Have a 1997 Dodge Ram ex cab 2wd with a 5.2 and it is giving off a p1398 obd code. Does anyone know how to fix this?

 

P1398 Misfire Adaptive Numerator at Limit

From what I have seen online.... this is a crank sensor being problematic. Get one from the dealer.... aftermarket ckps suck.

 

What else besides a problematic crank position sensor causes this code?

Have replaced:
- plugs
- ignition coil
- crank position sensor (Autozone)

Have not yet replaced, but plan to this week:
- wires
- cap & rotor

Have been told this could also be caused by a faulty camshaft position sensor, which is supposed to be located beneath the distributor cap. However, had trouble finding that part for my specific truck.

My exact truck is:
- 1997 Dodge Ram 1500, Laramie SLT, 5.9, Auto, 4x4.

My question is 3-part. Based on a very limited budget for parts, which part(s) should I replace first? Should I first replace the crankshaft position again, this time with a better quality one?Does my specific truck actually have the crankshaft position sensor, located on the black disc, under the distributor cap, should I replace this too, and if so, should it be done first or last?

Thank you for any response, any help is appreciated.

- Maven

 

Getting any other codes along with that one? (specifically, multiple cylinder misfire codes.)

Fixed your plenum yet? (see sticky at the top of this forum.)

Our trucks REALLY dislike aftermarket sensors in critical locations. Cam and Crank position sensors being right up there at the top of the list.

I would have a long, hard look at the cap and rotor, and while you have the intake box out of the way, take a peek down the throttle body bores, and see if there is oil pooling in the intake.

How did the old plugs look? (can you post a pic?)

Any other performance problems?

Don't spend any more money until you have had a bit of a look around the engine compartment..... It ends up being cheaper that way.

Welcome to DF!

 

Yes, I got several codes to start with. Isolated misfires on several cylinders, random misfires, and also a high voltage to fuel level sensor. First thing I replaced was the tranny... broke the crank position sensor doing that, replaced it with a cheapo because I ran out of money. Next was the misfires and fuel level sensor high voltage. Replaced the plugs, they looked horrible... corroded, huge gaps. Broke #3 trying to get it out (135k, never been done, truck sat loooong time before I bought it). Used easy out, broke that. Brought to garage, they pulled the head to get the plug out, and replaced all gaskets except passenger side head. That cost me $600... just to get the plugs done basically. Still had random misfires, so I replaced the ignition coil. No more random misfire codes, but did get the high voltage at fuel level sensor. Replaced the fuel pump. Evap line from pump is still damaged. Ran much, much better... but still had the original symptoms, which were 1) running extremely rough at idle in very cold temps - below 20 degrees - until engine warmed up, and 2) skipping/hesitating/misfiring under semi-aggressive power, like when climbing hills at high rpm between 50-70 mph.

Now I have the P1398 code - misfire adaptive numerator at limit. Still having both symptoms, although the fuel pump did make a dramatic difference.

That's pretty much the whole scoop I think. Can't think of anything I missed. What do you think based on all of that?

- Maven

 

I think your plenum is blown, which introduces oil into the intake, which then gets burned, fouls plugs, and clogs cats. Pretty standard fare for these trucks..... It's pretty much a universal problem..... Definitely something you should look into.

Too bad you weren't here before you spent 600 bucks on plugs..... If you were going to dig down to the heads anyway, I would have just suggested replacement. The stockers suck, and are VERY prone to cracking. Ah well.

In any event, The aftermarket crank sensors don't really play well with our trucks, but, since your symptoms essentially haven't changed with what you have done, time to start looking elsewhere.

The missing under load is another symptom of blown plenum. You have a vacuum leak there, and when you really load the engine, it goes to open loop, and just runs off tables for how much gas it gives the engine. With the vacuum leak, it's getting more air than what the tables account for, so, you get interesting problems. (this is also a possible symptom of a crappy crank sensor.....)

Did they do anything with the pan gasket on the intake when they had it off? That gasket probably came with whatever gasket set they got..... did they actually change it becomes the question. I would check that, and also look down the TB, and see what the inside of your intake looks like first.

 

These are typical problems of a blow plenum gasket. It's not to bad yet or you will get back firing threw the intake under load. Many of us opted for this...
http://www.hughesengines.com/Index/p...p?partid=27091

 

So I just went and asked the mechanic who worked on it... he obviously didn't remember. His default answer was yes, but the leftovers in the gasket kit told a different story.





And since he didn't replace the pan gasket, it's probably safe to assume that he didn't inspect it for damage/cracks/leaks. I'm feeling like that gasket should DEFINITELY been replaced while it was apart, especially since it was in the kit.

So now I'm thinking I'm gonna go back to the garage and see if they will tear it down again free of charge. If they won't, then I'll probably change out the crank position sensor, because that's easier than tearing it down to do the plenum.

I will check the TB bores tomorrow, and post what I find there.

 

Any recommendations on where to get some good heads?

 

Look for Clearwater on eBay, or at cylinder-heads.com. They offer a new part with a beefier casting that's said to hold up much more betterer.