XJ40 ( XJ81 ) 1986 - 1994

XJ6 Fuel Issues - RESOLVED

 
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Old 04-29-2019, 09:36 PM
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Default XJ6 Fuel Issues - RESOLVED

Car died last week, no fuel pump. I pulled the tank and changed the pump. The car will start but there is a lot of hesitation at the throttle.

I am certain the pump is installed properly in the module. I have a lot of pressure up at the rail, I do not have a pressure tester yet so I have no exact figures.

I am unsure if I switched the lines for the module in the tank. What is the feed side of the rail? Is it at the pressure damper, or is this the return? At present I have pressure coming out of the dampner side... Help I am running out of ideas.

Thanks in advance.
 
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Old 05-01-2019, 02:30 PM
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It is the pressure side was a good time as any to check by changing the fuel filter. Car still runs rough though. Have any of you made or know the fittings to make a fuel pressure tester off the rail?
 
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Old 05-03-2019, 02:11 AM
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For anyone wanting to know itís a 14mm comp.

Still canít get it to run right....

Changed pump and have 40 lbs. As soon as pump is off all pressure dissapears. Check valve is prob bad in module but, I donít think this should cause a no start condition if I jump the pump relay...

Changed the plugs, and they all spark. If I spray quick start in manifold, it makes no difference. So do I even have a fuel issue?

Put at tdc and checked dist and even timing marks on cams and they looks ok...

please help. What am I missing?
 

Last edited by nunger1330; 05-03-2019 at 02:34 AM.
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  #4  
Old 05-03-2019, 02:18 AM
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Weird that the easy start doesn't fire up the motor if she' s sparking, eh?

As you only messed with one thing, (fuel pump/supply) most likely it is a fuel issue ..I think Don has a thread here about fitting a non-return valve up front in the engine compartment to compensate for a failing one in the module?

<edit> check valve fitment wasn't in engine compartment! see next posts</edit>

Did you change the fuel filter at the same time as you did the pump?

Larry
 

Last edited by Lawrence; 05-03-2019 at 09:53 AM. Reason: correction
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  #5  
Old 05-03-2019, 02:41 AM
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I put a wix filter in at the same time. I would
like to think itís fuel but it really is strange. I saw someone also put one in the tank off the module, just donít know if it worked. Thanks for your help, Iíll try to find that thread.
 
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Old 05-03-2019, 09:25 AM
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What is the vin of your car?

These cars are very different from early to late ..most of us on the forum add the vin to our signature so people can try to help with the correct info.

Here is a long thread on another forum about fuel check valve theory and the effects of a failing one - apparently car will run without one but will be hard to start ...anyway, read it for yourself before doing anything!

https://forums.jag-lovers.com/t/xj40...acement/285444

HTH

Larry
 

Last edited by Lawrence; 05-03-2019 at 09:37 AM.
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  #7  
Old 05-03-2019, 12:14 PM
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Interesting read. I am going to pull the tank/pump again this weekend and see if I can put one next to the module. I like the idea of the pump working as little as possible.

Vin is 694447.
 
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Old 05-03-2019, 08:57 PM
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Hi Neil,

The check valve works in conjunction with the Fuel Pressure Regulator (FPR), which is at the forward (return) end of the fuel rail. If either component loses its ability to hold pressure you may have difficult starting, but if the fuel pump is operating properly it can usually overcome a failed check valve and weak FPR and provide sufficient fuel flow for the engine to run properly.

One simple test of the FPR is to pull the vacuum hose off the fitting and look for signs of wet fuel - if you don't see any, crank the engine briefly and check again. Wet fuel indicates failure of the diaphragm, which not only means the FPR can't hold pressure but that raw unmetered fuel is being inhaled into the intake manifold via the vacuum hose, leading to rich running.

However, there are known issues with the fuel pump electrical supply that could be contributing to your issues. The fuel pump relay is near the right tail lamp behind the carpeted trim. If it is acting up your pump may run intermittently.

