wassup Jaggers.. Jaguar dre here.hope all is well. i have a problem with my 88 xj40 not starting. my battery that always read at 13 on battery level(which is decent) has went completely dead and my jag has shut off. before it shut down completely, I've been having to jump start a few times before driving but now it clicks until the battery drains out. i'm thinking it could be the alternator but I'm not sure. I would like to know is it any possible way i can make sure that's the problem before i start throwing parts and money at my jag. been sad lately riding pass my jag broke down in front of a building that's not my home. help me please...I'm not a mechanic so i want to make sure whoever is doing it knows what the problem is. thanks Jaguar dre

 

Hi Jaguar Dre,

Most auto parts stores can test your battery, starter and alternator for free if you can get your car started so you can drive it to an AutoZone, O'Reilly, Advance Auto, etc., they may be able to diagnose the cause of your issues at no cost.

On the other hand, a good independent mechanic may have more sophisticated test equipment and may be able to provide a more in-depth diagnosis, though he or she may rightfully expect to be paid for his or her time.

Cheers,

Don

 

Symptoms like you have can sometimes (quite a lot of the time, really) be caused by a bad connection at the battery terminals.

One or another of the terminal connectors can oxidize and cause a high resistance which will prevent the battery from getting its full charge top-up from the alternator.

Over time, the batttery will go dead flat and even if jumper cables are used, the resistance in the flat battery can prevernt the juice getting through.

If this is your problem, disconnect the battery teminals and wire brush or scrape the connectors until the lead is shiny again, then either fit a new battery or take your battery to be tested. A flat battery cannot be tested btw, so the battery must be fully charged before performing the tests. Unfortunately, a "smart charger" cannot successfully revive a dead flat battery back to 100% as the internal resistance will be such that the smart charger cannot overcome - with the result that any tests performed will signal a bad battery.

An old school charger with a big heavy transformer will however charge a flat battery back up to maximum and allow the battery to be properly tested.

Larry

 

Dead battery.

 

Welp I did get a chance to get the battery charged, tested and the battery was good but still no firing. I did more research and thought it to be the alternator but it seemed fine. I did more research and thought it to be the crankshaft sensor so i had it replaced with another sensor from my other jag. still no firing . Then i proceeded to research more and replaced the ignition coil. still no firing. I did manage to get a start-up once when i ran wire straight 2 wire crank from the posts to spark plug wires and realized gas was seeping through one of my fuel injectors from old seals so i covered the fuel injector pressing down on the engine and strangely, i got a crank until i started giving it gas and then it boggled down not firing again. The next day i went to the parts store and purchased the injector seals and replaced them all. plugged my battery back up, charged it, tried to jump start the car and still no firing. This jag is kicking my *** guys..!!

 

Hi Jaguar Dre,

Be very careful with any attempt to bypass wiring or apply battery power directly to any component in your Jaguar. It is very easy to fry the Engine Control Module (ECM), the ignition amplifier module, the Transmission Control Module (TCM), or some other sensitive component, which will only make your diagnostics that much more difficult and expensive. The XJ40 uses a ground-switched system in which voltage is present at all times in most circuits, and devices are activated by completing the circuit to ground/earth, so you really have to know what is what before you attempt to bypass or directly power any component.

You can download the wiring schematics for your car here:

Jaguar XJ40 Electrical Guide 1988

Have you checked the Vehicle Condition Monitor for any stored Diagnostic Trouble Codes? To do so, turn the key to position II (ON) but do not crank the engine. Press and release the VCM button on the trip computer to the right of the steering wheel and watch the small odometer window below the speedometer for a message. DTCs appear in the form of Fuel Fault or FF and a numeral, such as Fuel Fault 6 or FF7. Let us know if you get a message and we'll try to help.

When the engine is rotating/cranking, does the tachometer read about 200 rpm? If so, that usually means the Crankshaft Position Sensor (CPS) is providing a plausible signal.

A very common cause of crank-no start on Jaguars is low battery voltage sag while cranking. If the voltage sags much below 11 volts while cranking, the ECM will not trigger the ignition to fire. Do you have a voltmeter that can react quickly enough to voltage swings to measure the sag while cranking?

Have you confirmed that your fuel pump is running? The '88-'89 models had a known issue with wiring between the fuel pump relay and the pump.

Another issue the '88-'89 cars had was the Coolant Temperature Sensor (CTS) wiring shorting out on the hood, which is an easy thing to check. The CTS is on the thermostat housing at the front top of the engine. The CTS is the two-wire sensor and the single wire sensor drives the temperature gauge in the instrument cluster.

Is it possible you got some fuel that was contaminated with water? Or, if the drain in the rubber gaiter around the fuel filler neck is clogged, is it possible rain water has pooled around the filler neck and found its way into the tank?

Have you checked the condition of your distributor cap and rotor? Eroded terminals and rotor tip are a common cause of starting/running problems. While you have the cap off for inspection, pull the rotor off and inspect the distributor shaft for any side-to-side play and for any signs of arcing down the shaft, which is also fairly common.

Have you disconnected and cleaned the battery power connections at the starter, alternator and cleaned both ends of the engine ground strap? High resistance in these circuits due to corrosion or looseness are common causes of poor battery charging, poor starting and other electrical gremlins.

Please keep us informed.

Cheers,

Don

 

yes thanks guys i'm kinda embarrassed to say after changing my crankshaft sensor, my fuel injector seals and the ignition coil... i did all those things to find out it was only my spark plugs and rotor button that needed changing...smh...yes it only needed a tune up. lol. it is now up and running. i identified the problem after 4 different mechanics couldn't and did it all myself. thanks guys....even though i'm back running,now i have to figure out why my circuit failure light is on and why fuel still seems to leak out of one of my fuel injectors.

 

Great job! It's so satisfying, isn't it!