Ok, yesterday when checking the pressure, it started to spray gas out of the fitting at 62 psi. today I verified the gage by setting air compressor to 40 psi and hooking to gage, and the gage was right on at 40 psi. so gage is verified. after replumbing with non leaking fittings and attaching the gage at the output(return line) of the left regulator, and turning on the key on, it buries the gage at over 100psi. when the fuel pump stops it drops to 80 psi. Then I took the old regulator on the bench and hooked the pressure gauge to it and pumped 80psi of air pressure into it, the gauge read 80 psi. should the reulator restrict the pressure to somthing lower if working properly? This is becoming a real brain teaser!!!!

 

You are confusing me with the gauge setup. You said it is deadheaded when connected? If that is the case you need to tee it into feed line. If the car was a good running vehicle it would run normal and you could read fuel pressure. If you are removing the fuel line and connecting to the gauge then your test method is your problem. Any chance you can upload or send a pic of how the gauge is installed?

You can do a search for a fuel gauge test port. Also you can use a nitrous adaptor. Then just buy a 1/8" MPT to Schrader adapter. Then you can use a fuel pressure gauge you buy at any corner parts store.

 

Update... Yesterday when I connected the gage and tested pressure it was at 62 psi, but spraying at a fitting. Today, I removed the gage and verified it was acurate by setting air compressor at 40psi and pumped air into gauge. Gage read 40 psi as well. So Gage is verified pretty accurate. I then connected the gage to the output (return line) of the left regulator. so basically measuring pressure after both regulators, and the pressure to the tank. When I turned the key on, (no start) it pinned the 100 psi gage! then after pump turned off it dropped to 78 psi. I then grabbed the old regulator off the bench and connected the pressure gage to the outlet, and pumped 80 psi of air into it, gage read 80 psi. Shouldn't regulator output lower pressure on output?

 

Greg, Your right I need to "T" the fitting. I will try this and retest. jumpering the coolant connector did nothy by the way.

 

my fuel temp sensor is busted to bits. im hoping that this was causing my 5gal/hour enriching issue.

 

That is a fuel temp switch not sensor. And it will not cause your super rich fueling.

 

Ok, I attached the gage per the link below. Here is what I know. If I attach the pressure gage as a dead head. it's over 100 PSI, if I attach it per the picture (flow thru) which is basically the pressure measured at the return line of the left regulator, the presuure is basically 0. gage jumps to about 20 psi when pump kicks on then drops. Does anyone have a link to a regulator like the stock ones that is adjustable? I have tried every combination. only thing that makes car start is disconnecting the fuel line to the left regulator. jumpering the fuel sensor, or the coolant sensor have no effect on this.

 

You are measuring the pressure in the return line. 0 psi is a normal reading. It is telling you the line is not blocked. Dead head pressure of over 100 psi is normal.

You still do not have the gauge connected properly. It needs to be before the left bank pressure regulator. Tee it into the feed line. This is line line with pressure.

 

The gauge may read as high as 60 psi with the engine off. The regulators are referenced to the manifold vacuum. When the engine is off, the regulator is at full pressure. When vacuum is applied the regulated pressure drops.

With the gauge T-ed into the supply line, you pressure at idle should drop to about 38-42 psi. You can simulate this with the engine off by putting 18-20" of vacuum on the regulator lines, but keep in mind that the pump will not be running unless the engine is running.

One thing that is curious - you say the engine runs when you disconnect one of the regulators. It's not likely, but is it possible that one of the regulators is installed backwards?

 

With no vacuum at the regulators you should have about 45 psi. With vacuum you should have about 36 psi.

 

Depends on the make of the regulator. The gennie Bosch items will peg at 45-50 at zero vacuum, but some of the aftermarket ones peg out at 60 or better.

 

Can the injectors go bad, meaning the pressure, even at 40psi would be to much? I'm just chasing my tail on this thing. I refuse to believe that the old regulators were bad, and the new replacments are bad as well. I'm still going to plumb the pressure gage before the left regulator. But I'm thinking it is going to be normal. reducing the rail pressure is the only thing that allows it to run.

