ntomsheck

Hey guys, I'm new here, but not new the automotive scene. A little back story since this is my first post, and the story might help with trouble shooting.

I bought my 1998 cherokee sport almost two years ago for 250 bucks. It didn't run when I bought it, but it was just the neutral safety switch, so I just jumpered the proper pins so it would start. I let my friend borrow it last summer, since I can drive my other car over the summer. Long story short, he got mad at me, and drove it without coolant for 30 miles. This blew a hole in piston #1 and scattered the aluminum fragments all over the engine. I replaced it about a week ago and I've been getting her back to running condition over this time

It runs and idles fine, except after about 7.5 to 10 minutes (timed it), it starts sputtering. This sputtering is beyond just idle. If I depress the throttle slightly, it'll land on the RPM I've selected, but will still sputter and slowly drop. It sputters for about a second, then revs back up to standard idle speed for a second, then sputters again. While driving, it will buck and sputter when it falls into this routine.
However, if the car is turned off for even a second, and restarted, it will run like normal again. Eventually, it starts the sputtering routine again.

While it's sputtering, the smell of fuel is quite strong from the exhaust. It gets to the point of stinging the eyes if you're near the tailpipe. There is also a really loud sucking noise coming from the air intake - much louder and prominent than when idling perfectly.

The only codes it's throwing, is an EVAP system error (p0443) and a chrysler specific transmission miscommunication (p1694), which I attribute to the neutral safety switch still not being fixed. No matter how long I let it sputter, it will not throw any new codes.

At first, this symptom sounded akin to a bad/clogged cat. When I went under the jeep, and tapped the catalytic converter, I could hear the honeycomb rattle. I welded on a "replacement" to see if that would solve the issue, but it does the same thing. (Don't worry, I'll replace it the proper way soon). I also replaced the IAC, but not because of this issue. I replaced it when I detected symptoms of a bad IAC (wont start unless gas is slightly depressed). The new IAC functions well.

A very important piece of information: The previous engine in here had a similar, if not the same exact problem. The following parts were carried over from the old engine:

Crankshaft position sensor (since it's the same transmission)
Flexplate and transmission safety plate (the sheet metal that goes between the engine and trans - it had a slightly different configuration)
Water temperature sensor
Fuel rail/injectors
Throttle body (including TPS, but IAC is new)
Ignition pickup sensor (swapped that, instead of swapping the whole distributor)
Ignition coil
All accessories, incl water pump (water pump, power steering pump, A/C, alternator, clutch fan, tensioner)
Starter.

This seems like an ignition issue, but rather than just wallet-bombing the ignition system, I'd rather do it once and do it right. Does anyone have an opinion of what this could be? I would like to blame the pickup coil, but I would think this would cause more problems than what it is. I'd also think it would throw a code. Same goes for the CPS, MAP sensor, and TPS.

This sputtering problem will happen at any temperature, and the amount of time it takes to start is the same. It takes 7-10 minutes whether it's at full temp - thermostat open, or 7-10 minutes if I start the engine cold.

The previous config was: stock 4.0L, AW4, NP231
The new engine was from a 97 grand cherokee, still a 4.0L, same trans/transfer case

Thanks you for taking the time to read this!

captainwoot

Not sure but check the basics as your old engine experienced the same issues,
Check your fuel pressure (the way you describe "stinging your eyes" indicates a "lean" condition. low fuel pressure could do this.
If your fuel pressure checks out, check the strength of spark, possibly a poor ignition coil.
If all of that checks out, how about a vac leak at the intake manifold? try spraying intake cleaner to see if the idle changes or smooths out.
Good luck!

ntomsheck

I always though 'eyes burning' indicated a rich condition, but now that I think of it, it makes sense. Poor spray pattern and whatnot.

I will test the fuel pressure when my buddy gives me back my fuel pressure tester. What is the standard operating pressure for these, 45psi like GMs?

