[James Seahill]

When my 1981 truck gets to temp, the fuel pump has been quitting on me. I've tried different fuel pump relays--no change. When I jumper the relay socket, the pump runs and I can move on down the road. Before the engine reaches temp, and after it cools down, the engine runs normally. I'm thinking the coil, the fuel pump itself (overheating?), the warm pressure regulator, the wiring from fuel pump to coil, or? Any ideas?

 

[briano1234]

No most likely it is the fuel pump relay.

They have a tendency to over heat, and have the leads get cold-soldered.
After running about 20 minutes or less they heat up, and the joint get cold soldered, and open, when it cools they work. Rinse lather repeat.

Jumpering it out proved that the relay is bad.

Be warned that not all replacements are the same.
www.cabby-info.com has the low down on how to get the right one the first time.
see page 6.
http://www.cabby-info.com/Files/Relays.pdf

 

[James Seahill]

I have the same problem yet---good relay, when the engine gets to temp and runs for awhile, it cuts out==the relay functions, the system pressurizes, but the engine won't start again until it cools down. There appears to be no problem with the pump, the relay or the ignition control unit, which I switched out along with the relay. I also installed a new coil. Is there something in the ignition system that could be effected once the engine warms up? (other than the icu, which has a heat bank to draw of the heat) I just remembered this---in the past the power wire to the fuel pump relay has overheated to the point that it's melted some of the plastic in the fuse box. Also, the fuse for the pump has apparently overheated and started to melt the socket in the fuse box, besides blowing a fuse on occasion.----so, wiring or a short at some point?

 

[briano1234]

I don't have a ton of experience with the CIS and quirks, but for electrical, if your fuse socket shows melting then you have a Current flow heat build up issue.
I have seen that quite a lot on different cars, planes, and computers/lcd panels.

Typically it is a sign that you have resistance in the circuit, in cars and things it is usually due to corrosion/cold solder joints.
in the Fuse panel it is good to take the ground off the battery, then remove and reseat all fuses and relays once a year to clean the connection between the fingers of the socket and the relay as there is a differential metallic corrosion exacerbated by the current of the circuit that allows electrolysis to happen more frequently. It is a good habit to do this once a year.

Fuse panel fingers are Brass, the Fuses are soldered aluminum, or copper, or the relays are copper, soldered steel, or aluminum/soldered, and the Brass reacts with the different metals at the atomic level causing the electrolysis to happen even with the car off.

Here is the only fuse that I failed to reseat on ownership and about 8 years after I got the car.


It was the a/c fuse at the very top of the fuse panel......yep missed it.

Here is the inside of the 89 fuse panel with corrosion on f1 and f2.


I know that when I have wires that get hot or show signs that they have gotten hot, I usually take the time to remove the Battery cables and clean them at the Battery and opposite ends. I know that the battery ground (neg) to the frame and the frame to engine are subject to battery outgassing and or road salt/debris, and getting then cleaned/shiny, then spraying that battery corrosion preventer goes a long way to less electrical gremlins, If you haven't replaced the Battery to frame and frame to engine cable, it wouldn't hurt to upgrade at this time.

CIS usually has a WUR warm up regulator that has an issue with corrosion. Usually I have heard this happens, and or the Fuel pump relay new with Iffy connections can develop cold solder joints as well and a lot of folks carry a spare in the glove box to prevent stranding.

I would also suggest that you clean your cable ends at the fuel pump as well. I went so far as to take mine off and clean and solder them as I didn't trust the Crimp only connectivity that the OEM's do to the wires, yes corrosion can occur between Bare copper wire and the Crimps, where cleaning and soldering prevents this in the long run.

Last issue is the condition of the Fuel pump, and is it making noises that you can hear?

I have had fuel pumps on mine whine and stop working when they overheat due to a bad in-tank fuel pump or connection hose.
You might try running a couple of tanks of fuel with MMO (marvel mystery oil) about 8 oz in the tank, it tends to clean out the fuel varnish.
Fuel Pumps when they start going bad can also do this intermittent thing.

In my case on my digifant I had a similar issue, and it ended up being a bad fuel pressure regulator that would by-pass all fuel from the fuel rail back to the tank...
It too took me a few tries to narrow it down. You might refer to the Bentley/Haynes troubleshooting guide for the CIS.

