Do I have PCM going bad

[mybckup]

For the last while I while driving I have a random missfire and my O2 sensors quit and fuel milage is gone. Tested 02s and they are ok. Injectors are ok. But when trying to use a scan tool I loose my signals from O2s, temp, timing, coolant temp and so on. Yesterday I drove to Bradford and ran good with good fuel milage. Running Shell 93. But coming home it used almost a half tank of fuel. It is about 80kms each way. The sound of the motor sounds like it is at base timing and labouring. I did have a bad EGR which I changed and ran good for about 200kms and now back to sucking fuel.
Could this say my PCM is on the way out?
At a loss here on what to look for. Any help would be great.
Thanks

[ZR]

Start with cleaning all grounds (including body grounds + main cable at the block).

[hammerhead]

I was having similar issues with the coyote in my f150 in bank two. Code leading to cat and maybe O2 sensor codes. Been having misfires with it for years but in the last couple of weeks the check engine light finally came on and pointed towards the cat. I had another car purchased at ford dealer cleared the code and traded it in. With it only being five years old and no exhaust leaks + 237,000 on it I was suspecting the cat or one of or both sensors. The engine burned a lot of oil in my opinion and I would occasionally dump in heavy oil and oil with zinc. In my case I’m suspecting a dirty cat or maybe sensors because of oil consumption and some of the oils I chose.

[Minaccia]

It sounds like a complex issue and the symptoms you're describing could indeed point toward a failing PCM, especially if you're losing signals from various sensors like O2 sensors, temperature, timing, and coolant temp. Here are a few things to consider:

PCM Issues: Given that the vehicle ran well for a while after the EGR replacement but then reverted back to poor fuel mileage and signal loss, a failing PCM could be the cause. The PCM controls various sensors and fuel management. If it's malfunctioning, it could result in inconsistent performance, sensor signal loss, misfiring, and poor fuel mileage.

Wiring/Connections: Before concluding that the PCM is the issue, check for loose or corroded wiring or connectors. A loose ground wire or poor connection can cause intermittent sensor readings and could explain the random loss of signals.

Vacuum Leaks: A vacuum leak could also cause misfiring and poor fuel economy. If the PCM is trying to adjust the air-fuel mixture based on faulty readings, this could cause erratic behaviour. Replacing the EGR may have temporarily alleviated a vacuum-related issue, but other leaks could still exist.

Fuel Pressure/Delivery: Check the fuel pump and fuel pressure regulator to ensure proper fuel delivery. Poor fuel pressure could cause the engine to run rich, leading to high fuel consumption.

Misfire & Base Timing Sound: If the motor sounds like it's running at base timing and labouring, it might suggest an ignition timing issue. A failing PCM could fail to properly adjust timing, or there could be issues with the crankshaft or camshaft position sensors, which control timing.

Since you've already checked O2 sensors and injectors, the next logical steps would be to:

Test or swap the PCM if possible.
Inspect the wiring harness for any damage or loose connections.
Ensure fuel pressure and vacuum lines are functioning properly.

[Laffs]

My gut says power delivery or ground issue.

Like ZR said, first check your grounds both chassis and battery. Also if the battery is older than a few years, I'd have it tested as well as put a meter on the alternator while running to see what its putting out. From there I'd look all my fuses related to PCM and at the PCM power relay output from the CCRM.


Before the problem started had you changed anything or done anything to the car? Washed under the hood or changed any parts?

[ZR]

Forgot to ask, what yr is it?

[Laffs]

I searched his history and it appeared to be a New Edge, 2000 MY.

[ZR]

^ Mint thanks, stand by my suggestion of where to start.
There is also a ground (s) at the ECM to check.

[mybckup]

Sorry I did forget to mention the car is a 2000 4.6l 2v.
Since reading all the replies I have check and cleaned almost all + and - connections except by PCM. So far seemed to be good.
Now the second thing I didn't mention in my original post was that when the sensors go N/A on the scanner they are random and not at the same time. The O2s will go from say 0.281v to 0.8v to N/A for a couple seconds the back at 2v and so on. The only CEL codes were for p0300 random misfire and for B2S1 slow to react.
Correct me if I am wrong if it was say a poor power supply or ground wouldn't the N/A's happen at the same time and not different times?
I took her out for a little tour last night and seemed to be ok. This always seems to be random and under different weather conditions (warm-cold-day or night) nothing to say ok it's going to happen today.
I have ordered a new cam sensor FoMoCo to try.

Thanks

[ZR]

^ Stock ign coils? Any other non stock parts (IE headers with 02 extensions / gauges etc)?
No random is exactly the kind of thing poor connections cause.
Did you clean main ground cable down by the motor mount / oil filter?
Did you clean body grounds on the rad support?
On some there is another one just in front of the drivers side strut tower.

[Darkhorse]

Not saying it's impossible for the PCM to be the issue, but It's really really rare that it is. I was in that situation, where I was convinced it was, I bought a new one and in the end it was just a bad ground/faulty wire along the way. It's a tedious job to figure out where the fault is, but my experience says PCM failures are very very rare, especially with OEM, and codes never lie. The code will say where the issue is, or multiple issues are.

Tunes also never change, once saved.