi
2. Put a clamp on the IP return hose
3. Zip tie the fuel shut off solenoid back
4. Disconnect injector lines from IP
5. Crank engine - look for fuel

If you for sure have fuel to the IP and it's not coming out of the injector ports then the pump is indeed stuck in the closed position. At this point you can either try to force the IP to open up or have it rebuilt. You can buy an injector cleaning kit and use a solvent of your choice to force fluid into the pump from the fuel inlet. This will take time and require air pressure. You can crank the engine some during this process. Lastly, it's a "r&r" (remove and repair) situation by sending it off to a shop which is $$$. Our pumps are a little special internally so parts are harder to find. I had a pump rebuilt in November and was quoted on the average of $3100 for a full rebuild. I got away with $1800 for a minor parts kit and labor to clean it plus my own labor for install.

 

[Jbulach]

Still a handful of things to check after that before just writing the ip off.

 

[LCA078]

I can only remember maybe one or two IP failures in the time I’ve been lurking around here, verse’s probably a hundred sucking air and another hundred with bad batteries.

The hour or so I spent going searching this forum led me to believe the same. I know it's always a crapshoot when buying one of these trucks but at least I'm hoping to do an educated crapshoot if I purchase. Last thing I need is another time- and money-sucker sitting out in my motor pool...

The 8.3 suffers from dry rot fuel lines, stuck fuel shutoff, and (if a tractor/dump/wrecker) bad fuel tank selector switch. These are your most common problems. As of the past two years I've seen a large trend in stuck IPs for this engine due to the fuel and lack of operation.

Since I've not heard of a stuck IP, I'm guessing you're referring to gummed up insides or maybe even something got past the filters? I found a couple contractions on the web that allow pressurized fuel/oil/solvent/cleaner/etc. to be forced into the IP inlet which would hopefully dissolve the deposits. Is that what you're referring to?

I do like the quick and dirty way to test by putting a schrader valve on a fuel cap. I should be able to rig one up myself before I go see the truck and then use my roadside 12v air pump pretty quickly. Is there a vent I need to cap off on these trucks? I can't remember which version has a vent and which ones don't.

 

[Jbulach]

Yes, just a razor and couple 1/4” push connector is all you need. Regulator is nice so you don’t rupture your tank.

 

[Jbulach]

Hopefully a clearer view of my setup.
I keep it and an air hose to run off my glad hand in my truck at all times.

 

[LCA078]

That's a really slick set up! Where did you get those 1/8" push-locks? I use them for my fan misting/cooling system in the work area but the ones I use are a bugger to get undone without a lot of cussing. Hoping you know a special brand that are much easier to install/un-install....

 

[Jbulach]

That's a really slick set up! Where did you get those 1/8" push-locks? I use them for my fan misting/cooling system in the work area but the ones I use are a bugger to get undone without a lot of cussing. Hoping you know a special brand that are much easier to install/un-install....

Well crap, wasn’t thinking clearly, the vents are 1/4” dot tube! Mine are out of a lot of Alkon brand made in Brazil that I’ve had around forever. Probably bought from New Life Transport, not sure if either still exist though? Also they separate easily with just your fingers. If you get one you have trouble with, use a 1/4 wrench or whatever size tube you’re working with and use it to push against the release ring while pulling the tube out. Just like Chinese finger traps though, the harder you pull on the tube without pushing the release all the way in, the better they grip.

 

[LCA078]

You know, the funny thing is I wasn't thinking too. I knew they were 1/4" tubing but I'm so used to connecting them to our pumps with 1/8" NPT nipples that I got used to calling them 1/8". <insert face palm>

And yeah, we use an 8mm wrench to push against the release ring but sometimes it's takes two of us to get them apart. Even used vise grips on the release rings so I could use both hands pulling the lines apart. I'll probably just buy an assortment of 1/4" and 3/8" push locks off amazon with a few feet of air line and keep them spread out amongst my trucks for roadside repair . IIRC, the air line is mostly all 3/8" and only a couple fuel lines are 1/4", right?

 

[TechnoWeenie]

The 8.3 suffers from dry rot fuel lines, stuck fuel shutoff, and (if a tractor/dump/wrecker) bad fuel tank selector switch. These are your most common problems. As of the past two years I've seen a large trend in stuck IPs for this engine due to the fuel and lack of operation. There are a few minor tricks you can do to get the pump to free up but so far it's 50/50 on if it works or the pump needs to be rebuilt.

