Obd 1 code 172 question

[black_demon69]

Question is referring a 94 with a 4.0l
172 Oxygen sensor not switching – system is or was lean – Single, Right or Rear HO2S – Fuel control

Could 3 fuel Injectors that are not firing correctly cause this code.?
Are there any other possible causes besides the obvious possible vacuum leaks?

 

[RonD]

Sure loads of reasons, but when its specific to just one side of a V6 or V8 engine it narrows it down a bit

172 is lean on Bank 1, passenger side, right side of V6 engine

Lean means the computer is having to open the fuel injectors on that bank at least 15-20% longer that it had calculated to get O2 sensor on that bank to read correct voltage, .3 to .5 volts

O2s read Oxygen levels
An exhaust manifold leak sucks in air, so you can get a false Lean from O2
Misfires don't burn any oxygen so O2 sees that as Lean, too much oxygen
Yes a lower intake vacuum leak would do that as well, upper intake or MAF sensor issue would effect BOTH Banks of a V6

Yes, bad or plugged fuel injector on that bank would mean computer has to open other 2 injectors longer

Lower fuel pressure can cause it as well but would effect BOTH banks

Also old O2 sensor, they last 100-125K miles then need to be replaced, they start to show Lean when failing


1994 4.0l computer uses Batch Fire fuel injection, so it opens 2 injectors on right bank and 1 injector on left bank at the same time, then on the next RPM it opens 2 on the left and 1 on the right, then repeat

So not Sequential fuel injection, just FYI

 

[black_demon69]

Cylinders 1,3,and 4 missing and Injectors don't tick. I need to hook up a noid light on those Injectors to see if they are getting the required power and ground. FYI engine was just rebuilt so all electrical connectors were off. And before rebuild there were no codes and engine had no misses at all.. I did fix some frayed wires and such while engine was out...

 

[black_demon69]

Fuel pressure is around 40psi and o2 sensors only have about 40k..

 

[RonD]

I just looked at the 1994 injector wiring and it looks like it does bank Batch Fire
All injectors get 12v, key on, from their red wire
1, 2 and 3 are grounded, at the same time, using 1 Tan wire from computer
4, 5 and 6 use 1 White wire

I thought it was 1, 3, and 5, and then 2, 4 and 6, so odd and even, but diagrams are never wrong.....right, lol

Coil pack often gets me
3 4
2 6
1 5
front

That 5,6,4 side gets me, either at the coil pack or on the drivers side spark plugs


You can disable coil and then crank engine a few times, pull out spark plugs, look for WET or DRY tips

 

[black_demon69]

Injectors are definitely not firing on cylinder 1,3,and 4. They have power and are being grounded (hooked up a noid light to all 3). There's no Injector Tic on those 3 Injectors. So I guess all 6 will be getting replaced.

Does anyone know of a good place to get Injectors or possibly recommend alternative Injectors?

 

[black_demon69]

Update 3 of the 6 Injectors don't fire. Funny thing is they were working fine right before rebuild and now 3 of them don't work.

And yes they all have power and a ground.