Hey guys. I am, once again, another fool who decided to pick up a non-running beautiful example of a V12 Jaguar. I guess I am glutton for punishment.

Anyway, between resources here and elsewhere, I managed to go from a no crank to cranking, which is a good start. Apparently the starter relay has gone bad and I bypassed it with a standard relay based off of the instructions here:

Jaguar Specialties

She cranks over no problem now, but I do have left over wires from the original starter relay. Are these used anymore?

I also traced the no start back to the fuel pump being dead. From the looks of it, they already tried replacing it with a Walbro, which looks like a nice unit, but it appears to be dead already. Is there a chance that the filter sock in the smaller sump tank clogged it and killed it? I did notice cracks in the bigger hose that comes from the sump to the fuel pump that needs to be replaced, is this 1/2" hose?

Another goofy thing I noticed is a speedo bounce. Shouldn't the tach bounce instead? I've already managed to "drive" the car a mile and it hasn't moved an inch!

Anyway, thanks for the help and I can't wait to get this beauty up and going!

 

Check the fuel pump for function, by putting two wires to the battery. I would more so expect that the ECU can't pit a signal to it.

Do you have a spark when cranking?

 

I have yet to get that far in terms of spark. The amp on the intake looks crunchy/corroded as is, so I have a new Delco unit I was going to swap in if it didn't shoot spark.

As for the fuel pump, I did just test it directly with the battery and nothing. Before, I could hear the fuel pump relay click off after the 2 second prime.

There was an old school keypad security system in the car at one point, and taking a part some of the lower dash panels, it looks like the system was removed and things spliced back in normally. They did leave the non-functioning keypad in though. I feel like I will be cleaning up hacked wiring before getting to the original mess.

 

One reason I walk away from cars I want to buy: wiring interference. I hate it when people cut into and trim wires how they want. You can search for years... I'd recommend getting a manual with the wiring diagrammes to make sure everything is correct and then check. Do one task at a time. If you have no spark, work to get a spark. If then still have no fuel, work and see if you can get that done.

 

Possibly.

What are the colors of the left over wires?

If one of them is white/red ....a smaller gauge than the white/red that goes to the starter.....it might be worth investigating. It gives the ECU a 'start signal' according the S57 diagrams.

I *think* what it actually does, more specifically, is tell that the ECU the engine is being cranked by the starter so it (the ECU) can A) turn the fuel pump on and B) increase the injector pulse width slightly for a slightly richer mixture


Speedo bounce when cranking often suggests a voltage drop problem....poor supply voltage or poor grounding....which may or may not be related to your no-start situation.

*IF* you have a voltage drop problem to the speedo then you might well have a voltage drop problem to the F.I. system as well....which might prevent the F.I. system from working properly. These F.I. systems really like lots of volts and amps !

Cheers
DD

 

I've had my fair share of wiring nightmares. I currently help a friend out with 944s and 924s, and the early 944s always end up getting hacked together at the fusebox. Even the one I originally bought had a double splice at the ignition switch that went from a 12awg down to a 18awg back to a 12awg. I'm just glad I found it before driving it at all.

I'm just more curious about the speedo bounce instead of the tach bounce. Is that normal behavior or did someone reverse some wires somewhere?

 

I will investigate the other wires, and I do believe there is another white/red left over. Would it be acceptable to tie that into the starter wire, or does the starter relay act as multiple relays to handle the different levels of current?

As for the gauges, I assume it's at the gauges themselves. I am also getting 9V at the gauge while I can clearly read 12V+ at other various locations (at the starter relay brown wire for instance).

 

Yes



No.

The original relays simply had multiple exterior posts connected to the same contacts internally....to accommodate this sort of situation.


Well, if you're only getting 9v at the gauges then you have a problem somewhere....most likely dirty connections somewhere along the line and/or weak/dirty contacts at the instrument printed circuit....or at the connector from the printed circuit to the main panel harness.

Cheers
DD

 

An optional solution would be using a "dual 87" relay. Same at what is shown in the Jaguar Specialties tech-tip but it has two '87' terminals rather than 87 and 87A


Cheers
DD