So picked up an XJ6 as a road car(fantastic on the hwy !!!!!) and the wife and I have been wearing the new off around town and have just experienced my first Jag moment lol. car running fine shut off, came back to car and turns over ..... no start. Looks to be ign not fuel, Not a novice but new to the Jag so please let me know what I am going to be dealing with ie. does have cps or is pickup in dizzy, use ign amplifier module? any known typical gremlins ie. relays,ecm(if ele ign with cps) crapping the bed, ign switch failures, wiring/connector degradation ?
Have gathered typical tools but if will need anything atypical to test in a timely manner pls suggest.....(ex.8 foot jumper wires to get power to coil, etc.)
Thinking out loud here ......are there typical eliminations in the diagnostic process like with many manu's if rpms register while cranking cps/ hall effect good....etc?


New to forum and thanks for patience !!!!!!!
Overview of ign system, component location, and any suggestions would be appreciated !!!

Sincerely,

Fred

 

Hi Fred,

Welcome to the forum! Congratulations on your nice Jag, but sorry you've experienced some trouble with it already. There are a few very common causes of a no start on the XJ40:

1) There is a switch in the J-gate gear selector mechanism that tells the Engine Control Module (ECM) that the gearbox is in Park or Neutral and is safe to be started. Over time the switch wears and needs to be readjusted (or sometimes replaced). Try starting the car with the gear lever in the Neutral position, or jiggle it around in the Park position to be sure it is fully seated.

2) The Crankshaft Position Sensor (CPS) you mentioned is a common failure point, and since the ECM depends on the CPS signal to determine ignition timing, the engine will not start if the ECM doesn't receive a correct CPS signal. The typical clue is that while cranking the starter the tachometer shows 0 rpm (the rpm should be 200-250rpm while cranking). Most chain auto parts stores such as O'Reilly can get a replacement CPS within a day, or they are available from all the Jag parts specialists like SNG Barratt, Coventry West, Welsh Enterprises and others. The CPS mounts on the front end of the engine and mounts with one 8mm screw.

3) You don't mention how long you were out of the car before restarting it, but another common issue is vapor lock due to a failing fuel pressure regulator (FPR), which is supposed to maintain +/- 40 psi in the fuel rail. When it fails, shutting off the engine/fuel pump creates a sudden loss of pressure that allows the fuel in the rail to boil and vaporize. A contributing issue is that the two check valves in the system, one on each side of the fuel pump, tend to also fail over time, so fuel pressure can escape back into the tank via the fuel pump canister. To overcome this problem, you can try turning the key to position II (ON) for a few seconds (without cranking the engine), then off, and repeat several times. Each time you turn the key ON the fuel pump will run for about 2 seconds in a "priming burst" to re-pressurize the fuel system before the engine is started. Repeating this several times can help overcome the compressible fuel vapor in the rail to fill the fuel rail once again. After turning the key ON several times for about 3 seconds each, try cranking the engine to see if it starts.

4) The XJ40 is very sensitive to battery condition and voltage, and if the voltage drops to between 10V-11V while cranking, the ECM will not trigger the ignition to start the car. Problems with the charging system, such as corroded battery power connections and ground points throughout the car, can lead to poor charging and starting and shortened battery life. If you suspect your battery is not charging well (or if you measure the voltage while cranking and it falls much below 12V), let me know and I'll send you photos of all the battery power connections and grounds to clean in order to improve the situation.

5) I hate to ask obvious questions, but we assume the car has at least a few gallons of fuel in the tank?

6) The fuel pump circuit is known for various problems in addition to failure of the in-tank pump itself (not as difficult or expensive to replace as you may fear). Below is a link to a procedure for testing the fuel pump circuit that has worked for me every time I've needed it (courtesy of Bryan N at the Jag-Lovers XJ40 forum):

JagFORUM Logon

Those are the things I can think of off the top of my head. Hopefully others will have additional things to suggest.

Let us know how it goes and I hope the issue is easy to diagnose.

Cheers,

Don

 

Thanks again Don for the response and sharing your knowledge, Is it safe to assume that the XJ40 ign system gets signal from cps and the ecu triggers injectors/coil? Is this system one that Power is constant and ecu output is ground to "fire" or Ground constant and output is Power to "fire" ?

 

In going thru the XJ Ebooks I just found
2)the CPS located at 10 oclock on crank pulley.

In the overview for the ign system verified the EMS ecu controls injectors and coil via amplifier but did not state whether system supplies Power or Ground to fire....my guess is Ground but confirmation would be much appreciated !!!!

