Jooman07

So my CEL came on the other day and I had the code read. Came out to P1391 which is the Crank Position Sensor. So...I replaced it.

Now it is running worse than before. Before it would run rough intermittently and feel like it was going to stall. Now I can't even get it above 5 mph without it fighting me. Idling doesn't seem AS bad as in gear but I can tell something isn't right. I was only able to drive it around the block and it was very painful to do so. Another annoying thing is it isn't throwing a CEL anymore. But it has to be something to do with the CPS cause thats the only things that has changed. So what the heck could it be now?

tjwalker

A P1391 can be EITHER a crank sensor or a cam sensor issue.

Test your camshaft position sensor. It's located inside of your distributor. You'll need a manual with the procedure and a meter.

Another thought. What brand crank sensor did you use for a replacement?

Good luck and keep us posted.

Jooman07

everything I have searched pointed to crank sensor. the code said either crank or cam, but when I search either here or google it all comes back to crank sensor. I even searched for a part named Cam Position Sensor and found nothing.

tjwalker

You have a cam sensor. Trust me. I've replace a bunch of them on your vintage (98). Some parts stores call them a "synch sensor" or something else.

But don't buy a sensor before you test it out. Half our of your time and you can get a better idea of whether the cam sensor is in play.

Don't get tunnel vision. Your code can be either. Test. Good luck.

Jooman07

Ok I will test it tomorrow when I get a chance. But the thing is now, why in the heck is it worse that it was before? Along with NO CEL...

tjwalker

OBDII is far from perfect. Don't overthink it. You either have a crank sensor circuit issue or a cam sensor circuit issue. You've pulled a P1391 and you gotta trust where the codes point you. ALWAYS.

Testing is the only way to determine which is which. I would also try getting a can of electronic contact cleaner and thoroughly spraying the connectors for both the crank and the cam sensors.

You need to adopt a testing based strategy to figure out what is going on. That's exactly what any good tech. would do if you took it to a shop.

Jooman07

Yeah i do the same type of fault isolation when i work on aircraft but the tech manuals we use are a lot better than a haynes or chiltons. i didn't know anything about testing the cam sensor cause when i searched for it, all it did was direct me to the crank sensor. i searched for sync sensor and now i see what you're talking about. i just can't figure out what would make it run worse now.

Roler

Aircrafts....you should hang out with CCKen

Haynes and the likes are very limited. They give a generalised picture of things in a Cherokee. Get your hands on a factory service manual. All you need. Let me know if you need help tracking one down. Got one for my year (since its a post update it will likely be much the same). Even got a parts catalogue , if you want go all hyper. PM me since cant post links " in public"

DFlintstone

Here, a little down on the right looks like some good info> http://www.ausjeepoffroad.com/forum/vbindex.php

Radi

Generally, if something becomes worse after you make a change, undo the change and see if the problem resolves.
You changed the CPS and it runs worse? Put the old CPS back in and see what happens.
You may have replaced a perfectly fine CPS with a spotty aftermarket unit while the actual failed part remains undiscovered.
I've not seen TJWalker steer anyone wrong, the Synch sensor would be a logical next step in testing.

Parsnip

Just to answer your curiousity on why it could be crank or cam-
A crank sensor is largely responsible for timing of injection and spark ignition, where as the cam position is more of a finer reaading...or at least that's a nice easy way to think of it without digging to deep.
A vehicle will run without a cam sensor, albeit rough, poor, and with the computer constantly guessing where exactly the pistons are, when to spark, when to fuel, etc.

Roler

I wonder who thought you to look in that corner of cyberspace, D

perez1989

Check all your Vacuum lines. Worse case is your Fuel Pump and Fuel Filter.

Jooman07

Checked the continuity in the crank position sensor per my Haynes manual and it checks out fine. The old one does also. Checked for chaffing in the wires too and saw none. I have no clue what else it could be. The code still pops up P1391. This is a 98 and according to my manual it does not have a cam position sensor. Only the crank.

DFlintstone

It's got something in the dizy, they just call it something different.