Code 172 and engine running hot.

[dentond]

Hey,

Details of truck:
4.0L V6
'94 Ranger
4x4
~120000 miles

Problem:

I have had the CEL on for about a week+ with the O2 Bank #1 Lean code. Living on a college campus, I didn't drive long distances much so didn't notice any real problems.

However, when I drove home at the end of college, I noticed the engine was struggling a little and would stumble on hills when the cruise control was on. The CEL takes about 5 miles to turn on depending on how warm the engine is, don't know if that means anything significance.

Most recently, I had to drive 750 miles for my summer internship. Truck made it but the truck also started running hot when in the mountains, yes, the engine will get warmer in those condition, however, the needle was almost past the "A" in normal on the dash compared to a higher "O".

The only thing that I have had time to do is clean the MAF but I don't know that only one of the lean codes would be thrown if it was air flow or vacuum. I am a bit concerned that the injectors could be bad but again, odd only one side would have the problem.

Sorry this is so long, appreciate the help in advance.

 

[dentond]

Checked vacuum today, the vacuum is working fine according to this page
http://www.therangerstation.com/Magazine/Summer2003/VacuumLeaks.shtml

Is there a simple way to check for plugs in the radiator? And, need some help on the 172 Code.

 

[RonD]

When an engine is first started cold, the computer is running in Open Loop, in Open Loop the 02 sensors are ignored, because they are cold, they need to be above 600degs to operate so a delayed CEL code for an O2 lean/rich would be expected.

Engine running lean will cause hotter cylinder temps so over time engine coolant temp will rise.

I think you do have an actual lean condition, not a sensor error.

This could be caused by a vacuum leak, extra air means more air than fuel in the mix, so lean mix.
Does your engine idle at approx. 700rpm when warmed up?
If idle is closer to 1,000rpm then vacuum leak could be the issue, the IAC(idle air control) is a "controlled" vacuum leak, if engine is warmed up and you unplug the wires from the IAC the engine idle should drop, engine may even stall, that means IAC is working, if there is no change in rpm then IAC needs to be replaced.

It could also be caused by a faulty/dirty injector, in the 4.0l, and most fuel injected engines, the injectors are fired in Banks not individually, so cylinder 1, 2 and 3 injectors all open/fire at the same time, this keeps fuel vapor in that side of the intake all the time, but if one injector is not firing it could cause a lean mix on that Bank.

The O2 sensors are similar to spark plugs in that they do wear out, some say 60k miles is replacement time, I have 300k on my 4.0l O2s, so ...........
But they do wear out.
If the O2 sensor on that bank has a problem then I doubt it would be reporting lean condition 172, you would have a lean condition, slight overheating but it wouldn't set a code because a faulty O2 sensor wouldn't detect it.

Lower than normal Fuel pressure could cause a lean 172 on only 1 bank, this has to do with the O2 sensor on each bank and its sensitivity and the injectors on each bank.
Because engine was running warmer than usual then all cylinders could be running just at lean limit, but only 1 O2 sensors is picking it up.
I would remove vacuum line on the fuel pressure regulator, front of the fuel rail, and check it for gas or gas smell, if you smell gas replace regulator as the diaphragm is leaking, although this should cause a rich not lean condition.

If possible have the fuel pressure checked, it should be 32psi to 42psi, check key on engine off, the engine on, then key off and see if it holds the pressure for 10 minutes.

Running a can of Seafoam in the fuel tank can help clean injectors, they can get a build up like a varnish that limits the amount of fuel that can pass when they open, so a lean condition happens.

Also change the fuel filter, $10 and not hard to do, this wouldn't cause your issue but prevents other issues.

 

[kimcrwbr1]

The only thing I can add is if the O2 sensor is getting raw fuel it can show a lean code also. If it is running lean you must be careful you can burn valves/pistons and score the cylinder walls. You can normally smell fuel out the exhaust or on the dipstick if its overfeeding from a injector stuck open or bad regulator. A fuel pressure test will rule out leaks if it holds pressure after you turn the engine off unless the check valve in the fuel pump is leaking backwards. Put a long screwdriver on the injectors while its running and put your ear on the handle you can hear them firing. Be careful of moving parts. Acetone makes a good injector fuel system cleaner. Add 4 ozs of acetone to 10 gallons of fuel and take it for a road trip. Run the tank close to dry and then top it off with regular gas. that will dissolve the varnish that builds up from ethanol fuel we are forced to use. Acetone is a real strong solvent dont use more than 4 ozs for ten gallons and dont leave it in the system very long just run it through and quickly add fresh gas. Then change the fuel filter if you havent done so lately. The best radiator flush is half and half water and bleach. Drain it and back flush it out in both directions with a high pressure hose the plug the bottom hole and fill it up with bleach water and let sit overnight. The next day flush it both ways again good. what I like to do is kink the garden hose the longer the hose the better, when you release it you get that blast of both pressure and volume.

 

[kimcrwbr1]

Bleach is a good flush for the heater core also.

 

[dentond]

The engine idles around 700, maybe 750 RPMs. I had a problem with the IAC awhile ago and I changed it out. Unplugging it makes a huge difference.

I tried checking for vacuum leaks, butane torch and blew it around suspect areas and made no difference that I noticed.

I put a new fuel pump on it when I bought it (two years ago) but I've gotten a bad one out of the box before so I will check the fuel pressure when I get the chance. Gonna have to find a pressure gauge to check it with though. Also, I replaced the fuel filter and noticed the fuel burnt my arm (not hot burn but chemical burn) when the fuel came out of it. Never had that reaction before. Not sure if it is significant.

Thanks for the tips. I'll keep you updated.