Issue with the erratic engine operation of my xj40 4.0 1989

Starts ok most times, but occasionally with a slight miss. Slight sluggish with power but will build up speed and cruise at 100ks per hr.

After about 20 minutes of cruising the engine becomes erratic with sudden loss of power and in a few seconds will build up power.

Sometimes the engine will start to rev up and down. Then comes good and we are on our way again.

Notes and checks I have completed.

• New Bosch injectors installed
• New high tension leads installed
• Compression check all good as per manual recommendation
• Low Vacuum around 12 to 13 in.Hg. (Unable to detect leaks but have tried using small doses of spray butane) open to ideas
• Changed intake manifold gasket making sure all surfaces were clean and ran a straight edge on the head and manifold.
• Exhaust appears to be even flow.

As I am a new member the chances are that this subject may have been discussed with others having simular problems. Still learning to navigate my way through the various forums.

Regards

Garry XJ40

 

Hi Garry, and welcome to the forum. I'm a new member myself, but a longtime Jaguar XJ40 owner. There are many possible contributors to your symptoms, but the low vacuum should be dealt with first since you already know it's an issue, and unmetered air is a common cause of rough idle and running. Inspect the intake air plumbing for cracks or poorly-sealed connections. Some common places for leaks are:

If the hose clamps are overtightened at the large elbow, the plastic can bend inward and create a loss of seal with the hose.

The accordioned hose that fits between the elbow and the throttle body (TB) can be difficult to fit to the underside of the TB, so remove the hose clamp and ensure the hose is fully seated all the way round the TB and that there are no cracks in the hose.

There are plenty of vacuum hoses that can crack or harden and lose their seal, the EGR valves and carbon canister purge valves sometimes get stuck in their open positions, the breather hoses are known to crack, the gasket around the Idle Air Control Valve is known to fail.... Be diligent and you'll find the problem.

You don't mention the quality of your spark, but the ignition coils and amplifiers are known to fail with age (you also don't mention a new distributor cap and rotor, which should be replaced as a matter of course).

Fuel delivery is another possible problem. Fuel pump relays can develop intermittent faults, and the fuel pressure regulators and fuel pumps are known to fail eventually.

The Engine Control Module uses the Coolant Temperature Sensor, MAFS and O2 Sensor inputs to determine the fuel mixture, so if there is evidence of a lean or rich mixture on your spark plugs or inside your tail pipes, those components should be inspected.

If you don't have the Haynes manual and the Jaguar Daimler Heritage Trust DVDs for the XJ40 (JHM1172 and JHM1130), I highly recommend you acquire those as soon as possible.

You'll find lots of information at this forum. Keep us informed and we'll try to help you sort everything out.

Cheers,

Don

 

Garry,

I've moved your question from the New Member Area - Intro a MUST to XJ40 forum. This is the place to post technical questions about your model.

Graham

 

Garry,

I noted that in another area of this forum you had received a post advising you to clean the exterior of the Throttle Position Sensor or Throttle Potentiometer (TPS). The TPS is definitely a common source of performance issues on the XJ40, due primarily to oil contamination of the TPS itself or its electrical connector. Your symptoms don't remind me of common TPS issues, but it is certainly worth servicing the TPS as part of your maintenance.

The TPS is mounted on the underside of the Throttle Body, on the same vertical shaft as the Throttle Butterfly Valve. (To avoid confusion, note that the Mass Air Flow Sensor mentioned in the referenced post is in the air intake plumbing near the Air Cleaner/Air Filter housing, some distance away from the throttle body and TPS).

Since all the functional parts of the TPS are either inside the red plastic housing, covered with wire insulation, or inside the plastic electrical connector, it is unlikely that cleaning the exterior of these items will do much more than improve their appearance. To do any good you have to get inside.

The first thing worth doing is to disconnect the electrical connector and flush both halves thoroughly with zero-residue electrical contact cleaner spray. Oil and other grunge tend to contaminate the connector. The most common problem this has caused on our '93 is the dreaded "Limp Home Mode," which locks the transmission in 3rd gear.

