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Discussion Starter #1
Short version: I'm no Mr. Goodwrench but I'm still fairly handy. Is replacing an MDS Solenoid something that I could do myself? Is it as straightforward as removing the intake manifold, removing the existing solenoid (carefully, I've read they're fragile), installing the new solenoid, and re-installing the manifold? Are there any gotcha's or things I need to know about?

Long version: I was visiting family this week about 400 miles away and my car started vibrating about 30 miles from my cousins house. It vibrates rough on idle and accelerates roughly, but smooths out at highway speeds. It just so happens that my cousin owns a used car dealership and had his mechanic take a look at it. It's throwing code P1417 and based on my symptoms and everything I've read, it's pointing at the MDS solenoid. I change the oil regularly and always use 5w20 (although the last oil change was the first time I used synthetic....Valvoline SynPower 5w-20). The mechanic would have replaced it for me but we couldn't find one locally (rural Virginia) and I wasn't going to be around long enough to order one.

Also this may or may not be related, but about 2 months ago I was getting code P0307 - cylinder 7 misfire. I changed the plugs (I was overdue anyway) and the ones I pulled from cylinder 7 were in much worse shape then the others. They were also loose, and the code didn't reappear but it seems odd to have 2 issues with cylinder 7 so closely together. Maybe coincidence, maybe not.

Oh, I've got about 106,000 miles.
 

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Loose plugs in cylinder #7 didn't do you any favors!

Have you inspected the wiring harness(es) between the PCM and the solenoids for any problems?

The problem may be with the deactivating roller tappet for #7.
 

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Can you explain this a little more?
DIAGNOSIS AND TESTING
The Multi Displacement System has the following detectible issues:
Solenoid circuit
Fail to deactivate a cylinder(s)
Fail to reactivate a cylinder(s)
Low oil pressure

CONDITION Low oil pppppPOSSIBLE CAUSES CORRECTION

MDS does not activate 1. Low oil pressure 1. Check for proper oil pressure
MDS does not activate 2. Bad oil temp sensor 2. Replace oil temp sensor
MDS does not activate 3. Malfunctioning MDS Solenoid 3. Replace Solenoid
MDS does not activate 4. Malfunctioning MDS Tappet 4. Replace Tappet

MDS Does Not Deactivate 1. Low oil pressure 1. Check for proper oil pressure
MDS Does Not Deactivate 2. Bad oil temp sensor 2. Replace oil temp sensor
MDS Does Not Deactivate 3. Malfunctioning MDS Solenoid 3. Replace Solenoid
MDS Does Not Deactivate 4. Malfunctioning MDS Tappet 4. Replace Tappet
 
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Discussion Starter #5
Thanks. I just deactivated MDS with my Predator and now it runs fine, does that help narrow down where the problem may be? Although at this point I may just leave MDS disabled and call it good; I'll run a few tanks through and monitor fuel economy.
 

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How did you
Thanks. I just deactivated MDS with my Predator and now it runs fine, does that help narrow down where the problem may be? Although at this point I may just leave MDS disabled and call it good; I'll run a few tanks through and monitor fuel economy.
Thanks. I just deactivated MDS with my Predator and now it runs fine, does that help narrow down where the problem may be? Although at this point I may just leave MDS disabled and call it good; I'll run a few tanks through and monitor fuel economy.
How did you deactiviate the mds
 

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If it were me, I'd finish troubleshooting this issue and, at a minimum, eliminate the MDS Solenoid as the source. If it is a lifter problem, it'll do nothing but get worse and you may end up replacing the cam and lifter(s). The activation/deactivation pins in the MDS lifters have been known to fail.
 

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I've never done it but the MDS solenoids don't look very hard to replace to me. They're just under the intake manifold, so it's a matter of removing the intake manifold and replacing them.

It's apparent that your MDS isn't disengaging as it should. Clearly it did though, that shutting off MDS got it running fine indicates you're not totally F'd, that the lifter still mostly works. Just that either the solenoid or lifter is unreliably disengaging. I can't think of an easy way to diagnose if the MDS solenoid itself is the issue without taking it out, at which point you might as well replace it. There may be some electrical resistance tests that can be done but I don't have details on that and it wouldn't verify it's working properly, only that the electrical portion hasn't failed.
 

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I've never done it but the MDS solenoids don't look very hard to replace to me. They're just under the intake manifold, so it's a matter of removing the intake manifold and replacing them.

It's apparent that your MDS isn't disengaging as it should. Clearly it did though, that shutting off MDS got it running fine indicates you're not totally F'd, that the lifter still mostly works. Just that either the solenoid or lifter is unreliably disengaging. I can't think of an easy way to diagnose if the MDS solenoid itself is the issue without taking it out, at which point you might as well replace it. There may be some electrical resistance tests that can be done but I don't have details on that and it wouldn't verify it's working properly, only that the electrical portion hasn't failed.
A couple things on the MDS Solenoids. If they've been in there a long time, it can be a little difficult to get them out without destroying them. They tend to get pretty solidly stuck. As far as troubleshooting goes, a good high end scanner will activate/deactivate each one individually. However, I don't believe It'll actually tell if the solenoid is "compIetely" activating or deactivating it, just whether the solenoid is moving the plunger, I have an Autel MS906BT and it's real easy to do with it.

A little personal experience note on one of my MDS equipped vehicles. On my somewhat modified (see signature) 06 5.7 Jeep (114K on it), every once in a while I get a misfire code for No. 6 cylinder, an MDS cylinder, and I am starting to keep track of it just in case something is slowly starting to act up. (NGK plugs and SOS high output coils are all good.) I never feel a misfire and it runs fine all the way up to about 6300 RPM. Once I clear the code, it may not come back for months or it could come back in a week. So far, with the MS906, I am not finding any traceable problems so I am just keeping an eye and ear open. The MDS is and has always worked flawlessly on both of my similarly modded 5.7's, and I am figuring if there is going to be a problem, it'll likely be with the lifter(s) since both have 6500 RPM redlines. If it takes out one or more lifters, it'll probably take out the cam too. The good news is that it probably won't happen overnight and will most likely give quite a bit of warning if/when something starts to fail.
 
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