Unclogged the exhaust, ZJ still won't start

[rccolacc]

All on a '97 ZJ with the 5.2- 185K miles:
On the way home from work today Jeep randomly dies (acts like it's out of gas) about 20 minutes into the commute. Gas gauge says 1/8 tank roughly (60 miles to empty on the computer), so I just assumed it was out of gas. Got a buddy to bring me some gas. Put 5 gallons in it, and the Jeep won't start. Try off and on for 15 minutes. Then randomly it does start and runs fine. Start to go home. I get about a mile, and the thing starts bucking and coughing. My buddy says he saw black smoke and sparks come out of the exhaust at one point. Jeep dies and I coast it to the side of the road. I notice the cat sounds like it's cooking, and the muffler sounds like it's got rocks in it-- I assume the cat's clogged. I use a sawzall and cut the cat out, and sure enough the thing looks like a bunch of melted stuff inside of it (I'll post a picture soon). I thought I'd found the culprit. Go to start the Jeep and all it does is turn over and over. Not a chance of even firing a little. I gave up and left the Jeep there for the night.
I don't think it's a fuel pump issue-- the fuel pump sounds fine when you turn the key to prime it. The motor's getting fuel (the thing smells like raw fuel when you're starting it). I removed a spark plug and it looked OK. Buddy held it against the block and proved it was getting spark. Left the battery unplugged for several minutes thinking the computer needed reseting. That didn't help...
Oil looks fine. No chunks of metal in it or anything.
Any ideas? I was thinking possible bad gas (from the buddy that brought me the stuff in the can). I might put some fuel treatment in it tomorrow and try it. I also was going to check a few more of the spark plugs to see how they look. Any other things to try? I'm running out of ideas. I thought for sure the clogged cat was the culprit and that was it. I'm not sure what it could be now.
Thanks for the help.
-RC

[BigDaveZJ]

What'd you do with the downstream O2 sensor????

[Goosed76]

What'd you do with the downstream O2 sensor????
Good question...:confused:
But wouldn't it still start in open loop?
I've ran an 06' WK with the entire drivers side exhaust manifold removed(just to get it out of a stall at work, not drag racing it through town), but it should start when cold, regardless of O2 sensor input.
What was your fuel mileage like prior to this? Any notable decrease?
Whats the plug gap? Firing outside of the engine is different than firing inside a compressed volume of air and fuel.

[DJJordache]

check all plugs and check the fuel pressure at the shrader valve on the fuel rail

[BigDaveZJ]

It also sounds to me like the fuckered cat is a symptom, and not the problem.

[rccolacc]

Downstream O2 sensor has been cut off for a while now. It throws a code, but all that sensor does is make sure the cat works or not. It doesn't affect performance (according to the service manual anyway). I'll check fuel pressure. I'm also thinking the spark plug gaps may be off. What are they supposed to be? I don't have the manual with me right now. Is it .035?
What about the upstream 02 sensor? Would it start if it was bad or not working? I'm thinking it would, but I'm not sure.
Jeep has been performing fine the past few thousand miles. I get about 15mpg on the highway, but I thought that was about normal for an old vehicle.
Thanks for the help.
-RC

[paulkeith]

just make sure those downstream sensor wires aren't shorted to each other or the chassis. if you're getting spark, probably not the issue...but worth a check. check your fuses too.

[rccolacc]

Upon further inspection yesterday, the cat is not totally clogged-- just is about 1/2 melted away. I changed out the spark plugs. Old ones looked OK generally. A few had carbon buildup and one had the porcelain missing around the electrode. Still won't start though. Turns over a lot, but will never fire up. I'm getting spark, and I assume fuel because I can smell it. Now I'm wondering if maybe it's getting too much fuel-- like maybe the pressure regulator went out.
I looked all over the fuel rails for a test port for pressure and it doesn't have one. I looked in my service manual, and it states that some engines have them and some don't. The show you test the fuel pressure by disconnecting the fuel rail and connecting what looks like and inline gauge.
I figured out from the manual the fuel pressure regulator is on top of the pump mounted pretty much on the tank. Is it vacuum controlled? Could a vacuum leak cause the regulator to malfunction? A friend suggested that it could be a vac leak. I'm not sure. I'm going to try to borrow a fuel pressure gauge today from the dealership to check it. If the pressure's too high, can I assume a bad regulator, or do I need to check vacuum too?
Thanks for the help.
-RC

[DJJordache]

one more idea that I have actually experienced with random engine dying: check the coil wire and coil lead on the cap for a ton of corrosion and bad connection.... I had mine randomly die and that was the issue, new cap and coil wire and back in business.