Looks like a pretty typical management system compared to my Saab's - Benz. Do the ECU's oooppps have to start using Jag language so ..... Does the EMS ecu'scrap the bed very often? How about the ignition amplifier's ?

Maybe the most important question for a New XJ40 Owner......
What components should I put on the "Need to acquire Spares List" and keep in the trunk with the picknick basket and bottle of vino ?

 

Hi Fred,

'

In addition to the XJ40 eBook at the Jag-Lovers forum, go to the download area of this forum under HOW TO LINKS (the permanent thread just above your thread) and scroll down to downloads to see what's available here.

Download the Haynes XJ40 manual here:

http://www.mediafire.com/download/xt...8Haynes%29.pdf

And download the AJ6 4.0L Engine Management System OBDI Diagnostic Guide here:

http://www.mediafire.com/download/36...Management.pdf

Download anything else of interest in the Download section.

I also recommend two DVDs from the Jaguar Daimler Heritage Trust (jdht.com). Click the SHOP tab, then find and click Technical Publications in the left menu. They've redone their website and I couldn't find the JHM1153 4.0L DVD but the Supplementary Info DVD is there with a new SKU: 61130. Here are the old item numbers of the two DVDs I recommend:

XJ40 4.0L 1990-94 Service Manuals, Etc. (approximate title, old item number JHM1153 (I think - my DVD was produced before they applied product numbers)
XJ40 (XJ6 & XJ12) Supplementary Model & Service Information, old item number JHM1130

(It's possible that some or all of the info on these DVDs is now available from the download area here - The DVDs contain the official Jaguar Workshop Manuals, Electrical Manuals, etc.)


Actually the coil and ignition amplifier are always powered and the distributor serves as the rotary switch to connect the coil/amp power to each plug in firing order. The plugs are grounded through the engine block and ground strap, one end of which attaches to a starter mounting screw and the other to the body at the inner left fender. Since I mentioned battery power and grounds in my previous post, I'll include links here to photos of our '93, which will be very similar to your '94:

Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page


Jaguar uses both terms, ECU and ECM (Engine Control Module) in its publications, but as Jags have gained more and more ECUs (Electronic Control Units) such as the ABS ECU, Driver Seat Memory ECU, Climate Control ECU (CCU), Air Suspension ECU (ASM), Transmission ECU or Control Module (TCM), etc., Jaguar has increasingly used the term Engine Control Module (ECM) to describe the device that controls fueling and ignition, so that's the convention I use. The photos at the link below show most of the control modules (the ABS ECU is in the trunk near the fuel filler neck but most of the other brains are behind the passenger side knee bolster):

Welcome to Jag-lovers - Members Photo Viewing Page

The XJ40 Lucas ECMs are generally robust. Corrosion of connector pins is not unknown (it's even more common on the CPU), but suspicions of ECM corrosion seem to be a lot more common than confirmed cases. Ignition amplifiers are also generally robust but the electrical harness to the amplifier can harden and the insulation can crack. I replaced our ignition amplifier preemptively at 190,000 miles because I found a NOS replacement for $20.00, but otherwise the original one was working fine so I kept it as a spare. Coils, on the other hand, do tend to fail with age and mileage. The plastic case becomes brittle and cracks (on ours it cracked around the wire terminals). Fortunately replacements are commonly available and inexpensive (I think our local O'Reilly had more than one option in stock).


The photo album below shows the kit I've assembled over the years, which I keep in the trunk along with a basic tool kit, jumper cables, a couple of quarts of oil, a quart of Dex/Merc, and a roll of duct tape. Some of the items are not really essential, such as the brake accumulator and pressure switch, but if you need them it's nice to have them since they're not as readily available as some parts. Essential items include a known working CPS, distributor rotor and cap, extra relays, fuses and bulbs, and either a short piece of insulated wire or a resistor for jumping relay sockets:

Welcome to Jag-lovers - Members Photo Viewing Page


If you get bored and want to see the innards of a car similar to yours, I've posted a few photos of our '93 here (I've also begun posting photos of our '04 X350, so don't let those confuse you):

www.tinyurl.com/DonBPhotos

P.S. I just noticed your revised signature and that your '94 XJ6 has only 77K miles - it's barely broken in! With a few exceptions, I think it's more likely that you're going to be addressing age-related issues more than wear-related issues, at least for the next 25K or so.

Cheers,

Don

 

Thanks for the additional info Don,
I will be get it diagnosed this weekend and report back as to which system and component or wiring to component was the culprit.

 

Crankshaft Position Sensor was the culprit !
Thanks again for the input and links !!!

 

Very common! Thanks for reporting back to add to our collective knowledge for diagnosing these sorts of symptoms.

Cheers,

Don