Yeah. That or I'ma sacrifice me a chicken.
Yeah. That or I'ma sacrifice me a chicken.
I'm coming back to this because it's still missing and getting worse. In addition to the previously listed stuff I've put on a new ignition coil, cleaned the IAC, and recleaned a bunch of grounds. Also have a new Cat and downstream O2.
So after monkeying with all of the ignition parts and seeing no change in the issue I'm leaning towards a fueling problem. The pump check valve is getting iffy, so I know a pump is in the future, but I don't thing the fuel pressure is running low because the truck runs great at WOT and higher rpm driving. Also, I don't have the schraeder valve on my fuel rail, so I'll have to buy a $50 adapter to check it. Haven't got there quite yet.
Since I just had to replace a crumbling/clogged cat, I'm wondering if the upstream O2 is giving bad readings and causing a fueling condition at idle. I'm not getting any CELs but I'm thinking maybe it's close but not quite right. When I first crank the truck it idles nicely without missing, I'm assuming that it's still in open loop at that point. If I unplug the upper O2 I should force it into open loop and make it run richer, right?
I'm thinking about disconnecting it just to see if it causes a change in the issue. It should throw a CEL but I can clear that later.
I know I suggested a fuel issue, and it might be, but have you done anything with the EGR? I don't remember seeing mention of it in your threads about the vehicle.
In reply to pres589 :
There is no EGR. It uses a dual O2 sensors instead of the EGR. The older 93-95 models had them, but not the 96-98 models.
Weird, I did about four seconds of internet truth seeking on this, and it appeared that there was EGR. Glad that you don't have to deal with that and one more variable.
Just t a side note, but i was watching the 02 sensor voltage while driving to my doctors appointment and it seemed to be reading low (lean) when im getting the miss/stumble. Not ready to say that's consistently the case, that's the first time I watched it. I'm setting up my torque pro app to monitor it now though.
This a puzzle. You've checked replaced all the usual suspects. Fuel delivery is possible. Also a clogged/wrecked cat can cause issues too. Maybe it is the O2 sensors. Just a shame that you have to keeping throwing parts at it.
ultraclyde said:Just t a side note, but i was watching the 02 sensor voltage while driving to my doctors appointment and it seemed to be reading low (lean) when im getting the miss/stumble. Not ready to say that's consistently the case, that's the first time I watched it. I'm setting up my torque pro app to monitor it now though.
This is exactly the symptom that I dealt with on the rover for a few years. Never did figure it 100% and I have a sneaky suspicion these days that it could have been a valve issue. I do hope you figure yours out sooner than I.
Was just checking in to see how things were progressing. You mentioned the O2's and I wonder if they were replaced with OEM units or? I was amazed that my 06 GMC Envoy (yes I know newer and more ECU stuff) was unwilling to accept an aftermarket (good brand I don't remember offhand) O2 sensor. Despite the fact that the O2 sensor was reading and apparently functioning fine. The ECU threw a total E36M3-Fit until I plugged in an OEM GM sensor.
I was at a total loss and a mechanic buddy told me how picky they can be. it made no sense to me at the time but I was at my wits end hunting the issue. I plugged in the OEM sensor and it was happy as can be.... No clue if Jeeps are that picky or not but another semi-affordable thing to look at.
I replaced the downstream with a Bosch....which I found out later is not a happy brand with Jeeps. They like either NTK or Mopar only.
BUT the downstream is only a check on cat function. The upstream sensor is the one that controls fuel mix.
Today I ordered an NTK upstream replacement. It was only $30 but I'm fast running out of $ to throw at this thing.
grover said:ultraclyde said:Just t a side note, but i was watching the 02 sensor voltage while driving to my doctors appointment and it seemed to be reading low (lean) when im getting the miss/stumble. Not ready to say that's consistently the case, that's the first time I watched it. I'm setting up my torque pro app to monitor it now though.
This is exactly the symptom that I dealt with on the rover for a few years. Never did figure it 100% and I have a sneaky suspicion these days that it could have been a valve issue. I do hope you figure yours out sooner than I.
