Can't find the vacuum leak 4.0 ohv 97 P0171 P0174

[MO5D3F]

OK, hello everyone, im new here but I've been reading related articles and just cant seem to pinpoint the problem. I'm hoping someone might be able to shine the light on the next step.

1997 Ranger OHV manual. When I got it it barely idled and had no power. After doing a leakdown I discovered bad valves. I pulled the heads and sure enough most of the intake and all the exhaust valves were toast. Took the heads to the shop and they found cracks. So I got new heads, put em in, and now she runs and has power. BUUUUUUUTTT....

I got codes p0171, then p0174 After clearing and testing it looks like only p0174 is coming and ready to be confirmed

I did several tests and im at the end of my rope. The only thing I can think of now is "could it be that I need to redo intake plenum and manifold gaskets again?" or "is the MAF not reading correctly?" or "WHAT!!!"

I have a couple questions:
1) does a minor exhaust leak cause lean codes? These headers both have a tiny leak right in the middle between the three pipes where they meet and join to one pipe.
2) is my maf not reading enough air? and so conditions are always lean? It reads up to about 20g/s
3) when I did the smoke test on the intake, after a long while there was a tiny (almost unnoticeable) amount of smoke coming out the engine oil filler. No leaks anywhere else. (i covered up the egr vent holes and the iac vent hole. Could this indicate my new intake manifold gasket is leaking? I thought it was more likely seepage past the intake valves and blowby but idk.

Things to note about this car is it has a few upgrades which I'm not so sure were upgrading anything. BBK 66mm throttle body, K&N cold air intake, and headers. It also had a jet performance chip mounted on the previous computer. I performed a smoke test on intake found some minor leaks and plugged em up. No more visible or audible leaks on the intake system. I have been testing with the pcv system capped off now to eliminate it for testing

Checked O2 sensors while idling with some maf cleaner into the Brake Booster vacuum tube. sensor go to about 0.9V and revs up then comes down and back to dancing between 0 and about .76v
Also cleaned the maf with maf cleaner.

removed and checked egr, and seems to be working fine except for the "acceptable leakage" out the vent holes on the diaphragm (which I ended up plugging)

TPS reads 0.87 volts when closed and reports well when I tested its movement slowly up and down

Maf reads about 4 grams per second at idle or .76v, also moves well while throttling.

short term fuel trims read about +-5%
Long term fuel trims read about 20% bank1 and 25% bank2 with only about a 2% variance
and of course if I throttle the trims go down to almost normal.

Fuel pulse width for both banks read about 3.5ms

IAC reads at about 42%

ECT reads 86 deg C or 186 F

IAT reads hot after started because it has a K&N air filter which seems to suck in hot air from radiator fan. starts at around 80deg F then goes to about 112F after warmed up hood open and idling.

It also reports manifold vacuum at about 61kpa

RPM holds at around 740

I did perform the IAC test, disconnected while idling and the engine died almost immediately

I also put in a new ecm as i was shooting in the dark no change. I had replaced the IAT only to find it reads the same.

Any insight???

THX

 

[MO5D3F]

add one more thing, I did do the carb cleaner test several times around all my intake components and nothing changed.

 

[Dirtman]

Exhaust leaks do cause lean codes. The o2 sensor can't read the amount of burnt fuel in the exhaust if some of the exhaust is escaping and not running past them. Putting the factory intake back on it will also probably help...

 

[MO5D3F]

one more thing,

I'm not sure if this motor has the bigger cam or not.

or if its supposed to.

 

[MO5D3F]

argh. ok, I guess I will have to take them off again and weld up those holes.

Or is it better to source original exhaust manifolds? I don't have them.

Thx Dirtman

 

[MO5D3F]

OK so I found out why the constant lean codes.

