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No run condition and Loping 3126 Cat 7.2 6x6

touareg62

Member
17
55
13
Location
Mohave County, Arizona
Hello Everybody,
I am in somewhat of a pickle as they say.

My engine has always been loping in the past on and off.
Changed the oil and filter. As of a few days ago crank but no start. This is the first time that ever happened, I think the two are related and finally caught up to each other. I ordered a new IPR from, www.Accuratediesel.com
This weekend I am going to check Oil pressure while cranking, with an proper gauge

Below find a link to videos.
My apologies as to the state of the interior.


Thank you all for the support.

GvK
 

Wingnut13

Well-known member
235
562
93
Location
Strafford, NH
First off, I’m no expert on these engines. I did stay at a Holiday Inn a while back, however from what I’ve read, mostly on RV forums…. Sounds like a Heui failure. I have been looking into it as my truck has done this from time to time. Best case you R2 the pump and you are good to go. Worst case seems to be the pump has contaminated the whole system where the injectors have debris in them along with the oil cooler. No codes seem to be present when this happens.

I hope your IPR fixes the issue.
 

serpico760

Well-known member
Steel Soldiers Supporter
643
1,623
93
Location
San Diego, CA
Hello Everybody,
I am in somewhat of a pickle as they say.

My engine has always been loping in the past on and off.
Changed the oil and filter. As of a few days ago crank but no start. This is the first time that ever happened, I think the two are related and finally caught up to each other. I ordered a new IPR from, www.Accuratediesel.com
This weekend I am going to check Oil pressure while cranking, with an proper gauge

Below find a link to videos.
My apologies as to the state of the interior.


Thank you all for the support.

GvK
Yeah that's strange maybe you could drop a line to this guy he might know what's up. Mine has never done that thankfully
 

touareg62

Member
17
55
13
Location
Mohave County, Arizona
First off, I’m no expert on these engines. I did stay at a Holiday Inn a while back, however from what I’ve read, mostly on RV forums…. Sounds like a Heui failure. I have been looking into it as my truck has done this from time to time. Best case you R2 the pump and you are good to go. Worst case seems to be the pump has contaminated the whole system where the injectors have debris in them along with the oil cooler. No codes seem to be present when this happens.

I hope your IPR fixes the issue.

@wingnut, @serpico760

Thanks for the support, I agree I hope the IPR will fix it. Should know Saturday since delivery is slated for that time. But agreed also, on the RV forums, it all seems to be coming back to the HEUI, at that point removing the injectors would be prudent for sure. Just when I received the title from Florida, (7months) goes to figure. LOL
 

fuzzytoaster

Well-known member
Steel Soldiers Supporter
4,285
3,100
113
Location
Fort Worth, Texas
Do the simple steps first and trace your fuel lines looking for cracking and damage. Air in the system can cause various symptoms you're seeing but the second video sounds like multiple cylinders are missing. The HEUI pump is working since it does run (or did?). We could speculate all day but without any solid diagnostics it's a SWAG (scientific wild @ss guess).

Find a friend who has CAT ET and talk to the ECM. Check HEUI pump pressures and perform injector actuation tests. There are a few sensors on the driver side of the engine that send oil pressure and fuel pressure info to the ECU and they've common failure points. When they fail or failing trucks can run rough as if they default to a stock setting, go into safe mode, or even start once but never again.
 

touareg62

Member
17
55
13
Location
Mohave County, Arizona
Do the simple steps first and trace your fuel lines looking for cracking and damage. Air in the system can cause various symptoms you're seeing but the second video sounds like multiple cylinders are missing. The HEUI pump is working since it does run (or did?). We could speculate all day but without any solid diagnostics it's a SWAG (scientific wild @ss guess).

Find a friend who has CAT ET and talk to the ECM. Check HEUI pump pressures and perform injector actuation tests. There are a few sensors on the driver side of the engine that send oil pressure and fuel pressure info to the ECU and they've common failure points. When they fail or failing trucks can run rough as if they default to a stock setting, go into safe mode, or even start once but never again.
@fuzzytoaster

I was looking to get this, (Price is reasonable) https://ironfieldspares.com/products/3177485-cat-et3-diagnostic-tool
But yes as you suggested will check the basics first. I always thought loping meant air being pulled in, but it being gone for some time and then return it threw me off a bit.
 

