1999 Ranger smog test fail p1072 p1075

[Millwall]

Hi Everyone,

I have just got a 1999 Ford ranger 4.0 v6 OHV. No return fuel system.
I got given it and it came from a county here in NC which doesn't require a smog test to pass inspection. I think therefore it has suffered years of neglect as there have been multiple reasons for the check engine light to come on. split vacuum hoses, ill fitting oil filler caps, misfires, and gassy oil. all which I have now rectified.
My problem is that i did a ton of work to get it through inspection only for it to fail the smog test fault codes p1072 and p1075 causing the CEL to come on.
After cleaning the MAF
replacing the fuel filter.
replacing the coil leads and plugs ( kinda standard thing i do when I get a new vehicle)
replacing the o2 sensor on bank 2 as it was reading poor voltages,
removing the intake to check the plenum gaskets and injector seals and rebuilding
examining all vacuum lines,
the long term fuel trims on bank 1 & 2 are both sitting at -25% and STFT hover between -5 and +5%. I have been a diesel mechanic for the last 25 years so I'm handy with a spanner and can follow a line of process and deduction. but I decided to bite the bullet and take it to a shop. the shop came well recommended and to be fair they didn't start throwing money and parts at the problem, but they didn't find a conclusive answer to my problem.
So its down to me again minus a couple of hundred $$$, So I'm asking you guys if you can help me as Ive seen many knowledgable posts on here and I hope maybe someone can help.

My thoughts are.. its running rich on both banks in equal measure and at an equal rate so that would point to a fault which will affect both banks, so no injectors (although its not impossible for 2 injectors to be knackered), compression or exhaust leaks as these would affect only 1 bank and probably at different rates, so that leaves in my eyes the following possibilities.
Fuel pump (the shop assured me the pressure was about 64/65) so that seems normal.
fuel damper... I have no idea how to test this?
2 leaky fuel injectors (1 each bank)
2 bores with low compression (1 each bank)

another thing I would add is that on idle the throttle absolute position is at 18% ( is this normal? if not how can I calibrate it?)
also on idle the calculated engine load is at 38% and goes down as you apply the throttle at standstill ( seems strange to me)

another point to note is that on a road test and monitoring the live data on hard acceleration the LTFT does come down.


So if anyone has any suggestions of possible other causes that I may not be thinking or can offer any advice based on the info i have given then please do it would be much appreciated.

Thank you.

 

[Macgiobuin]

Check for these: faulty mass air flow sensor or wiring harness to same: shorted wires could be sending wrong voltage to computer indicating more air than is actually flowing. Also check for clogged EGR tube or valve: many EGR valves have a sensor dedicated to telling the computer that it has opened; but if the tube is clogged and the DPFE sensor is not doing its job, then you might be running rich; then check Idle Air Control Valve; if it is cruddy, clean it out like this: get a beer can, cut off the top, put the IACV into it with the electric connection sticking out the top, fill it with Sea Foam. Let it sit overnight, or feed it 12 volts off and on 100 times a minute for 5 minutes, working out the travel of the plunger while submerged in the fluid. Good luck.

 

[ranger7ltr]

You are running rich based on the codes...

Your fuel pump pressure is within spec and the you have changed a lot of parts...When you changed the O2 sensor did your scan tool read the changes in the exhaust stream or did it continue to not register any changes?

Frankly how does the truck run???

Is your scantool reading any changes of oxygen in the exhaust stream on either bank???

You have an over rich condition not a lean condition which leaking injector seals or intake gaskets would indicate...How low is the compression in the 2 cylinders and are these 2 cylinders on the same bank or different banks? If the cylinders are not firing or not firing to burn the fuel going into them your o2 sensors will read the excessive unburned fuel as a lack of oxygen in the exhaust and register a rich condition...

Now the leaky injectors will cause this problem as well...I will guess the leaky injectors are on the 2 low compression cylinders??? If the compression is more than 10% lower than other cylinders you may have a problem with combustion that is due to cylinder/piston/ring wear...Could also be caused by leaking valves and/or valve guides or stem seals[extreme case though]...And the 18% @ idle is normal for the engine...

One last thought; since both banks are running rich are the o2 sensors actually correct for the application? It is possible to have the wrong sensors in place and they not provide correct feedback to the ECU hence the error codes...And since a bank 2 sensor will fit the bank 1 threaded bungs...

Let us know what you find; I would like to know what is causing this issue... My 99 Explorer Sport has the same engine but I have not ever had this problem with mine in the 8 years I have owned it...

