Hello Rob. You are literally surrounded by fellow members on your doorstep and some brilliant independent Jaguar techs also. I have no doubt you will soon hear from several real XJ heroes here - Don, Grant, Doug etc - Don, in particular has laid out some excellent write-ups that touch on your issues, which I suspect, may point to a significant (as yet undiscovered) induction air leak or injectors issue. Have you checked the fuel rail pressure? If so, what is it?

However, I also suggest that beyond your immediate technical issues, you skip over to the Queensland Regional Forum to introduce yourself and learn of the many local resources. Even for a "south of the border" interloper like me, your fellow SEQ members are a great lot - very friendly folk whose generous company I have enjoyed on several occasions. Together, we have had many a great get-together and shared plenty of all things Jaguar.

Cheers,

Ken

 

Yes well quite recently another member had the same thing happen to his car, he too was in Australia and replaced everything, just like you!

Eventually the issue got solved and IIRC it turned out to be the wrong model year or aftermarket CPS or fitment/wiring ..you can read the saga here ....

https://www.jaguarforums.com/forum/x...elp-me-192451/

Larry

 

This is very similar to the issue I am having. I replaced the fuel pump but am only getting 20 psi at the rail. I also found a corroded connection at the maf and replaced the connector and the maf with no effect. I believe I have a bad pump. While it was NIB it had been sitting for almost 5 years.

How is the actual fuel pressure?

 

I read the first post and thought it was you Joe. Sorry. I have to think there is something clogging your lines- either or both. Maybe in swapping parts out something got loose into the lines and is acting as a flapper valve? This has never happened to me (knock on wood) and after my own problems this year I Even More hope it doesn’t. Good luck. I hope someone comes up with a better answer for you than this.

 

Hi Rob,

Welcome to the Jaguar Forums! It's great to have you with us.

I'm sorry to hear that your Jag is unhappy. Before you install any more new parts, there are a lot of diagnostic steps you could take that might help identify the problem or problems.

For example, have you checked the Vehicle Condition Monitor (VCM) for any stored Diagnostic Trouble Codes (DTCs)? To do so, turn the key to position II (Ignition ON), but do not start the engine. Press and release the VCM button on the trip computer to the right of the steering wheel. Watch for a message to appear in the small display window below the speedometer where the odometer/mileometer usually appears.

On the '93-'94 models, DTCs appear in the form of "Fuel Fault" or "FF" and a two-digit number, such as "Fuel Fault 19" or "FF34." If you see one DTC displayed, write it down exactly as it appears. To see if there are any additional codes stored, open the fuse box in the center console and identify Fuse 9 for the Instrument Pack. On your RHD vehicle, the fuse you are looking for will be the ninth fuse from your driver's seat, or the second fuse from the left. With the key still in Position II, pull the fuse and watch the speedometer and tachometer needles. When the needles drop a little below zero, replace the fuse and turn the key to OFF. You have just cleared the top level DTC. You can now turn the key to position II and press the VCM button again to check for another flagged DTC. If one appears, write it down and repeat this process until no DTCs appear. Post any DTCs you find here and we'll help.

There are numerous possibilities that could cause your symptoms. Here are some wild guesses off the top of my head:

If the fuel pump is not receiving full electrical power due to a problem in its electrical circuit, it may not be able to supply sufficient pressure for engine speeds above idle. This could be due to corroded or loose electrical connectors and/or corrosion on the ground point referenced by the fuel pump (in the rear right of the trunk below the Bulb Failure Module (BFM)).

Intermittent operation of the fuel pump relay or oxygen sensor heater relay (which is in the fuel pump circuit) could lead to insufficient fuel pressure. You could test this by temporarily swapping in different relays from the row on the firewall/bulkhead in the engine compartment.

A combination of failure of the Fuel Pressure Regulator (FPR) and fuel check valve could lead to insufficient pressure in the rail at rpms above idle.

The fuel pressure at the rail should be 34-38 psi with the vacuum hose to the FPR connected, and 42-45 psi with the vacuum hose disconnected. Pressure should not leak down more than 10 psi within one minute after shutdown.

A clogged catalytic converter could inhibit engine speed.

Another possibility is a problem with an individual sensor signal or a combination of problems, especially with the most critical sensors such as the CPS, MAF, O2S and Throttle Position Sensor (TPS). These can all be tested - see the diagnostic section of the EMS manual I linked to earlier. The CPS can be checked with an ohmmeter for approximately 1.35 kilohms static resistance. An oscilloscope is necessary to see the CPS signal.

Check the resistance of both tracks of the TPS across the full rotational range of the throttle butterfly valve. It seems remotely possible a dead spot in the ECM track could cause the ECM to believe the throttle is closed at engine speeds above 1100 rpm, prompting the ECM to engage overrun fuel cutoff.

Air leaks are common, such as cracks in the intake plumbing between the MAF and the intake manifold gasket as well as the crankcase breathing hoses. Check the underside of the accordioned hose between the intake elbow and throttle body. If the hose clamp is overtightened, the intake elbow can partially collapse, creating a significant air leak. Other issues that create the equivalent of an air leak are a stuck-open EGR valve, carbon canister purge valve or vacuum control valve (Rochester valve), or secondary air injection solenoid.

When the mechanic changed the distributor cap and rotor, did he check for any play in the distributor shaft? We assume the firing order of the spark plug leads has been confirmed correct?