[rccolacc]

Just read some more in the service manual. Looks like the regulator is not vacuum controlled, so vac leaks shouldn't matter. It also looks like the regulator is also a fuel filter. Hmm... Wonder if some trash got in there or something.
I'll check the cap and rotor. Coil was putting out juice fine. Pretty sure the spark plugs are working, but I'll check again.
I'll try to get a fuel pressure gauge today.
-RC

[FrozenZJ]

I'm going to go with low fuel pressure. That would give you those results.

Could also be a bad PCM injector circuit or the relay has taken a dump. Usually thats all or nothing though.

[rccolacc]

After spraying ether in the intake, the Jeep still wouldn't start last night, so I quickly gave up the theory that the problem was in the fuel system. The cap and rotor looked a little questionable (some corrosion on the rotor), so I replaced it-- still no starting. Checked the coil and it had spark, but the spark plugs didn't. Replaced the coil (it was only a year old) thinking maybe it was just weak, and the Jeep pops off imediately. It was amazing. I think the weak coil was giving me fits. It would show spark at the plug (when I checked it on the side of the road), but then not later on. Maybe the combination of questionable plugs and corroded cap and rotor made the coil get weak faster. Who knows. I'm just glad it's fixed and I didn't have to drop the gas tank.
I still had the cat off when I started it, and man did it sound awesome (exhaust dumping where the cat was). I went ahead and completely gutted the cat to be done with it. I'll finish welding it on tonight after work and be done.
Thanks for the help guys.
-RC

[Goosed76]

I take it you don't have emission testing where you're at?
Good to see it fixed and back on the road man.

[black_zj]

3 years ago I had an 8 month old Napa coil die on me while driving across the country, good thing I had an extra with me in the middle of Illinois. It was the last thing I checked because it was "new", but a fellow Jeeper stopped and helped me diagnose it.

[DJJordache]

I was kinda close I have failed 3 stock style coils..... I now run the Crane ignition system that comes with a big coil:D

[Goosed76]

I was kinda close I have failed 3 stock style coils..... I now run the Crane ignition system that comes with a big coil:D
How is the Crane setup working for ya? Worth the money? I have the Accel Coil right now....

[DJJordache]

It's great, but worth the $ that is up to you... I tried to find the one I am using on summit but it's not there or I'm not remembering the part number correctly.

it is multi spark under like 2500 and has a stringer spark to redline, it also allows you to gap the plugs larger to like .045" or .050". its tough to say how much just the ignition changes things since I have so many other parts working together....

[Goosed76]

isn't that usually the case- bunch of mods working together. I just found the crane ignition that was like a universal for everything from Honda Integras to Corvettes, is that the same unit?

[DJJordache]

pretty sure this is the one I have: will have to check later...
http://cranecams.com/?show=browseParts&lvl=5&prt=1967&action=partSpec&partNumber=6000-6301

[Varkyl]

rccolacc,
you should also get the crap out of your muffler. Since your cat was coming apart those pieces have to go somewhere. And they normally get caught there. This can and will cause performance issues.

[rccolacc]

Ok I thought I fixed the Jeep with the coil, but the problem is back. Today I drove the Jeep about 10 miles. This morning, the Jeep drove fine except it hiccupped about once right after I started it. One the way home, the Jeep bogged down and died at a stop sign. Soon after that it was bogging down and stalling a lot right as I was getting to my house (didn't matter if I feathered the gas or not either). Now, the Jeep won't run for more than 2 seconds, and it's very hard to start. I'm pretty sure I'm smelling rich exhaust too. I don't suspect it's the O2 sensor because the PCM only reads it when it's in closed loop mode and this hard starting is happening with the motor cold (just now). It's raining and cold so I gave up for the night. Tomorrow I'm going to check the TPS and MAP sensors. I'm thinking it could be making the motor go rich. I'll also try to get a fuel pressure reading.
I got the pieces of cat out of the exhaust, and then I gutted the cat when I put it back on, so I don't think the exhaust is a problem anymore. I also don't think it's a spark issue because basically it's all new as of this week (new plugs, cap, rotor and coil). Surely the coil hasn't gone bad after 10 miles...
I really don't want to drop the tank if I can help it. I'll let you know how the diagnosis goes on the TPS and MAP.
The Jeep is wearing me out this week. Can't wait to get it running right again...
Thanks for all the help guys.
-RC

[rccolacc]

Jeep was fine all day Saturday and Sunday, never gave me any trouble. Odd.
I broke down and took the Jeep to a repair shop today though. It was acting up again on the way to work so I dropped it off. The problem ended up being the wiring harness going to the coil was shorting out against the block. They wrapped the wire with tape and then a extra piece tubing and called it good. Drives great now.
glad to have it fixed, and hopefully for a while...
-RC

[Goosed76]

that will do it, lol.
Hope all is finally fixed for ya. Shorting coil signal wires will definitely give you an intermittent issue.