 

[Millwall]

Your fuel pump pressure is within spec this is according to the garage I took it to I myself havent confirmed this as I dont have a fuel pressure tester.(and I did have to ask them if they checked it) and the you have changed a lot of parts...When you changed the O2 sensor did your scan tool read the changes in the exhaust stream or did it continue to not register any changes?

To be honest I will change a fuel filter and oil & filter any time I get a new vehicle regardless of wether there are problems or not. It never hurts to change a filter and perhaps its more applicable to diesels but any time I have a fueling fault to diagnose the first thing I always do is change the filter. The spark-plugs leads and coil I changed because of the misfire I probably didn't need to change them all but to be honest I'm not messing about with 1 plug 1 lead,chop the lot and I know I'm good.
I replaced the O2 sensor because the voltages were reading erratically and on a narrow voltage range. .3 -.5 I changed it and now it reads .1 -.8 which is what I expect the range to be. I only changed the one because the other one was giving a good sweep of voltage range. I'm pretty confident that the o2 sensors are fully functioning accurately

Frankly how does the truck run??? It has a bit of a murmer at tickover with an occasional "pop" but when you accelerate its running pretty sweet. I'm putting the murmer and "pop" down to the fact its running rich, I'm also thinking this could possibly be down to an incontinent injector or 2?

Is your scantool reading any changes of oxygen in the exhaust stream on either bank??? I'm not sure what you mean sorry. the STFT readings are fluctuating between -5 & 5 If I disconnect the battery then re-connect it and monitor the data the STFT runs gradually from 0 to -25 LTFT are 0 at which point the LTFT kicks in and the STFT settles down and hovers between -5 and .5 and the LTFT jumps up and stays up at -25 even after switching the ignition off and resetting the ignition the LTFT stays up at -25% these problems and the timings of them on each bank are practically symmetrical, I would expect going by that, that the problem has to be before the mix enters the heads, after that any problems(plugs leads injectors compression) may be similar but would surely be different

You have an over rich condition not a lean condition which leaking injector seals or intake gaskets would indicate...How low is the compression in the 2 cylinders and are these 2 cylinders on the same bank or different banks? 8% difference on one and 5-6% on the other and they are on different banks I think its 3&4. If the cylinders are not firing or not firing to burn the fuel going into them your o2 sensors will read the excessive unburned fuel as a lack of oxygen in the exhaust and register a rich condition...

Now the leaky injectors will cause this problem as well...I will guess the leaky injectors are on the 2 low compression cylinders??? If the compression is more than 10% lower than other cylinders you may have a problem with combustion that is due to cylinder/piston/ring wear...Could also be caused by leaking valves and/or valve guides or stem seals[extreme case though]I agree this could be the case but I'm not ready to dig that deep yet I'm looking rule out the alternatives before I face this possibility...And the 18% @ idle is normal for the engine... Thanks for the reassurance on the idle %

One last thought; since both banks are running rich are the o2 sensors actually correct for the application? It is possible to have the wrong sensors in place and they not provide correct feedback to the ECU hence the error codes...And since a bank 2 sensor will fit the bank 1 threaded bungs...
I'm not quite sure what you mean. if the problem is on both banks and the sensors were somehow swapped over then surely the info would be back to front which could cause confusion were the fault only on one bank but as it's on both and in equal measure I don't see a problem.

Let us know what you find; I would like to know what is causing this issue... My 99 Explorer Sport has the same engine but I have not ever had this problem with mine in the 8 years I have owned it... I absolutely will it's the least I can do for you taking your time to try and help me. I appreciate very much your input.

 

[Millwall]

Check for these: faulty mass air flow sensor or wiring harness to same: shorted wires could be sending wrong voltage to computer indicating more air than is actually flowing. Will do hadnt thought of that I have checked the readings from the MAF and I will post them to see what you think. Also check for clogged EGR tube or valve: many EGR valves have a sensor dedicated to telling the computer that it has opened; but if the tube is clogged and the DPFE sensor is not doing its job, then you might be running rich; then check Idle Air Control Valve; if it is cruddy, clean it out like this: get a beer can, cut off the top, put the IACV into it with the electric connection sticking out the top, fill it with Sea Foam. Let it sit overnight, or feed it 12 volts off and on 100 times a minute for 5 minutes, working out the travel of the plunger while submerged in the fluid. Good luck. I did give it a bit of a rinse with brake cleaner but I will definitely clean it up a bit more as per your method. Thanks for your ideas.