Questions on fuel pressure and smoke test results. Need help figuring out OBD-1 code 172 on 94 Mazda B4000.

[Pyromancer]

94 Mazda B4000, truck started throwing a 172 code (lean passenger side bank) I haven't been able to get rid of yet. Code does not pop up until I have been driving for awhile which seems consistent for this type of lean code.

What I have tried:
1.) Sprayed around engine with carb cleaner looking for vac leaks.
Couldn't find anything.

2.) Pulled and checked all the spark plugs on the passenger side.
All plugs looked good.

3.) Checked for exhaust leaks and re-torqued all bolts on passenger side exhaust.
No leaks, code still happening.

3.) Swapped the 02 sensors plugs.
Truck threw codes 172 and 176. Reading that this should have caused the truck to read lean on one bank and rich on the other I went ahead and tried replacing the O2 sensor and connecting O2 sensors back the way they should be. Still threw code 172 with new 02 sensor.

4.) Unplugged MAF sensor.
Truck threw a few MAF codes as well as the 172 code. MAF codes go away with it plugged back in.

5.) Fuel Pressure Test.
Purchased a harbor frieght fuel pressure tester. Got 28psi at idle and 38psi with the vac to the pressure regulator unplugged. This seemed low according to some posts on forums, so I tried replacing the fuel filter and then swapping the regulator, no change.
Last night I pulled the bed back, tested the ground and voltage at the pump. Ground is fine, pump voltage 9.6V key on, 12.6V key on with pump test lead from OBD-1 connector grounded.
Swapped the fuel pump. Still 28psi at idle and 38psi vac unpluged. 36psi truck off vac connected and fuel pump grounded.
Truck doesn't leak down more than 2psi in 3min, but does slowly leak down. Removed return line and vac from regulator no leaking at the regulator.

6.) Built a DIY smoke tester from a soldering iron and smoke tested the engine from throttle body.
Found a leak from the behind the EGR diaphragm. EGR was only a couple years old and under warranty. So I have swapped the EGR twice with two brand new ones at this point and all 3 leaked from here. New one is better than the last two but all leak. Pic is from EGR #2 the first one I got as a replacement. Really wondering if this is normal? Smoke is being pumped in with a bike pump but machine is attached with a hose going into a rubber glove with a finger cut off to get smoke into the throttle body, so only maybe a couple psi on the system to get this result.

7.) Visually inspected spark plug wires and sprayed around the engine with water mist looking for sparks.
Wires seem fine, they are pretty new so doubt its the issue. Coil pack is new as well.

My questions:
1.) Does my fuel pressure seem OK?
According to my Chiltons pump test procedures, I believe I am in spec. It tells me 35-45psi with pump lead grounded so pump is running, I get 36Psi. It also tells me 35-45PSI with truck running and vac to regulator unplugged, I get 38. Finally it gives me a leak down test procedure that says to ground the pump, remove ground and note pressure, I get 32psi. It then asks is this pressure drops more than 2psi in 3 minutes. I drop maybe half a PSI in that time, I also timed for 6min and didn't quite get to 31psi on the gauge. Takes over 30min to drop to 30psi, but it droped to 20psi overnight. This all seems OK by the Chilton book, but some posts in this forum tells me I should seeing 30-35psi with the truck idling, and 40-45psi with the vac line disconnected. What is correct?

2.) Does the leak at the EGR seem OK?
I have gone through 3 of these EGR's now, with all 3 leaking at the same spot. One Borg Warner, two Standard brand. It seems that its just a tiny leak around the shaft for the plunger in the EGR. When I think about this I don't know how this EGR design would not leak a small amount of air in that spot. It is a shaft that needs to move in and out of the egr valve how could they completely seal that and have it move? I also question if this was the issue why would I only be getting lean on one bank and not both? Is the EGR good or am I just super unlucky?

3.) Anything else I should try?
As it sits the truck has a new O2 sensor, a new fuel pump, a new fuel pressure regulator, a new EGR valve. I'm not a fan of just throwing parts at this thing and have saved all the old parts as future backups, but am really scratching my head here. Did I get two bad EGRs in a row? Is the new fuel pump or regulator bad, and if so why would I get the exact same pressures as the old ones? Only other thing I can think of would be maybe an issue with the injectors. If they were leaking I would expect a rich code instead of a lean code though. If I had a leaking or stuck injector, I would also expect the plugs to not look normal. I'm not sure if there is anything I can do to test those, or if I should just get it back together when the fuel filler hose comes and try running a couple tanks of injector cleaner through the truck. Anything I am missing? Is there something I haven't checked but should? Thoughts?

With the bed back I noticed my filler hose was cracked and am waiting on a replacement before I put the bed back and try to drive the truck again.
So has not been driven or pulled codes since step 5, but nothing has changed, and I have just found things that have me scratching my head.

 

[SenorNoob]

It would seem to me that lean passenger side only is unlikely be fuel pressure or an intake leak. Unless the driver side also has a leaky injector making up for it?

Have you tried pulling spark plugs to see if one cylinder is burning differently? Or not at all? NVM. I see you tried that.

As for the fuel pressure, how sure are you that the gauge is accurate? Can you compare with another vehicle?

