I agree, pay close attention to this kind of stuff, the identifying numbers on your existing computer, Catch Codes and all that. Keep your old computer for a while if you can, don't immediately give it up as a core while buying a new one because you can never "go back to what it was" during diagnostics if you don't have it.

 

I used to build all kinds of little Radio Shack kits & power supplies & such, most advanced thing I ever did was a microwave HBO antenna made from a coffee can as the collector and chicken wire as the reflector. It worked kinda-sorta but needed to be in the attic, it wasn't weather-resistant by any means.

 

I gave up electronics when I figured out electronics = Math!
Then got back into it in the early eighties when computers were making a scene.

The most advanced thing I've done is design and build the data collection system I used in my truck.
Thanks to modern calculators and design software!

-Enjoy
fh : )_~

 

Yes. I changed the filter twice over the last 6 years. The last changed was 2 months ago. Thanks!!

 

Might look good in a garagemahal.

 

Sold!!! Remind me.

David gave me a 1950s-style hub cap I just today stuck up on the wall, needs to be cleaned & polished and maybe I'll get to that someday...

 

What I remember having learned from my electronics stuff (say, 12-16 yo, late 70s/early 80s) is that RF signal processing stuff is different, somehow it's more than just the NPN/PNP transistors (opamp? I forget).

I think about today's technology, these things called Arduino or somesuch... guy I worked with built himself a media center server out of one, it's a handheld thing about the size of a pack of playing cards. think about it but it'll probably never happen.

 

To many parties, only remember the stuff I cared about that far back ...

The Arduino UNO is what I originally started with to build my data collection system, look in my album, I have a pic of version 2 proto using the Arduino Mega 2650.

Probably ought to let the OP have his thread back ...

-Enjoy
fh : )_~

 

"Conversely, on damp and/or rainy days, when the key is turned to the on position but not in the start position, the external pump turns on but runs and will sometimes take 2 to 3 minutes until it stops running."

Thinking out loud again; So the Pressure Regulator would have nothing to do with this condition.
But worth changing it someday because they do fail, and stick as they get used and older.

 

On those wet days when the fuel pump is constantly running I assume there is no moisture getting near the ECM? I'm not aware that the fuel pump is driven by any sensors. I think it's just a simple timer.

With that said, when I recently replaced my ECM the very first time I went to start the truck the fuel pump was on for much longer than usual. I was concerned there was an issue, but so far I haven't been able to repeat it.

You have only one fuel tank, right?

 

If it's not a daily driver you might be able to rule out the computer completely by just removing it from the truck (store in a dry place). On one of those wet mornings bring it out and plug it in and start it up. Do you still have problems?

 

(Thinking of wet operations) So, there is an EEC-IV test connector, one of the pins will turn on the fuel pump if grounded. Bottom right connector, pin 97, Tan/Light Green wire. So, what if that wire was shorting to ground?

 

My understanding is when the key is turned on, the ECA turns on the fuel pump relay for just seconds, then the ECA uses the PIP signal to switch the relay on and off. If the ECA reads less than 120 rpm, it will cut off the fuel pump.

 

Pretty close. I'm older than dirt, so excuse my reminiscing about the old days when Microsoft was a start up in Bill Gates garage. If only I had bought stock.....

I used to do some discrete component controller design. The circuit used to run the fuel pump in an EECIV ECM is a pretty clever and simple circuit commonly known as a watchdog timer. Basically, what you have is a 1 second timer. The idea is, when the timer runs out, the fuel pump signal is removed from the fuel pump relay, which drops out, shutting off power to the fuel pump. The timer starts to run when the ECM first powers up and the timer is constantly restarted by the PIP signal. Any PIP signal within the 1 second run time of the timer will restart it. With a running engine, the PIP signal is always present and the timer will not run out until the signal stops. This is why you hear the fuel pump run for 1 second when you turn the key on and do not start the engine.

Now, there are a few things which could cause the fuel pump to run longer than 1 second without a running engine. The signal from the ECM to the fuel pump relay is a supplied ground. The ECM removes this ground when it does not want the fuel pump running, (the 1 second timer has run out). The relay contacts may stick, causing the relay to not respond to the removal of the ECM signal. You already addressed this by changing the fuel pump relay, so that is not the problem in your case.

The ECM signal to the fuel pump relay may be shorted to ground. This is exactly what happens when you use the fuel pump test connector to run the fuel pump. Note the ECM supplies a ground to operate the fuel pump relay. The other side of the relay coil is always ignition positive. That is why you will always see positive voltage on the fuel pump relay coil. Don't mistake that condition for proof that the fuel pump relay is "getting power". It is the ground side that is switched! You can easily test for this condition by monitoring the voltage at the fuel pump relay test connector. If it is near battery positive, the fuel pump will not run. If it is near 0 volts, the fuel pump will be running. It would take a fairly rare combination of contamination and moisture to make a short to ground sufficient to operate the fuel pump relay, but a faulty ECM could be a cause.

If you suspect something other than the ECM is causing a short, try disconnecting the ECM and measure the voltage at the fuel pump test connector. It should be near battery voltage and the fuel pump should not be operating. If it is 0 volts, check to make sure the fuel pump relay is operating and correctly installed. If you have something between 0 and full battery voltage, you may have a short, but this would be a very unusual condition.

Another condition is that the internal watchdog timer in the ECM may think it is seeing a PIP signal. This likely would be an ECM failure, but in very rare cases this could be faulty connections between the distributor and the ECM, or possibly a faulty pickup in the distributor. Disconnecting the distributor would likely be an effective check, but such a failure again would be extremely rare.

I have read that the original design of the fuel pump watchdog timer calls for a 1 second run. Anything other than this would indicate a failure and that failure likely would be within the ECM. The concept of the circuit is fairly simple, but the function is integrated within the microcontroller of the ECM and repair is not something the average hobbyist could accomplish. Used ECM's are plentiful and cheap. The main issue is getting one programmed with the correct strategy for your vehicle. Matching catch codes is the best policy, but a full discussion of programming is far from what I can accomplish.

Hope this long winded and boring post is of some help.

 

Question; On a rainy day, with the engine fully warmed up, do you have this fuel pump issue?

NotEnoughTrucks2014 - just read the post above, great stuff!! I agree about a constant short is not likely, was thinking about an intermittent one. This rainy day thing has me….. But I think this lad may be looking for another computer in his future....