Feedback on ECM source

[eagle23]

I have a 1991 Ford Ranger that I may need to replace the ECM. I am getting some diagnostic work done soon.

I did the usual dist cap, rotor, plugs, wires, etc. Also replaced a variety of sensors that have improved an intermitent rough idle. All helped, but none did the job.

I am beginning to suspect the ECM. The intermittent nature of the problem is part of the frustration. No CEL's.

In doing some internet searches, Auto Computer Exchange and Auto Computer Systems. Prices look decent but I'm looking for feedback from anyone who's used them.

Thx!

 

[Trav]

Did you clean the injectors? I mean off the truck not with an in tank product.
Carbon issues?
Fuel pressure?
Fuel pressure regulator?
Compression?
Dirty EGR?
Lazy O2 sensors?
MAP/MAF sensor?
Any codes?
If the truck runs well otherwise with no CEL the ECM itself would be low on my list.

 

[The_Jeff]

+1 on the FPR it went out on my 94 and was intermittently sucking raw gas into the intake. Try pulling the hose and plugging it with a golf tee to see if things improve.

 

[punisher]

Ford PCMs are built like tanks. In over 10 years as a driveability/performance tech at Ford, I replaced ~ 3 PCMs, one for a faulty AC compressor clutch driver (On a Ranger by the way) and 2 or so for reprogramming problems (known fault on some early OBD II PCMs). Not saying your PCM is OK, just saying the chances of a faulty PCM are really, really small.

What engine? How intermittent is the rough idle? Hot or cold?

 

[eagle23]

All, thanks for the ideas.

I should have provided more background, and apologize for that. It’s a 1991 with original 83k miles that I bought from the original family 3 yr ago. It's the 3.0 V6 and automatic.

I have replaced (in no particular order over the past 2 yr):
-MAF sensor
-O2 sensor (there’s only 1, though some books say 2)
-Throttle position switch
-Idle air control
-Fuel pressure regulator (helped but no cure)
-Distributor
-Ignition module
-All injectors (reman off Ebay). These were last and I thought would do the trick
-Heads

I had to replace the heads with reman units when two of the studs for the exhaust manifold broke off in the head and couldn’t be extracted. It happened at the dealer and I knew with an engine 19 yr old at the time it was a possibility. I provided them Dover reman heads, as Dover is in the Atlanta area and has a good rep. Changing the heads didn’t change the idle.

As I said all these incrementally helped but did not cure it. Part of why I was willing to do these one at a time is they weren’t that expensive and for a now-20 yr old unit I thought could be operating at the low end of specs or slightly out of specs but not enough to throw the CEL.

Still original is the ignition coil. There is no EGR on this particular engine, though I understand some 3.0’s use them.

The rough idle is not horrible, just intermittent when hot though getting more frequent which I hope will help with eventual diagnosis. When the AC is on (compressor activated), it helps smooth the idle completely so whatever the compressor is triggering is helping. That’s why I circle back to the ECM and something electronic, though I could be wrong.

I may go to the local Ford dealer week after next for diagnosis but thought it would be helpful to see about ECM resources. I’ve read the ECM can produce weird idle situations like mine but never enough to throw a code.

Punisher, your experience is helpful about the Ford ECM’s. I’m glad to know they’re stout. Any other thoughts are appreciated though I know it’s hard to diagnose from afar.

I started looking on line for ECM resources in case things pointed that way which is why I was asking if anyone knew about those resources.