 

[James Seahill]

Thank you Brian. Prior to my trouble, I bypassed the fuel pump relay socket on the fuse panel and wired directly to an off the shelf relay---it has worked fine until now, but the power wire to the relay has melted plastic around the place where it plugs into the new socket. I am suspecting the control pressure regulator now--one of the fuel pump relay wires(87)activates it. Do you know if when the engine is up to temp whether a failure at the control pressure regulator (warm mode) would cause the engine to stall? I have a spare CPR I'm willing to test with, but the Bentley says when replacing the regulator, you should replace the "gasket." I switched from an 81' 1.7 to an 83' 1.7 about a year ago and didn't see a gasket when I removed the regulator during the engine switch. It looks to me like the control pressure regulator mounts flush to the block--metal to metal. At least, that's how I've always seen them mounted, and I've switched engines and retained the same fuel system a number of times. I've never seen a gasket for it.

 

[briano1234]

It could cause issues I suspect as it is the Warm up Regulator (similar to a choke). I too have never heard of a gasket
the ETKA may be of help to you.

https://volkswagen.7zap.com/en/usa/

 

[James Seahill]

What exactly is a "cold" solder, please?

 

[James Seahill]

after checking, it was actually the power wire from the relay to the pump, and not the power wire to the relay (from ignition) where the overheating occurred at the relay ---would this indicate wiring problems between the relay and the pump?

 

[briano1234]

Possibly, the issue with overheating is usually caused by a motor working harder, and the battery is trying to deliver the current, is it the wire that is bad, that caused the issue or was it an over current that caused the heat build up.

You can splice in a new wire, and eliminate that, you can clean up the connections between the motor and ground and the motor and the power source. If you haven't checked or replaced your Battery to frame and frame to engine, I would do so, as you are only going to improve things.

A cold solder joint occurs where current is allowed to over heat the connection on a board or circuit. Usually where the contact pins are soldered to the board in question. Looking at it I can usually see instead of a shiny clear solder flow it looks mottled gray, and sometimes you can see a difference between the solder next to the pin, as compared to the circuit board. Water can cause this to happen if the circuit is moist. When the Connection overheats, then you have the solder pull or flow to the heated side, and since it is in use the connection goes intermittent because the solder is melted, and not causing a good connection. When the Car Dies, and the relay cools off the solder will reharden, and flow....but it isn't a good connection it is resistive and it will happen again and again, rinse repeat....

You can replace the relay with new, but if you haven't cleaned and or fixed everything then you will have it eventually happen again.

I have seen this on different things over the years, and can spot a iffy solder joint. Using a soldering iron, and sucking the old solder out from around the pin, then cleaning it with and paper, or a wire brush, then reapply fluxed solder will resolve the cold solder joints in the relay or circuit. But making sure that the rest of the circuit as in the grounds and power help. If your pump was whining then you are having a delivery issue as if it has an in-tank pump, then you may have in-tank pump issue or a connection hose that is making the primary work harder to deliver the fuel. Same as if your fuel is full of contamination or rusty particles because of your tank, then your pump isn't running efficiently and whining to let you know that it is going out. I have seen Primary pumps whine and then they over heat and stop, but then when cooled off they work again, until it all happens again.... Yep it is hard to find, and or finger out, but testing and cleaning starts to eliminate issues.

https://www.google.com/search?q=col...UIDygC&biw=1280&bih=666#imgrc=Cr1i17mk6JE4XM:

shows you some of them.

 

[James Seahill]

Thanks for all the information--I need to address corrosion at the fuse/relay box and find out why there has been overheating on the fuel pump wiring circuit. Here is what may be a surprise to those who are following this: I discovered one of my spark plug wires wasn't seated well in the (old) distributor cap and that the center contact was questionable. The rotor had recently been replaced. After replacing the cap and making sure the plug wires were all seated well, all of my stalling problems disappeared. The truck runs fine now, cold engine or not. There is interplay between the ICU, the coil, the hall sender and the fuel pump relay--no oxy sensor or computer on this model--basic CIS. My guess is that the signaling interplay between the fuel and ignition systems was interrupted by the situation with the plugs/distributor. It runs now as well as ever--no problems with the pump, relay or electrical wiring that is interfering with normal operation

 

[briano1234]

Great...Yes a bad wire or connection can cause weird things to happen.