The second, more involved service you can perform on the TPS is to carefully drill two small drain holes in two corners of the plastic housing and flushing the housing with electrical contact cleaner. Take care to place the holes close to the edges of the housing since the resistance traces of the potentiometer occupy much of the central area of the housing. It is also possible to remove the cover from the housing with some careful prying/prising. There is no need to disconnect the TPS from the throttle body, and it is undesirable to do so, unless you determine that its voltage is out of range. But in order to drill and flush the drain holes without risk of damaging the TPS, the throttle body must be removed from the intake manifold.

The links below show photos of this work. Check my other photo albums for air intake plumbing, throttle body, and lots of other service operations.

Cheers,

Don

Welcome to Jag-lovers - Members Photo Viewing Page

 

Gary,

I concur with Don's reference to inspecting/changing the oxygen sensor. You and I have the same model year, and after re-reading your symptom description, I would suspect the O2 sensor.

About 10 years ago I was frequently traveling between Mobile and Panama City Beach, FL and ran into problems of cruising along and having sudden power loss or it would cut and surge erratically, eventually going into limp mode or altogether dying. Happened several times, the car would sit and cool down, start okay, then after warm-up, the behavior would act up again.

For whatever reason my mechanic at the time changed out the O2 sensor and all was well, and has been ever since. Though I haven't seen specific reference to there being a batch of bad O2 sensors (none I recall), this seems to be common place for MY 88-90.

If your not inclined to purchase the part, the Haynes does describe a test procedure where both Ohms and voltage output is measured to ensure they are within specs. I know there is an online Haynes manual in the TSB section, scroll down and find the link titled "Download Area", then find the link to the XJ40 manuals.

https://www.jaguarforums.com/forum/g...r-index-50609/

Good luck

 

Hi Don,

I removed the Throttle Body and carefully removed the TPS cover which released a considerable amount of oil. Yes this unit was full.
I purchased some electrical cleaner (aerosol) and cleaned both the wiring connection (blue) and the TPS (Red) areas.
I also drilled 2 small holes in the cap while it was removed. (3mm diameter)
Installed the throttle body using new gaskets.
Resalting from this exercise I can now use my cruise control and the intermittent revving of the engine has appeared to normalised.

So thanks very much for your input on this. I still have to follow up on the Vacuum issue which is my next move.

The engine is still sluggish but I will check the O2 sensor as this seems to be a possibility.

I will post some photos when I work out how to attach them

Again thanks.

Garry Vincent
XJ40 1989

 

Garry,

Good work, and congratulations on the good result! We'll look forward to seeing photos and to your continued work to track down the vacuum issue and to check your 02 sensor operation.

Cheers,

Don

 

Garry,

I saw your post show up on the X308 forum in a non-related thread so I've copied and pasted it here so our XJ40 experts can comment. Cheers, Don


Garry E Vincent
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Garage is empty, add now
Join Date: Feb 2014
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Garry E Vincent 1989 xj40
Hi Again,

Following up on my last post with trying to solve the low engine Vacuum.

I removed the front spoiler to view the charcoal canister tracing all hoses . I found the purge valve had been disconnected from the connecting hose. The electric connection was still in place.

I removed and inspected all components and testing the purge valve I found it was faulty.

Having trouble locating another I carefully dismantled the one I had to find it was caked with dirt/dust/grime.

I rebuilt and moulded back together. Tested ok and reinstalled.
checked the jaguar manual for a schematic to make sure the installation was as it should have been.

Unfortunately this had no affect on my current Vacuum readings. I will keep looking.

Could some one assist with another issue.

• FAULT 23. The book reads Fuel supply as the description with in the Function column it reads " look for poor feed back control in rich direction" Sorry but I don't understand this.
• The other one is the elimination on the dash indicating a failed fuse in fuse location No 2. I checked all fuses and all ok. I removed the side cover making sure that there was no others fuses hidden away. ( as this vehicle was pre owned ).

Thanks again

Garry Vincent
1989 xj40 Sovereign.

