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c-mac

MP8 boost pressure dtc's

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I don't know why but these various boost pressure dtc's and complaints of intermittent pow loss have been coming in lately. This is an oilfield fleet so its hard to get feedback from the drivers, there's no telling who will be driving any truck at any time. Anyway If no boost leaks are detected, the EGR seems to be working ok and VGT test runs good would you say I have a boost (intake) pressure sensor that acting  up  intermittently?  Or what have you guys been seeing? Thanks in advance.

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What your seeing Could be a boost sensor However another issue that can pop up is the VGT sticking when warm we have had this happen and it is very hard to nail down with out ( Just popping) a different turbo on that's a foreman's term for doing a semi difficult job to find out it was the wrong thing to do! 

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Like FJH said. If you have PTT/VCADS software, Get truck up to opearating temp and do a VGT turbo function test and watch the motor effort of the turbo actuator. If its getting over 128 it could be the vains sticking in the turbo.  In that case you need a new turbo.   If you dont have the PTT software then I'd replace the boost sensor and also replace the harness end if its a non-DEF model. The dealerships have the harness ends. Also check the intake manifold for broken bolts and check the after cooler's top and bottom tubes for being blown out , its very common.

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On 7/5/2016 at 9:16 AM, fjh said:

What your seeing Could be a boost sensor However another issue that can pop up is the VGT sticking when warm we have had this happen and it is very hard to nail down with out ( Just popping) a different turbo on that's a foreman's term for doing a semi difficult job to find out it was the wrong thing to do! 

My shop calls popping a "15 minute job" Also I'm not sure what MackPro is referring to as an after cooler?

Edited by c-mac

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He's referring to the air cooler mounted in front of the radiator, check the tubes for cracks.

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Ok, thats what I thought on the cooler. Anyway I ran the VGT function test and it seemed to work fine. The vgt effort never got over 60 or so. I did replace the boost sensor but it did no good. I dont have a cdl so I can't take it out and drive it myself. I can't get much boost pressure by gunning it in the shop but when I do it gets about 7 or 8 psi .I thinking I would have to be a pretty bad leak to set a dtc and have lack of power. I've had trucks come in with the oring blown out of the air cooler line at the cooler and it was whistling and didn't set a code or show any lack of power.

Quote

 

 

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You say various boost codes? Different fmi's? What are the code numbers?

Possibly not actually a mechanical issue but maybe electrical. High resistance in the circuit for example.

Might pull the connectors off of the ecu and check for oil wicking. I've seen that cause some really strange things.

Edited by steeler

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I wrote those code numbers down but i think I through the paper away. This is like a plague, every day I'm getting another tractor or two. Today I got to ride in one on the road, it seemed ok at times and then fall on its face while going through the gears. There is a service bulletin to check the pin connectors in the round VGT harness connector. I have done several of those but not in the last two years. the drivers complained of surging low power ant times. Those tractors were easy to troubleshoot, with key on engine off you could wiggle the VGT harness connector and you could hear the VGT motor run. When running the VGT tests on the tractors I'm working on now the sweep test goes from 0 to 100 with 40 effort hot. I assume there is a sensor and thats not just reading what the the VGT is suppose to be doing. But now that I think about it we had a few older, like 08 models that the inner part of the turbo gasket fell down into the turbo and stopped the VGT from doing a full sweep. So I guess there is a sensor. This is an oilfield fleet of abused and neglected tractors that has a lot of idling time on them. example.. 4 years old truck with 9800 miles and 6800 hours. Our company is hanging on by the skin of their teeth with this downturn in the oilfield right now o I just cant go throwing new turbos at the trucks and that not be the problem. Also currently I am the only mechanic addressing the technical issues with these trucks ranging from 08 to 2013 models, and I stay covered up with SCR problems. I need some help!

