Few issues, maybe related to ECM?

[Brad474747]

I've got a 94 B4000 and I've been having some issues with my CEL (consistently lean bank 1, code 172) no matter how many times I've replaced the o2 sensor it'll still pop that lean code... I didn't have that issue with bank 2, flip flopped the o2 sensors (formerly bank 1 to bank 2 and vice versa) and the sensor that WAS good and not throwing a code on bank 2 threw the same lean code on bank 1. And the original bank 1 sensor that I moved to bank 2 still threw the lean code (136)

It also pings quite a bit above 2500rpm on acceleration under load and I can't even make it to interstate speeds without it pinging, or even maintain any speed higher than 55 uphill without pinging

We just got it back from the shop where they replaced the passenger head, but they couldn't get their code reading computer to link with the ECM to pull the codes, the mechanic told me he wouldn't be surprised if there was an issue with the ECM

I'm at a loss here, we've been chasing the CEL for over a year now, where do I need to start to nail this down?

 

[enjr44]

Well, what that code is trying to tell you is that the engine is running lean!!! And so is the pinging!!!

The computer uses the information provided by the O2 sensor to adjust the fuel to air mixture. That mix is supposed to be 14 pounds of air to 1 pound of gas. The O2 sensor measures the amount of O2 in the exhaust and sends that info to the computer. When the amount of O2 in the exhaust is so high the computer cannot adjust the injector pulse time to get the fuel mix correct, it throws a/the code.

So, are you still getting codes for both banks lean? Or just one bank? It maters because there are different reasons for a lean condition on one or both sides of the engine.

If both sides,,,, the MAF could be dirty and reporting the wrong amount of air entering the engine. Clean it. Or you have an air leak between the MAF and throttle body on the upper intake. Or low fuel pressure. Or a vacuum leak at the upper intake manifold. After the engine is warm, pull the connector off the IAC valve. The idle rpm should drop to 500 rpm of less and maybe even die. If it does then you probably don't have a vacuum leak. Oh, and a dirty fuel filter can cause low flow (but good static pressure).

If the code is only one side it could all of the above (one O2 sensor is more sensitive than the other). Or a vacuum leak in the lower intake manifold. Or an exhaust leak before the O2 sensor. Or high resistance in the wiring to that bank's injectors (unless it is a CA vehicle which did not uses batch fire).

Computers do fail and sensors do fail; just, not very often. And, your shop should be able to analyze this???

 

[RonD]

Lets start from scratch.

136 is O2 sensor not switching, voltage is low
"Oxygen sensor not switching/system lean"

O2 sensors detect Oxygen levels in exhaust.
Their voltage is generated internally by a chemical reaction, .1v to .9v is the range, under 1 volt
.1v is high oxygen levels, denotes possible lean burn
.9v is low oxygen levels, denotes possible rich burn
.45 is where computer tries to keep the O2 voltage by adjusting the air/fuel mix.

O2 sensors change(switch) voltages within that range a few times a second when engine is running.
No switching means voltage is not changing even through computer is adjusting the fuel mix.

So 136 means, that O2 sensor is at .1v and not changing even if computer adds more fuel to that bank.
That could be a bad O2 sensor or a bad wire from O2 sensor to computer, at these lower voltage levels it doesn't take much to reduce voltage, a little corrosion or exposed copper wire can lower voltage.
Even a little water intrusion at the O2 connector or Computer end

Another code the computer could have used but didn't is 171 = Oxygen sensor not switching - system was at adaptive limits
This one means computer was adding more fuel to get O2 sensor voltage up but reached the computers limit on open time for injectors and the O2 voltage was still below .45v, the sweet spot
So the code it didn't use tells a bit more, wiring or computer issue is more likely.

With O2 reporting lower voltage then computer should be running that bank Richer.
MPG would be down if that was the case.

With an actual lean condition your MPG should be great
And yes you would get pinging under load with a Lean condition, but if engine has been running Richer for awhile you will also get carbon build up in the cylinders, which will also cause pinging under load

What did the old O2 sensors look like, blackish means Rich running

You replaced that head, why?

What do the spark plugs look like on that bank?
dark brown or blackish means rich running.

You can unplug the O2 sensor on that bank, make sure wires can't drop down on the exhaust pipe, then drive the truck to see if pinging is gone.
CEL will come, computer will be forced to use preset factory fuel mix based on RPM, TPS and MAF data, which is rich, for safety reasons, see if pinging stops.
If you still get the pinging then it probably isn't Lean mix pinging, but unhook other O2 sensor and drive again to make sure.

Your swapping of the sensors could mean both banks were actually running lean, just unreported on Bank 2 until the swap.