 

Garry,
It's just my own ignorance, but I'm a bit confused as why your '89 has the 'later' fault codes. Perhaps you have a very late '89?

Anyway, I can't imagine that the code 23 isn't related to the continuing sluggishness and the replies posted above suspecting the 02 sensor. I'd be going down that direction if I were you, probably followed closely by the temp sensor or even the thermostat.

cheers,
Scott

 

Scott, Good eye! I just checked Garry's first post and he states his car is a 4.0, so it must be what we would consider a '90 MY in the U.S.

Don

 

06 April 2014
Jaguar XJ40 1989 Sovereign 4.0
VIN SAJJHALD3AT 595426
Eng No 9EPCA101348
Garry E Vincent. Australia
Thanks for the previous assistance with my issue of the erratic engine.
I would like to think we are slowly getting there. Process of elimination. Plus I am leaning as I go.
First as you guys requested I check the throttle potentiometer. This was removed and found to be full of oil. Replaced with 2 small drilled holes to allow drainage.
Second, I replaced the Bosch Oxygen sensor. With a NTK Brand. I hope this was a good move. I questioned the supplier but yes he’s a salesman. If you guys think that the problem could still be in this area please advise.
The initial result was good smooth running much better that I have had. Then all of a sudden the motor was back to it old erratic self.
Note. When the engine is running well it’s a pleasure to drive and sitting on 100 kph smooth running.
It’s about this speed when things start to go wrong. You go to back off the speed gently but the result is a sharp adjustment both increasing and decreasing
On start-up it can be very smooth running. Then the next time it’s running on 5 cylinders. I would track it down to a particular cylinder by lifting one plug lead at a time. I have done this a couple of time to find that each time I checked it was a different cylinder.
Please note that I have previously replaced all injectors with New (Bosch) and all new high tension leads.
The distributor cap is ok and spark looks good.
Timing checked.
Fuel pressure is very good.
All new plugs. NGK BCPR6ES
Vacuum still low. (10 to 12 in-Hg)
I may be slow at responding to letters of advise as my work takes me away from home base.

Regards Garry

 

Hi Garry,

The NTK O2 sensor may or may not be a good choice. If it came with factory-installed connector(s), it may be fine. If it is one of the "universal" type sensors to which a connector had to be installed, the installation of the connector may be critically important, since the OE sensors in the XJ40 are designed to draw ambient air through the spaces between the copper conductors in the wiring harness, and if the electrical connector is not properly installed, that miniscule airflow can be blocked, depriving the sensor of its ambient air reference. The internet is full of accounts of failure of the "universal" style sensors.


These are probably not the source of your troubles, and you will get a lot of contradictory opinions, but the OE plugs in the XJ40 were Champions, and at least one very knowledgeable XJ40 owner proved to his own satisfaction that Champions were superior to NGKs in his XJ40. See the photos at the link below:

Welcome to Jag-lovers - Members Photo Viewing Page


I haven't looked up the vacuum spec for the XJ40, but if this is low as you say, it would appear to be at least part of your problem. Since the engine compression seems good, there must still be a leak somewhere.

Reading your symptoms again, one thing that occurred to me is that a failing Coolant Temperature Sensor (CTS) could contribute to your issues. The ECM uses the signal from the CTS to determine cold-start fuel enrichment, then as the engine warms up, it gradually adjusts the fueling by shortening the injector pulse duration or "on time" so the engine doesn't run over-rich.

Another distinct possibility is the Crankshaft Position Sensor (CPS), which reads a toothed wheel on the front end of the crankshaft and tells the ECM the crank position. The ECM uses this signal to determine ignition timing angles, so if the CPS is acting up, it could create erratic behavior. If the CPS is more than several years old or you don't know how old it is, it would be worth inspecting its electrical connector (between the distributor and upper radiator hose on our '93) for looseness or contamination, and inspect its wiring harness for damage. If you don't know the age of the CPS, it would be wise to simply replace it preemptively and keep the old one in the trunk/boot as an emergency spare, since sudden CPS failure is a common no-start cause on the XJ40.

Keep us informed - you're going to solve this one for good!

Cheers,

Don