How long is awhile for the CEL to come on again? In my case it took 5-8 minutes of run time before the O2 had stayed lean long enough to cause a CEL and I never got a code for at max adjustment even though it clearly was.

Can you get a voltmeter on the O2 wiring and have someone drive while you watch or have a scan-tool that can do datalogging? (I think those are fairly rare for 94 though.)

Longshot, but clean the MAF?

 

[Pyromancer]

As for the fuel pressure, how sure are you that the gauge is accurate? Can you compare with another vehicle?

How long is awhile for the CEL to come on again? In my case it took 5-8 minutes of run time before the O2 had stayed lean long enough to cause a CEL and I never got a code for at max adjustment even though it clearly was.

Can you get a voltmeter on the O2 wiring and have someone drive while you watch or have a scan-tool that can do datalogging? (I think those are fairly rare for 94 though.)

Longshot, but clean the MAF?

I rented a fuel pressure gauge and then ended up buying my own from harbor freight when I determined I might need it for longer. Both gave the same readings so I'm pretty sure its accurate. I don't have an other truck to compare to. Was hoping someone here would be able to chime in an tell me if my pressures look good.

CEL coming on varies a bit. I would guess about 10-15min of driving though.

No data logging that I am aware of for obd-1 and rigging up a volt meter to read while I am driving could be tough. Would love to look at the fuel trim but I don't think there is a way with OBD-1. When I get it back together I can get it warmed up and throw a volt meter on the O2 to try to make sure it is switching though. I watched a couple youtube videos on it. Seems like it is a mixed bag for having a volt meter that reads fast enough to catch it though. I did confirm that there's no break in wiring from the 02 connectors to the PCM though, learned B4000 wiring to the PCM is different than a ranger in the process.

Unplugging the MAF didn't help and it seemed fairly clean but I hit it with some electrical contact cleaner anyway.

Thanks for the reply.

 

[SenorNoob]

I was able to see switching pretty easily with a harbor freight freebie meter. Not super accurate but possible to see. My computer is in the passenger side kick panel so reaching it with the meter was pretty easy. It did have to be bolted on though. (case grounded)

 

[Pyromancer]

I was able to see switching pretty easily with a harbor freight freebie meter. Not super accurate but possible to see. My computer is in the passenger side kick panel so reaching it with the meter was pretty easy. It did have to be bolted on though. (case grounded)

PCM on the 94 is driverside under hood. Not easy to get a multimeter on when driving. I will test with it warm and idling after I get it back together if it's still happening though.

 

[Pyromancer]

Seems to be resolved now that the truck is back together. I'm not sure it was the EGR, or fuel pump as again the new ones behaved like the old ones. It is fxed for now though. I did add some injector cleaner to the tank and am going to run a bottle or two more through the truck to be on the safe side. Will update if the issue comes back.

 

[RonD]

Yes, as said with a lean or rich code thats specific to only one bank of a "V" engine it would have to be something specific to that bank
So O2 sensor on that bank
injectors on that bank
Lower intake gasket on that bank
Exhaust manifold gasket on that bank, leaking exhaust sucks IN air, lean code means too much air in exhaust on that bank

O2 sensor can only "see" Oxygen(air), so lean and rich are not directly fuel related like the terms imply
Lean code means the computer is ADDING more fuel to try and lower the Oxygen level in the exhaust on that side

O2 sensors only last 100k miles or 12 years which ever comes first, and they go lean as the chemicals they have are used up, these are the only sensors that wear out

If there was an air leak in lower intake then the unreported air would be throwing off the computers calculation, so it would have to add more fuel to that bank

If one of the 3 injectors on that bank was clogged up then computer has to add more fuel using the other 2 injectors
(1994 is Batch fire injection, so the 3 cylinders SHARE the 3 injectors)

If there was an air leak in exhaust manifold then it would be a False Lean, computer adds more fuel and engine is actually running richer that it should, would show up as darker spark plug tips
Failing O2 sensor is also a False Lean, same darker tip spark plugs
And these False Leans cause lower MPG over years before you would get a code, so changing O2 sensors at 100k miles or 10 years is always a money saver in fuel savings

 

[Pyromancer]

It seems to run without codes now. Although since doing all this now if it sits it will initially fire right up, then died half a second later, if I go to start it again it's fine. Woundering if the new pump is just losing prime or something.

 

[RonD]

Try cycling key on and off 2 or 3 times before starting and see if it makes a difference

 

[Pyromancer]

Try cycling key on and off 2 or 3 times before starting and see if it makes a difference

I will give it a try. I tested this morning to see if just sitting over night was enough to replicate this and it wasn't. Truck fired right up after sitting ruffly 12 hours. I'm thinking maybe it only does this after a couple days of sitting. Given how loose the leak down specs are for the pumps on this year I am wondering if the new pump just holds prime ever so slightly better as to let the truck fire on the first crank after sitting for a couple days and then there's just not enough fuel in the lines yet to let it run. I seem to remember in these situations the truck used to crank over a couple times before it started. Now it fires up immediately, dies, then fires immediately and runs fine. After new fuel pump, filter, and regulator I have a hard time believing any of them are bad since truck runs fine despite this. Wouldn't be the first time, but this doesn't seem like a big enough issue to do more than figure out how long it takes for this to happen and see if cycling the key for a couple seconds first fixes it right?