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some do and some don't but there all inactive. I cleared all the codes on one and let a fella go drive it. He said he could only get 50mph before turning around and coming back. When I checked it it only had three boost codes. I haven't had any formal training on these trucks, I was an import dealer auto tech for 25 years prior. I've been learning these trucks by the seat of my pants for the last 6 years. I have no manuals and have no idea what the code letters mean with the dtc's. I sure was hoping one of you guys would say its this or that. I drove one around the yard yesterday and it felt like the boost was "dumping" then surging back, if that makes any sense. Maybe like the bypass valve decided to open up just for shits and giggles.

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Yeah if you could get those code numbers I'd be glad to look at the diagnostic tree and maybe give you an idea on what to check.

I wish these were as easy to diagnose as the AI or Etech, but those days are gone sadly.

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Ok, SPN 1127 engine turbocharger boost pressure FMI 18 and 10

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For EPA2010 (MY 2010 and Newer)

image.png

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Thats pretty much what guided diagnostics told me. thanks I need to get a book like that though

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What's the best way to check for leaks in the intake system? Just take off the intake to the turbo and through a test gauge setup on it? I have the same problem

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We are having a similar problem. i think we have narrowed it down to a wiring issue somewhere on the wires from the boost pressure sensor.

2011 chu613 mp8

i am replacing the boost pressure sensor again just to verifiy its not the problem.

Friday i will be replacing the connector for the sensor, we will go from there.

 

Truck lost power,each time the boost pressure would drop to nothing, several trips to the dealer and other shops, each time it cam back it ran for a little bit then fell on its face every time.

This morning I wiggled the wires on the sensor it ran fine until i hit a bump the back down.

now I cant get it to run right again!

we will see what a new sensor and a connector does.

anybody know what the readings on the 4 wires on the boost sensor should be?

 

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On July 5, 2016 at 7:39 AM, c-mac said:

I don't know why but these various boost pressure dtc's and complaints of intermittent pow loss have been coming in lately. This is an oilfield fleet so its hard to get feedback from the drivers, there's no telling who will be driving any truck at any time. Anyway If no boost leaks are detected, the EGR seems to be working ok and VGT test runs good would you say I have a boost (intake) pressure sensor that acting  up  intermittently?  Or what have you guys been seeing? Thanks in advance.

We found motor oil from the head traveling down the wiring harness to the top plug on the computer causing a short circuit. Try checking for the presence of oil in the plugs on the computer. We are trying to clean the oil out of the harness and re sealing the harness where it comes from the head. 

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I did find oil in the lower connector to the ecu. I cleaned it all with contact cleaner but didnt help. I didnt know about a problem with the harness connector to the pressure sensor..the one on top of the intake manifold just back from where MP8 is embossed on the side. thats the only one I see. On another truck I found a very bad exhaust in the J shaped pipe from the egr to the cooler, maybe when it pressures up it could be blowing boost back that way and leaking. ought to have the gaskets and clamps today. I'll let yall know if it helps.

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Well I got the exhaust leak taken care of but the problem is still there.

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Mack "fixed" my truck but I still have only 5 MPG and low power, truck starves for air near 1600 rpm. Starts skipping and missing until I let off the gas and mash it again. 28 psi is the highest boost gets. 

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1 hour ago, Keffer inc said:

Mack "fixed" my truck but I still have only 5 MPG and low power, truck starves for air near 1600 rpm. Starts skipping and missing until I let off the gas and mash it again. 28 psi is the highest boost gets. 

Use the hand throttle to wind the motor up to 1200(ish)rpm and soak all the intake hose connections with soap and water mix.  Best bet would be when it's doing a "passive regen" (?), not sure if the MP8 is the same, but my MP7 runs about 5 psi boost when this occurs....

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how was your truck running before you did injectors? I'm thinking mine may be bad now instead of a boost issue. No matter what gear or loaded/unloaded, about 1,500 RPM is when it starts to shake and loose power. Feels like a misfire,

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not sure about the rpm but it seemed to be about 15 or so. every time i shifted it would pull normal for a second then no acceleration. grab another gear and the same thing. Feels like a gas engine with an ignition breakdown.

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