So; on this particular 3.2 engine I have had significant problems with starting that had prompted many online purchases regarding 'no spark'.

The latest problem is that it starts fine; but, now it cavitates above 1500rpm. Even less with the other original sensor at 1000rpm.

Prior to replacing the CPS, the engine ran fine. It was just a bit hard to start. Once started it ran really well and had no rpm issues at all.

I have already replaced;
-Plugs
-Leads
-Distributor cap
-Rotor
-Coil
-Condensor

CPS was the most recent.

In need of a bit of help as the car will not go past 20kph. Bit annoying while trying to get to work.

 

Hi WattsXJ,

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

First of all, please tell us the year and model of your Jaguar so we can give you the most accurate suggestions.

From your description, I gather you have resolved the hard starting issue and have replaced numerous parts.

I am familiar with the term cavitation as it applies to vapor pockets in flowing fluids, but I assume by the context of your use of "cavitates" you mean the engine runs roughly above 1500 rpm? And are we to understand that with the original CPS the rough running began above 1000 rpm?

There are numerous possible causes of rough running at higher rpm, such as fuel starvation (fuel filter or pump?), excessive air (EGR system, carbon canister purge valve, idle air control valve, ?)

Is the behavior different when the engine is cold or hot?

Please give us as much information as you can, beginning with the year and model of your car, and we'll try to help.

In the meantime, please visit the https://www.jaguarforums.com/forum/n...-intro-must-5/ and post a required introduction so we can learn something about you and your Jaguar and give you a proper welcome.

Cheers,

Don

 

Hi Don

-

Model information

1992 Jaguar xj6 or xj40 with the 3.2 engine.

-

Fault - Engine runs rough when the throttle is applied. Anything over 1.2rpm it will misfire.

The car begins to backfire, misfire, and run ruff when any throttle is applied. Associated; that the engine shakes about and does not sound right.

-

Notes;

Before this started the car was intermittently hard to start. By that I mean, it was no trouble some days: Some other days, it would crank fine but it would not start. No spark was the diagnosis.

Since the most recent attempt to fix it has developed the problem with any applied throttle causing the engine to run rough.

Previously the engine would run really well. No problems with rpm, and it would sit really well on 110kph on the freeway.

-

Recent work on the car;

Having the choice of 3 new CPS sensors as spares I swapped them with no luck. Ruling out the CPS sensor as the fault. It was suggested that the connection was the fault. In saying that the new sensor helps the car start reliably and having a new one in there helps.

The male connection to the CPS was changed and tested. The new connection has less resistance, but the fault remains.

It starts first go now, but will not increase in RPM without misfiring and running roughly.

It makes no difference between cold and warm.

-

Note; swapping out the Ignition Amplifier Unit.

I have been thinking of replacing the ignition amplifier unit. Originally when I cleaned the connection with "connection cleaner" it started for the first time since the no start fault occurred. It was covered in grease or vaseline.

However, this fault and its causality may not be related. As the next day the car did not start and resumed its crank no start problem.

Note; when the car starts and is warm it ran reliably for the rest of the day. This prompted fitting a new CPS.

-

Fault as it remains.

Any applied throttle or increase in RPS causes the engine to misfire.

Car starts fine.

-

Kind Regards

Terry Watts.

 

Hi Terry,

I just saw your post before heading to bed - we're traveling all day tomorrow but I will try to reply tomorrow night.

In the meantime, check the Vehicle Condition Monitor for a stored Diagnostic Trouble Code (DTC). To do so, trn the key to position II (Igntion ON) but do not start the car. Press and release the VCM button on the trip computer and watch the small display window below the speedometer where the odometer/mileage display normally appears. DTCs are presented in the format "FF" or "Fuel Fault" and a two-digit number. Write down any message exactly as it appears and post it here and we'll try to help.

Cheers,

Don

 

Hi Don

In the interim, I will check the VCM for any faults. I will also disconnect and reconnect the battery to reset the EFI system. This worked on another car with a similar problem. Where possible I will clean the MAF and Investigate the throttle pot sensor. Nutting these things out takes time. I am also suspicious of the cruise control system in general, as it does not work. Previous faults with the car have been a fuse 2 warning, but this went away when the CPS was changed.

