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Unread 06-20-2015, 11:12 PM   #1
dallas121469
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New Niner Seems Sluggish

Purchased a new to me '98 5.9 and while driving it just doesn't seem to have the get up and go of my older 5.9. The only non stock item on my older 5.9 is a K&N air filter. It does have 31" tires but drive train is otherwise stock. It also has 256k miles The newer one has a flowmaster muffler which I'm not thrilled with but otherwise seems stock with only 120k miles. I will change all the filters and the plugs but other than that what could be causing this sluggish "feeling"?

Could I swap the computer or some other part to see if it is causing it?

I've not had any power problems with my old one so I'm a bit stumped.

I believe previous owner replaced the map sensor recently. Would a map sensor from a 5.2 liter be the same or could it possibly be the problem?

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Unread 06-21-2015, 03:18 AM   #2
PolkaPower
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Quote:
Originally Posted by dallas121469 View Post
Purchased a new to me '98 5.9 and while driving it just doesn't seem to have the get up and go of my older 5.9. The only non stock item on my older 5.9 is a K&N air filter. It does have 31" tires but drive train is otherwise stock. It also has 256k miles The newer one has a flowmaster muffler which I'm not thrilled with but otherwise seems stock with only 120k miles. I will change all the filters and the plugs but other than that what could be causing this sluggish "feeling"?

Could I swap the computer or some other part to see if it is causing it?

I've not had any power problems with my old one so I'm a bit stumped.

I believe previous owner replaced the map sensor recently. Would a map sensor from a 5.2 liter be the same or could it possibly be the problem?
It might have the death flash.
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Unread 06-21-2015, 07:55 AM   #3
TreeFeather
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How can you not be thrilled with a flowmaster muffler? Its way better than that stock pos that rots off once every two years. Granted if its a 40 series I can see it being loud. Do the usual checks tune up plenum check etc..
Mine was really sluggish when my plenum was leaking. A crappy cat will do it too.
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Unread 06-21-2015, 08:49 AM   #4
dallas121469
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Fixes

I use this as a daily driver and the flowmaster is too loud and the in/outs were too big for the factory pipes so it looks ridiculous. Not my main issue though. lol

1. How to figure out if it has the "death flash"? And is it reversible? Swap PCM's temporarily?

2. I've run other vehicles without cats. Is it possible with the 5.9? I know there is a sensor after the cat so thats why i'm asking.

3. I've read about the plenum gasket and other than oil consumption, loss of power and poor mileage is there a way to diagnose this issue without driving the vehicle? Not insuring, registering or driving it until I get everything fixed.
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Unread 06-21-2015, 09:10 AM   #5
dallas121469
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Damn.

After posting my reply and then checking my PCM it appears that it has the "death flash". There is a sticker that says "authorized software update" on the core support. This makes me very sad. lol. I hate when people do stupid **** like this. You knew when you bought it that it used premium and got crappyy mileage!!!! Just wish I would have known about death flash before purchasing it. Could have talked him down a bit more. Now to find my solution.
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Unread 06-21-2015, 09:18 AM   #6
TreeFeather
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Okay the cat yes you can remove the cat without a check engine light but we don't recommend things like that on this forum. (its against the rules) I have seen people remove the filters from there cats. But like I said (against the rules) you can check your plenum by looking down your throttle body with a flashlight (with the throttle open) If you see oil or burnt oil its bad. reguardless check the plenum because its very common and can ruin that 5.9.
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Unread 06-21-2015, 09:26 AM   #7
dallas121469
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Apologies.

I keep answering my own questions. Sounds like going back to a Jeep dealer is expensive and time consuming. I read that an aftermarket tuner is a possibility so will just look into those options.
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Unread 06-21-2015, 10:52 AM   #8
PolkaPower
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Quote:
Originally Posted by dallas121469 View Post
I keep answering my own questions. Sounds like going back to a Jeep dealer is expensive and time consuming. I read that an aftermarket tuner is a possibility so will just look into those options.
The only tuner worth a damn is the SCT tuner Flyin Ryan writes tunes for. Google him. He's on the speed freaks and Dodge forums.

Although his tunes are great, it might be less expensive for the dealer to reflash your PCM to the stock tune since you would need to buy the hand held unit and the o2 sensor for data logging with the SCT as well as the tune price.
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Unread 06-21-2015, 10:55 AM   #9
StPaul59
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Quote:
Originally Posted by dallas121469 View Post
I keep answering my own questions. Sounds like going back to a Jeep dealer is expensive and time consuming. I read that an aftermarket tuner is a possibility so will just look into those options.
If they could reflash it back normal it shouldnt cost more than 1 hour labor. Can these be reflashed? Its a hell of a lot cheaper than any tuner.
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Unread 06-21-2015, 11:35 AM   #10
dallas121469
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Thanks for the input. I'll call the local Jeep dealer on monday and find out.
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Unread 06-21-2015, 03:09 PM   #11
RWC
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Just because you have an authorized software update doesn't mean it's death-flashed. There were two or three other updates unrelated to the timing map. I think one was for the MAP sensor, and the other was emissions related.
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Unread 06-21-2015, 05:55 PM   #12
TreeFeather
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Mine says it was flashed in 99.doesnt say why or for what.
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Unread 06-21-2015, 09:03 PM   #13
dallas121469
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Is there a way to determine what was done to the PCM?
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Unread 06-21-2015, 09:57 PM   #14
Uniblurb
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If you have numbers along with any info on your sticker you may be able to find some info out in this speedfreaks thread.

http://thespeedfreaks.net/showthread...ll-of-them!%29

There's some info on TSB at the end and thought it was interesting where they said in the middle of the thread SCT could over-write the Cali flash.
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Unread 06-21-2015, 11:52 PM   #15
kg6mov
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The death flash isn't bad if you're still running premium.
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I heard someone yell "mall crawler" from the back porch. I'll go see who said that. Be right back.
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