My 94 Explorer Sport is firing WAY too much gas in the cylinders for some reason. Often, I have to kill the fuel pump with the intertia switch, crank it, and then turn the fuel pump back on before it dies. It often surges hard at idle, too. Here's what I've looked at so far:

Fuel pressure:
KOEO - 40psi
Running - 35psi (stable)
During cranking - fluctuates between 40 and 43psi
Running with regulator vacuum disconnected - 43 to 45psi

Codes:

KOEO Test
116 coolant temp sensor out of range (the engine was cold during the test)
556 primary fuel pump circuit failure (what is this? The fuel pump seems to be working correctly)

Engine Running Test
116 coolant temp sensor out of range (the engine was still cold)
137 / 173 O2 sensors detecting rich conditions (not surprising)
411 Unable to control RPM during Low RPM self-test (the engine was surging during the test)
412 Unable to control RPM during High RPM self-test (ditto)
543 Fuel pump circuit open Battery to PCM (I had the ineritia switch off while cranking)

It seems like a bad regulator or leaking injector would show up in the fuel pressure test. Any ideas???

 

You didn't mention if the fuel rail could hold presure pressure for 30 minutes with the engine off. I would be thinking leaking injector. You probably would have noticed gas in the vacuum line if the regulator was bad.

 

I haven't left the pressure gauge on for that long yet. I'll give that a shot and let you know.

 

OK, I finally had a chance to check to see if the fuel rail is holding pressure after the engine is off. Here are the results:

Time (min) Pressure (psi)
0 40
15 40
30 36
45 30
60 26
120 16

I think this is telling me that I don't have an injector leak. I'm not sure what to do to troubleshoot this thing. Any suggestions???

 

The KOEO and KOER tests need to be done on a warm engine. Also before you address any KOER or CM codes, all KOEO codes must be corrected. According to my book, 113 = engine coolant temp higher or lower than expected and 556 = fuel pump relay primary circuit failure. I'd suggest getting a service manual with flow charts to guide you through the process of correcting the problems associated with the codes. As you read through the flow charts for different problems, you will note that a given code may have the potential to trip another code, although that other code is not really a valid problem. This is where the flow charts will help you, they give you a systematic approach to repair.

First, I'd clear all codes and take a 3- 5 mile drive. Then I'd pull codes again, following the proceedure in the book that comes with the code reader. I'd also get my hands on a manual with the flow charts. I have a hunch 113 is happenening because you did the test on a cold engine but if the coolant temp sender has failed that too has the potential to cause a rich condition. 556 puzzles me; my references talk about fuel pump relay failure, wiring probs between eec relay/fuel pump relay and other wiring failures; these don't make sense since your rig runs.

 

Holding pressure looks good. I wonder if a problem with an injectors electrical driver is keeping it on. Try that test again. This time with the key on and engine not running. This would apply power to the injectors but the pump would shut off after a few seconds. Maybe an injector wire is shorted to ground, there are two banks. Nothing else would explain dumping that much gas. That's all I can come up with.

 

Someone here wrote me once that the fuel pressure regulators have been known to stick in an open condition & deliver too much fuel & also would not show itself via fuel in vacuum lines.

Hope that helps some.

 

When the pressure regulator sticks open, fuel is returned to the fuel tank and the rail pressure drops.

 

I've learned a great lesson in the K.I.S.S principle. The truck was telling me what was wrong with it from the beginning, but I was overthinking it. I assumed that the original code 116 that I was getting was because the KOEO test was performed with a cold engine. I re-ran the test with the engine hot and still got the code. The thermistor for the ECT sensor has completely failed, and was reading about 10Mohm. The truck just thought it was trying to crank in -100 degree temperatures. Replacing the ECT sensor has made it crank and run like a champion.

 

You and everyone else learned a good lesson in troubleshooting codes from a
computer controlled engine. I cannot remember where I read this, but the author made a point to emphasize that you ONLY work on one code at a time, and start at the lowest code given, because it can affect other later codes. His test theory was:
1. Pull codes
2. Work on lowest code
3. Clear computer and re-run tests
4. Goto step 1

Dialtone

 

Frankly, I find this all hard to believe. Just can't accept that a coolant temperature sensor can dump that much gas into the system. The computer should have gone into a default mode when it detected an open sensor. It could have used the IAT to know it wasn't in an extreme cold condition. I don't think they have summer co-op students programming the computers. Just as likely, wiggeling wires around fixed this.

 

Think about the programming this way.
IAT sensor measures incomming intake air stream temp.
If the engine is NOT running, there is little or no airflow comming into the engine SO
IAT sensor reading is not valid (or accurate enough to use) at this time, SO
the computer defaults to using ECT sensor for fuel calculations during cranking.
Just some thought from a programming point of view.
Dialtone

 

Not realy. The engine would never be colder than the IAT. So, you would know that the engine wouldn't be starting at -100. That isn't really the issue. Regardless, the computer would default to some value and not just dump gas. Engines with the FPR leaking gas into the manifold start easier than he reported. Countless people have reported bad temp sensors and not had these problems.