If both banks are running lean then MAF sensor comes into play, upper intake or ported vacuum leak, as well as Fuel Pressure issues

 

[Brad474747]

Ron,
as far as MPG average i've been getting around 13-14 city, i just filled up yesterday and got about 17.9 mpg (actually the best i've gotten, changed my driving habits too so that's part of it im sure) with about 2/3 city over interstate driving

old sensors were brownish if i remember correctly

i didnt see any exposed wires in the main o2 sensor harness when i've replaced the sensors

head was cracked due to overheating, (had almost no compression on cyl 3, the shop pulled the head and found the crack), the thermostat housing had stripped threads and needed to be rethreaded, that much was done when the shop had it and it's holding coolant better than wine an alcoholic's wine glass

havent had the plugs out to inspect them yet, will probably do that today and snap pictures for reference, i'll also test unplugging the o2 sensors over the course of the week to see how it performs

MAF has been cleaned and tested, no issue there.
we've smoke tested the vacuum system and didnt find any leaks.
Fuel pressure has also been checked and there was no issue there either.

enjr44,
we know it's lean but we're trying to figure out why

Fuel filter has approximately 2000 miles on it

as far as sensors go it would throw the lean code for bank 1 but not bank 2, i would flip flop the sensors to see if the code would follow the sensor or if it would throw it on both banks, which is what ended up happening. after the flip flop i would replace the bank 2 (formerly bank 1) sensor under warranty and the lean code wouldnt come back on bank 2 (the pinging also reduced in frequency as well). i have yet to replace the bank 2 sensor again so right now the system is registering lean for both banks, im gonna take care of the bank 2 sensor some time this week

our shop tried to hook in through the OBD1 port with their code reader but it wasnt linking with the computer and that they wouldnt be too surprised if it was a computer issue of some sort, i've been pulling codes via jumper and KOER test.

should be worth noting that we only take it to our shop when it's something much more time consuming or difficult for us to do in the driveway

also worth noting that it did pass emissions the day after we got it back from the shop WITH the CEL on, reading both banks lean (surprised the guy at the emissions station)

i was discussing the probability of a computer issue with my brother and my dad earlier before writing the OP and had a thought as far as ECM issues go, is there a possibility that there's a bad resistor on the bank 1 fuel control circuit that may be reading a lean condition and burning out the sensor?

would i be correct in assuming that if it's a bad ECM the shop would have difficulty linking it with their code reader?

 

[RonD]

Since you are able to pull codes an OBD1 code reader should be able to as well.
But......not all OBD1 readers play well with Fords specific OBD1 protocols.
In 1995(1st year for EEC-V computers in Rangers) it was hit and miss with OBD2 readers on Rangers
1996 was first year Ford actually used standard OBD2 protocols.

The fact the CEL is working and you can get codes means computer is at least partially sane.

Since MPG is high and computer is confirming Lean mix, and there is pinging under load, all things point to an actual Lean condition in the engine.

And the computer can't correct it.
Fuel pressure is at 35psi
There is no EGR system on 1994 4.0l(except in calif)

So I would do one more test.
Unhook battery for 5 minutes, this will clear current Lean codes.
Start up cold engine.
O2 sensors can't be used until they are above 650degF, which takes about 5 minutes of 12volt heating and the hot exhaust, so computer should ignore them during the warm up
So you should not see CEL come on during that time.
If it does come on then Computer issue could be the source of the Lean running.

Now there is a second thing that just came to mind.
'94 4.0l will be Batch Fire fuel injection, not sequential.
Batch fire only uses 2 wires from the computer to control the 6 fuel injectors
3 on one wire and 3 on the other.
What if one wire wasn't working or not working well.

Look at the wire colors on the injectors, all will have a Red wire, that wire is daisy chained from 1 injector to the next, it has 12volts when key is on.
Then 3 injectors will have a Tan wire and 3 will have a White wire, see how those are connected, could be by bank, 1, 2 ,3 or could be 1, 3, 5 and 2, 4, 6
These are the Ground wires the computer uses to open the injectors, 3 at a time and it alternates grounding them, Tan wire then White wire, then Tan wire, ect....

The intake valve opening creates the vacuum to suck the air/fuel mix in, Batch Fire is just one step up from carb so only 3 injectors opening would still allow engine to run, but leaner, even if computer cranked up open time.
And it would be leaner on one bank more than the other.

After IDing the wire colors get a hose and listen to the injectors while engine is idling, see if one set(same ground wire) is sounding different from the other set.

It is a long shot, and could be a computer issue causing limited Grounding on one set.

 

[Brad474747]

It is a California emissions engine with the EGR valve, it's been tested and functions properly

Is that last test something I'll want to do should all else fail? Or is that something I should lead with? Whenever we cleared the codes before the cel would always come back on immediately

What does this 2 wire harness you speak of look like? After we bought the truck we did replace a 2 wire harness on the upper intake by the ignition coil because one of the wires was messed up, when we bought the new one I remember it being injection related but I'm not too sure cause it's been a year since it got replaced.
Brother isn't convinced it's related to injectors due to how smooth it's running, he thinks that if it were an injector issue then it wouldn't be running as well as it is.

Brother is curious if the coolant temp sender may have anything to do with it, he said it's a common issue on Nissans vg30 engine

UPDATE: we unplugged the o2 sensors and reset the codes, under the same acceleration conditions it still pinged, I'm gonna pull the codes again and I'll update again

UPDATE#2 still reading codes 172 and 136 with unplugged o2 sensors

 

[Brad474747]

Bump

Another update, plugged the sensors back in and cleared the codes, started it and CEL came back on just as quick as it normally does...

At this point we're starting to research ECM replacement, hopefully that fixes my problem...

 

[Brad474747]

What are my chances that my pinging is related to something other than fuel delivery? Like crankshaft position sensor, cam position sensor, knock sensor, etc? Wondering if we have been going about this wrong from the beginning, and the pinging isnt fuel related. It does smell fairly rich when running.