The Jeep MDS System can be a challenge
How to turn off the MDS feature with the Mopar HEMI Multi-Displacement-System found on Jeep, Chrysler, Dodge & Ram vehicles, without using a professional tuner. Not to disable it completely as its generally a good system and will save fuel, but to give you the consumer or driver more choice in how and when it's deployed.
The MDS (Multi-Displacement System) is Chrysler's form of engine variable displacement. When the vehicle's throttle is closed or steady, it shuts off four of the eight cylinders in a V8 engine. MDS activates when you're traveling at a constant speed, decreasing emissions and improving fuel economy by up to 20% according to the manufacturer.
How to turn off your Jeep MDS without a tuner
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Its pretty simple if you watch this video. Cutting to the chase, on Petrol (Gasoline in North America) with MDS is fine. On LPG (Autogas - which is Propane 95% and Butane 5% blend), it makes the 4 cylinder running cycle a real strain as the LPG has 10-15% less power. So use the auto gearbox to select one gear lower than the highest to disable MDS on LPG or (Gasoline) 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.
How my own Jeep's MDS problems started back in 2015
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.
I used the economy diagnostic tool the OBD2 JScan app and caught the error code one day while the rough running was happening. OBD Error Code: P1414 Definition: Cylinder 4 reactivation control performance failure. That confirmed which MDS solenoid had failed. This is in Bank 2 of the engine. Also watch out for P3497 Cylinder Deactivation System Bank 2 error code.
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.
Living with my MDS problems
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.
Pushing the MDS Parts Cannon Button
Its not that expensive to fix the Mopar HEMI Multi Displacement System or MDS. Buy all 4 Solenoids. This is also a good time to do an engine oil flush to clean all the oil debris inside your engine after 100,000 miles.
What MDS parts to buy
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.
What not to do when you deal with MDS issues
After I'd had the MDS Multi Displacement System repair done I suddenly got loads of new MDS error codes.
P3400 Cylinder Deactivation System Bank 1
P1411 Cylinder 1 Reactivation Performance
P0301 Cylinder 1 Misfire Detected
P0300 Random Multiple Cylinder Misfire Detected
So lesson learned here, 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...
So basically I had the same job done twice and that was completely unnecessary. Maybe I should have done the engine oil flush before changing to MDS Solenoids out?