Ronmar

Well-known member
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113
Location
Port angeles wa
With all diesels I start with the basics first. Fuel is life… What does the primer bulb feel like? If the system is full of fuel like it should be, the primer should be firm from the start as you should be hydraulically pushing against the pressure regulator at the far end of the system from the first push. If there is air in there, it will compress and the bulb will feel spongy.

So step one, you need a firm bulb and to find what is letting air in if it is not firm.

On the 3126 LMTV the fuel flows from the tank, to the primary filter where the primer is, thru the fuel lift pump on the HEUI pump, thru the secondary filter and to a port on the front of the cylinder head to feed the gallery. On the back of the head is a pressure regulator and the fuel returns from there to the tank.

The lift pump is a plunger pump driven off of a cam in the HEUI pump. More RPM = more pump strokes). Between the lift pump and the secondary filter there should be a T fitting with a test port. You need to hook a 100 PSI gauge there to check for baseline fuel pressure(I show how to do this in a video linked below). The pressure regulator is a simple spring loaded obstruction that requires a certain amount of pressure to force it open. With the primer bulb you should be able to push it to 10PSI At the test point. while cranking you should see ~10 PSI. At idle 20-25PSI and as you increase RPM it should increase and plant itself at 60PSI.

Step 2 measure primary fuel pressure.

The whole fuel injection scheme is based on this baseline fuel pressure. When there is problems it becomes hard to start and does not run properly. Your video could be explained by this. if a bad leak is mixing in air, the lift pump at its slower idle pulse rate will reach a point where it cannot deliver enough fuel, so you don’t get that 25PSI of hydraulic pressure in the gallery, along with a bunch of air and you cannot feed all the injectors Enough fuel to fire properly. You bump up the RPM and the higher lift pump pulse rate moves more fuel and increases gallery injector feed pressure so the injectors start to work better. It does not take a significant ammount of additional fuel to go from idle to high RPM unloaded though, so I imagine if you tried to run like this under load, the injectors would once again act like they are starved as they would have trouble delivering more fuel…

The fact yours runs better at higher RPM is very telling. I do not believe a HEUI issue or damaged/clogged spool valves on the injectors would work better at higher RPM…

Cat licensed the HEUI system to ford, it is what is found in all the power-stroke diesels. I know in that system, insufficient baseline fuel pressure kills injectors. I have never seen this stated in any cat documentation, but it makes sense that it will also cause damage if not corrected. Why neither manufacturer chose to monitor it is beyond me…

Here are some videos I did on the 3116 fuel system. The 3116, 3126 and C7 use the exact same baseline fuel system. The only real difference is it flows thru the head the opposite direction on the later engines.


Here is what a small air leak looks like on a primary fuel pressure gauge… you will notice this small ammount of leakage is not big enough to really effect the engines ability to run...


if your baseline pressure is good, you will need someone with the cat software to communicate with the ECU to monitor the HEUI pressures and operation…
 
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fuzzytoaster

Well-known member
Steel Soldiers Supporter
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Location
Fort Worth, Texas
@fuzzytoaster

I was looking to get this, (Price is reasonable) https://ironfieldspares.com/products/3177485-cat-et3-diagnostic-tool
But yes as you suggested will check the basics first. I always thought loping meant air being pulled in, but it being gone for some time and then return it threw me off a bit.
That unit only works on equipment. I orchard that exact kit from that site and it wouldn't communicate with anything due to being 24v. Look into a Dearborn Protocol Adapter aka DPA 3+/4+ on ebay. There are military ones but all should act the same of that generation. If you can't find one I have a spare I could part with. I use it for all my Cat issues and programming.
 

ramdough

Well-known member
1,554
1,729
113
Location
Austin, Texas
Hello Everybody,
I am in somewhat of a pickle as they say.

My engine has always been loping in the past on and off.
Changed the oil and filter. As of a few days ago crank but no start. This is the first time that ever happened, I think the two are related and finally caught up to each other. I ordered a new IPR from, www.Accuratediesel.com
This weekend I am going to check Oil pressure while cranking, with an proper gauge

Below find a link to videos.
My apologies as to the state of the interior.


Thank you all for the support.

GvK
I had a similar issue on my A1. The solution for me was a fuel additive.

Here is the thread with resolution.



