1994 Explorer 4.0, learning OBD 1 diagnostics, trying to avoid the parts cannon!

[JunkCollector]

I bought a new rig recently after getting out of RBVs for a good while, and am looking into some key issues that it's throwing at me. I've ran several KOEO tests. I'm seeing a left O2 sensor "too lean" and "too rich" code, "EGR flow lower than expected" "fuel pump secondary circuit fault" and randomly MAF and TPS codes. It starts and runs, with a dead miss, so I'm unable to run KEOR tests. It will run very poorly unless idling or wide open, almost as if there's no fuel. If I kill the key when it's hot and start it back up, it'll run better for about a minute, then start the same thing again. I also believe there to be a slow leak at the fuel rail and through research I know for a fact that's causing at least some of it, but it seems sometimes the FPR will make up for it, and other times not.

I'm going to replace the O2 sensor and check into the fuel pump monitoring wire as a first step. Also need to figure out where a few evap hoses are supposed to lead. Is there anything else I could be missing that is causing these issues, something common that would make it act up? Fuel pump and filter are new, from previous owner. I know it's a bit early to make a thread without fixing the obvious issues, but I'm not looking to fight it for months on end with no outcome. Thanks guys!

PS here's the current codes in numbered form, pulled with a scanner
176
177
332
543
111 (system pass code I believe)

 

[franklin2]

With the dead miss, I would first check the engine out mechanically. I would run a compression check on all cylinders just to make sure you have no mechanical issues.

 

[RonD]

4.0l OHVs wear out spark plugs, and #3 spark plug can be a pain to change, so previous owner may not have ever changed it
Motorcraft or Autolite seems to last the longest, NGK is a good 2nd choice

+1 on the compression test

176 (M) Oxygen sensor not switching – system is or was lean Left on Front HO2S – Fuel control
177 (M) Oxygen sensor not switching – system was rich Left on Front HO2S – Fuel control

Change BOTH O2 sensors, also run a can of injector cleaner in the gas tank
Clean MAF sensor, once a year

332 (R,M) EGR did not open/respond during test or if memory code, did not open intermittently – EVR or PFE
This code needs to be cleared and then come back a few times to be valid, just FYI

Once engine is running put a vacuum hose on the EGR Valve
With engine idling suck on the vacuum hose and engine should start to run rough, if so EGR Valve is opening and exhaust can flow thru the tube from exhaust manifold
If not EGR valve is stuck closed or tube is clogged

There is also an EGR modulator(solenoid), its a Vacuum Control Valve, PCM(ECM) uses this to send vacuum to the EGR valve to open it
Follow the EGR valve's hose back to the EGR Modulator, check that both its hoses are air tight

543 (O) Fuel pump monitor circuit shows no power – Power / Fuel Pump Circuits
In the engine bay fuse box is a Fuel Pump(FP) fuse(20amp) and FP relay
With key on you should hear the FP relay "click" on, then hear the fuel pump run for 2 seconds, its in the tank and not quiet
Then FP relay "clicks" off
Repeat key on and off as much as you need to confirm FP relay and fuel pump operation
Under/behind the glove box on the firewall is the inertia switch, has a red button on top, and a 2 or 3 wire connector, if 3 wires then one of the wires is the Monitor circuit for the above code
Press the red button down if it has popped up

 

[Bear in the woods]

May want to check the fuel tank. They tend to get full of trash. As you drive it gets worse. When you shut it off it lets the trash fall off. Runs better for short while. Then the trash clogs the sock filter on the pump again. Most people never check when they put in a new pump

 

[ericbphoto]

I would follow RonD's advice. Personally, if it was mine, I would fix the miss and the fuel issue. Get it to run that way. Then see if you still have those other codes. Fuel pressure issues and a miss will send funky stuff down the line for the O2 sensors to read. They could just be giving good info that indicates fuel and spark problems.

 

[JunkCollector]

I've replaced both O2 sensors, as well as the TPS since I had it, miss seems to be cylinder 1 and it has spark, feeding it injector cleaner, fuel leak was the fpr o-ring, also repaired, as well as several vacuum lines. Will diagnose the miss and fuel pump monitor wire further when weather improves. It cold starts poorly and pings now, but cleaning the MAF will likely help with that. For now it can take me back and forth to work when it snows, which it's currently doing, which is all I need of it until I build it up some this summer. Thanks guys, replacing both o2s was a 100% improvement overall!

 

[franklin2]

I thought some of the 4.0's had a very common intake gasket problem with a TSB on it. Runs poorly when cold, then straightens out. Not sure exactly which intake gaskets were the problem.

 

[SenorNoob]

I haven't heard of that one. There was one for coolant loss. Fix was 95 or 96 changed intake gaskets. Aftermarket changed back to the earlier style the next year...