Thanks. I had the opportunity to talk to someone who was involved with the design 15 years ago and all the little details were intriguing. I'm sure after that time I've forgotten some of them. Prior I played a lot with the 7.3 system, so I was "primed" on learning about the HFCM at the time.

I'm in the process of doing a video on the fuel pump relay and band-aiding that issue. Pete was kind enough to go out and check the voltage change at the pin for "ground control" at the PCM since my truck is down. One modifier had reported its switching positive to negative, and some people have installed ice-cube relays for a failed CJB.

The ice-cube relay size is appealing as it easy to find a replacement, but I worry about recommending using those we don't know the current switching capability within the PCM, which may be why Ford is using the relay on the CJB. Its coil does not have a high current draw while the common ice-cube relays are much higher. Doing something for yourself and reducing the possible life of the PCM is one thing, telling others to do it is another. So my way around is using the existing working CJB relay to drive an external relay, that would put three relays in a row but it would keep the CJB relay from seeing the pump's high voltage spike on breaking.

For a failed relay, it's not that hard to sister in a similar one as a parallel off the back connections. There are too many soldering connections I believe for the DIY'er to hack into the CJB and just replace the relay, even some of the repair vendors shy away from ours.

 

Jack, by what methods do you clean the aluminium so wonderfully?

 

I believe it was @Hartwig that had some good pictures of the insides of the CJB and relay positions -- I looked up the relay numbers from those pictures, and it seems they are discontinued - but there is a current production crossover



I think the reason why repair is not done is the labor involved in getting to the circuit board, to replace the relay -- it does not look all that bad to me, but in a shop setting where time is money, it would cost too much -- good thing I have the time

The addition of a diode across the fuel pump power wires would eliminate the kick back from the motor - some relays have this built in. I think most of the CJB problems come from aftermarket fuel pumps being added that pull more current than the system was designed for - an added relay should bypass the problem

 

since i know about the problems of the fuel pump relay, i am thinking about adding another relay between the actual relay in the CJB and the fuel pump, so the relay in the CJB only transmits the control signal to another additional relay.
I had done some testing because I could not believe that Ford had such a bad solution for the fuel pump relay

 

the inside of the CJB. a complete disassembly is not possible without soldering

 

I've got all the pictures and the info on the relays, mostly just waiting for a good voice day and if someone knows the current flow capability of the PCM. Even the replacement relay is discontinued and a new one should be available in March, although Panasonic has one available.

I know someone who developed Empty Nose Syndrome from the surgery, so I'm really apprehensive about doing it.



"i am thinking about adding another relay between the actual relay in the CJB and the fuel pump, so the relay in the CJB only transmits the control signal to another additional relay."

This issue has been going on for some time.

That's one of the ways that I've laid out Hartwig but pulled out of the other thread. There are three ways of dealing with this. If the PCM would be able to take the current load without degradation it would be a lot easier. Ford has done this layout over a number of platforms in the light truck line, but the ones on the other platforms do not have the number of posts soldered.

 

Unsoldering those 57 connectors is what holds back repair -- to bad they didn't use a ribbon cable - repair would have been simpler

 

With the current load, it would have been a hefty ribbon. But there's a lot of potentials for one of those to be a bad solder in the field, so I can understand why repair shops shy away from this more complicated repair. Automotive Circuit Solutions will replace a relay for $130.

Do you have a SWAG on what milliwatts the PCM solid-state circuit could handle?

 

Datasheet lists this as a 30amp contacts and 685mW(57 ma) coil consumption -- I find it hard to believe the circuit board would handle 30 amps, but that is Max -- reliability of the contacts at that load would be short

the PCM just a SWAG likely would be about 0.5 amp -- we have seen the control circuits get shorted because of chaffed harness, so there may be a current limiting factor in the PCM to eliminate shorting damage

https://media.digikey.com/pdf/Data%2...Fs/G8QN_QW.pdf

 

I have the Datasheet for the replacement but could not find one for the original relay.

The CJB does have a 1,000-ohm resistor across the relay coil, so I've bumped it up to 82ma and 1.165mW stock. The typical ice-cube with a resistor is 85-ohm with (if) a 680-ohm suppression resistor, so 188ma and 2.67mW. So still under the SWAG. One person here has put in a relay with the coil grounding through the PCM and we've not heard it faulting. Two others elsewhere. I just get real hyper about screwing with something that can cause other's issues, without knowing what they designed in there.

Without a running truck, I can't measure the draw on the fuel pump, but they have it fused with a 20a. If they followed SAE rules for the pump fuse it should be about 15a draw for the pump. The fuel heater was a 30a running through the CJB ('03/'04).

 

For those of us with the fuel heater relay still in the CJB, an easy way to take the strain off the embedded relay and put it on the old fuel pump relay. which is replaceable.