Sent from my iPhone using Tapatalk
 

touareg62

Member
17
55
13
Location
Mohave County, Arizona
@ramdough

Thanks for the thread, I bought the fuel additive already as suggested by @Mullaney good stuff! Seemed to run better at the time. Yesterday I pressed the Bulb at the filter, bulb was soft and had to pump 3 times or so to firm it up. But 10sec later it was soft again. @Ronmar had some good insights and after seeing a leak at the bottom of the bowl, decided to by the whole assembly from dieselfiltersonline.com cost was worth (266,-) the peace of mind, this way I know what and when I put the assembly on and keep track of service intervals better. Tomorrow I will receive the Scanner suggested by @fuzzytoaster so we will see what story the truck will tell. :)
 

GeneralDisorder

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Steel Soldiers Supporter
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113
Location
Portland, OR
@ramdough

Thanks for the thread, I bought the fuel additive already as suggested by @Mullaney good stuff! Seemed to run better at the time. Yesterday I pressed the Bulb at the filter, bulb was soft and had to pump 3 times or so to firm it up. But 10sec later it was soft again. @Ronmar had some good insights and after seeing a leak at the bottom of the bowl, decided to by the whole assembly from dieselfiltersonline.com cost was worth (266,-) the peace of mind, this way I know what and when I put the assembly on and keep track of service intervals better. Tomorrow I will receive the Scanner suggested by @fuzzytoaster so we will see what story the truck will tell. :)
You are supposed to pump it till water/fuel runs out of the drain on the bowl. That's how it's supposed to work. It's somewhere in the maintenance schedule or PMCS..... can't remember where I saw that. But yeah it will dump water/fuel from the bowl once the primer gets hard so I bet it's not "leaking" per-se. Mine the drain was plugged up solid on it and I was able to clear it after taking it apart for cleaning and replacing the element.
 

Ronmar

Well-known member
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Location
Port angeles wa
It actually says it around the ring on the primer. Open drain and pump bulb to discharge water… ideally you should open the drain and nothing should happen Until you pump the bulb. if you open the drain and it sucks air back in, the flapper bypass valve is leaking and fuel is running back down the supply line as the weight of the fuel down that line is heavier than the bowl and will siphon back that way once you open the drain port.

I think though that he was referring to an air leak Because the primer bulb was going soft. The water separator bowl and primary filter are prime locations for a leak. Mine leaked there, had a hairline crack on the bowl And would leak fuel back thru the return over time, replacing that fuel with air Giving me a soft bulb and hard starting, ir rough initial idle.

the problem with suction side leaks is they can leak air pretty bad and you will have no indication of it from the outside. I finally found that bowl leak by filling the system with fuel, disconnecting and capping the return at the tank, then disconnecting the supply at the tank and connecting a pressure regulator there and injecting about 15 PSI to pressurize the entire fuel system. After a few minutes I found fuel on the outside of the bowl. I replaced that filter and bowl with a Baldwin BF1222. Which is a one piece metal filter and bowl with drain valve.

Air leaks can be tricky. The hands down best way to make sure you have them all is testing baseline fuel pressure Or putting a sight glass in the return line. I would not consider any fuel system work “finished” until I ran baseline fuel pressure…
 
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Ronmar

Well-known member
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113
Location
Port angeles wa
Oh great pics! Mine had a really long bug leg or a thick horse hair in it when I got my truck. Was one of the first things I had to fix to get the primer working…

That flapper is the normal entrance pathway into the filter for fuel when the engine is running. The lift pump moves a pretty large volume of fuel when running. That flappers purpose is to allow the very small low volume primer bulb to operate in parallel with the high volume running pathway. When that flapper doesn’t seal the primer won’t work either, it will just suck fuel back thru the leaky flapper instead of lifting fresh fuel from the tank.
 
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touareg62

Member
17
55
13
Location
Mohave County, Arizona
Hello all.

Quick update on the No Run condition. After checking fuel system and pressures there where no issues on that side.
So moved onto the HEUI side of things. Checked the driver on the pump which was okay. Hooked the Ecat tool to the truck with the offroad adapter, ecat showed low actuation pressure of 238PSI where desired would be 1236PSI, but they will fire at 870 or so. I was close to removing the HEUI pump but the miles where so low on the engine that I could not justify going that route so I went the sensor route frst. I disconnected the high pressure sensor Item 5 on the attached screen grab and the engine would start up and run perfect. But when plugging in the sensor the engine would start to lope again. So went to the CAT dealer they had them in stock, which is saying something in my mind. 244 bucks later engine purs like a cat. Thank you all for the help and advice.!!

the SIS cat, I bought on ebay. https://www.ebay.com/itm/144809231591

Cheers,

GvK
 

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