Intermittent check engine light at max speed/RPM

[tuckerj84]

I could use some help diagnosing a persistent check engine light and power reduction.

2006 M1083 A1R C7

It started with an intermittent check engine light only at max speed/RPM. It seems like the ECM may have since derated itself, and while the check engine light no longer appears, there is significantly reduced power. The only code I can find has to do with boost pressure - 102.7.

• I stated by checking the wastegate actuator. This seems to be function properly - VIDEO.
• I then checked the operation of the wastegate on a test drive and it barely opens. VIDEO - you can barely see it move. Perhaps because it's derated???
• Checked boost pressure. It's only producing about 13 psi. VIDEO
• I haven't been able to locate any air leaks in the charged air cooler or associated tubing.

I'm leaning toward replacing the boost control valve. Does anyone know if this could partially fail? I would think it would work or not at all and it seems to be at least partially working.

Am I on the right track? Any other ideas?

 

[GeneralDisorder]

The 3126 and C7 transducers always fail due to age. All of mine went out in the first year of me daily driving my 2008. Replace the boost pressure, atmospheric pressure, and oil pressure transducers. The boost pressure transducer in particular puts the ECM in limp mode. It won't add fuel because it can't trust the boost sensor - no fuel = no power = won't build boost. You should be seeing 26+ psi of boost.

Get your replacements from the CAT dealer ONLY. Aftermarket are usually crap and often don't work right out of the box.

And get a laptop with CAT ET. It's much more useful than a little gauge.

If you are interested in the 370 HP tune for that truck let me know.

And I *hope* you got rid of the XML's in your profile photo......

 

[tuckerj84]

The 3126 and C7 transducers always fail due to age. All of mine went out in the first year of me daily driving my 2008. Replace the boost pressure, atmospheric pressure, and oil pressure transducers. The boost pressure transducer in particular puts the ECM in limp mode. It won't add fuel because it can't trust the boost sensor - no fuel = no power = won't build boost. You should be seeing 26+ psi of boost.

Get your replacements from the CAT dealer ONLY. Aftermarket are usually crap and often don't work right out of the box.

And get a laptop with CAT ET. It's much more useful than a little gauge.

If you are interested in the 370 HP tune for that truck let me know.

And I *hope* you got rid of the XML's in your profile photo......

Thank you sir! A was looking for a problem rather than the addressing the sensors. Makes sense.

Do you have a good source to purchase CAT ET?

I need to chat with you soon about a 370hp tune as well. Just want to get this thing dialed in first.

 

[Ronmar]

What were the conditions of that boost pressure video? Were you driving or in gear?

 

[tuckerj84]

That was parked, engine warm. Full throttle for a short duration.

It is consistent with driving though. I could take another one, but results are about 12-13psi max. Usually closer to 11psi average when driving.

 

[Ronmar]

Boost is usually dependent on load. Do a torque converter stall test. Second gear, stand on the brakes and add throttle. It should top out at the converter stall point ~ peak torque and full engine load. You don’t hold these too long as it really warms up the transmission fluid that should deliver max boost if the system is capable of it…

 

[GeneralDisorder]

Thank you sir! A was looking for a problem rather than the addressing the sensors. Makes sense.

Do you have a good source to purchase CAT ET?

I need to chat with you soon about a 370hp tune as well. Just want to get this thing dialed in first.

I'll send you a PM. You need manuals for that truck also.

 

[GeneralDisorder]

That was parked, engine warm. Full throttle for a short duration.

It is consistent with driving though. I could take another one, but results are about 12-13psi max. Usually closer to 11psi average when driving.

The wastegate requires pressure to open and with computer control, you generally make the wastegate actuator about 1/3 of the max boost that you plan to run. That way when you do open the wastegate it responds very quickly, and if there's a problem you can drop the boost to "wastegate" level. Based on your readings the wastegate is likely around 1 bar (14.7 psi) - the wastegate varies somewhat depending on exhaust flow and back-pressure on the wastegate flapper. A really good turbocharger will exhibit about 2-3 times the boost pressure in the exhaust manifold before the turbine wheel so you have ~30 to 45 psi of pressure against the wastegate in addition to the actuator. Since the computer has seen a problem with boost pressure you are likely in a perpetual limp mode.......

Actually had this happen on my truck twice. It did clear the code on it's own both times. Once I pulled over and restarted and the other time I was in traffic and so the reduced power wasn't really causing a traffic jam so I just buried the throttle and when I eventually got to about 50 mph it cleared on it's own and the power came back. Has never happened again after replacing the boost transducer.

BUT I did have this happen to an A1P2 down at the base and in the case of that truck the boost pressure transducer had failed but not electrically. It was STUCK at zero psi after sitting for a couple years. The guys couldn't figure out what was up with it (no check engine light), and had done some fuel system and other services but the truck would not go over 10-15 mph. I noticed in CAT ET that the boost pressure was just zero, and oil pressure was stuck at 41 psi (engine off). So we replaced both. This didn't resolve the limp mode though - there was some derate code present and the ECM was absolutely pissed off and I never did figure out how to clear it. I ended up flashing that ECM to wipe it and that fixed the problem. So you might have put your ECM into a state where basically only someone with dealer level CAT ET with flashing capability can unlock it. I can do that but if you end up in that situation in the field the best solution is probably to carry a spare ECM since flashing the ECM is a process that most people aren't going to be doing. There may be some other way to clear that fault but I couldn't find it and haven't run across that a second time yet. It does sound like that's what you have going on though.

 

[tuckerj84]

Boost is usually dependent on load. Do a torque converter stall test. Second gear, stand on the brakes and add throttle. It should top out at the converter stall point ~ peak torque and full engine load. You don’t hold these too long as it really warms up the transmission fluid that should deliver max boost if the system is capable of it…

Got up to 23 psi using this method. I have the sensors on order and will start there.

 

[tuckerj84]

Boost pressure sensor took care of this one. Now on to other projects...