Okay so I have a 1976 5.3 xj12 fuel injected. I was having issues with hot start so I replaced the coolant temperature sensor. Ran the car until operating temp to test the hot start. Car was starting and running great. Turned it off and came back later to start it and it wouldn't start at all. Through process of elimination I found that I have spark and a working fuel pump. I'm not not getting power to the fuel pump at crank. I have ordered a new relay from Moss, but I'm suspicious that it might be something different. I read in different places that the oil pressure switch might cause this or an inertial switch may cause this as well. Is this a possibility for my xj?

 

Alan, you are is the USA I see, and some things may/will be different to our cars.

Oil switch NO, unless its a 6cyl with Carbies, which it aint.

Inertia switch, doubtful, but simply pull the plunger up, and repress it down. Ours are on the LHF door pillar, just next to the passengers Left knee.

Spark you have, good.
Fuel pump working, OK, I will assume you are hearing the 2 second "burst" when the Ign is first entering the ON position??
But is there fuel IN the rail/s. Get a helper to operate the key from OFF to IGN position (NOT start), and you feel the fuel rail. You should feel the fuel "rushing" through that rail every time they go to Ign from OFF. There are more complicated and messy ways of testing fuel in the rail, but this is simple, quick and has worked for me for years.

Injector pulse, oh boy, here is where the fun starts.

1st test, Ign ON, open the throttle capstan (the round alloy wheel that the cable wraps around), SLOWLY, and you should hear the Injectors "click" about 9 times, as the internal wiper passes the segments.
This ONLY clcks teh last 6 Injectors that were operated at the last shut down, NO idea how or why, and never bothered to find out.
BUT
It was running, so spraying is probably still happening.

The tests get more intense after all these are ticked off.

Memory, what a joke, but here goes.
That fuel pump relay will have an Orange wire. This is the EARTH of that relay via the ECU. For TESTING PURPOSES ONLY, earth that relay terminal (spare bit of wire) to a screw/bolt/whatever, nearby. This will cause the pump to RUN whenever the Ign is ON, and may sort your issue. Leaving it like that is a NO NO, hence the testing ONLY wording. The D Jetronic ECU is purely Analogue, and built like a brick outhouse, and I have never had issues with one. Not so the later P Digital fiasco.

Lets know what you find, it will be simple, they are simple cars/systems.

 

So the reason why I know the pump is working is because I hotwired it to 12v for a short time using a power probe tool. I used a pressure test kit to find out that I'm not getting fuel after turning on ignition or at crank. I can only assume that the pump isn't getting power since it's a working unit.

 

AHA, the mud clears, thank you.

That points to that relay you have ordered I reckon.
There is a 2nd wire from the Start Relay to "kick start" that Pump Relay while cranking. Memory again, White/Red thinner wire from Starter Relay to Pump Relay, which is only alive during cranking.

I dont remember where the ECU gets its signal for pump relay continuation once started, possibly the Tacho feed from that Ballast Unit.

 

Thank you. All signs were leading to the relay. I'm just hoping that the one I ordered from Moss works in my car. It doesn't look like the original Lucas unit. It's smaller and plastic like a series 3 even though moss claims it's for a series 2.

 

I used a generic 5 pin cube relay on one of my PreHE cafs for the Pump Relay.
Just picked up one with 2 X 87 terminals, no A or B terminals. Rated at 30 amps. Pumps draw about 6 running, maybe 15 at initial rotation draw.
Been there 20 years now, only thought of it when you mentioned the one being sent to you.

 

Okay. So this is probably a similar situation. Moss sent me a relay that will work. I just need to figure out what wire goes on what lead. I'm not very good with wiring or electrical problems.

 

Alan,

I will dig out the wiring diagrams tomorrow, its after midnight here, and the wife just called stumps.

I will work out what goes where and post back.

 

Thanks so much.

 

So I went into the garage this evening after work and hotwired the pump so it would turn on with the ignition. The car fired right up. I'm convinced now that I made the right choice ordering a new relay. It's most definitely the problem.

 

OK, found my notes,

On the existing pump relay the wiring SHOULD be as follows:

N = Solid Brown = terminal 30 of the NEW relay.
KB = Pink/Black stripe = terminal 86 of the NEW relay = 2 wires on the one terminal both KB.
O = Orange = terminal 85 of the NEW relay.
NS = Brown/Slate = terminal 87 of the NEW relay.

