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Chris
Chris, Shop Foreman
Category: Dodge
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Experience:  ASE and Chrysler Certified Master Tech
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1997 Dodge Ram 1500 magnum 5.9L Misfire. 150,000 miles. To

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1997 Dodge Ram 1500 magnum 5.9L Misfire. 150,000 miles.
To the best I can tell this misfire started with Check engine light reset. For years there has been an check engine light on and off, siting recirc valve issue. Usually fuel cap.
After this reset it began to (misfire) "chug-chug" at idle siting, #5 cylender. Cylender compression 135 psi all with in 10%
Changed in this order; First, spark plugs (no change), added fuel injector additive to fuel (no change). Then replaced the fuel injectors with rebuilts (runs better but no change to misfire). Next the rotor, cap, spark wires (runs better yet, but no change to chug-chug misfire at idle, . At 1000 rpm and up it seems to runs smooth.
I purchased vehicle new. Synthetic oil change every 5k miles. K&N Filter kit.
Any suggestions as to the next step would be appreciated.
Thanks Jim
Submitted: 4 years ago.
Category: Dodge
Expert:  Chris replied 4 years ago.

Hello and welcome to just answer Dodge. The 5.9L has had issues with the valve seats and will cause misfire(s). I have seen this at mileages as low as 40,000 miles. If you are at 150,000 miles, that is really good. There have been valve seat issues, and also combustion chamber cracks found in the cylinder head(s). One other thing I see from time to time on these engines is the intake manifold "belly pan" that can leak and cause misfires and other driveability problems. One way to check this is to look down into the throttle body with the throttle wide open. If you see a lot of oil sitting on the bottom of the intake pan, then the manifold pan gasket is leaking. However, it probably is a valve seat/cracked combustion chamber that is causing your #5 misfire because the misfire is only on that cylinder. A compression test may not always be a good indicator of a valve seat issue. A leak down test would be a better way to confirm this.

Hope this information is helpful, and let me know if you need more assistance with this.

 

Chris

Chris, Shop Foreman
Category: Dodge
Satisfied Customers: 9816
Experience: ASE and Chrysler Certified Master Tech
Chris and 6 other Dodge Specialists are ready to help you
Customer: replied 4 years ago.

Thanks Chris,

I will look down the intake.

1. Is there any way to see that valve seat without pulling the heads? Would one expect to see a burned slot between the valve and seat?

2. Should I do the leak down before pulling the heads to be sure, or are you confidant there is a valve problem from your experience.

3. The thing that bothers me is that I remember the instant or trip it started misfiring. When stopping at a sign or light it really makes this misfires stand out. Between this moment and another it seemed to have started. Can a computer reset cause such a thing n any way?

4. Do I have reason to suspect of the short block or lower end as well?

Expert:  Chris replied 4 years ago.

There really is no way to visually see if there is a valve seat problem without pulling the heads, and even if you could, you still would need to pull the intake and exhaust manifolds to look down into the intake and exhaust ports. Yes you would need to do the leakdown test before pulling the heads. A computer "reset" would have nothing to do with this. It is purely a mechanical issue. As far as a short block replacement, that depends on how much longer you plan on keeping this truck, and also if you have a reason to do that (oil consumption, lower end noises etc.). One other thing that I was thinking is this; Have you noticed unexplained coolant loss? Do you have to add coolant to the reservoir bottle every now and then, but do not see any leaks? If so, this is another indication of a combustion chamber crack.

 

Chris

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