upalms

OK this is getting old, I replaced the clutch last week and buttoned everything up. I drove around for a few days, then headed up to Lake George, about a four hour ride. The day before I was coming home up a very steep hill by my house and had to downshift into 3rd, didn't think much of it just thought I wasn't carrying enough speed.

I had had trouble bleeding my slave when I did the clutch and brought it to a local garage, while there I had the CE light on, it had been on for a while, months, I figured the cats were on their way out and I'd replace them before emissions, it always ran fine - Bank one, Sensor two, south of the cat came up, I figured I'd replace it when I got back.

When I got on the highway the exhaust sounded unusually loud, I dove about a half hour and the exhaust was getting louder and louder, and I'm loosing power on hills, having to downshift, and the CE light starts blinking, then it starts pinging every so often. I'm thinking to myself the head pipe where it meets the exhaust manifold must have heated up and loosened up. I knew a garage along the way and pulled off, when I got to the bottom of the ramp I had really no power, just enough to make it to the garage.

The guy helped me and we tightened up the exhaust, the left side was loose, the right a little but not bad. I started it up, idled good, no CE light, I tried to take it for a test drive but didn't get very far. As soon as I put it under a load the light came back on and the idol went rough, no power, and it started popping out the back, I believe. We plugged in a scanner and it showed Multiple Misfire. So I ran across the street and got a new O2 sensor and replaced it, while under it I started checking around and gave a tug on the right side downstream sensor and it came loose, so it wasn't completely clipped in, so I'm assuming it wasn't working either, so both downstream sensors not working. I'm figuring the new sensor and the other clipped in, we'd clear the codes and I should be good - Nope.

We got everything together, still low/rough idol, still no power, also when you rev the engine, it doesn't seem like there' a lot of exhaust pressure coming out the back, but since I've never checked it before, can't say for sure

I had it flatbeded back to my house and hopped in the Grand Cherokee for the trip and just got back. I was thinking if the cats got flooded due to the sensors it might have cleared out over the four days. Nope, still the same.

I started googling around, and went out and started it to see how many times the CE light blinks, it doesn't stop just keeps blinking? No Pinging though sitting in the driveway, I didn't bother trying to drive it.

The plugs were changed probably a year or two ago, and I have a set of LiveWire plug wires on it, the back left by the firewall seemed iffy, so we changed to no change. What happened didn't seem to be sudden, not like I've read where other people suddenly had the light start blinking and lost power on the spot, this seemed to span a half hour or so to go from running good to no power, and like I said the exhaust slowly started getting louder and louder.

This truck has been off the road for almost a month now, I have to get it sorted out and back on the road. Cats? Coil Pack? Wires? Plugs? Doesn't seem like a wire/plug issue to me, and all the code I get is just multiple Misfire, no particular cylinder, I would think if the coil pack went it would go one cylinder at a time, not a bunch all of once? And why aren't I getting which cylinders are misfiring?

HELP!

upalms

BTW, it's the 2007 JKU, Anyone? Ideas??

cidd

Plugged exhaust ?? Easy to check drop the pipes and see what happens

upalms

Yeah I think thats what I'm going to try first

mr72

You melted the cats by driving for months with a misfire. You have to fix misfire immediately or you risk destroying the catalytic converters. Now with plugged exhaust there may be other collateral damage like cracks in exhaust.

upalms

OK, so an update, yes it's still not on the road. I replaced the cats, Bank 1 downstream cat came out in a pile of charded soot, it started and ran OK for a few laps around the blocks then the CE started flashing started going down on power. Went to Autozone and they scanned it "Multiple Missfire" - Still, and a voltage thing on the Bank 1 Sensor 1, it said the recommended fix was EGR valve.

So I replaced the EGR, that was F'n fun, got it started still running shitty, now my buddies scanner says my timing is 56 degrees retarded????

So did I slip a timing belt? Is there a way to adjust the timing ?? I thought the cam and crank sensor were adjusted via the scanner?

WTF?

upalms

Any help guys, this is maddening, if I send this to a shop it's gonna cost me $$$

mr72

Yeah, that's very wrong advice. This is not an EGR problem at all.

Don't worry about that. That "timing" is not at all related to the timing belt and you can't adjust it.

P0300 "multiple misfire" means one common cause is preventing correct firing of >1 cylinder and not repeatedly enough on any specific cylinder to cause a P030X code (where "X" is which cylinder, like P0303 means misfire cylinder 3). So you have to limit your causes to things that may affect all cylinders in a sort of random way.

