I love the future!

I am aware that in my capacity as a Paranoid Desert Recluse I am supposed to hate all things technological and especially all things connected. And I do fall in line with some of that: I truly don’t understand why anybody’s toilet needs its own internet connection, for example, and you’ll never see me looking at a computer screen without electrical tape over that creepy little camera lens because sheesh.

But sometimes the future is fun and convenient. You may recall that in the last big care package drop my older brother sent me a fuel gauge set for diagnosing what’s going on with the Jeep’s fuel system. That was shortly before my trip to the city and it spent all June locked up in the powershed. But today I dragged it out and hooked it up to that very convenient Schrader valve on the fuel rail…


…and learned that the running fuel pressure was 23psi. Which didn’t really tell me anything useful because I don’t know what the spec is. Not a big problem, I do have a manual and if that doesn’t work I have this hip, cool new thing called the internet. But that would involve taking half an hour or more to go inside and do that research, which would surely let the air out of my Jeep maintenance project…except that I also have this amazing magic elf box right here, which I just used to take that picture.

And so leaning on the fender in the sun I just typed “fuel pressure jeep 4.0” and was immediately rewarded with multiple sources all of which agreed that the pressure ought to be 45-55psi. And that is useful information.

For several annoying little reasons I believe the Jeep is going to be spending a week or two in town before the month is out. But I must admit, I do enjoy certain aspects of living in the future.

About Joel

You shouldn't ask these questions of a paranoid recluse, you know.
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9 Responses to I love the future!

  1. Jim Price says:

    New fuel pump will fix that and vapor lock should be a thing of the past. At 23psi I’m surprised it is still running.

  2. terrapod says:

    sounds like one of the two fuel pumps is limping or you have a clogged filter. I assume it has direct injection? do some diagnostics, find where tank fuel pump goes to filter and measure pressure out of tank. Then hook line back up to filter and measure pressure on other side of same, should be close to same. if both those are in spec, then it is the second high pressure pump. also heck manual, a bad pressure sensor might be sending bad signal to pump. you used to do this for a living if I am not mistaken, I am just a shade tree engineer. 😉

  3. Jim Price says:

    There is only one fuel pump and it’s in the tank. No direct injection, it’s a multi-port injection system which requires roughly 50psi to operate properly. As the pump gets old and wears out the pressure it is able to produce drops. When it gets low enough the engine will just stop running. And 23psi is pretty close to where an MPI engine is going to stop running. Changing the fuel pump is easy. It’s dropping the fuel tank that is the PITA part. If you want to run by my place Joel, we’ll run it in the shop and I’ll do it for you.

  4. terrapod says:

    Thanks for the clarification Jim, I am more accustomed to DI of late and have not worked on Jeeps for 30 years.

    Looked up the pumps and they seem to run between 90 and 200 bucks depending on if just the motor/pump is replaced or the whole assembly (I checked Autozone which is pretty much everywhere).

    I am sure e-bay might be less cost but unknown source. How go the finances Joel?

  5. Joel says:

    The finances are in shockingly good shape at the moment, which is why I’m debating whether I even want to do the job myself. Between this, the nagging front-end coolant leak I seem incapable of fixing myself despite three tries, and my desire to find adequate rear shocks that will work on a jacked-up Jeep, I’m thinking strongly of sneaking it back into town and leaving it there for a week. Besides, those gas tank straps have probably been right there since it came out of the factory and I’d hate to break off a bolt in my driveway.

  6. Mark Matis says:

    Fuel pump from the Rock:
    https://www.rockauto.com/en/catalog/jeep,2001,wrangler,4.0l+l6,1373723,fuel+&+air,fuel+pump,6256

    Looks like their most popular one runs $51.79

  7. Norman says:

    A thought: A friend, confronted with the Modern Trend of burying fuel pumps inside the tank, developed the habit of switching to externals when confronted with dropping a tank for the third time (3 different cars, but still…). Running a tank dry doesn’t kill the pump for sure, but certainly increases the possibility of an early demise; the pump depends on fuel both for some amount of internal component lubrication and a lot of cooling. I am aware that emptying a tank to the last gallon or so , while easily possible, does the pump no favors. There’s a reason the little yellow fuel light comes on at the 3.5 gallon mark.

    It took some fuel plumbing legerdemain, but a brand name electric pump securely tucked against a frame rail solves the problem, gets the pump out where it can be swapped in 10 minutes, notably without having to drain a full tank to do so.

    Pro Tip: If one goes this route, it’s beneficial to, first, gently scrub the tank when it’s empty, and second, use the absolutely largest filter one can find on the pickup tube because a clogged filter becomes the one reason a tank needs to be dropped. Big filters, however, may not fit compactly in the tank sump (assuming the tank has one) and once it starts sucking any amount of air it’s Game Over.

  8. paul says:

    This is very interesting. A friend has a ’90, I think, Cherokee 2 door with a “I don’t know” what it is straight six. Four litre? It has about 230,000 miles. Doesn’t use a drop of oil, either.

    It vapor locks. We replaced the injectors. Rather, I did because my eyes are better. That didn’t fix anything. Then he bought a kit of insulation stuff to wrap the fuel rail and injectors. That was a waste of money and time.

    When he fills up at the very rare station that sells gas without ethanol, the Jeep doesn’t vapor lock.

    So of course, in his head, the entire problem is ethanol. Well, wire into the fan relay and have a tiny rocker switch…. so when he goes into the grocery store he can make the cooling fan run. And it works.

    But… no. I ain’t buying it. My ’96 Stratus never had a problem. My ’91 Dodge pickup never had the problem. And as weird as the ’81 to ’83 Imperial fuel systems were, never a problem.

    I’m going to buy a fuel pressure gauge. I think someone needs a new fuel pump.

  9. Paul Joat says:

    I had a jeep Comanche with a 4.0 that became hard to start and wouldn’t run right at full throttle but it idled fine and ran down the highway without any issues, I put a fuel pressure gauge on it and it was at about 25 PSI instead of the 50 PSI it should have. It turned out that it wasn’t the pump that failed but the little piece of rubber line that connected the pump to the hard line on the sending unit had split and was leaking.

To the stake with the heretic!