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Tips
Tips

How Do I check Fuel Pressure at Injector Rail 99 XJ8?

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Michael J.

Jedi Warrior
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Car was running and abruptly shut off. Turns over but will not start. Fuel Rail has a tire valve-like port on the injector rail. What kind of pressure gauge connection is needed to read fuel pressure at this port? Car has 140,000 miles on it. Friend had a fuel pump failure at similar miles. I can't hear pump with a stethoscope while turning engine over. Fuel relay closes and contacts are not burned. How do I rule out a pump failure?
 
Well....you buy a fuel pressure testing kit. I have three different ones for different applications. Adaptor for the rail, quick disconnect, hose, gauge, drain hose with valve. I don't know without looking what your pressure should be, but 38PSI is the last US car I checked.
Key off, remove the cap and depress the valve. Get any petrol? Crank it for just a moment and try again. Check valve should hold pressure to get a squirt. If nothing, pump is DOA.
You crank the engine for just a moment, door open, and let go the key. You should hear the pump running for oh, 10 seconds or so. Enough to overcome the lack of oil pressure signal or PIP signal to the ECM or relay.
In the shops, fuel pump working or not was always an easy audio test. Then it got more busy.
If, on the relay, you have power in, and cranking gives you power out, the pump or ground is the problem.
Some of these newer cars have the safety circuit on the ground side, so if no oil pressure or PIP signal, all the power in won't give you a run condition.
If you can access the plug to the tank, you'll have fuel level, fuel level ground, probably low fuel warning, and power in to the pump and ground out from the pump. Probe the power in while an assistant momentarily cranks it. If it shows power on then off like the output of the relay, then find the ground for the pump and probe that. If the crank test shows no power, pump is bad. If it shows power on and off like the input, you're reading through the pump and something is open in the grounding circuit.
Did you run out of petrol?
That will burn pumps out right now.
Seen too many of them.
Dave
 
It is the pump. There is just over a half tank of fuel. I could not hear the pump, even after removing the carpet at the front of the trunk and exposing the tank. I had my better half turn over the engine and still could not hear the pump operate. I was able to hear the relay operate. There is a white plastic connector on top of the pump with four wires. According to the diagram in the electrical guide, Brown and Blue wire is power to pump. With voltmeter, turning over engine confirmed power to the connector. When my friend replaced the pump in his 99 XJ8, he cut an access hole in parcel shelf rather than draining the tank and removing the tank. At least on my 99, with the upgraded sound system, there is a removable hardboard vinyl covered panel that can be removed. I will make a sheet metal panel to install with pop rivets or screws after replacing the pump from the top. OEM pump is pricey at $572. Thanks to TOC for the tips, which were helpful in confirming that the pump had failed.
 
You don't have to drain the tank. The fuel hose connections are roughly above the diff, and you rotate the clips to release them, and wiggle the hose out of the connection. (can be tough to do.). If all the internal connections in the tank are OK, no fuel will spill, except the residual in the lines. Removal of the tank in these cars is not all that bad.
 
After changing the pump, car still would not start. Fuel filter is above the left exhaust over axle pipe. You may be able to change it without dropping the left rear silencer, but I could not get wrench clearance even with crow's feet. Fuel will siphon when the connections are loosened, so prepare for that surprise. Car started right up after changing the filter.
 
If the pump came apart, the filter gets plugged.
Once a year change EFI filters.
Period.
And, I always used to put once can of NAPA 6600 EFI cleaner in the tank on each service. Customers never, as in ever, had to have any "injector service".
 
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