There is also a connection in the fuel pump wiring harness behind the battery that overheats and blackens with burned insulation. Also, on the top of the tank there are a diode and capacitor crimped across the two fuel pump wires and covered with heatshrink tubing. These help reduce RFI, but are known to fail and either cause a dead short, or a reduction in voltage to the pump motor.

I mention the above two items because I don't think they are included in the excellent diagnostic procedure by Bryan N at the Jag-Lovers forum, which may help you determine if your problem is electrical rather than the pump, check valve or FPR:

XJ40 - '93 / '94 Fuel Pump Circuit Test Procedure
Bryan N

With ignition OFF
Remove fuel pump relay (black base, right rear corner
trunk above BFM)
Do you get 12 volts at pin 30 (Brown/yellow) of the fuel
pump relay base from fuse C6 in right fuse box?
If yes, jump pin 30 (Brown/yellow) and pin 87 (Blue/red)
in fuel pump relay base - does the pump run continuously?
If pump does not run, fault is in the wiring / connector
between fuel pump relay and pump
If pump runs, suspect fuel pump relay is defective.
Replace / re-fit fuel pump relay
Remove oxy sensor heater relay (yellow base on firewall)
Do you get 12 volts at pin 30 (Brown/pink) of the oxy
sensor heater relay base from fuse C4 in right fuse box?
If yes, jump pin 30 (Brown/pink) and pin 87 (Blue/purple)
in oxy sensor heater relay base - does the pump run
continuously?
If pump runs, suspect oxy sensor heater relay is defective
Replace / refit oxy sensor heater relay
Remove EMS main relay (black base on firewall)
Do you get 12 volts at pin 30 (Brown/yellow) of the EMS
main relay base from fuse C1 in the left fuse box?
If yes, jump pin 30 (Brown/yellow) and pin 87
(White/brown) in EMS main relay base
Turn ignition ON
Do you hear the fuel pump give its half-second priming
burst? [You can repeat this many times and you (or an
assistant listening at the open filler neck) should hear the
half-second 'whirr' of the pump every time you switch the
ignition ON]
If yes, suspect the EMS main relay OR the EMS ECU is
defective (the latter, very unlikely but possible)
Turn ignition OFF
Replace / re-fit EMS main relay
Remove Ignition 'ON' relay (on a '94 it may be in a
white base on the firewall or it may be buried under the
dash behind the radio, which may make the following rather
difficult!)
Do you have battery voltage at pin 30(Brown) of the
Ignition 'ON' relay base?
If yes, temporarily jump pin 30 (Brown) and pin 87
(White/pink) in the Ignition 'ON' relay base
Do you hear the half-second priming burst from the pump
each time you jump those pins in the Ignition 'ON' relay base?
If yes, suspect the Ignition 'ON' relay is defective or
even fuse A5 in the left side fuse box - but if either is
defective, you will get NO dash lights when you turn on the
ignition, so you should have already noticed that.

Please let us know what you learn.

Cheers,

Don
 

Last edited by Don B; 05-03-2019 at 10:29 PM.
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  #9  
Old 05-04-2019, 12:16 PM
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Thanks don!

They all checked out. Have batt voltage at FPR, EMS, O2 and IGN. Fuel pump will run continuous with jumpers o2 and FPR, bursts with EMS. The wiring checks out to the pump. I re-wired the fuel pump plug a few months back and it was burnt and replaced with another plug. That was soldered and heat shrunk.

What is bugging me is why would it not run with quickstart in the manifold? The symptoms are the same. I replaced all plugs and they all sparked...air?

Neil
 
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Old 05-04-2019, 01:54 PM
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Originally Posted by nunger1330 View Post
What is bugging me is why would it not run with quickstart in the manifold? The symptoms are the same. I replaced all plugs and they all sparked...air?
Hi Neil,

I didn't ask before, but if your tachometer does not read approximately 200 rpm while cranking, suspect your Crankshaft Position Sensor.
 
