fuel pump, or relay

50rck · 01-26-2010, 03:57 AM

I am not sure which problem I am having, and I am hoping for some suggestions. I replaced the fuel pump 2 years ago, and the filter only a few months before that. About a month ago I tried to start the Jeep one morning in about 20 degree weather, it cranked, but no fire. Had the wife try it around noon, and no problems. Since then we have had temps close to 10 degrees and I have had no problems. I do not think it is the computer, as I do not seem to have the symptoms that everyone else has with that. But yesterday while driving into work I had made it about 20 miles when the motor just shut off. I pulled over, pulled the fuel lines and tried to start it. There was no fuel coming out of the lines. I thought it could either be a clogged filter, or the pump I recently replaced had gone bad. But I waited almost 12 hrs and tried to start it, and it fired up.

So now I am wondering if the pump is working intermittenly, or if the relay is going bad. If its the relay, any ideas on how to check? The ground seems good at the e-brake. I haven't pulled the line from the tank to filter and checked the flow yet, I was hoping some others could chime in while I check that. I was just trying to keep from dropping that stupid tank again if I could help it. Its a 1991 4.0, I think the pump I bought was a Crown brand with the sending unit all in one package. The factory pump got over 230,000 miles, I would hate to replace the pump that only has 10,000 again.

**rustywrangler** · 01-26-2010, 05:36 AM

Swap the relay in the PDC with the AC relay. Easiest way to tell.

When you say pulled the lines, I hope you mean at the filter.

**Que89YJ** · 01-26-2010, 06:35 AM

Jumper the fuel pump relay. Its quick and easy. If you have flow then its not your fuel pump and you need to check other things like your crank sensor. Use a voltmeter or a test light and make sure you have voltage on the coil. Do you have any fault codes? Take a look at the FAQ to see how to determine what codes are present.

50rck · 01-26-2010, 01:32 PM

when i checked the flow yesterday, it was from the rail, I just wanted to see if fuel delivery was the problem. I replaced the filter and was able to get it home, barely. On the way, while going up a steep hill, I hit the gas just to check it. It did a real bad hiccup on me. So i didn't hit the gas hard until I got home. Once into the neighborhood, I hit the gas hard in 2nd, and 3rd gear, and then once in the driveway I held it at over 4000 rpm's for about 30 seconds, and no problems. I turned over the old fuel filter and tapped it on the driveway to see what would come out. Nothing large in size, but the fuel was black in color, and some small carbon deposits fell out, but only about 3 or 4 pieces, and they were very small. I'm still not convinced its the pump, but I have a new one on order anyway, and I'm going to replace the skid plate since that 2 foot in diameter hole in the OE one is not helping me any. And I broke a strap last time, so two new ones of those are on the way. I am going to head out and check for codes after this.

Another question: Does that pump keep a steady pressure, meaning does it spin at the same speed? Or is it depending on how much pressure you give the gas pedal?

Mark05059 · 01-26-2010, 02:00 PM

the pump puts out the same pressure/speed all the time. The fuel pressure regulator (in the motor area) is what adjusts the fuel pressure

50rck · 01-26-2010, 04:07 PM

Quote:

Originally Posted by Mark05059

the pump puts out the same pressure/speed all the time. The fuel pressure regulator (in the motor area) is what adjusts the fuel pressure

I'm still learning, so don't get upset, but I don't think the '91 4.0 MPI motors have a fuel pressure regulator. At least not according to the manuals. Fuel pressure regulator seems to be part of the TBI system. Unless I am way off here. The way it reads, sensors tell the computer when to fire the injectors, and how much (or wide) to send the fuel into the manifold.
The more I read it does seem that the pump puts out the same speed at all times. Which makes me wonder why I had the bad sputter when I hit the gas going up the hill, or maybe that was just a coincidence. It was suggested to me by the dealer that it could also be the ASD relay (automatic shut down). Given the age of those relays I am just going to replace all of them since there are only 4 (got rid of my AC). Of course I could also still have some funk in the lines.