I considered some mechanical possibilities but the way it came on slowly and keeps getting slightly worse makes me think it's in the fuel or spark control system.
I finally found something that affects the miss! I unplugged the temp sensor, forcing the system to run slightly rich if I understand correctly. It idled PERFECTLY. Smooth like glass.
So I'm fairly certain I'm getting a lean miss at idle.
Is it a bad pump? I'll have to buy a $50 adapter to check the fuel pressure, or a $200 pump and a weekend swapping it to find out.
Is it a bad injector? They all checked out fine on resistance but that doesn't rule out physical problems.
Is it a bad O2 signal? The signal seemed to be the same, but I've already got a new one on the way.
Is it a bad pcm? Well... no oscilloscope or scanner to see the signal output..dunno?
Temp sensor is a cheap enough to throw at it. If you leave it off for now, what codes pop up?
Can you get a scanner on the thing? That should be able to tell you if something is driving the fuel trims really screwy or if one sensor is reading something obviously wrong.
In reply to dirtydog :
Pretty sure the temp sensor is good. It gauge reads exactly where I would expect it to. The code is for a bad temp sensor with it unhooked, but the truck also stumbles pretty good when you pull away from a stop. Not worth trading one drivability issue for another leaving it unhooked.
in reply to rslifkin:
not that I've found yet. I'm running the torque app but it doesn't have access to all the stuff a pro scanner would. That's really what I need.
Try the Torque Pro app with the ActiveOBD plug-in. Will cost you $11 for both but that combination will read a lot of Subaru specfic stuff.
In reply to Hal :
I can get basic info like that on torque for the Jeep. Sadly there's not a plug in that pulls deep info for Dodges. Partially it's because Dodge has always been very tight lipped about their PIDs, but also this system is old enough there's just less info there. I'd love to see the injector pulse widths but it ain't happening with an app.
Just the basic OBDII parameters you can get out of the Jeep should get you something useful. Yeah, you won't get injector PW and some of that stuff, but you should be able to get intake temp, coolant temp, MAP and TPS values along with short and long term fuel trims. Those should be a pretty good starting point for diagnostics.
I'm running all those with an active gauge spread on Torque already. They all look to be within normal parameters.
I'm headed out of town for a couple days for a surprise business trip to Charlotte. I found a highly recommended local shop that's willing to put the Jeep on their scanner for free and see what they can find. They have the adapter for the fuel pressure check and will go old school on it if necessary and bill me for the time. I'm going to drop it off tonight and let them play with it this week while I'm out of town.
Right now, my money is on the following, in decreasing order of likelihood:
We'll see what the answer is. The funny thing is that 3/4 of those are all $200 fixes.
If it turns out to be injectors, let me know. I've got a set of the 4 hole, 24 lb/hr Ford Racing injectors that'll fit the Jeep sitting in a box doing nothing. They've got something like 50k miles on them from new. If you end up needing them, they're yours for the $5 - 10 it'll cost to ship them.
In reply to rslifkin :
Awesome. Thanks!
Initial testing shows #4 cylinder has good compression but is leaking down. This was from one of the other guys at the shop, not the main guy, so I'll get more details later.
Anybody want to buy a Jeep? Lots of new parts, slight miss at idle. Probably just needs plugs...
Any idea where it's leaking to? If it's valve / head related, this might be an excuse for some upgrades 
Or, worst case, find any 96 - 98 ZJ with a 5.2 / 5.9 or a 96+ Dodge pickup with a 5.2 / 5.9 and swap it. A good running engine should be cheap.
well, not yet. As I understand leakdown, it means some sort of problem with valves, head, or headgasket, right?
No money for upgrades. Hell, at this point I've blown all the money for a basic repair of that scale by repairing other broken stuff.
The engine has 162K on it, and no blown headgasket symptoms. I just replaced a catalytic converter that was falling apart internally. What's the chance this is bad carbon build up on an exhaust valve?
Leakdown could be past the rings as well. But if the cylinder is pressurized for a leakdown test, it should be possible to find out where it's leaking to.
As far as carbon on a valve, it's possible. I'm not sure how likely though.
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