When the ignition amplifier was replaced under the coil, was any cracking or other damage noted on the coil body? Has the mechanic confirmed the plugs are all giving a good hot spark?

I've got to run but hopefully checks like these will help track down the problem(s). Again, the diagnostic section of the EMS manual is full of helpful information.

Cheers,

Don

 

Just to add to Don B’s excellent comment above, check that the distributor is timed correctly, there have been instances where once the engine is running the advance function moves the rotor out of phase to the contacts in the dizzy cap.

 

Robman25,

That's a good point, assuming the distributor may have been disturbed prior to the onset of symptoms. Note that on the XJ40 ignition timing is controlled strictly by the ECM; there is no vacuum advance. The distributor must be installed with the the rotor aligned with the distributor cap terminal for the No. 1 spark plug lead with the No. 1 cylinder at TDC on its compression stroke, but once done, the distributor can be rotated within reason with no effect on timing. The Workshop Manual and Haynes spell out the procedure. Here's what the EMS manual says about the distributor:




Rob (the Original Poster or OP):

Thinking some more about your situation, it would help us to know what led up to the onset of the symptoms? Did they appear suddenly, or gradually worsen? Was any work done just prior to the onset of the symptoms?

For example, could you have received some contaminated fuel at a fill up? If so, the new fuel filter may have been clogged as soon as the engine was restarted after the service.

Which reminds, me, the air filter is conspicuously absent from the list of items that have been replaced. Difficult-to-diagnose problems like this are sometimes the result of multiple components or systems operating out of spec, so if the air filter wasn't replaced and appears the least bit suspect it would be smart to replace it just to rule it out.

System operating voltage is another thing to consider, especially the voltage seen by the ECM. The ECM adjusts fuel injector pulse duration and ignition timing in response to variations in battery voltage, so if the battery is weak, or if the voltage sensed by the ECM is low or high, the ECM may be applying incorrect fueling and timing maps. The ECM might sense low voltage due to corrosion on ECM connector terminals or B+ power connections between the battery and ECM, problems with one or more fuse boxes (well-known), or corrosion on the grounds referenced by the ECM (also well known). The ECM might sense high voltage if the voltage regulator in the alternator has failed, for example. Combine incorrect system voltage with, for example, a failed CTS as Larry mentioned, and fueling could be way off.

Which reminds me, does the engine behave differently when it is first started cold compared to when it is warmed up? If so, that could indicate problems with the CTS, the O2S, the Idle Air Control Valve (IACV) and probably some other things.

Another thought: it may be possible that one of the timing chains has skipped one or more sprocket teeth due to a worn tensioner or dampers, though I don't recall hearing of this on the AJ6, but it's probably possible.

I don't think the '93-'94 models were as vulnerable to collapsed fuel tanks as were earlier models, but it might be worth searching the symptoms of a collapsed fuel tank just to see if they are similar to yours.

Cheers,

Don

 

Don:

Many thanks for your advice in this thread. I checked the VCM as you advised.

The Code was PRO. What does that mean and is it OK?

Rob

 

Robert Pro is actually PAD it is an indication that one or both brake pad sensors are contacting the rotor warning that you need to change the pads out.

 

Don, I agree that there is no Vacuum on the distributor, but disagree that the dizzy can be turned without effecting the engine. As you state the ECU controls the firing of the spark, my point was that at idle the spark is 'close enough' that it can jump to the correct terminal in the cap, once the ECU advances the timing the orientation can become too far out of register that the engine starts to miss.

 

Hi Rob,

I think I understand your point now: If the distributor was rotated so that the rotor tip was "just close enough" to the cylinder No. 1 terminal in the distributor cap so that the engine ran correctly at idle, then it is possible that when the ECM advanced the timing, the spark could jump to the terminal for the previous cylinder in the firing order, or in this case cylinder No. 4. This would not change absolute ignition timing, per se, but it would change the firing order, so the timing as seen by each cylinder would be wrong and the engine would misfire on all six cylinders. That's definitely a theory worth pursuing!

Cheers,

Don

 

Hi Guys:
I have checked most of the suggestions included above but still have not solved the reported problem of: Not being able to accelerate under load, even though the engine will idle smoothly.
So as a sign of desperation, I am taking it to a Jag Specialist on the Northside of Brisbane, QLD, Australia. Hopefully with their diagnostic skills and technologies they will be able to sort it all our for me. It is booked in for this coming Wednesday, 29/11/2017.
I'll keep you informed of developments.
Many Thanks for all your Forum Posts included above. They, and you all, are really appreciated.
Kindest regards
Rob

 

After the issues I have been having and I think I figured mine being a lack of fuel pressure.

I understand that the fuel pump was replaced but were you ever able to get a reading? With a ton of time spent searching and now finally understanding the problem you may have a fuel pressure issue. There are 3 O rings in the fuel pump module assembly and none of them are available and the assembly itself is no longer available.

Just as a suggestion have the dealer put a gauge on it even after you tell the pump is new.

I am going to modify my assembly to just pull fuel from the bottom of the tank. Though without a cup Ill run the risk of starvation on a low tank Ill have to live with it I think and just keep it above 1/4.

Link to my thread https://www.jaguarforums.com/forum/x...riving-190784/

Ill try and post pictures of my repair.

 

Correct Don, much better description than mine