I had a spark tester between the coil and dist, but I ran out of time before it could start sputtering. Should have more time tomorrow

I never thought of a vacuum leak. It would be quite coincidental if both engines had the same problem - I didn't swap intake manifolds. Not impossible though. I will certainly try all and report back.

ntomsheck

Some updates:
The Jeep took excessively long to reach the stalling/sputtering symptoms. It was close to 30 minutes this time. I had my fuel pressure gauge hooked up, as well as a spark tester between the coil and dizzy. The fuel pressure bounced around alot, very rapidly (between 47 and 53), but averaged out to 50psi. When it was sputtering stalling, it didn't drop one bit, stayed between 47 and 53, or at least between 45 and 55.

While it was sputtering, I also looked at the spark tester. There were no visible anomolies, such as a break in light, or anything like that. The rate slowed down, as expected, when it bogged. I also sprayed carb cleaner all around and removed a few vacuum lines, plugging them with my fingers to see if an entire line is bad.

Since this engine is MAP, and not MAF, wouldn't the engine simply speed up if there was a vacuum leak? It speeds up whenever I remove a line... can't imagine it would be any different if a gasket was leaking. I unplugged the MAP to see if maybe it would stay running, but that just killed it, and ended the test.

After work, I'll try adding carb cleaner straight into the throttle body to see if it's a fuel issue - perhaps injectors. I'll also check the plugs to see if they have any abnormal wear and try unplugging various sensor to see if they're outputting skewed values. I'll try plugging a couple more vacuum lines as well, mainly the FPR vacuum line (it still idles without it, due to factory defaults). Is it possible for an O2 sensor to cause this, yet still make the computer think it's working fine?

Bustedback

Replace the crank sensor.

captainwoot

I had an issue with my own, sputtering and stalling, found corrosion on the harness side of the front o2 sensor,I cleaned that and replaced both o2's and haven't had a problem since
It never threw a code.......

goldenlandscaping

Mine is doing the exact same thing all the way down to the time it takes to start mine is a 92 I really am stumped too check this thread https://www.cherokeeforum.com/f2/sputtering-57575/

AvidXJ

Mine had the same symptoms and it was the upstream o2 sensor. It only threw a code sometimes but it would go away again. I would check the o2 sensors as well as the connections as mine was caused by a frayed wire. Check out the thread(link) posted by goldenlandscaping. it describes my situation better

goldenlandscaping

yea i replaced my o2 sensor and checked the harness side wiring i have narrowed it down to bad connections at the pcm will update tomorrow when i get the new connector installed

ntomsheck

It would be nice if it were an O2 issue... that's cheaper than my current idea. When it was sputtering, I actually sat and paid attention to the fuel pressure gauge, and noticed that it would drop about 10psi, and then the engine would sputter about 50 milliseconds after... I went under the gas tank, and kicked it lightly. This fixed the fueling issue greatly. It was still rough, but it was an instantaneous different. I assume this is either a pump, or regulator issue now. I'll probably replace the entire unit, since my fuel level sender is screwy as is.

The harness side of the upstream O2 was actually quite clean. I still cleaned it off a little bit more, but that didn't help. Do these O2 sensors read similar to OBDI sensors? (>0.750V = Lean <0.750V = Rich) At least I think that was the turning point.

ntomsheck

Okay guys, just wanted to let you know I have resolved this issue. It wasn't throwing any oxygen sensor codes before, but after a 50 mile trip to a job site, I checked the codes. Lo and behold, a code 132. The check engine light has always been on, so there were not indications other than what the scanner told me. After replacing the O2 sensor, I also unplugged and replugged the purge solenoid a few times, in an attempt to clean the contacts (just as a 'why the heck not').

Replaced the O2 sensor, took a 10 mile lap around my town, and it didn't sputter once. Furthermore, I no longer have a check engine light... I thought something was wrong the whole ride. Checked the codes, and I'm no longer getting the 443, 132 and 1694. I'm still getting an 1899 (neutral switch stuck) and a 138 (rear O2 sensor = temporarily misplaced), but I guess these aren't enough to fire the MIL.

I gotta go break something now, to get that light back . That, and I need something new to diagnose...

Thanks for your help and suggestions about the O2 sensor. Without it, I would have just replaced the fuel sending unit unnecessarily and been out an additional $200