94 B4000 running lean

[shleeve]

Hi all, I got this B4000 a month ago, 137k miles and a pretty clean body. However it did have its issues. Due to certain engine codes I already replaced the TPS, IAC, and camshaft synchronizer. This cleared the codes I was existing them to. However, I still have a code 171. And I pulled my plugs and they actually are very white, so I am clearly actually running lean. I checked for vacuum leaks, replaced fuel filter, fuel pressure regulator, cleaned the maf sensor, ran seafoam through it and then replaced the plugs. With a fuel pressure test I am only getting 28 pounds when I turn the key on, and it stays at that when I run it, dips a bit when I hit the accelerator, and then slowly rises to about 36 pounds when I turn the key off. My next assumption is that my fuel pump is slowly dying and just very weak, but still pumping. Is there anything else that could be causing me to run lean or get slightly less pressure?

 

[cvar]

In my B4000, pesky lean codes p0171/p0174 were caused by leaky upper intake manifold gasket ($6 part ZZM5-13-095). Also replaced the Fuel Injection Plenum Gasket ($20 part ZZN2-13-111) at the same time, along with Fuel Injector O-Rings ($26 part ZZM0-13-253). That fixed it.

See http://www.explorerforum.com/forums/showthread.php?t=171819
and http://www.therangerstation.com/forums/showthread.php?t=94437

 

[RonD]

Fuel pressure on '94 ranger should be 35-40psi running.
28psi is not that far off, and I wouldn't expect it to cause a lean code, although it is low so fuel pump may need replacing sooner than later.

P0171 means fuel trim on Bank 1(passenger side) has a high number, usually above +20, this means the computer is having to open the injectors on that side longer than expected to get "normal" oxygen levels in the exhaust(via O2 readings).

P0174 is the same code meaning but for Bank 2(drivers side), so if fuel pump was the issue I would expect both 171 and 174 to come up, same if it was MAF sensor or general vacuum leak issue, as these effect both banks of the engine.

With just P0171 I would consider lower intake gasket leak on that side, or exhaust manifold leak on that side, it sucks in air which throws off O2 data, but if plugs are clean on that bank probably not exhaust leak.
Bank 1 sensor 1, O2 sensor issue, you can swap O2 sensors around and see if code changes to P0174, but if it was O2 going bad I would expect spark plugs on that bank to be darker color from running rich not lean.
Failing injector not passing enough fuel on that bank, but I would expect to see a difference in that spark plug when compared to the other 2 on that bank.


4.0l OHV engines are known for lower intake gasket leaks, the lower intake bolts loosen up.

 

[shleeve]

Hmm okay, I suppose I can try the gaskets. Anyone know a good deal on all the intake and fuel injection gaskets as a kit?

 

[RonD]

Now did you check for vacuum leaks before?

Do the same but focus on lower intake.
The fan often blows sprays away before they get to lower intake if that is how you check.
So use a short hose to put spray at the lower intake gasket.

 

[shleeve]

Now did you check for vacuum leaks before?

Do the same but focus on lower intake.
The fan often blows sprays away before they get to lower intake if that is how you check.
So use a short hose to put spray at the lower intake gasket.

Alright I will try that later. However, after clearing codes today and taking it for a good drive after replacing the camshaft sensor, I am getting different codes. Now I am getting 172,173,176,177. Any idea on that?

 

[shleeve]

I tried spraying starter fluid near the lower intake gasket and got no result. However, I also have a high idle and unplugging the Iac has no effect. My idle is around 900-1000 when warmed up, and my CEL is only coming off and on it seems at speeds of 35mph and above now. Is there anything else I can check before replacing gaskets? Could my MAF cause this? I cleaned it but did not replace it.

 

[shleeve]

Also if I unplug my MAF sensor while the engine is running it will die instantly is this normal?

 

[RonD]

I wouldn't replace gaskets just yet, vacuum leak will react to spraying so...............

Engine dieing when MAF is unplugged is not normal but can happen, but you should be able to restart it and drive it with MAF disconnected.
Computer goes to Open Loop and uses pre-set factory data to run engine to "get you home", CEL should come on.

Testing info for MAF here: http://www.therangerstation.com/tech_library/CleanMAF.shtml

Use a sewing pin to pierce the wires to get voltage readings.

Yes, failing MAF could cause your issues but I would expect both banks to show lean code

 

[shleeve]

I wouldn't replace gaskets just yet, vacuum leak will react to spraying so...............

Engine dieing when MAF is unplugged is not normal but can happen, but you should be able to restart it and drive it with MAF disconnected.
Computer goes to Open Loop and uses pre-set factory data to run engine to "get you home", CEL should come on.

Testing info for MAF here: http://www.therangerstation.com/tech_library/CleanMAF.shtml

Use a sewing pin to pierce the wires to get voltage readings.

Yes, failing MAF could cause your issues but I would expect both banks to show lean code

Both banks are showing lean as well as rich. My codes now are 172,173,176,177.

 

[shleeve]

I just tried driving with it disconnected, after a few failed starts it will start and idle and drive okay but as soon as I come to a stop and push the clutch in or shift to neutral my RPM will drop to 0 and it will die.

 

[RonD]

Odd that it would stall with clutch switch on(pedal down), there is no Neutral switch on Ranger or Mazda manuals, Explorer manuals had them.
Without MAF sensor input computer should be running air/fuel mix based on RPMs and throttle position(TPS)

I would test MAF voltages from that link, with MAF plugged in.
Hard call to say if it is MAF or computer issue at this point.