Fuel Pump or what?

[eldridge2668]

Ok, so I am not an expert mechanic, but I am not afraid to try and can't afford a mechanic (baby on the way, really need this vehicle to run right). I have a 93 Ford Explorer that runs just fine when the engine is cool. However, the warmer the engine is the worse it runs. It will start out with just not having much power and cutting out when trying to start out at a stop sign etc. Then as it gets warmer it will idle rougher and rougher, possibly die, and finally be near impossible to restart until it cools. Based on other posts we changed out the IAC, MAF sensor, and the EGR. None have fixed the problem. We searched for vacuum leaks and did not find any. It was suggested to us by a Ford mechanic that it is more likely a fuel problem than a vacuum problem. Money is tight and changing the fuel pump is not a quick task (its in the fuel tank) so I don't want to replace it only to find out that it still isn't fixed. We pulled the codes and got the following:

157 Mass Air Flows Sensor Circuit Below Minimum Voltage
186 Injector Pulse Width Higher Than Expected (With BARO Sensor)
Injector Pulse Width Higher Or Mass Air Flow Lower Than Expected (Less BARO Sensor)
556 Fuel Pump Relay Primary Circuit Failure
116 Engine Coolant Temperature Higher Or Lower Than Expected (I'm guessing this is because we just added a lot of water and very little coolant, this can be fixed easily just hasn't been the primary focus)
172 HO2S System Indicates Lean
136 System Indicates Lean (Bank No. 1)
332 Insufficient EGR Flow Detected
411 Cannot Control RPM During KOER Low RPM Check (This is because the vehicle chokes out and dies before it can finish the test. I tried multiple times and it always dies at the same time: right after it revs up and then drops the idle back down, it runs really rough for a few seconds and dies)

Based on the 556 code there is obviously something wrong in the fuel pump circuit, and from my understanding of everything if the fuel is not being pumped correctly then it could be causing the 172 and 136 codes. Further, then it is going to cause errors 157, 186, and 332 because there is not enough fuel to mix with the air being sensed. I know this is a really basic understanding, but is that the jist? If I am wrong do I have more than one issue? If I am right then I can definitely concentrate on the fuel pump circuit right? So finally, where do I start with that? Is it still possible it is just a bad pump or more likely bad wiring, connections, etc. somewhere?

 

[eldridge2668]

Suppose I should mention that 157, 186, and 556 where CM outputs. Maybe they just don't have much to do with my problem and I should be concentrating on the 332 EGR problem? Already replaced the EGR valve, maybe the DPFE? Can't really afford to do both, which would be smarter to start with fuel pump or DPFE?

 

[arco777]

The fuel pump sounds very likely. Symptoms of a failing fuel pump are running fine when cold, then as it heats up the pump starts to fail and gradually starves the motor of fuel until it stalls. Waiting for the pump to cool allows it to get going again for a short time, until it heats up again. I've had several vehicles do this and it was always the pump.

You can check this using a fuel pressure gauge. There's a test fitting on the fuel rail. You may be able to rent a gauge from a parts store; if not, they're usually about $30-40. You want to see around 38-40psi with the engine running, and it should stay pressurized for a while after engine is shut off (quick bleed down indicates bad fuel pressure regulator).

Fortunately there is an easier way to replace the pump than dropping the tank - just cut an access hole in the floor above the tank. This applies to many vehicles! You can use any tool you have (I used angle grinder with cutoff wheel) as long as you're careful not to damage fuel lines under the floor, and when you're done use the removed metal piece to fill the hole with a seal of RTV.

You should be able to find a good price on a pump online. Instead of a whole assembly with float and sender and bracket, you can get a fuel pump kit that has just the pump itself, a new strainer, and seals. I just checked RockAuto and prices start at $33 for a new pump with seals, and $2 for a strainer which is sold separately on the cheapest pump kits.

As for your EGR issue. Yes, the DPFE sensor goes bad. You might well have a bad one. But, it won't cause your engine to stall out, just very minor symptoms - you may only notice it as a Check Engine light. They start at $48 on RockAuto. You may want to replace the DPFE tubing while you are at it; new rubber tubing will cost only a couple bucks at a parts store.

 

[arco777]

Suppose I should mention that 157, 186, and 556 where CM outputs. Maybe they just don't have much to do with my problem and I should be concentrating on the 332 EGR problem? Already replaced the EGR valve, maybe the DPFE? Can't really afford to do both, which would be smarter to start with fuel pump or DPFE?

157 is probably from before you replaced the MAF. They start throwing codes a while before they go completely bad, so replacing your MAF may have been a good idea.

186 is likely from your computer driving the injectors hard to try to get enough fuel into the starving motor.

556 may not necessarily be indicating a fuel pump problem - the secondary circuit monitors the fuel pump voltage and sometimes this wiring goes bad. Does not always mean the fuel pump is bad. But it could be in this case. Mustangs for example are notorious for throwing this code and there is no associated problem with engine function.

On to the other codes...

116 is usually set when you run the KOER on a cold engine. No big deal.

172 - engine was starving for fuel.

136 - same as above.

332 - probably a clogged EGR passage, bad DPFE, bad EGR valve, any of those. But not causing your stall.

411 - not sure about this one, unless there's just not enough fuel to idle like the computer expects it will.