bigmistake Posted November 4, 2018 Share Posted November 4, 2018 Hey everyone, I'm still plugging away at my MJ. It is a 91, 2.5 I am pretty sure I've got a problem with my fuel pump, but I want to get the wisdom and advice of everybody here. I rented a fuel pressure test gauge and threw it on the fuel rail. Here is a quick video (audio is kind of garbage, might want to mute or headphones off): It looks like I'm only getting up to 15 while the engine is running, then it bleeds off immediately. Am I right in thinking it is the fuel pump? What else should I look into? Thanks! Link to comment Share on other sites More sharing options...
HOrnbrod Posted November 5, 2018 Share Posted November 5, 2018 Yeah, that's about 1/2 of the pressure you should see. Did you pull the vacuum hose off the pressure regulator while it was running? W/o vacuum, fuel pressure should jump up ~8-10 psi if the regulator is working. How old is your fuel filter? If you don't know, change it. Link to comment Share on other sites More sharing options...
bigmistake Posted November 5, 2018 Author Share Posted November 5, 2018 I replaced the fuel filter a week ago. I thought I disconnected it and didn't see a change... I will double check I disconnected the correct hose tomorrow when I get back under the hood. I found a pretty good video of lots of debugging I can do, so I will start working my way through the list. Link to comment Share on other sites More sharing options...
Jeep Driver Posted November 5, 2018 Share Posted November 5, 2018 You have TBI? If so, pressure should instantly rise to 15-17lbs and remain there. If TBI, pressure is supposed to bleed off to 0 immediately after shut down. Link to comment Share on other sites More sharing options...
HOrnbrod Posted November 5, 2018 Share Posted November 5, 2018 OP, if you have a 91 model it's an MPI system. Link to comment Share on other sites More sharing options...
kryptronic Posted November 5, 2018 Share Posted November 5, 2018 OP said its a 91, so it's multiport injection. Could be the fuel filter, pump or pressure regulator. Based on the fact that it's not holding pressure after shutdown, I'd vote fuel pump. Link to comment Share on other sites More sharing options...
HOrnbrod Posted November 5, 2018 Share Posted November 5, 2018 Yes, but he's only getting up to ~15psi so I think the regulator diaphragm is probably shot. Start it up, pull the vacuum hose, and see what happens to the pressure. Link to comment Share on other sites More sharing options...
Jeep Driver Posted November 6, 2018 Share Posted November 6, 2018 MPI is not going start on 2lbs and it's not going to idle at 15lbs. Gauge behaves as a TBI with a weak pump. Doubt it's a 91. Link to comment Share on other sites More sharing options...
bigmistake Posted November 6, 2018 Author Share Posted November 6, 2018 It is definitely a '91. So, I pulled the vacuum hose and the pressure didn't change at all. I guess the pressure regulator is bad, too? Link to comment Share on other sites More sharing options...
Jeep Driver Posted November 6, 2018 Share Posted November 6, 2018 Amazing...... Link to comment Share on other sites More sharing options...
kryptronic Posted November 6, 2018 Share Posted November 6, 2018 Your build thread says you got OBDI code 51 on Oct 28. Did you resolve that? I'm guessing not. Check engine vacuum to be sure that's good before you replace anything. Symptoms point to the regulator and/or the pump, but you've got more testing to do to narrow it down. Link to comment Share on other sites More sharing options...
HOrnbrod Posted November 6, 2018 Share Posted November 6, 2018 36 minutes ago, bigmistake said: It is definitely a '91. So, I pulled the vacuum hose and the pressure didn't change at all. I guess the pressure regulator is bad, too? Sounds like it. Did you make sure the regulator vacuum line actually is pulling a vacuum and not just sucking air? If the vacuum is good, with the engine running and the fuel pressure gauge hooked up, find the return fuel line where it is rubber (under the fuel rail after the quick connectors) and momentarily clamp it shut with a pair of pliers while watching the pressure gauge. If the pressure rises on the gauge, you will need a new pressure regulator. Link to comment Share on other sites More sharing options...
bigmistake Posted November 6, 2018 Author Share Posted November 6, 2018 3 minutes ago, HOrnbrod said: Sounds like it. Did you make sure the regulator vacuum line actually is pulling a vacuum and not just sucking air? If the vacuum is good, with the engine running and the fuel pressure gauge hooked up, find the return fuel line where it is rubber (under the fuel rail after the quick connectors) and momentarily clamp it shut while watching the pressure gauge. If the pressure rises on the gauge, you will need a new pressure regulator. Nope! I'm kind of learning all of this as I go... I will go try that while I still have the gauge. Thanks! 10 minutes ago, kryptronic said: Your build thread says you got OBDI code 51 on Oct 28. Did you resolve that? I'm guessing not. Check engine vacuum to be sure that's good before you replace anything. Symptoms point to the regulator and/or the pump, but you've got more testing to do to narrow it down. How should I go about checking the engine vacuum? I don't currently have any check engine lights on, but I'm guessing the code is still valid? Link to comment Share on other sites More sharing options...