1. Tap a fuel cap and install a Schrader valve to pressurize the fuel system to 5 psi
2. Put a clamp on the IP return hose
3. Zip tie the fuel shut off solenoid back
4. Disconnect injector lines from IP
5. Crank engine - look for fuel

If you for sure have fuel to the IP and it's not coming out of the injector ports then the pump is indeed stuck in the closed position. At this point you can either try to force the IP to open up or have it rebuilt. You can buy an injector cleaning kit and use a solvent of your choice to force fluid into the pump from the fuel inlet. This will take time and require air pressure. You can crank the engine some during this process. Lastly, it's a "r&r" (remove and repair) situation by sending it off to a shop which is $$$. Our pumps are a little special internally so parts are harder to find. I had a pump rebuilt in November and was quotes on the average of $3100 for a full rebuild. I got away with $1800 for a minor parts kit and labor to clean it plus my own labor for install.

^^^ ALL of this.. basically stole my post..

Diesel engines are stupid simple. They require 3 things.

Air.
Fuel.
Compression (heat).

Find out which one you're not getting, and you solve your problem.

Being this is an M939 series, you have to worry about the pickup tube and the now 30-40 year old rubber lines. Any amount of air can cause a loss of prime and require extended cranking.

Alternatively to the schrader valve trick, you can disconnect the supply line at the pump, and plumb in a temporary line directly to a small container with diesel in it, to rule out bad lines - then prime it. If it starts right up, you know you have a line or pickup tube issue. Pickup tubes are about $50 and you can replace your fuel lines for about $100 if you DIY.

You could also have algae in your tank and/or a clogged fuel filter. All of the above are much more likely than a bad pump.

 

[fuzzytoaster]

Since I've not heard of a stuck IP, I'm guessing you're referring to gummed up insides or maybe even something got past the filters? I found a couple contractions on the web that allow pressurized fuel/oil/solvent/cleaner/etc. to be forced into the IP inlet which would hopefully dissolve the deposits. Is that what you're referring to?

I do like the quick and dirty way to test by putting a schrader valve on a fuel cap. I should be able to rig one up myself before I go see the truck and then use my roadside 12v air pump pretty quickly. Is there a vent I need to cap off on these trucks? I can't remember which version has a vent and which ones don't.

It's all internal on the IP at that point - gummed up that is. It's just from the truck sitting and the new style diesel gumming it up. Yes, forcing Marvel Mystery Oil or a blend of your choice to hopefully free up the internals. I've had luck once on a really stuck pump by clamping off the fuel return on the IP and putting 15 psi of MMO in the the injector cleaner tool that was plumbed into the the inlet on the IP. I sprayed some PB blaster down into the injector ports too for good measure. It took a long time and a I cranked the engine when I remembered to.

The M939 trucks have a vent but it's usually small. I recommend an air compressor as there's quite a bit of volume to fill. The plastic lines on top of the tank may be brittle or leaking too.

 

[LCA078]

Alternatively to the schrader valve trick, you can disconnect the supply line at the pump, and plumb in a temporary line directly to a small container with diesel in it, to rule out bad lines - then prime it. If it starts right up, you know you have a line or pickup tube issue.

I've heard of guys taking a cheap hand pump garden sprayer from Home Depot and filling it with diesel to recover tractors, dozers, etc. stuck in the field. You can easily vary the amount of pressure you have from 5-30psi by how much you pump it. The couple gallons of diesel is more than enough to bring a big hunk of iron back to the road and out of the mud when lift pumps go out, you run out of diesel, a fuel line gets clogged, etc. But this only works for recovery when the IP fuel return line returns the excess fuel back to the supply line system (ie- it returns the fuel back into the circuit after where you plumb in the sprayer) or doesn't have a return (really old systems I think).

I think...again I only think as I've never done this before... that we can use the garden sprayer method for troubleshooting and basic starting of our trucks but recovery is not practical since the IP fuel return line goes straight to the tank. You'll empty a couple gallons of diesel in a couple mins through the IP return line. At least that's what I understand about the NHC250. No idea how large the return flow is on the 8.3.

But, between you and Fuzzy, I wonder if I can even just use the hand sprayer as a quick "air compressor" to pressure the fuel tank. I keep thinking I'll need to carry my tools to the truck in question and I don't want to work on it too much if I haven't bought it. So trying to figure out the simplest way to trouble shoot the fuel system without having to drag out the equivalent of a contact/recovery team worth of stuff.

 

[TechnoWeenie]

Also, wouldn't be a bad idea to flush the pump at this point, if you get it running.

I'll have to find my other post about it.

 

[TechnoWeenie]

https://www.steelsoldiers.com/threads/m929-questions.214516/#post-2511392 - and a couple below that.

M929 Questions

If you want to get stuff out of the tank and lines, then yes. You can also run biocide if its been sitting for a while. If you want to purge the pump, injectors, etc and clean them out, then you disconnect the supply line going to the IP/PT pump, and your mix of seafoam, power service, ATF/OIL...

www.steelsoldiers.com

 

[LCA078]

Thanks for the suggestions- those are great tips. I should do that to all my trucks as I'm sure there is a ton of gunk in the lines and other system parts.

