G'day,

Does anyone have a circuit diagram for the 6CU ECU. I have the fuel pump issue and would like to repair. Sending it off to AJ6 is not practical as currently its taking 3 months for post with covid 19 in Australia.

Any help would be appreciated.

Paul in Oz

 

The 6CU is not nearly as reliable as the later 16CU, which is a straight swap in. I would buy a 16CU, there are loads on UK ebay.

 

Paul,

Firstly, welcome to the Forums.

When the beast is sorted, please do an Intro in the New Members Area.

I am 100% with Greg on this.

In Vic, touch base with Doug at JagDaim in Ringwood.

OR

Lucky Phil at Prestige Spares, Ringwood.

Good luck.

 

G'day Grant and Greg,

Lucky Phil is a very good mate of mine, and has sold prestige Spares.

I don't want to simply buy a replacement, I want to FIX the part, or find a low cost alternative.

Good Parts are now getting harder and harder to find. We need to be able to build Throttle potentiometers and other items when they disappear, or be forced to buy from a shrinking specialised supplier base with growing margin expectations.

The 16CU would be over $1500 australian dollars, when I could probably fix my unit for a 50c component.

The people who had the board level skills and experience for things such as this are disappearing, and it is in the hands of us younger guys (Im 50) to become the repositories
of this knowledge. These forums will be the only places one day soon where the average guy can come to try and glean knowledge about long dead technologies that don't
force them to buy from specialist suppliers at huge markups.

I am currently working on a low cost HE Throttle potentiometer replacement based on a bosch part and will post my result when I get time to finish it.

Thanks for your feedback but I shall continue my search and post my results when I fix/reverse engineer the bugger.

I do have to admit I am not a concourse guy. I will happily replace a part with something I have made from modern materials and technologies to ensure my ride is reliable.

When I brought my first Jaguar V12 30 years ago, I spoke to a highly respected Jaguar Mechanic with 50 years of experience at the time. I asked him what the v12 was like?

He replied " There is nothing wrong with the engine, it just all the crap bolted to it!" ;-)

Paul

 

If you were closer id give you one of my spares lol i think i have a 16cu for older not-marelli cars around somewhere

 

Get a 16CU. Far more robust. There are diferences in 16CUs, with or without Marelli, with or without O2 sensors. Be sure to get the right one.

 

While I applaud your goals because I regularly do the same thing what we are trying to tell you is that the 6CU's are plagued with issues. I've experienced it, as many others have. They are highly susceptible to cold and cracked solder joints, leading to intermittant and sometimes permanent issues. In my case, it led to the engine running fine, then it would start running rough, quit, then be impossible to start. Tracing it down took months because it was so intermittant. It would run fine one day, and not start the next. Finally did a definitive diagnosis with a swap from another car of a 16CU. Put back the 6CU, and it acted up. Banging/twisting the 6CU would allow it to run normally, for awhile. Opened up the 6CU, and reflowed hundreds of the most likely solder joints around connectors, etc. Never found the smoking gun joint, but it worked fine after reflowing. But I didn't trust it, because I didn't know if I'd reflowed the right joint or not and I didn't know how many joints were about to crack. I didn't want to be left stranded. 16CUs simply don't have the issues. Ive repaired many black boxes on many of my own cars rather than replacing them, and the 6CU is the only one I didn't trust after fixing it.

I haven't found any schematics at all. Bywater is likely the only one who may have them. Lucas has changed hands and been reorganized so many times, their successors might not even have them.
​
If you are only finding $1500 16CUs, you aren't looking in the right places. Keep looking.

 

Point taken..... Not trying to Flame anyone, just find a cheap solution to a common problem. I see it reported often.

I have 3 HE XJS's, and only one has this issue with the Fuel Pump, and all run fine in other ways.

Maybe the warmer climate here is more forgiving ;-) or I'm just lucky....

Anyway, I will try to reverse engineer the Fuel Pump issue in the next few months, and if I succeed I will post what I find.

Though I have just joined the Forum, I have often referenced it for issues, and have great respect for both Grant and Gregs contributions. I'm just a stubborn bugger when it comes to fixing things......

"Wire was invented when two scotsmen found a copper coin at the same time, and neither would let go" ;-)

Heres what I found on the topic since:

https://www.triumphwedgeowners.org/u...as_4cu_ecu.pdf.... very nice piece of work.

This is Bosch related.

Fuel Pump Control (FPC) - Sheet 2

The FPC operates the FPR during starting and normal running. The FPR is controlled by T552, which when on, provides ground to the FPR. When the key is turned to the "on" position, +12V is supplied to the ECU, and the FPR is activated for 1.5 seconds. At power-on, T101 is on and T102 is off because C101 has not charged to 1.4 V yet. While T102 is off C102 is charging and T103 is On. Eventually C101 charges and turns T102 on which pulses T103 to off via the discharge of C102. The pulse charges C551, turning the FPR on, then C551 discharges (taking about 1.5 sec), turning the FPR off. Turning the key to the "start" position sends the Start signal to the base of T552, activating the FPR. If the car starts, and the engine speed is greater than 100 rpm, pulses from the ES pump up capacitor C551, turning T551 and T552 on, activating the FPR . If the engine speed drops below 100 rpm, there is insufficient pumping to keep the voltage on C551 high enough to keep T551 on, shutting off the FPR.

 

Have you swapped ecu's with one of your other cars and the fuel pump works ok?
It may still be just bad solder joints. Back tracing from the connector pins might lead somewhere. I hope you have some high powered magnifying glasses as you'll need them.

 

I have access to another that a mate says has same problem.

So I will collect when I go to the big smoke and have a go at the bugger.

Will keep trying to gain more on the Circiuts and will post when I have some good oil.

Regards
Paul