My grand Cherokee idles rough, has cylinder misfires as well as a transmission code stating the solenoid is stuck open. The shop I took it to stated the engine is going bad based on the compression test. however when I researched the compression test results, it is within normal range. I also researched causes of these particular misfires and saw it could be due to the throttle position sensor and o2 oxygen sensor.
Can the community please help me so I have a better idea if I really do need a new engine?
Can’t help you if this is all the info you’ll share.
What engine? What error codes? The actual numbers please. ONE compression number tells us nothing, we need all…6, or all 8… whatever your engine has… again, you don’t say.
If you can’t supply these things, then yes, you need a new mechanic.
Other than more info being needed I have to wonder how and why they only charged 115 dollars for doing all of that guessing which includes swapping plugs, compression test, new coil, and how they tested all injectors working properly.
If by 175 PSI of compression you mean all cylinders are at that number then that is fine and should not cause a misfire.
Sorry for not providing more information, I am new to troubleshooting car issues and was unsure of what to share. It is a 5.7l v8 hemi engine, and the car is a 2007. I attached a picture of the OBD codes that o received on my reader. Please let me know what other information I should provide, thank you for your patience
I’m not a mechanic, but I’d think that MDS solenoid stuck open could possibly be causing all of those misfire codes.
I’m not really sure on the transmission codes either…although I’d think best case a solenoid has failed in the trans also.
Short answer, I think I’d want another opinion before calling the engine bad. The MDS system causes certain cylinders to not fire when the engine is under light loads in order to save fuel. So, it’s not a stretch to think that an “MDS solenoid stuck open” would cause misfires.
I agree. The MDS codes are likely causing the misfire codes and they should be considered first. The P1775 and P0841 are transmission codes that have nothing to do with the MDS codes and are a separate pair of problems to be addressed.
The likely causes of the MDS codes in order are:
Low oil pressure or blocked oil passage
Faulty MDS Solenoid
MDS Solenoid harness is open or shorted
MDS Solenoid circuit poor electrical connection
Faulty Engine Control Module (ECM)
Since this is a 15 year old vehicle likely with, on average, 150K to 225K miles (you didn’t post) on it, the blocked oil passages could be likely as could low oil pressure caused by a worn out engine. If your mechanic ran an oil pressure test and found the pressure very low and looked in your engine and found it all gunked up he may very well have concluded the engine needs to be replaced.
The MDS engines DO have a habit of destroying camshafts because the MDS screws up and the metal bits wreck the rest of the engine. Metal in the oil pan and a poor compression test result is a pretty good indicator as well as removing a valve cover to see if all the valves open when the engine is rotated.
You might well need a new engine but get a second mechanic to take a look and ask questions of them.