Turns out it was the MAF

I went to the junkyard and pulled 3 MAFs from explorers or rangers. Back at home with Key on engine off I pulled out my MAF and tested it with a 1psi smoke machine with smoker turned off. So it was blowing a constant amount of air. I distanced it about a cm away and went through all the mafs, hot plugging and unplugging while watching the read out with FORSCAN and the BAFX OBD2 Bluetooth adapter. out of all of them one seemed to read about %20 more air than the rest. I put this one in and started the truck. Fuel trims immediately went into the negative to level off at around 1-5% LTFT. Success!

Note after I had fixed significant exhaust leaks at both headers y union, there was no change to fuel trims.

when reading with my 1psi air hose about a centimeter away from the maf sensors, numbers were about 30 to 35 g/s (some variation as it was more sensitive to ambient wind and even my breath. If I were to blow on it I would read about 45g/s)

Note also I did not use any maf cleaner on the new maf, and it was visibly dirty.

I hope this helps some of you DIYers out there

MOSDEF

 

[bills32901]

OK, hello everyone, im new here but I've been reading related articles and just cant seem to pinpoint the problem. I'm hoping someone might be able to shine the light on the next step.

1997 Ranger OHV manual. When I got it it barely idled and had no power. After doing a leakdown I discovered bad valves. I pulled the heads and sure enough most of the intake and all the exhaust valves were toast. Took the heads to the shop and they found cracks. So I got new heads, put em in, and now she runs and has power. BUUUUUUUTTT....

I got codes p0171, then p0174 After clearing and testing it looks like only p0174 is coming and ready to be confirmed

I did several tests and im at the end of my rope. The only thing I can think of now is "could it be that I need to redo intake plenum and manifold gaskets again?" or "is the MAF not reading correctly?" or "WHAT!!!"

I have a couple questions:
1) does a minor exhaust leak cause lean codes? These headers both have a tiny leak right in the middle between the three pipes where they meet and join to one pipe.
2) is my maf not reading enough air? and so conditions are always lean? It reads up to about 20g/s
3) when I did the smoke test on the intake, after a long while there was a tiny (almost unnoticeable) amount of smoke coming out the engine oil filler. No leaks anywhere else. (i covered up the egr vent holes and the iac vent hole. Could this indicate my new intake manifold gasket is leaking? I thought it was more likely seepage past the intake valves and blowby but idk.

Things to note about this car is it has a few upgrades which I'm not so sure were upgrading anything. BBK 66mm throttle body, K&N cold air intake, and headers. It also had a jet performance chip mounted on the previous computer. I performed a smoke test on intake found some minor leaks and plugged em up. No more visible or audible leaks on the intake system. I have been testing with the pcv system capped off now to eliminate it for testing

Checked O2 sensors while idling with some maf cleaner into the Brake Booster vacuum tube. sensor go to about 0.9V and revs up then comes down and back to dancing between 0 and about .76v
Also cleaned the maf with maf cleaner.

removed and checked egr, and seems to be working fine except for the "acceptable leakage" out the vent holes on the diaphragm (which I ended up plugging)

TPS reads 0.87 volts when closed and reports well when I tested its movement slowly up and down

Maf reads about 4 grams per second at idle or .76v, also moves well while throttling.

short term fuel trims read about +-5%
Long term fuel trims read about 20% bank1 and 25% bank2 with only about a 2% variance
and of course if I throttle the trims go down to almost normal.

Fuel pulse width for both banks read about 3.5ms

IAC reads at about 42%

ECT reads 86 deg C or 186 F

IAT reads hot after started because it has a K&N air filter which seems to suck in hot air from radiator fan. starts at around 80deg F then goes to about 112F after warmed up hood open and idling.

It also reports manifold vacuum at about 61kpa

RPM holds at around 740

I did perform the IAC test, disconnected while idling and the engine died almost immediately

I also put in a new ecm as i was shooting in the dark no change. I had replaced the IAT only to find it reads the same.

Any insight???

THX

I ALSO DID THE SAME TO MY 1997 4.0 DID THE UPPER AND LOWER GASKETS AND HAVE THE SAME CODE P174 BUT THE TRUCK RUNS FINE SO I JUST LEFT IT AS IS INSTEAD OF THE BIG HEADACHE OF WHAT YOU WENT THROUGH.