I am trying to find out why my 1987 XJ40 won't run. The initial problem was that the car wouldn't start. I took out the spark plugs and they looked pretty eroded. I regapped the bad plugs and put them back in and the car fired right up. I let it run for about 10 minutes then the rpms started dropping and the car stalled out. I couldn't get it restarted. I changed the plugs, but it wouldn't start. It seems to be too rich to start. I checked for spark to all plugs, it was there. I checked the fuel rail by pulling it and watching all the injectors fire. I was able to get it started at one point, but anytime I stepped on the gas pedal it wanted to die out. Very strong fuel smell. I've checked a lot of the sensors involved with ignition and starting, all seem to check out fine. At this point in time the engine won't even sputter when trying to start it. I pulled the coil and the ignition module and I found something strange. The ignition module is a GM part, made in mexico. I don't know where it came from because I tried looking up the numbers on it and it doesn't exist anywhere. It has the same connector as the original and looks much like it, but it is GM not lucas. The part number is DAC10923 for the oem. The number on the GM is 466 669 7A06. I'm not sure what the problem could be. I was thinking of changing the module and the coil, the distributor cap and rotor. I don't think the plug wires are bad because they are completely clean and free of rust. Any help is appreciated. I was hoping for a cheap replacement for the ignition module, the OEM is anywhere from $100 to $300 dollars.

 

The crank position sensor (crank angle sensor) is a known fault that will keep the engine from starting/running.

That might be an issue??

bob

 

Hi nathansallade,

I'm sorry to hear your XJ40 won't start. There are many possible reasons.

Did this condition come on suddenly or has the car been struggling to start prior to not starting at all? If the car has been running fine, then the ignition module must have been functioning so I wouldn't worry that it is a GM part. Lots of aftermarket parts vendors offer parts that fit Jaguars.

Bob mentioned the crankshaft position sensor (CPS). If the tachometer shows 0 rpm while cranking the engine, the CPS has probably failed. If the tachometer shows about 200 rpm while cranking, the CPS may be functioning properly.

There are numerous other possible causes, and often a no-start is the result of more than one component malfunctioning. You mentioned that the spark plugs were badly eroded, which leads me to ask, how long has it been since the last good tuneup? Have you checked the air filter and replaced the fuel filter?

The first step I would recommend is to check the Vehicle Condition Monitor (VCM) for any stored Diagnostic Fault Codes (DTCs). To check, turn the key to Position II (ON) but do not crank the engine. Depress and release the VCM button on the trip computer on the dash panel to the right of the steering wheel, and watch the small display window below the speedometer for any messages that may appear. Fault codes are displayed in the form of a single digit number, possibly preceded by the words "Fuel Fault" or the letters "FF," as in FF8. If the code is followed by an asterisk, more than one code is stored. Record any codes you find and report them here and we will try to help.

Since you mention the strong fuel smell, the second step I would recommend is that you carefully pull the vacuum hose off of the Fuel Pressure Regulator (FPR), which is a metal cylindrical part at the front of the fuel rail. Crank the engine, then check the vacuum hose fitting on the FPR for any signs of wet fuel, which indicates failure of the diaphragm. This allows raw unmetered fuel to be inhaled into the intake manifold, leading to rich running that the ECM cannot correct.

Please keep us informed.

Cheers,

Don

 

The spark plugs were all working. Wouldn't that indicate that the cps is functioning? Mine is covered in gunk. I could try removing it to clean it. It is just hard to get to because of the hydraulic pump being there. I wish it was converted to a vacuum booster. The only other thing I noticed is that the pins in the distributor cap looked eroded a bit. I replaced the cap about 3 years ago. I'm not sure how long they last. I have to buy a new battery. The other one was old and tired.

 

Ok so you've got spark, so that suggests the GM part is working. Changing out the cap and rotor might be good policy but if she's sparking strongly on time then the other two other things you need are air and gas.

If the air is getting through via the intake and not from somewhere else (vacuum leak) all that's left is gas.

You either don't have enough, too much or the gas is no good, right?

The temperature sensor has a fairly important role in determining the mixture especially at cold start and these things fail from time to time. Not a bad idea to get a new one maybe?

BTW - did you do that Fuel Pressure Regulator test Don suggested?

all the best

Larry

 

I got a battery in it. I also cleaned the CPS, changed the distributor cap and rotor, and the coil, I broke a stud on the old one. I try to start it and it sounds like a completely dry engine turning. There's no sputter or anything. I decided to check the injectors and I have no power going to them with the ignition on. I must have messed something up with all my testing and searching. Where do the injectors get power from? Is it the main relay? Where is the main relay? Not a single relay is labeled in this car and there are about 100 relays. I know that the ECU provides a ground to fire the injectors. Could I use a relay from something like the antenna motor to replace the main relay?

 

Yes, on your '87 XJ40 the fuel injectors receive battery power via the Main Relay, which is on the relay panel below the glove box behind the knee bolster (it comes off with a few screws and a few plastic fir tree press fasteners). The Main Relay should be mounted in a purple base, and the wires that connect to it should be Black, Brown, White with Brown tracer line and White with Pink tracer line. You can definitely try swapping another nearby relay for the Main Relay if it has the same pinout and current rating.

You can download the 1988 XJ Electrical Guide at the link below, courtesy of our forum member Gus. The fuel injector circuit is shown on the Engine Management schematic, and the page before each schematic identifies each component and gives its location.

http://www.jagrepair.com/images/Elec...Electrical.pdf

You can download the Haynes workshop manual at this link. It has diagrams showing the relay locations for the various model years. Yours should be similar to the '88-'89 cars.

https://www.mediafire.com/?hx8bttsy4kxxr

Cheers,

Don

 

The main relay and fuel pump relay both work fine. I kept playing around with the connectors on the ECM and I got 12 volts back to the injectors, but the car still won't start. I guess the new weekend project is to verify spark to all the plugs and fuel from the pump during cranking. If those are fine, what would be the next step for verifying proper airflow? I don't the air filter is that clogged.

 

Hi Nathan,

Did you confirm that the sockets for the main relay and fuel pump relay are both clean of any corrosion or contamination?

The fact that you were able to restore 12V to the injectors by moving the connectors on the ECM would seem to indicate a problem with corrosion on the connector pins or possibly water ingress into the ECM. At the very least it would be worth flushing the electrical connectors with zero-residue electrical contact cleaner spray and checking carefully for any corrosion or signs of water having entered the ECM.

For diagnostic purposes you can always remove the air filter temporarily.

The ECM judges air flow via the Mass Air Flow sensor (MAF), so it would be worth cleaning the electrical connector for the MAF with the same contact cleaner spray.

Disconnect the battery negative cable before disconnecting any other electrical connectors, especially at the ECM. Many relays also have 12V present even when the key is out of the ignition switch, so disconnecting the battery will help prevent a short or a shock.

Cheers,

Don