I have a 1996 XJS with the AJ16 engine.

I just got my car back from the shop after being there for a fuel tank repair. It was leaking. They pulled the whole thing out, recoated it (again) and I drove it home this past Thursday. I stopped on the way home and filled up the tank. After that I took it home and it sat unused over the weekend.

This morning I tried to start it up and the engine would not start. It cranks, but no start.

Long story short, I pulled the hose going into the fuel pressure regulator and no gas on startup.

I know I should take it back to the shop, and it would have to be towed a good distance to get it there, but was wondering if theres any low hanging fruit I can check before sending it back.

So far I:
1. Checked the inertia switch. I pressed the button, no click, and I shorted the two wires together, bypassing the switch. No difference.
2. Shorted Blue/Red and Brown/Pink wires at the Fuel Pump Relay. (Terminals 30 & 87) No difference.

There are no Check Engine Light codes.

Anything else I should try?

 

Vee,

Have you got an assistant who can help you verify if:

- the pump runs for 2 seconds every time you turn the ignition on?
- the pump runs when the engine being cranked?

If the pump doesn't run under both of those conditions, I'd be checking the Fuel Pump Relay (Which you've bypassed anyway). Then I'd assume it was a Fuel Pump problem perhaps caused when reinstalled, so I'd take it back to the shop.

But if the pump does run under both conditions, I'd disconnect the fuel line at the filter (on the output side). If it doesn't flow fuel when cranking, I'd then disconnect on the input side of the filter and check again (in case debris from the tank coating has blocked the filter).

Good luck

Paul

 

I left the hose to the FPR disconnected while doing a variety of tests, never got anything out of it, so that pump is either not working, or blocked.

I may check that fuel filter, but it gets changed every few years, so it’s unlikely, but plausible.

Thanks for your thoughts.

I may pull that metal wall separating the tank from the trunk down to see if there’s something that got disconnected?

 

Hi Vee

Have a look at Childeric's thread to save me writing it all out again, as he has the Same Problem on his V12

Hope your Fuel Pump has not Burned out, or things could get expensive very quickly!

 

I will do that.

I have confirmed continuity of the Blue/Red wire from the fuel pump relay to the top of the fuel tank harness, where it goes into the tank.

That harness has four wires. Two black, the one blue/red and a Brown/Orange. It seems like a larger gauge wire as well....what is this wire?

 

Continuity checks out from:

1. Blue/Red between relay base and tank harness.
2. Brown/Pink to Battery Clamp
3. Black wire from harness checked out to ground.

That covers power and path to pump. If I short out the two terminals on the relay, bypassing the relay, it should power the pump, if possible, right?

 

OK, so I read up and this is what I've pulled out:
1. Fuel pump may be wired in reverse. Remember, I did drive this car home for about 15 miles. I even stopped at a gas station, shutting the engine off, and filled my tank. Started back up and drove the rest of the way home. Three days of inactivity and here we now are. Would that seem feasible for a reverse wired pump?

2. What if the shop reconnected the supply with the return hoses and reversed that connection under the car? Could that cause a problem?

The headscratcher here is that I drove this car home, turning the engine off then back on....

 

If I connect 12v directly to the black and white wires inside the tank, that connect to the fuel pump, the pump should run, right?

​​​Well, I tried it, but from outside the tank, through the harness terminals. I applied 12v and the PUMP RAN!!! It is not a dead pump.

I applied 12v to the fuel relay at Terminals 85 & 86, and it clicks…so I think that works?

EMS and ECM relays both click as I plug them in and out.

 

So I ran continuity tests on all the wires I thought were relevant. See attached.

Two things to note:
1. The continuity reading I got for the Pink/Brown wire from the Fuel Pump Relay to the Black / High Power Harness at the ECU. That was the only reading that came up higher than 0.03.
2. I ran a continuity test (successfully) from the EMS Power Relay base using the White/Red wire all the way to the Inertia Switch. Then I took it to the White/Purple wire, on the other side of the Inertia Switch, and it came up good as well.

What else can I do, or test?

 

Hi Vee

Its only the V12 Pumps that sometimes get wired in reverse, not the internal Fuel Pumps on the AJ16 (anything is possible but its very unlikely)

You have Separate Coil Packs on your AJ16 so who knows it could be a Failing Coil

You might not even have enough Fuel in the Tank! It could take 20 Gallons just to get to cover the Filter depending of course on how high the Filter is from the Bottom of the Tank

It could also be the 2 X Blue Hella Relays on top of the Fuses under the Passenger Knee Panel if the are not making good contact in their Holders (Prime Suspects!)

