Did a Good Samaritan Jump Start Hurt my Jeep? Random sputtering, missing, stalling.

[armyofchuckness]

Here's the MJ:

1986 2WD

2.5 liter 4 Speed

Freshly installed remanufactured long block with just over 500 miles on the clock.

 

That last part I feel is important to the story. In early March, I spun a bearing in the old motor, but I got a killer deal on a fully remanufactured long block and did a neat-as-you-please swap out. The thing ran absolutely beautifully during the break in period. Not a problem at all. Right at the very end of that break-in period, a buddy of mine with an old Dodge pickup needed a jump start. We did a straight battery-to-battery jump (which he insisted was fine, and since he knows more about cars than I do, I didn't fight him on it). After the jump, I was driving back to work when suddenly the engine started sputtering all over the place and died. I was going about 40 MPH in third gear. 

 

I quickly turned the key and the engine fired right back up, but ran rough and continued sputtering, especially around 2000 RPM. It died two more times, but immediately fired back up. On the drive home, it sputtered, but not nearly as bad. The next day, it drove like a champ. No problems. Then it sputtered on the way home from work a little. Then it ran fine again. Then it sputtered again. Seems to do just fine under idle, but definitely presents itself most between 1500 and 3000 RPM. When it goes, it almost sounds like the engine is turning itself off more than its dying, but then it kicks itself back on, which makes me wonder...

 

Is it electrical?

I've checked all the grounding straps, the dipstick connection, etc. I even did the recommended ground strap upgrades from this forum a year ago, so I don't think it's a grounding issue. The A/C and brake light fuses blew within 24 hours of the incident, but I haven't had any issues with anything else electrical since then. No weird fluctuations in the dash lights, A/C blower, or radio.

 

I poured through the forums, and kept running across O2 sensor symptoms sounding like this problem. Changed that out last night, and the sputtering was back in full force this morning. 

 

Other things that I've read that it could be:

TPS

CPS

ICU

Coil

Distributor indexing issue (This one intrigues me, since it's a new motor with the old distributor, but it ran so strongly before the jump start.)

 

But if it isn't electrical...

 

Is it fuel related?

I swapped the fuel filter out at the same time, just to see if that helped. It didn't. 

I haven't checked fuel pressure yet, but that's mostly because I don't know how. Again, I don't know if that would be a problem since I'm still pretty sure it's electrical.

 

What do you think happened? I'm really stumped, and unfortunately, I have very little time to diagnose the issue as I'm helping my family through a bunch of issues this week, and I need the truck to get around. Any advice you can give would be greatly appreciated. I'm gonna keep looking around.

 

Thanks for your help.

[Rockfrog]

From your description, testing fuel pressure will likely reveal a dying fuel pump (it will keep on idle but fail to keep with demand under load).

They generally show up at the most inopportune times.

[schardein]

Just did a 2,200 mile road trip in my 2001 Silverado w/ 265,000 miles on the clock.  It sputtered twice and died on the interstate.  Had to get a tow and repair.  It was the fuel pump.  

 

Interesting thing is although it completely died on me, the mech said he was able to bang on the fuel tank with his fist to get it to run enough (roughly) to pull into the shop under it's own power.

 

Might be worth trying next time it acts up?

[armyofchuckness]

Thanks, guys. I'm thinking I'll swap it and the TPS out just to be sure, but I wouldn't be surprised if it's the fuel pump. Appreciate the advice. Drove it this morning, and it acted like there was absolutely nothing wrong. No hesitation. No sputtering. Weird. Better safe than sorry though. Jeep has almost 160K on the drivetrain. Wouldn't surprise me if that was what's wrong. Thanks again for the advice.

[gogmorgo]

It's unlikely, but plausible given the recent install... Check to make sure the bellhousing bolts are tight. I had mine come out a while back, which caused similar symptoms to a bad fuel pump.

[armyofchuckness]

Just for future searchers' sake, I wanted to update and say it was actually the throttle position sensor that failed. I did get a new fuel pump and strainer, and that is on the docket for replacement. Can't hurt after 160K to make sure that's freshened up. Thanks for the tips, guys!