kryptronic Posted November 6, 2018 Share Posted November 6, 2018 2 minutes ago, bigmistake said: How should I go about checking the engine vacuum? I don't currently have any check engine lights on, but I'm guessing the code is still valid? You need a vacuum tester. The auto parts store should have one they can loan you. Or buy one - they're inexpensive. Your target is 18 in-Hg. If you get anything below 17 in-Hg, look for cracked or disconnected lines. Link to comment Share on other sites More sharing options...
bigmistake Posted November 6, 2018 Author Share Posted November 6, 2018 4 minutes ago, kryptronic said: You need a vacuum tester. The auto parts store should have one they can loan you. Or buy one - they're inexpensive. Your target is 18 in-Hg. If you get anything below 17 in-Hg, look for cracked or disconnected lines. Thanks! I will do that next. @HOrnbrod - I guess I'm not pulling a vacuum. I clamped the line and no change. Link to comment Share on other sites More sharing options...
HOrnbrod Posted November 6, 2018 Share Posted November 6, 2018 Do get a vacuum tester and test it. But if the pressure regulator has no vacuum applied, you should still see ~39 psi on the pressure gauge. W/o vacuum, as in normal ops, you will see ~31 psi. You have 15 psi of fuel pressure with no change of pressure when you clamped the return line. The pressure regulator isn't working. Link to comment Share on other sites More sharing options...
bigmistake Posted November 6, 2018 Author Share Posted November 6, 2018 I will order a new pressure regulator, and I'm guessing I should go ahead and get a pump as well. I should have clamped both lines before shutting off the engine to see if it held pressure... but I can't imagine it is leaking all of that pressure immediately through fuel injectors. Prices are all over the place for regulators. Is there a brand I should look for or avoid? Cheap Average Expensive And for the pump, I've read I should get a Bosch - the part that keeps coming up as fitting has lots of reviews saying it doesn't fit. Does anyone have a part number I should be looking for? Thanks for all of the help! I will post results when I get everything hooked up. Link to comment Share on other sites More sharing options...
HOrnbrod Posted November 6, 2018 Share Posted November 6, 2018 I much prefer Mopar parts over aftermarket. THIS regulator on Ebay is correct for your 91. For the pump get a Bosch 69302. Excellent write-up HERE and on Kryptronic's build site HERE. Link to comment Share on other sites More sharing options...
bigmistake Posted November 6, 2018 Author Share Posted November 6, 2018 Thanks! Parts ordered! Link to comment Share on other sites More sharing options...
kryptronic Posted November 7, 2018 Share Posted November 7, 2018 20 hours ago, bigmistake said: Thanks! Parts ordered! Make sure your gas tank is no more than half full before you pull the sending unit assembly. This vital piece of info somehow slipped my mind when I replaced my pump. Link to comment Share on other sites More sharing options...
Jeep Driver Posted November 7, 2018 Share Posted November 7, 2018 22 hours ago, bigmistake said: I will order a new pressure regulator, and I'm guessing I should go ahead and get a pump as well. I should have clamped both lines before shutting off the engine to see if it held pressure... but I can't imagine it is leaking all of that pressure immediately through fuel injectors. Prices are all over the place for regulators. Is there a brand I should look for or avoid? Cheap Average Expensive And for the pump, I've read I should get a Bosch - the part that keeps coming up as fitting has lots of reviews saying it doesn't fit. Does anyone have a part number I should be looking for? Thanks for all of the help! I will post results when I get everything hooked up. According to your vid.......your engine started and ran on 0 fuel pressure, you need to figure that one out. Defies logic, unless the injectors are dumping fuel. Link to comment Share on other sites More sharing options...
bigmistake Posted November 7, 2018 Author Share Posted November 7, 2018 1 hour ago, kryptronic said: Make sure your gas tank is no more than half full before you pull the sending unit assembly. This vital piece of info somehow slipped my mind when I replaced my pump. Good to know! I'm at about a half tank right now... will likely drain the rest off before I do anything. 44 minutes ago, Jeep Driver said: According to your vid.......your engine started and ran on 0 fuel pressure, you need to figure that one out. Defies logic, unless the injectors are dumping fuel. I will pull the rail this weekend and take a look before swapping the pump. Thanks! Link to comment Share on other sites More sharing options...
HOrnbrod Posted November 7, 2018 Share Posted November 7, 2018 Swap the new regulator in before doing anything to the pump. You may get lucky... Link to comment Share on other sites More sharing options...
bigmistake Posted November 7, 2018 Author Share Posted November 7, 2018 52 minutes ago, HOrnbrod said: Swap the new regulator in before doing anything to the pump. You may get lucky... That is my plan! I also went ahead and ordered a set of injectors that I plan on upgrading while I'm messing with all this stuff. Link to comment Share on other sites More sharing options...
bigmistake Posted November 9, 2018 Author Share Posted November 9, 2018 Fuel pressure regulator came in so I threw it on over lunch. It wasn't a miracle fix, but I think the engine sounded like it was running a bit better. Other parts should be trickling in over the weekend. Link to comment Share on other sites More sharing options...
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