 

[Csm Davis]

All of this is great troubleshooting but why not just buy the truck expecting a bad IP? Use that as bargaining tool, about 1k, then just fix it. If IP is bad you're covered if not you are golden! The IP is easy to remove and replace and a rebuilder can bump it up in timing and fuel without much if any additional cost during rebuild. Don't fix someone else's truck for free, they might decide to keep it. Don't like it but the world we live in.

 

[LCA078]

All of this is great troubleshooting but why not just buy the truck expecting a bad IP? Use that as bargaining tool, about 1k, then just fix it. If IP is bad you're covered if not you are golden! The IP is easy to remove and replace and a rebuilder can bump it up in timing and fuel without much if any additional cost during rebuild. Don't fix someone else's truck for free, they might decide to keep it. Don't like it but the world we live in.

I hear ya, CSM, and agree with what you're saying. I was really hoping to self-recover the truck as it's parked in an area behind a barn. The owner said I'd need to arrange it to be towed out as a typical RGN truck/trailer wouldn't make it to the truck. So you're right I shouldn't fix another person's problem...but it may end up being my problem if I'm not careful. Either way the deal is on hold at the moment as the owner's uncle is now interested in it. No idea how long that will last...

Thanks for the info that the IP is easy to remove and rebuild. I do like the prospect of adding a few more ponies to that motor if I get it.

 

[LCA078]

The seller called me back and asked if I was still interested in the truck. I hope to take a look at it in the next week or so and want to be prepared in basic trouble shooting of the fuel supply system and IP. I still think (hope) it's something easily fixed...

I've been reading up a lot on the 6cta engine in addition to what I learned from this thread and hope I can have the right tools to do a quick troubleshooting when I go look at it. I'm bringing a couple of fairly new Caterpillar Group 31 batts to crank so I need to be careful and not waste cranking without guaranteeing there's fuel being supplied to the IP.

First, I lifted the pic below from SteelSoldiers but I forgot which thread it came from so thank you to whoever I stole it from!

Here are my questions to ensure I'm getting enough fuel flow and pressure to the IP:
-First thing I'll do is zip-tie the cutoff lever all the way forward and have a pair of wire cutters at the ready if she does fire up. I don't want to waste time troubleshooting the solenoid so I'll just bypass it immediately. I'll also verify the lever actually moves the shaft and it's not stripped (I think I read about that being a possibility).

-I understand that fuel gets sucked in by the lift pump labeled #1, from the tank through the selector valve. The fuel pressure is negative (being sucked) prior to the lift pump and is where air usually gets introduced. After this lift pump, the pressure is positive, around 20-30 psi?? What is the min pressure after the lift pump during cranking?

-To verify it's not air being introduced from a leak before the lift pump, I plan to bring a pump up garden sprayer full of diesel and feed it into the lift pump where it would be sucking from the selector valve/tank. I'll bring an assortment of hose barb fittings and hope to simply attach it where the push-lok fitting screws on a 90deg elbow. Anyone know what the threads are for that elbow and/or the female inlet port of the lift pump?

-The seller said he tested pressures of fuel going into the IP but I have no idea how he did it. It looks hard-lined all the way to the IP after the lift pump. The fuel goes out the top of the lift pump, through a bent hard line to the block (hidden by a bracket), then through the fuel filter #2, then out the point labeled #3 then through a hard-line to #4 which is the IP inlet. Is that the correct path? How do you recommend I test the lift pump pressure? I hope there is an easy way to attached a gage and watch it from the cab but all I see are banjo fittings.

-Once I get the garden sprayer hooked up, I'll verify fuel is flowing through each banjo fitting at #3 and #4. Are there any screens I should clean out while I'm jacking around with the banjo fittings? Any hidden places that get gunked up?

-I understand there is a 10mm bleed screw on the back side of IP, pretty much directly behind #5, the overflow valve. If I have the garden sprayer pumped up to 20 psi, I should get fuel flow pouring out that bleed screw without cranking the engine, right? What I'm trying to do is ensure I have no issues getting fuel to the IP- let me know if I'm off in my thinking.

-Finally, #5 the overflow valve just dumps straight back to the tank, right? If I measure good inlet pressure from either the garden sprayer or from the prime button or when cranking, I assume the overflow valve is working. I'll have vice grips to pinch the line and verify it too.

- If it doesn't fire off quickly, I'll crack open the injector lines to bleed them and maybe add some Chemtool B12 and Marvel Mystery Oil to the garden sprayer to loosen any stuck parts. That's kind of my last line of defense...

-By then, if, and only if I have any battery left, I'll try to place each injector line in a jar of diesel and see if I'm getting blow-back from a bad injector during cranking. I heard an injector stuck open will effectively cause a no-start issue that mimics a bad IP.

-Anything I'm missing for a rapid check on trying to get her started?

Thanks again for all the great inputs.

 

[Csm Davis]

Think I see a problem already right above the banjo fitting on the lift pump there should be a sensor there or it should be capped off.