 

just get an adjustable regulator.

 

ok, guys... Gage mounted correctly between regulators is 40 psi exactly. From what I'm reading that is normal for this year XJS. So with that said, can the injectors fail under this pressure? meaning is there some type of o-ring that could leak gas into the cylinder under this pressure, but not leak and preform fine under lower pressure? I really don't want to find a adjustable regulator. I want it stock, and orginal but working.

 

Jeff,

I agree with you. Putting in an adjustable regulator is masking the symptom. Now that we have determined your fuel pressure is correct we need to find why it is running so rich. Have you measured the resistance of the coolant temp sensor. It is located on the left bank and has a two wire connector similar to an injector connector. Unplug it and measure, then plug back in. Once you know the resistance under the hood check it at the ECU in the trunk. The numbers should be the same. Make sure the ECU is unplugged when checking. You need a good DVOM for this. If you don't have one head to Radio Shack or Home Depot and buy one.

Other things to check:

TPS voltage(done while connected and key on)
TPS voltage sweep(slowly turn throttle while watching meter, it should change steadily)
Put a noid light on each injector(should blink when cranking)


When buying your meter make sure it has alligator clip test leads too. You will need to get a good connection when performing some tests. Holding the test probes on with your fingers does not work. Also head to the sewing dept and buy some hat pins. These work great for back probing connectors. Try not to stab through the insulation on wires. This will prove a problem later in life. If you must put a little clear silicone over the hole. When I set my TPS I just pull the connector slightly apart so I can get my meter leads on the connectors.

Don't give up or just randomly try stuff. That is a good way to get frustrated fast. Stay focused, make a list of ideas and work down the list making notes. You will find the problem. Believe it or not these fuel injection systems are very simple.

One last question. Did the car run fine and then all of a sudden you had this problem?

 

Greg,

Thanks for your input. I assume when you say check resistance at the plug you mean setting gage to ohms which I did. 2.083 was the reading. if I switch to volts and turn key on it's 5.5 volts. as for the ECU, not sure where that is, and how to find same two leads for coolant temp. might need your expertise on that end. I will get a light for injectors and test that next, but it runs smooth with less fuel pressure so I assume they are all working.Also can you direct me as to where the TPS is?

 

When you measured the resistance of the coolant temp sensor did you have it disconnected? Was your reading 2.083 ohms or 2.083 k ohms?

The ECU is in the trunk, RH side on bracket. The coolant temp sensor wires are YB Pin 19 and orange/blue Pin 5. With the temp sensor plugged in and ECU connector disconnected measure resistance. It should be the same as you measured at the temp sensor.

The TPS is under the throttle capstan. if you down load Kirby's "Experience in a book" the procedure for setting and checking it is in there.

Do you not have the JDHT.com DVD for your car? if not buy the DVD for your car. All the service info is there.

 

i dont think i ever did find out whether the TPS reference wire would distort the resistance reading of the CTS when measured at the ECU. it may read more than 2k ohms, but it shouldnt read less.

 

I have an 85 Jaguar xjs, i maintained it through the winter, but now it doesn't start. If i crank it for about 45 secs to a minute it finally comes to life, but dies immediately. while i am cranking on it the odometer starts going up in miles. i have changed the spark plugs and the coil. any ideas out there?

 

Did this ever get resolved. My car died at a stop light the other day and had to get towed home. I have spark and noid light flashes. cranks and wont start. it sat for 3 days before I could investigate. It started and idled fine. Drove it out of garage and left it idling. It stalled and did the same crank no start with spark and noid flashing.

disconnect fuel supply line and cranked over dumping fuel into a bucket and it started. ran for quite some time off fuel in the rail with no supply. reconnected and it wouldn't start. disconnected fuel pump relay and car will start with fuel pump not running. plug in relay and it dies. It will only run with fuel pump NOT running. I quickly plug it in and unplug it again to keep it running. Return line NOT blocked. Sounds like identical problem as this thread.

Have not checked fuel pressure yet as I need to get to a store, but after reading this thread it doesn't sound like the fuel pressure reg. helped this fellow out.