It could be the Fuse to the ECU that is also amongst all those Fuses

Worth Checking them all

Have a look at this Thread 'Carmen Won't Start' Page 93 'Cherry Blossom' Restoration Thread Almost every trick in the Book to try and Start my AJ16 Engine!

You also need a really good Battery showing in excess of 12 Volts to really '**** it over' as that could also be the problem

Good Luck

Alex

 

Thanks for the thoughtful response. I really appreciate it.

I had everything covered. Blue relays replaced, failing coils wouldn’t disable a fuel pump, fuses have been checked….until….

​​​​​..until you got to the battery. I had thought that the car was in the shop for months. The battery might have been jumped just before I picked up the car…then as I drove it home, it might have had just enough juice to restart after a fill up….then after sitting dormant for another 96 hours, maybe it has enough to crank, but not enough to fire up the fuel pump?

it was a variable I had to cross off the list. So it’s currently charging using my trickle charger.

Thanks for the continued thoughts. I’ll let you know tomorrow if this is the answer!

 

Hi Vee

Trickle Chargers have their place but I bought an 'Old School' Heavy Duty one off Amazon that also has a Quick Charge facility, not that expensive in the Scheme of things about £45

I wouldn't be without it, I can Fully Charge a dead Battery in about 8 Hours

Heavy Duty Battery Charger

 

I did find this:
Fuel Pump Control: Single Fuel Pump
The electrically powered fuel pump is controlled by the ECM via the fuel pump relay. After the ignition is turned on (position II), the pump runs for about 1 second to build fuel pressure for starting. When the ECM receives an engine speed signal from the crankshaft position sensor, it activates the fuel pump relay, which in turn switches on the fuel pump. The fuel pump will continue to run either until the ignition is turned off or until approximately 1 second after there is no speed signal.
NOTE: In the event of a vehicle collision, the inertia switch will switch off all ignition powered circuits, including the EMS power relay. This action will remove power from the ECM and cause the fuel pump relay to de-energize, switching off the fuel pump.

So I have to add the crankshaft position sensor to the list of suspects... I am seeing the tachometer needle move to 200rpm when cranking.

Based on this, it seems that the CKPS is only used AFTER the 1 second pump prime after starting the car. If I hear the pump run for the 1 second, but nothing after, then CKPS is likely. If not, then the CKPS is ok?

I think I have an old sensor in my collection of parts. Time to dust it off and see what happens?

 

Hi Vee

Crank position Sensors, seem to have a mind of their own on these Cars, that's why many owners carry a Spare one in the 'Glove Box' I had enough of having to pay 'Megabucks; for these and so I got one off 'Amazon'

Yes! Amazon! 'Bite it and Believe it!

Every bit as good as well known Brands and also a lot less expensive

 

Vee,

Correct. The pump running for a couple of seconds after ignition on is not influenced by the CKPS. So, as you say, if your pump runs on Ign On, but not on cranking, you'd start to look at CKPS, as clearly the Fuel Pump Relay is ok. So it sounds more like the ECM is not triggering the pump, due to a lack of input signal such as the CKPS.

Cheers

Paul

 

So if I bypass the fuel pump relay, I hear the pump run, but I don't see any fuel getting to the regulator? Is there something that would prevent that from happening?

I let it run for about 30 seconds.

 

Vee,

- Fuel Tank blockage
- Pump running but not working properly
- Fuel filter blockage

Maybe start with the easy one - disconnect the line going into the filter and see if there's fuel flowing at that point?

Paul

 

I think I’m going back through the top and insert a camera in there….

im thinking the hose wasn’t secured at the pump, so when I filled up the tank, the fuel may have dislodged it.

Thats my theory.

 

The hose was off the pump!

I was able to squeeze my hand in there and reattach it and even put a hose clamp on it! I was pretty nervous I was gonna lose my socket wrench!

I did find the old clamp that failed, or slipped off.


The fuel is green because of some dye I had added to the tank when I was still trying to figure out if the tank had been leaking.

Failed hose clamp.

 

Well, I hope it's over. I had the failing hose in the fuel tank replaced with a Gates 27093 hose, which is gasoline submersible and exceeds SAE J30R10. The shop seemed to use any old 5/16" hose when replacing the line from my fuel pump.

I'll still drive with the tools in my trunk, but I feel confident that this issue is behind me.

I do want to add, a 1' length of this 5/16 hose is adequate to make the connection. I thought Rock Auto cut this hose to length, but I received two 1' pieces instead of one 2' piece.