97' ranger 4.0: About a month ago I noticed that my Ranger exhaust had the unmistakable "sweet" smell of coolant. I replaced the the the lower intake manifold gasket with original OEM gasket as it was pulling codes P0171 and P0174. I reset the ECU. All seemed fine, until yesterday. Engine light back on and same codes pull up. Just wondering, Do the intake manifold bolts loosen over time (after pulling intake manifold) and I just need to re-torque them or is there a bigger issue?

 

It is unusual to get coolant into the exhaust via an intake manifold leak, not unheard of just not usual.
Usual with 4.0l is a cracked head from past over heating or a bad head gasket.

Most common reason for 171 and 174 at the same time is a dirty MAF(mass air flow) sensor.
MAF sensor tells computer the amount of air coming into the engine and the computer bases the fuel needed on that data.
After the fuel is burned the O2 sensors tell the computer if mix is lean or rich.
If the air flow data and the O2 data don't add up to the computers calculations of the amount of fuel that should be being used, you get a code.

Since you are getting codes for both banks/sides of the engine the common denominator is the MAF sensor, or computer itself.
If it was a lower intake leak, then only one bank would be effected, if it was a failing O2 sensor it would only have 1 code.

An upper intake vacuum leak can also cause the dual codes, to test for vacuum leak, warm up engine and let it idle, should be about 700-800 RPM, now unplug IAC Valve wires, idle should drop to 500 RPMs or engine may even stall, either is OK, it means there is no vacuum leak.
If idle stays high then there is a vacuum leak.

On the 4.0l the MAF is at the air cleaner and has an air plenum(tube) that goes to the upper intake, if that air plenum has a leak then it would have the same effect as a dirty MAF sensor, not all the air coming in is passing thru the MAF sensor.
The PCV(positive crankcase ventilation) system is part of this, the oil filler cap and dipstick seal the crankcase and valve covers.
The PCV Valve pulls air out and the vent hose(from oil filler tube to air plenum) allows "metered" air to come in.
Often if you unscrew the oil filler cap while engine is running engine may stall or idle will go high, you created a vacuum leak.

 

[QUOTE=RonD;2076416]

Most common reason for 171 and 174 at the same time is a dirty MAF(mass air flow) sensor.
MAF sensor tells computer the amount of air coming into the engine and the computer bases the fuel needed on that data.
You were correct about the MAF sensor. I bought a can of MAF Cleaner, cleaned and truck runs better, still has a miss due to the leaking head gasket.
Also, the intake bolts did loosen drastically, torqued them to 25-ft lbs the first go round then 59 ft lbs the second round when I replaced the lower intake manifold gasket. After checking them this time most of them were below 40 ft lbs. Thanks for your info RonD, but I have one more question. I noticed when ordering the head gasket set, some of them are marked "Set X" is this what I need for a 4.0?

 

The "X" is from the 8th digit in the VIN number for engine type
X = 4.0l OHV (1990-2000 Rangers)
E = 4.0l SOHC (2001 and up Rangers)

You want the "X"

 

Are you a Ford Master Mech RonD? Every response you have on the few issues I have posted have been very helpful. You should write your own repair manuals..." Repair Manual for Dummies"

 

lol, thank you.

They say you learn more from your mistakes than from your success's.

I have made alot of mistakes..................and still learning

 

Well I pulled the head and the gasket was in pieces. #3 cylinder definitely had signs of coolant entering the cylinder. Fixed.

 

Good work