IME the most likely cause of this is a bad crank position sensor or camshaft position sensor, whatever the JK has to inform the ECU of which cylinder to fire. Usually manifests when it gets hot, causing a hall sensor's pickup coil to open-circuit when it expands. Then the ECU doesn't get triggered to fire a cylinder, no spark or fuel happens at that cylinder and no pulse results in a cylinder misfire detected, and when this happens across a range of cylinders for a few cycles then you get a P0300. Another possible cause is a bad fuel pump so your fuel pressure is low or intermittent causing insufficient fuel at all cylinders at once. There are a dozen other possible causes like blown head gasket, many cracks in cylinder head, gross manifold leak, etc., but in most cases those will be related to recent work you have done so you would already be guessing them. Like if you just had the head replaced under warranty due to cracking, then I'd guess it wasn't torqued right and the head gasket is toast. If I were you, proactively I'd change the crankshaft position sensor and hope for the best. If that doesn't fix it then I'd do a compression test to rule out head gasket, head cracks, valve issues, rings, etc., and if that test passes go on to fuel pump as a likely cause. A home mechanic probably doesn't have what it takes to test fuel pressure so I'd just replace the fuel pump if it has more than about 80K on it.

One thing that may be a bit mystifying to me is how you'd cook a cat with a misfire caused by a bad CPS, since a bad CPS should also result in not firing the cylinder because to cook the cat you'd have to dump unburnt fuel into it. Does a the JK's ECU do sequential injection? I'm guessing in this case it must be firing the injector for a given cylinder whether it got a signal from the CPS or not. Anyway...

Just to cover the base, one other possible cause is if you changed the timing belt and got it off by a tooth on one cam so there's a lot of valve overlap but usually when that happens you get a P0300 while the engine seems to run fine or even maybe seems to have an extra bit of low-end torque while being louder than normal and having a decidedly lumpy idle. The other thing may be if you changed the spark plugs and forgot to plug in (fully) the coils-on-plugs on >1 cylinder but usually that'd give you something like a P0301, P0302, P0303 etc. and not a P0300 alone, since you'd have consistent lack of firing on the same cylinder(s).

I'd have to say it's a 90% chance the problem is the CPS. I don't really know how all of the signals work on a pentastar, I know in my Miata there were two, a crank position sensor and a camshaft position sensor, and the cam sensor was used to trigger fire or not fire and the crank position sensor was used to detect phase angle so the ECU could adjust spark timing, so of the crank sensor was bad you'd get retarded timing and "limp" mode and if the cam sensor was bad it'd misfire.

BTW for future reference, the EGR valve only opens under very specific conditions like light load cruising in a specific RPM range. If it's bad then you'll get a P0401 "EGR Flow Insufficient" code. That will light the CEL while you are driving down the road under the conditions when the EGR should open and won't clear until you manually clear the codes (doesn't go away by itself). That's the only code that indicates anything is wrong with the EGR. Make note, don't trust the Autozone guy for recommendations on what is wrong.

The "voltage thing Bank 1 Cylinder 1" may have been a P0131 "O2 sensor circuit low voltage bank 1 sensor 1" or P143 "O2 circuit low voltage bank 1 sensor 1" ... you need the actual code. Get yourself a code reader, it will make your life about 99% easier. Then use a web site such as this one to help you figure out what's wrong:
https://www.obd-codes.com/trouble_codes/

The OBD2 will give you an initial idea where to look and reporting the actual codes will help keyboard commandos like me to give you more targeted advice.

upalms

Thanks for the detailed reply

I thought about the cam/crank sensor, but the Snap On scanner said they were in sync? I can replace them but I'm just throwing parts at it, Haven't touched the timing chain, what about the coil pack?

Fuel pump?

mr72

What year is your Jeep? It probably has coils-on-plugs, no coil pack. Each plug has its own igniter and ignition coil right on top of the plug. So you can basically rule this out unless you have a P030X (X being the cylinder number) misfire code. If you get P0300 then it can't be the COPs.

CPS (whichever one, cam/crank/etc) is not something you can test with a scanner. It's a hall-effect sensor, which basically means it's a pickup coil. It's a coil of wire wound around a steel bobbin encased in plastic (most likely.. haven't seen it on this vehicle myself). Kind of like a one-string guitar pickup. If the wire has a hairline crack in it somewhere inside the coil, then once it gets hot enough the whole thing expands a little bit and it's enough to cause the crack in the wire to open up, which is a very common cause of a P0300. Eventually it may expand/contract enough times that it goes out entirely even when cold. You will be stranded and the vehicle won't even start if this happens. There are ways to test it but you can get one at NAPA or Autozone cheap enough to make it not worth the risk especially at that mileage, I'd just replace. It's one of those "will ruin my catalytic converters and then suddenly leave me stranded" parts that is not worth risking if there's any chance it's bad. And there's a good chance yours is bad. IMHO. If it was my Jeep I'd replace it and and never look back.

And BTW if this turns out to be the root cause, then truly you're going to find that like a $35 part caused all of this problem including the bad catalytic converters. Point is when the check engine light comes on and BLINKS that means TURN OFF THE ENGINE IMMEDIATELY. otherwise prepare to buy catalytic converters.