Low fuel pressure, pump or regulator

[lonestar]

I was haveing a starting and idling problems which caused the engine to sputter and die, but was fine while driving. I checked the fuel pressure and it seems to be low. I started this new thread to help people using search.

After installing guage and priming fuel system by tuning key to run pos, it read 35 psi. After starting it slowly bled off to 20 psi in about 5-10 min ans started idling rough. I also tried to remove vacuum line to regulator and pressure did not change. When I removed fuse for pump and pressure dropped to about 18, it gave all the sputtering symptoms I was having.

According to Haynes.
Pressure with vacuum hose attached - 30-45
Pressure with vacuum hose removed - 40-50
Max Fuel pump pressure 65 psi

I changed the fuel filter less than 3 months ago, after it was completly clogged, would not run longer than 1-2 minutes. Previous owner had new pump installed, maybe it's fried though.

Is there anyway to check fuel pump output pressure?

 

[Alec]

I'd say fuel pump relay or FPR.

 

[MrShorty]

I'm sure you could check the fuel pump output pressure if you wanted to. You'd need to break a connection in the supply line, attach the fuel pressure gauge, and turn the key on.
Another possibility is restricted fuel lines.
I don't know that Haynes includes it, but Chiltons and other manuals include a detailed fuel pressure testing flow chart that works through the entire fuel delivery system. If you can get a hold of a copy of that chart, you might find it useful. It's available in the vehicle repair guides at www.autozone.com but it's a little difficult to find. They've hidden it under "fuel pumps" in the fuel system section. They've hidden "fuel pumps" under the SFI section, which always gets me, because our trucks use a multi port fuel injection system.

 

[lonestar]

I would disregard the relay, the pump is getting power.

 

[Opera House]

It may still be the relay

The engine will run with as little as 6 volts to the pump because most of the fuel is bypassed back to the tank. So any bad connection adding resistance can cause this problem.

I didn't understand the comment about removing the fuel pump fuse. You should be able to read the max pressure by turning the key on but not starting the engine. If it held to 20 for 5-10 minutes, that wouldn't be much of a leak.

If removing the vacuum hose didn't change the pressure perhaps the hose has a leak or not connected. This could also indicate the pump doesn't have enough pressure. Remove the pump fuse again and measure the current. Under 4A you are going to have trouble. The engine will stop at 2A.

I would still lean toward the regulator. I had problems with my 92. Sometimes it would be fine and then it would have rough idle and stall. Cut open the regulator and found a bevel worn on the seat on one side. This would cause it to stick open and drop pressure. Since there is no good way to test the FPR, I'd just replace it. I monitored the pump current in cab for about a week and would watch it drop and come back to normal.

It is obvious this gremlin harrased the previous owner. By the way, a new fuel pump made the problem worse on mine.

Gauges are often inaccurat. Pressure should be about 33-34 at idle and 39# with vacuum line off.

 

[justsearching]

It's probably the pump or reg but relays can do this. If you repeat the test, does it take as long for pressure to drop the 2nd time? I'm thinking that points to working heat affecting the pump or relay. If you still suspect the relay you can jump it to see if pressure changes.

Dave

 

[lonestar]

Just did another check. Checked to see if the regulator ws stuck open. Removed return line and nothing. It seems the pump is not building up enough pressure.

I removed the fuse as the engine was running.to depressurize the system. When the pressure dropped down to 18 is when I started getting the sputtering and stumling symptom.

I don't understand how you measure the current at the fuse. Should I test the current with the fuse in, or remove the fuse and jump the gap with a multimeter.

I can also measure the pump voltage from the EEC test harness according to autozone.com repair guide.

Is there any way to test the relay? I thought realay either work, or don't.

 

[410Fortune]

If there is even a question replace the relay.

I suspect the fuel pump after reading the symptons.
Also if you are going to drop the tank and replace it, get a good pump, not a cheapo.

The pressure should change when the vacuum line is pulled. You also may consider a new regulator.

Let us know what you find.......

 

[justsearching]

For relays, if the coil side fails it's simple as they look completely dead. The other side is more like a spark plug, and loses efficiency as the contacts erode.

I haven't tested for an Explorer pump so can't tell you what amp numbers to look for. However, if you test cold, when it has good pressure and compare to after it drops you may see a large increase in draw. If so that points to the pump. If the draw drops with lower pressure then more likely the regulator or relay.

If I were in your situation I'd jump or replace the relay for a quick test. Simple and cheap relative to a pump or regulator.

Dave

 

[BLUZ]

So the filter was completely clogged and he just replaced the pump? Is there some junk in the tank that is causing this problem? Can you remove the pump and check it out? Maybe want to check this and check your new pump's filter as well.

 

[lonestar]

The filter was probably the original filter, I guess after 160k, it might be clogged. The original owner probably replaced the pump becuase the pump went bad, and the clogged filter probably strained the new pump to death.