50rck · 01-27-2010, 04:37 PM

I got the tank dropped and blew out the fuel lines today. I am also in the process of replacing both the fuel pump relay, and the ASD relay (for some reason parts stores only stock one or zero of these, so I have to go to a few different stores.) I checked the codes and don't see anything that alarms me. I was wondering if a sensor going bad could trigger the ASD relay to shut the motor off, and would then cause the pump to also stop working. I am not sure how this works, but does the ASD relay cause the fuel pump to stop, as well as no spark. The worst part about this problem is that when it goes away, I can't figure out what caused the problem because everything is working again.

50rck · 01-28-2010, 08:12 PM

I got everything put back together and it is running fine right now. All relays have been replaced, cleaned out the tank, put on new fuel lines. Put in a new fuel pump, and sending unit, but the gauge still doesn't work. Either the float is still hitting little box inside the tank around the pump, or the gauge itself is bad. But its not a big deal to me, I just fill up every 225-250 miles. It was suggested that the crank sensor could be going bad. I talked to the dealer mechanic about that: He said that YES the motor would shut off due to no fire from the coil, but the pump would still work, which would not be my problem since I was not getting any fuel. It seems to idle smoother with this new pump too. So maybe the old pump was bad to begin with, or I just had something in the lines or filter, and it has been blown out. We shall see over time.

**idaholtby** · 01-28-2010, 08:37 PM

Quote:

Originally Posted by 50rck

but I don't think the '91 4.0 MPI motors have a fuel pressure regulator. At least not according to the manuals. Fuel pressure regulator seems to be part of the TBI system. Unless I am way off here..

Just for your own knowledge, the '91 does indeed have a FPR. It is located on the end of the fuel rail (front) and has a vacuum line and a fuel return line attached to it. It regulator the pressure to 31psi and with the vacuum line disconnected, the pressure will increase by approx 8 psi. I hope your new pump fixes your problem, the chunks in the line may be a symptom of it, but I wonder if you ever checked for codes, and if so, what were they? Also you state that your symptoms differ from those that had a confirmed ecm problem with bad capacitors. Does your CEL lamp come on when the ignition is first turned on (before going to start) when this problem is present?

**Que89YJ** · 01-29-2010, 05:20 AM

The way you are describing the imeadiate shut off doesnt sound like a fuel pump. It sounds like a cam or crank sensor. If or when it happens to you again check for voltage at your coil with the ignition on the check for spark at your plugs. I hope the pump fixed it though. Gremlins are a PITA.

jerseyt719 · 01-29-2010, 05:51 AM

DISCLAIMER - I'm a girl....

I heard of someone else having this problem and after going through all the possible fuel issues, it turned out to be the positive battery terminal.

Just thought I'd throw that out there, if it makes sense(?)....

50rck · 01-29-2010, 06:03 AM

Quote:

Originally Posted by Que89YJ

The way you are describing the imeadiate shut off doesnt sound like a fuel pump. It sounds like a cam or crank sensor. If or when it happens to you again check for voltage at your coil with the ignition on the check for spark at your plugs. I hope the pump fixed it though. Gremlins are a PITA.

I don't think it was either of those sensors. According to what I was told, when those go bad, the fuel pump will still work. My fuel pump was not working at all. But the crank sensor was my first thought.

**Que89YJ** · 01-29-2010, 06:40 AM

No, when the crank sensor goes the fuel pump is dead too. It takes down the asd relay so yoou dont have feed to the fuel pump. It can go intermittant too like you describe. The cam sensor usually leaves the fuel pump operative when it goes just no spark. Try the crank sensor.

50rck · 01-30-2010, 12:58 PM

Still having the issue. Got a code this time. #54-distributor/stator pickup. Guessing that is the camshaft sensor. I still have my old distributor, so I am going to put that in and get it home, then order a new one from the dealer this time. The after market one I bought looks a bit different from the OE one. The rotor off the after market distributor won't even fit on the OE distributor. I hate buying parts from the dealer, but they seem to work longer.

Que89YJ: You were correct, brother. Dealer mechanic was wrong.

With that cam sensor bad, the fuel pump also wouldn't work.

Fhajad · 01-30-2010, 01:13 PM

Dealer's gonna cost an arm and a leg for a new one.

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