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Mav’s M1088A1 Conversion

Mavcaster

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This is interesting. First off, I watched a video of a guy who owns a motor home with a cat engine. 3116 or 3126. He had low oil pressure at 90k miles and put in a new oil pump and bearings. That fixed everything. My truck idles cold at 40 psi. Cruising cold at 60 psi. Warm idle at 17 psi. All within spec. My neighbor has a c7 in his lmtv and has 80 at cold idle and like 60 cruising warm and 40 at warm idle. In other words, more oil pressure than me. So I went to Empire Cat in Tucson to inquire about a new oil pump. She required my engine serial number which I had. If I recall correctly, the original oil pump part has been superseded like 4 times. The latest iteration is a Gerotor type. (is the original not a Gerotor?) She acted like they knew there was premature pump wear and changed the style of pump. I dont know this to be fact, but she was knowledgeable. There are two pumps for a 3116. A new and a reman. Both are like $1800 but the reman returns $1100 with your core making it $700 and change in the end. So, I would be curious to know how difficult changing the pump is and which pump you go with? I may be doing the same someday.... is this the pump you are getting? Thanks, and would love to see more pics!

20R-7247: PUMP GP-GRTR | Cat Parts Store
I’ve watched that same video a few times myself and had considered changing it too until I saw the price but now I just have to. I don’t have the pump out yet so can’t confirm but it’s my understanding the original pump is a gear pump and not gerotor. My 3126 has 54K on it though for reference, possible that it has been upgraded I dunno. I don’t recall oil press being on the high side so likely not the new pump in there. And yes that is the reman p/n I am looking at as well.
 
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RRaulston

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Please
I’ve watched that same video a few times myself and had considered changing it too until I saw the price but now I just have to. I don’t have the pump out yet so can’t confirm but it’s my understanding the original pump is a gear pump and not gerotor. My 3126 has 54K on it though for reference, possible that it has been upgraded I dunno. I don’t recall oil press being on the high side so likely not the new pump in there. And yes that is the reman p/n I am looking at as well.
Please keep us updated with pics!!! Just curious, but how did you discover this? and I'm wondering if the teeth caught something in between them like a piece of metal?? Anything in the pan??
 

GeneralDisorder

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I would have probably run it too if it wasn’t for the crack almost clean across the pump arm.
Yeah I saw that but that's not the sack of buttholes - the pump just drops off the bottom of the engine. The UGLY part is the chipped drive gear tooth because I'm fairly certain changing that requires removing the timing cover.

And it's pieces of those teeth that broke the pump housing - tip of gear tooth gets broken off in the root of the driven gear teeth and comes back around and pushes the gears apart - breaking the pump housing.
 

Mavcaster

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Maryland
Yeah I saw that but that's not the sack of buttholes - the pump just drops off the bottom of the engine. The UGLY part is the chipped drive gear tooth because I'm fairly certain changing that requires removing the timing cover.

And it's pieces of those teeth that broke the pump housing - tip of gear tooth gets broken off in the root of the driven gear teeth and comes back around and pushes the gears apart - breaking the pump housing.
Exactly what I was thinking too on what caused the crack but that top gear also comes out with the pump so shouldn’t be too bad of a job.
 

Mavcaster

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Location
Maryland
Please

Please keep us updated with pics!!! Just curious, but how did you discover this? and I'm wondering if the teeth caught something in between them like a piece of metal?? Anything in the pan??
I found it because I found metal debris on the chip collector when changing the oil. Decided to pull the pan to have a look around but did not see the broken tooth or the crack or anything else so closed it up. When torquing the pan, one of the bolt holes must have been over tightened in the past at some point because it pulled out when I went to put torque on it. It still caught most threads I could feel so decided to see if it would seal with only one bolt loose…well it leaked so drained the oil and pulled the pan again to repair that bolt hole with a helicoil. While I had the pan off and since it had ran since the last time it was off, that broken tooth showed itself and funny enough was pointing right at the crack that I missed during the previous inspection.

Not something that I wanted to deal with but at least I feel better about the metal found on the plug now.
 

RRaulston

Well-known member
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Location
Sahuarita, Arizona
I found it because I found metal debris on the chip collector when changing the oil. Decided to pull the pan to have a look around but did not see the broken tooth or the crack or anything else so closed it up. When torquing the pan, one of the bolt holes must have been over tightened in the past at some point because it pulled out when I went to put torque on it. It still caught most threads I could feel so decided to see if it would seal with only one bolt loose…well it leaked so drained the oil and pulled the pan again to repair that bolt hole with a helicoil. While I had the pan off and since it had ran since the last time it was off, that broken tooth showed itself and funny enough was pointing right at the crack that I missed during the previous inspection.

Not something that I wanted to deal with but at least I feel better about the metal found on the plug now.
Not what you wanted to see but finding it may have saved your engine. That is a mess you didn't want for sure!
 

GeneralDisorder

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There are TONS of these pumps on ebay also. Here's a 2008 pump that looks nice and you can see it is the gerotor style (makes my hopeful that my 2008 A1R has this style already). Reputable seller by the looks of the feedback. For the ridiculous price I would be tempted to save the $500 or potentially $1500 if they won't accept your core.

 

Mavcaster

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Maryland
I asked for p/n verification on that pump just to be sure the pumps are the same. If so I’ve got no problem buying a used pump.
 

GeneralDisorder

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There's obviously a huge market for these. Aftermarket one's are everywhere and are CHEAP. I would not worry about it "working" - I would worry about the metallurgy and the heat treat of the gears and rotors, etc. Longevity might be the insidious killer here and the false sense of security of having a "new" oil pump might compound the damage. I wouldn't risk it. As with a lot of regular car parts - I would prefer a low mileage, good condition "factory" part over some aftermarket piece with a questionable pedigree - especially a part so vital to engine longevity and one so absolutely inaccessible for regular inspection. Absolutely out of the question in my opinion.
 

GeneralDisorder

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I suspect you have an issue with the injection actuation pressure sensor or it's wiring. The low +5v supply voltage code is making me suspect the sensor is going short circuit internally and pulling down the ECM's +5v sensor power supply although that only shows a single occurrence. I would be checking the wiring carefully - on my truck the wiring connector to my oil pressure sensor is intermittent and I sometimes have my gauge peg out or drop to zero. Seems to be a connector pin fitment issue - I sprayed it down with Deoxit and it's.... "less intermittent" I guess you would say. I likely need to replace the harness connector in my case.

A google for "cat 3126 injection actuation pressure sensor" indicates they are a very popular item being sold all over the place with both genuine and aftermarket suppliers.

Ran across this (not for the 3126 but going to be basically the same troubleshooting steps):

 
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