5.7L hemi #6 Cylinder misfire

[sjead26]

I have a 05 Jeep Grand Cherokee Limited with a 5.7L hemi with 130K. I recently had a #6 cylinder misfire code and after troubleshooting it was due to a faulty lifter. The repair corrected the issue for only about 2,000 miles. I got the same symptoms and eventually followed by the engine check light. I took it back to the mechanic that originally fixed the problem only to find out the diagnostics showed another #6 misfire. He says it was caused by a faulty MDS and is recommending that I buy a performance flasher to deactivate the MDS.

Has anyone experienced a similar issue, and would you recommend to deactivate the MDS?

 

[Abodybomber]

Something's amiss here.... I personally would do a leak down test,make sure that cylinder is sealed like it needs to be. Not much on newer Hemis,might try posting this in the Hemi forum. Welcome.

 

[RustyRatRod]

Might try introducing yourself first, then post this in the appropriate forum where it will get a lot more traffic.

Welcome aboard.

 

[OldmanRick]

Welcome to FABO, from a former Capitol Raceway participant . Sadly, I'm not a "computer controlled" guy, but I hope someone here can give you some guidance.

 

[sjead26]

Hello to all, my name is Steve Ead I currently own a 2005 Jeep Grand Cherokee limited with a 5.7L. I wanted to thank everyone for there responses with my current issue with the #6 cylinder miss fire that I posted. So far after the lifter replacement and I upgraded the computer software with the Diablo sport intune and disabled the MDS has made a huge difference in the overall performance. To early to tell but I hope this will be the last issue I have with this issue.

 

[Dusterhoss]

My Brothers 09 Ram 1500 Hemi just had the same issue on a #7 Cylinder misfire. We changed valve springs, plugs and swapped injectors and it would always come up on the #7. Ended up being a cam. The lobe got wiped out from a lifter that was rotating in the lifter bore and eventually ate the cam... New Cam and now it runs fantastic!

 

[BillGrissom]

The lobe got wiped out from a lifter that was rotating in the lifter bore and eventually ate the cam...

Interesting. For those that don't know, roller lifters aren't supposed to rotate about their axis. There is a spring plate to orient the rollers. If the lifter ever moves too fast, perhaps it can pop out of the plate, or maybe the engine was assembled wrong. In our LA engines, re-trofit roller lifters have a link bar between each pair to orient them, which seems more robust.

 

[67DARTGTCONV]

I would not disconnect the MDS. First of all make sure you are using the right WEIGHT of oil.
If not change it first.

The MDS system has MDS solenoids that are located under the intake manifold. They have a high failure rate. If you have verified coil and injector are not the problem, this is prob what the is causing the problem. You do not have to remove the heads! Intake only.

While there check the MDS lifter, they also have been know to stick in the collapsed position

The lifters cannot turn as they are held in with a plastic retainer.

also check the valve spring and see if it is broken. If it is remember to ID the rocker arms as the are different between intake and exhaust. The intake usually has a I stamped on it.

Take care also that the push rods are also different lengths between the intake and exhaust.

In the lifter pic the pins are pushed in for MDS operation allowing the lifer to collapse. They will be stuck in

The yellow in the MDS pic is showing oil flow for MDS operation

Lastly the heads to have to come off if you notice a lifter problem

 

[68DartProject]

I had a similar problem on my 08 Dodge Ram 5.7 Hemi. The computer kept saying that I had a misfire on number 3 and 2 coil pack on number 3 cylinder. I was told that the lifter was the cause as well and that I needed it replaced. Or and I heard this also; flash the computer to turn the MDS off as well. I just didn't think that was the issue to be honest. So we took off all the coil packs and check the ohms and check and rechecked the plugs. Everything looked good. Put everything back together and again the same problem. I took the coil pack off that cylinder and changed it out for another one. Well the misfire went to the new cylinder we changed it too. So make a long story short. I thought it was a bad coil but ended up being the rubber boots that come off the coil was split and was causing the misfire against the inside of the head. Which was really annoying cause it ticked all the time too; since new. Put new boots all the way around and no more misfire and that tick is gone. I really never noticed much power lose just a miss when i was at idle. Worth checking out. Just my 2 cents.

 

[DaveBonds]

Here is the deal with the new hemis and why they misfire...

The spark plug positions on each cylinder are very sensitive to fouling. When I tuned the 6.1 MP crate I put into a '59 Coronet, it fouled the first set of plugs after five minutes, due to a slightly rich condition showing on the AEM. They do not like anything, but perfect, iridium plugs.

A lot of the 5.7s have a serious valvetrain issue. Chrysler shows an update on new valve springs, due to people constantly breaking them from excessive heat.

There is a tag on these vehicles that recommends mid grade or better fuel. You can run regular, but when you do, you stress the cylinder head and its components.

The ECU can take timing out of the new hemis, but it cannot lower static compression below what they are, which I believe is somewhere in the 9.5:1 range or better.

So, even if the ECU picks up a KR signal from detonation and backs off all of the timing, it is still going to throw tons of exhaust gas temp through the roof, under load, on regular fuel.

The best thing you can do to a new hemi is run at least mid-grade and if you live in the hills or tow, run premium when you need it, as well as a synthetic or synthetic blend oil, to help drop engine and exhaust gas temps.

My friend's Durango just broke a valve spring. He took it to his friend, who is a fleet mechanic for the Arvada Police that has already replaced the springs in six of their fleet trucks and discovered this issue.

Be sure that its not just a lifter. You may have a crushed, collapsed, weak or broken valve spring.

If I ever own a 5.7 or 6.1, the first thing I am doing is replacing all of the valve springs.

Hope this helps.

 

[sjead26]

Thank you all for all the responses about this issue. I will say it has been almost 5,000 miles since the lifters were replaced and the computer was tuned. With the MDS disabled it runs so much smoother as the shift point from 1st to 2nd is set at 5,400 RPM. I have actually increased my everyday driving mpg from 15.3 to 17.2 all I can say is I am happy with the increased performance and especially the gas increase which is averaging almost 40 more miles a tank.