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Old 05-04-2019, 02:06 PM
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It reads 100 rpm, is that too low?
 
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Old 05-04-2019, 02:38 PM
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Originally Posted by nunger1330 View Post
It reads 100 rpm, is that too low?
Reduces the odds that your CPS is the suspect, but could suggest your battery voltage is low. If the voltage while cranking falls much below 11V, the ECM will not trigger the ignition to fire. It might be worth checking your battery voltage and charging it to 12.6V if necessary, then measuring the voltage sag while cranking the engine.
 
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Old 05-04-2019, 09:00 PM
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Crank voltage was 10.81 and batt voltage was 12.64... Gas + spark should=fire. Today I checked ECU voltage and ground they were all good. And cleaned all the intake side MAF throttle body and things. Pressure when cranking is 42lbs. I really am stumped.

I am going to try to see if I can get a buddy with a pdu over here.
 
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Old 05-04-2019, 10:33 PM
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Originally Posted by nunger1330 View Post
Crank voltage was 10.81 and batt voltage was 12.64... Gas + spark should=fire. Today I checked ECU voltage and ground they were all good. And cleaned all the intake side MAF throttle body and things. Pressure when cranking is 42lbs. I really am stumped.

I am going to try to see if I can get a buddy with a pdu over here.
Hi Neil,

That cranking voltage may be too low. Have you confirmed that you have strong spark?

The OBDI system has a built-in means of displaying Diagnostic Trouble Codes via the Vehicle Condition Monitor. With the key in position II (ON) but the engine not cranking, press and release the VCM button on the trip computer to the right of the steering wheel. Watch the odometer window below the speedometer for a message to appear. DTCs appear in the form of Fuel Fail or FF plus a two-digit number. Only one code is displayed at a time. If you find one, write it down exactly as it appears, then pull Fuse 9 (second from left) in the center console fuse box, and watch for the speedomter and tachometer needles to drop below zero, indicating the first DTC has been cleared. Replace the fuse and repeat the process of checking the VCM for any additional codes.

Cheers,

Don
 
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Old 05-05-2019, 12:02 AM
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Try a spare rotor and swap out the oxygen sensor heater relay with the one next to it on the firewall.

Unplug and replug the MAF and Coolant temp sensors too.

Then click your heels three times and repeat, start you b--tard!

Larry
 

Last edited by Lawrence; 05-05-2019 at 12:07 AM.
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Old 05-05-2019, 01:13 PM
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I had no check engine codes. What do mean by strong spark? If I disconnect all the plugs and ground them out they all spark. I’m not sure if that’s what you mean. I’ll try to get another rotor Monday.

I tried cranking swapping relays and pulling MAF And CTS. Still wouldn't fire, clicked heels and everything, lol.

I really appreciate the suggestions.

Neil
 
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Old 05-05-2019, 02:23 PM
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Originally Posted by nunger1330 View Post
What do mean by strong spark? If I disconnect all the plugs and ground them out they all spark. Iím not sure if thatís what you mean.
Strong sparks are usually white to blue, weak sparks are yellow to red.

You can also inspect the inside of the distributor cap for excessive wear of the terminals, signs of arcing, and to confirm the graphite button in the center king lead terminal is not stuck up in the cap.
 
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Old 05-06-2019, 12:24 AM
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Forgot to mention that another thing to check while you have the distributor cap off is for signs of arcing from the rotor down the distributor shaft, which has been known to occur. Also check the distributor shaft itself for any excessive play.
 
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Old 05-06-2019, 05:20 PM
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Had to pay attention to the honey-do list after a week today. I can get back at it tomorrow. I really appreciate all the jag therapy.
 
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Old 05-07-2019, 06:19 PM
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Don you are a wizard! She is running beautifully again. There was corrosion under the distributor and sure enough it was arcing down the shaft. Didnít think to take a pic before I took off the corrosion. Thank you all so much!
 
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