The wire from the Starter Relay to "kick start" the Pump Relay during cranking is ONE of those KB on terminal 86.

Good luck.

Yell out if you need more, or something is unclean.

The fact it is sweet with the "hot wire" does point to that relay.

 

Thank you so much. I will report back when my new relay arrives.

 

okay now I'm stumped. New relay installed using your directions. The car will start. Run for a few seconds then stall. Try to start again it just rolls over. Wait an hour or so will start again for a few seconds. Still a fuel issue or should I search somewhere else?

 

BUGGA.

At least there is some progress, albeit not what we want.

7 coffees down and my thoughts in some order are:

1) Remove that Orange wire from that new relay, use a new wire, and attach one end to the relay, and the other end to a good Earth point nearby. This will remove the ECU and all other systems from controlling that relay. The pump SHOULD now run whenever the Ign is ON, so PLEASE be careful, as in common sense.
If this solves it, then the ECU Earth Path, internal, has failed. Never seen that on a D Jetronic. You can leave it like that, BUT, legislation, Insurance, etc etc may deem that WRONG.

2) If that does NOT solve it, the cause is either A) Spark dropping out, B) Injector Pulse dropping out, C) Fuel supply, which we have covered sort of in "1". "B" is the most likely.

The fact its running for a few seconds and dying, then not starting for an hour, is causing some brain strain, BUT, when it dies, reach in and "feel" the Ign soil, is it COLD, WARM, or HOT, its just so I can think in a straight line and NOT run you all over the place.

When it dies, unplug any spark plug lead at the plug, insert any old spark plug into that lead and earth it anywhere it basically falls, and crank it, is there spark?

I have a few things to do, I will keep thinking, and wait for the results of the above.

 

okay, so I woke up this morning. Immediately after breakfast and coffee went out to test injector pulse. With the ign on I turned the throttle. Very pronounced clicks as my injectors are all brand new. I hotwired the relay again and it's still doing the same thing. Starts for a second or two then stalls. I will go purchase a spark tester today to make 100% sure my spark isn't dropping off. I doubt this as my coil, plugs, wires, and distributor cap are all brand new. Could also be a bad or failing trigger board no?

 

Alan,

That was my next point of cal.

The original trigger board was a 3 wire board, PITA
The replacement is a 4 wire, Bullet proof.

You mention leads, cap etc as NEW, did you replace the rotor at the same time??

My reasoning, Some replacement rotors DO NOT have the imbedded magnet in the heel to trigger the trigger board, hence a few seconds running on initial fuel squirt, thats all.

 

I did not replace the rotor at that time. This was last summer and the car has been driven several times since I changed the ignition parts. I'm leary about taking the distributor apart because I'm far from a mechanic and I'm worried about breaking something that I don't have the skill to fix.

 

Goodo.

That means its still got a magnet, move on to the spark loss for now.

More thoughts:

The fact you had it running properly with the fuel pump hotwired, still has me at that relay, and the relay that supplies that relay.Something is dropping out, and I need to study the wiring diagram better tomorrow, as its late here, and COLD out in the shed.

Unplug the wire on the Pump Relay that is on Terminal 87, jump 12V to that wire, the pump should run, verifying that wire is good, and not broken, run the engine like that to prove a point.

If that works, then we need to look at upstream of that pump relay.

 

Alan,

You are possibly still asleep, time zones and all that.

I have the wiring schematics, my one eye is having issues following the fine lines. The daughter is on her way, and she is brilliant at reading these.

We will study this this afternoon, its 1PM here now, and get the results up on this Thread as soon as we can.

Back soon.

 

Alan,

Still sorting this, and it 7PM. Bloody hard to read and one item appears missing on the schematics, which I find very hard to fathom.

The Inertia Switch appears NOWHERE. It is mentioned in the Legend, but tracing ALL wires related to the Pump, ECU, Starter, etc, circuits, show NO switch anywhere. It cuts Fuel Pump Activity, and could be all that is wrong with your car, but these schematics are terrible if that is not shown.

Please go to your car and reset that Inertia Switch, OR, simply join the 2 wires together, On our RHD cars it is on the Passengers (LH) A pillar just inside the door seal, and tucked just below the dash lower casing. The passenger could hit it with their foot if not careful when getting in and out of the car. NO idea if its the same side or the other side on LHD cars.