I'm still pretty convinced it's the pump. Possibly it's not getting enough juice (current), I'll have to check the voltage and amperage to be sure.

Opera, how to you check the amps. Do I just remove the 30 amp fuse and stick in the test leads straight from the meter. If the amp is only around 4 amps, why would they use a 30 amper.

 

[Opera House]

Remove the fuse

and let the meter complete the circuit. I found a crimp on connector end like a 1/4 inch spade connector fit in nicely into the fuse clip. I made one with a connector designed for a screw connector. I cut off one leg of the U so it also fits into the MINI fuses. The fuse is 30 amp because it is the last thing you want to blow. Basically it just to protect the wires. The test harness will tell you if the fuse clips and relay have resistance. It will not tell you the voltage at the pump. If the filter is clogged again, pump current will be higher than 5A. Pump also has a sock filter that could clog. Incidently I have a Jeep that I replaced the pump on. It probably wasn't bad. When I pulled the pump out, the pump fell off the hose. Clamp had never been tightened on the hose. Maybe last guy was forgetfull.

 

[lonestar]

Thanks, I'll check it tonight.

Also if you are going to drop the tank and replace it, get a good pump, not a cheapo.

Who has a good pump?

Autozone
Master Pump (without strainer) $70
Master Strainer $6
Master Pump Assembly $120

Napa
NAPA Tru-Flow Fuel Pump (OE) (with strainer) $62 or $90
NAPA Tru-Flow Fuel Pump Assy $116

I wonder what is the diff in the NAPA pumps, both rated at 65psi, 18 gph.

 

[410Fortune]

Napa uses Echlin I believe which is OEM for Ford.

Car Quest is the only other I trust for something like this.

No Checker, No Autozone, No Pepboys.

if you're gonna drop the tank, put in a good pump, not the cheapest.

 

[lonestar]

Getting 3.5 A at fuel pump fuse. Important reminder, always remember to change test leads when changing from testing amps to volts. I was just touched the leads across the battery and I think I almost fried my meter, wires got real hot.

BTY, the $62 Napa pump is the cheapest, + it comes with the strainer. I wonder what is so special about the $90 pump.

 

[Opera House]

When I last measured mine

At about 120K I got 5.25A idle w/vacuum removed cold pump and 4.66A at warm idle. Thr pump current normally drops about 0.25A after about 2 minutes of running as the pump heats up to a stable temperature.

Pump current is basically proportional to pressure.
1. Your current indicates the gears are either worn.
2. Intake filter sock is clogged.
3. There is a leak internal to the tank at the pump outlet.
4. There is extreme electrical resistance in the line dropping pump voltage.

How sure are you that this pump was actually replaced. That much wear would be unusual.

I measured pump voltage by removing the tank electrical connector and inserting two very thin strands of wire that I got from some stranded wire then putting the connector together. You could also stick pins in the wires on the pump side. At least you don't have to drop the tank.

I bought a Zone pump and a factory Ford one. The Ford had better bearings. But let's face it, you won't be driving this 60K from now.

 

[lonestar]

Put in new pump last night. Now I'm getting 8-8.5 A. It also seems to start easier when cold. I'll check the pressure again later.

The idle now seems to be surging between 700-800 RPM constantly (up, down, up , down), or maybe it is just more noticable with more fuel. I was thinking that the computer may need to relearn since now it is getting more fuel. Drove to work and I noticed the CEL on, then it went out, but idle is still surging. I'm thinking either IAC or MAF. I'll scan for codes.

 

[Opera House]

Reset the computer

When I replaced my FPR, it drove better but didn't seem right even after 200 miles. Disconnected the battery and it was like new. Adaptive systems don't work well when things get too far out of wack.

 

[lonestar]

Well, I have had more problems. FPR was bad too, would not start after lunch, pulled vacuum lines and they were full of fuel. Drained vacuum lines and replaced FPR.

Stater motor finally crapped out on me. Replaced starter, starts and runs great.

Now it blows white smoke. I noticed it about a month ago while filling up, a little white cloud, just thought it was cold, now it's blowing alot of white smoke, and the antifreezreis low, so I figure a head gasket. GEEZ, it never ends. Atleast I don't see any water in the oil.

I also read a thread where another thread FPR went bad all of sudden and caused white smoke, but I don't see why. I then he ended up replacing brake booster.

I'm really debating on what to do, 180K, it runs great and doesn't use a drop of oil, but I have already spent almost $800 in the last few months, tires, steering gearbox, fuel pump, regulator, starter. I'm thinking about taking a look at the head gaskets, but what if its the head? What's next?

 

[mbmech157]

On 2000 XLT SOHC where exactly is the FPR? A picture would help a lot. Also, is it easy to change?