Here we investigate my own experiences with a pre-VVT 2005 Jeep 5.7 MDS Hemi engine. At 70,000 miles, one of the MDS solenoids stopped working (there are 4 on this engine), the Mopar HEMI Multi Displacement System or MDS.
The resulting symptoms where the engine would not go back to 8-cylinder mode, it stayed in 4-cylinder mode resulting in terribly rough running. Only cutting the engine and restarting cured this.
This is a major engine repair so you can manage the situation as I did for 6 years and 50,000 miles by just locking the Mopar HEMI Multi Displacement System or MDS off. There are 2 simple ways to do this. 1. Manually shift from D to 4 while driving. 2. Press the Tow/Haul button so the light comes on.
Sometimes I forgot to do this and got caught out with a repeat performance of non 8 cylinders running, resulting in me having to stop the engine and restart it. (Not a good idea on the UK’s new “Not so Smart Motorways”) or long tunnels.
If you have an eco-light fitted, it will tell you that you are running on 4 cylinders, but as the one MDS solenoid not working plays havoc with the whole system and delays the 8-cylinder reactivation, no frantic pressing of the Tow/haul button will fix this on a run. You cannot use the Tow/haul button or shift out of top gear 5th to 4th to switch back into 8 cylinder running mode when this failure occurs. I know I’ve tried! Just pull over.
Diagnose the fault properly before you go any further. I used the economy diagnostic tool the OBD2 JScan app and caught the error code one day while the terribly rough running was happening. OBD Error Code: P1414 Definition: Cylinder 4 reactivation control performance failure. That confirmed which MDS solenoid had failed.
You will eventually need to get your just empty every pocket Jeep wallet out and buy some new parts. Or with Rockauto your PayPal will do the same. Its not that expensive to fix the Mopar HEMI Multi Displacement System or MDS
Buy all 4 Solenoids. Mopar part number 53032152AD are fine. They cost around $100 US each. You will need a new intake gasket set. If you drive a 2005 model, get new set of ignition leads, also do all of your injector seals or o rings, replace any plastic parts that have gone brittle. The time to do this is now as you are stripping down quite a bit of the engine. Also do an oil service. Future proof the car or truck.
Do not buy Dorman part number 916511XD. It may be tempting as they are $45 or so, plus there are YouTube videos that tell you they’ll be fine. The photo below shows a Dorman MDS Solenoid after 500 miles. Basically clogged up. They have a severe lack of magnetism, which is the whole point of a solenoid’s function, to turn on and off. The result was a half open solenoid that stopped cylinder 1 from even firing. So only 7 cylinders on a V8…
Misfires, rough running, erractic MDS function, error codes. Stories on YouTube of broken lifters, broken rocker arms, worn and gouged camshaft lobes, lack of vacuum on the intake, leaking gaskets, cracked heads. A mechanics dream of stripdowns. We had the rocker cover off to check for the worst, there was nothing but a clean engine.
So basically I had the same job done twice that was completely unnecessary and its a shame Rockauto would not even credit me for these sub standard Dorman parts. Very short sighted in business sense.
That’s the story folks, spend the extra $200 on spare parts, or you’ll be off-road in a bad way for weeks on end! Plus you’ll pay a lot more than you bargained for with double repair bills.
After all this MDS faffing around trying to make the system work, I gave up. I had it disabled and the Jeep has never run better. MPG has hardly changed. Why use this system still if it causes so many problems? If you really want to save money by fuel consumption in a HEMI, then drive a bit slower and keep cruise control on a bit more and save money that way. No more hesitation from technology that is unnecessary. Plus MDS can crack your block due to uneven heating and cooling, a whole other story!
But then my service mechanic fiddled and managed to cancel the MDS disable code that my engine tune had put in place and then could not reset the MDS as I wanted it to be… OFF. At this point I gave up. Cutting to the chase, on Petrol (or Gas in North America) MDS is fine. On LPG (Autogas which is Propane 95% and Butane 5% blend), it makes the 4 cylinder running cycle a strain as the LPG has less power to offer. So use the gearbox to select one gear lower than the highest to disable MDS on LPG and you’ll be fine. Or use Tow/Haul. If you are driving at 80 mph on the flat the MDS won’t even try to engage, so you can use the highest gears on automatic gearbox still, but downshift manually when slowing, coasting or on a hill.
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