Not Running for longer that a few minutes

[Warren99]

I just recently put a new valve cover gasket on, and a new belt. The new belt let me discover that my fan clutch is stuck on. But the main issue that randomly arose is the engine firing for a second, then immediately turning back off. I have since then found out that if it happens, and I wait 2-3 minutes, it will start and run normally but after 2 minutes of idle, or driving it will shut off and repeat the same issue. I replaced the fuel filter, that didn’t fix it. And I also fid and oil change including the oil filter (not expected to fix it but it’s something that I needed to do anyways) My best guess is that the fuel pump is too weak, or the fuel pressure regulator has gone bad. I got a friends fuel pressure gauge to test the pump, but haven’t used it yet. I can’t prove it, but i swear the fuel pump sounds quieter than usual. If the fuel pressure gauge proves the pump to be good, what’s a way I could test the regulator, remove the vacuum line? Or are there any other things I should check.

[jdog]

Check the ballast on the driver's fender

[Dzimm]

Check your CPS over real good.  My blue truck did this exact thing to me one night coming home from work and ended up needing a tow at 2AM..  that was fun.. 

At first I thought fuel pump but eventually found my CPS wires were close enough to the exhaust that they had melted and it was causing a short and shutting the truck off.  Replaced it and all was well again.

[Warren99]

4 hours ago, jdog said:

Check the ballast on the driver's fender

How do I check it? Nothing seems obviously wrong with it.

[fiatslug87]

You can just bypass it by connecting the two wires together.

[Warren99]

18 minutes ago, fiatslug87 said:

You can just bypass it by connecting the two wires together.

I kind of figured, but I wasn't sure if that could cause anything bad to happen. Literally all I know about ballast resistors was from a quick search and I know they limit the voltage to the ignition coil, idk how or why.

[jdog]

On the older Chrysler they did, jeep used em on their fuel pumps

[Warren99]

13 hours ago, jdog said:

On the older Chrysler they did, jeep used em on their fuel pumps

Ok, so if I bypass the two wires, then worst case scenario is the fuel pump will run too much but the regulator will dump the fuel back into the tank. Just can't permanently bypass it because the pump will be working too much.

[jdog]

Yes and you can leave em connected it just makes it louder

[fiatslug87]

18 hours ago, Warren99 said:

How do I check it? Nothing seems obviously wrong with it.

According to this post it should have 1.2 ohms resistance.

 

 

[Warren99]

On 2/4/2021 at 12:20 PM, fiatslug87 said:

According to this post it should have 1.2 ohms resistance.

 

 

Will try this later today.

[Warren99]

When the engine was shut off the resistor read about 1.2 ohms. But still all I did was wire bush off some light corrosion and now it’s fixed.

[Zenobian_84]

IMO, I would keep an eye on it; worst case scenario, they are normally available at the parts stores. When I had my stint up at Chrysler for 6 months a while back, I worked on a guy's old 88 who bought it brand new. Was having some of the same issues you described (along with a slew of other issues due to being a Michigan truck for close to 20 years), and found out that the posts inside had a lot of corrosion on it, along with finite cracks on the ceramic assy. itself, causing some intermittent stumbling and rough starting when trying to crank. Replaced that and some of the vacuum lines on the engine and eliminated the issue.

Originally they were put in place as a noise reduction piece for the fuel pump, and without it, you can hear the pump "whirr" louder when running. If you don't want to replace it down the road, just splice the leads together and shrink wrap it to keep moisture out.

[Warren99]

Ohhh ok. That helps a lot thanks.

[Eagle]

On 2/4/2021 at 10:05 AM, Warren99 said:

Ok, so if I bypass the two wires, then worst case scenario is the fuel pump will run too much but the regulator will dump the fuel back into the tank. Just can't permanently bypass it because the pump will be working too much.

 

The XJ and MJ 4.0Ls in 1987 didn't have the ballast resistor. It was added for the 1988 model year to reduce the noise of the fuel pump. You can bypass it permanently without doing any harm.