No rush with the response time. Whenever you can is fine, and it is hard to know what is going on at this stage. Tomorrow morning it will be about 3 deg, so I may be a bit delayed getting out of the house and into the garage.


Terry.

 

Hi Terry,

I'm in a rush again so can't give a long reply, but on an XJ40 you can easily check for spark (and in doing so check the ignition amplifier, coil, distributor & rotor, CPS, and ECM). Remove a spark plug, reconnect it to its high tension lead, lay it on a block of wood or other insulated surface, and use a jumper/booster cable to connect the threaded sleeve of the plug to a good ground, such as the engine ground strap or one of the ground points in the engine bay. Crank the engine and watch for spark. It helps to do this in a darkened garage or at dusk.

Poor fuel delivery due to a clogged fuel filter or failing pump can cause starvation at higher revs. You can test for fuel flow by disconnecting the fuel inlet hose at the firewall/bulkhead end of the fuel rail and directing it into a suitable container. Crank the engine for 15 seconds, and multiply the amount of fuel in the container by 4 to calculate the litres-per-minute.

Is there any chance the fuel in the tank is contaminated?

There are many other possible causes or contributors to your symptoms, so it will be very helpful to know if the ECM has flagged any DTCs. We'll look forward to an update when you've check the VCM.

Cheers,

Don

 

Update

So no error codes on the VCM.

So this morning I removed the battery to reset the system. This had no effect. Started the same.

The car then started fine, however, once throttle was applied the car started to run rough. When the throttle was left to idle the problem went away. The problem seems to increase with application of the throttle. The more you apply the more it will shake, then it will backfire. The resting RPM is below 1000, about 800.

I removed the throttle pot cable and the car cut out. It started fine when reconnected. The car was idling up and down while I was checking this. A trick I used to use was removing the TPS and if the engine ran better without it at idle it would have meant a bad sensor. The result though was a cutout, as the TPS is linked to the rest of the pot. The test was inconclusive as a result.

-

I removed the air filter, no problems there. On sharply accelerating the body, the injectors make a trademark sound through the plastic body. They seem to be firing ok.

The car responds to the throttle cues well, so the TPS may be ok. Increase RPM seems to be the main problem. Jab the throttle and it responds well, then reaches above 1k and it splutters. Move up slowly and about 1k rpm you get the same.

Really frustrating.

-

Spark is ok.
The coil is ok.
The condenser is ok.
Rotor and the distributor cap is ok.
Ignition amplifier cable is ok, not sure how to test the unit itself.

-

Yet to do; clean the MAF and inspect the throttle body with everything off.



-

Rather stumped with this one.

Hunch it is a timing problem? but have no idea what could be causing it.

-

 

Sounds like a fuel supply issue, filter, regulator or worst case scenario, pump or crap in tank.

Just my 2 cents

Larry

 

Hi Lawrence

I will look into this tomorrow and will have to order a new fuel filter as it is. No record of when it was last changed. Only had this one for 7 months so replacing it is on the list.

Plenty of fuel pressure up the top. Not sure about the flow rate. Will see how it performs.

-

 

Terry,

Are there signs the engine is running rich, such as dark smoke from the exhaust?

Are there signs of an obstructed catalytic converter? Any rattling sounds from the exhaust? Does the flow of exhaust gasses seem insufficient? Does the cat turn red hot when the engine is warm? One test is to remove the O2S and see if the engine revs better. Not the easiest thing to do but see the photos in my album at the link in my signature.

I asked earlier if there was any difference when the engine was cold as opposed to warm, and you replied that it made no difference. Does it behave any differently during the first 20 or 30 seconds after a cold start? This is the period when the ECM is fueling under open loop while the O2S heater warms up. After this delay, the ECM goes into closed loop fueling and references the O2S signal to adjust fueling richer or leaner as needed to maintain stoichiometry. Just curious to know if there might be a clue that the O2S may be unhappy.

Another possible issue is the coolant temperature sensor, whose resistance is supposed to vary with temperature. When the CTS fails, or there is a problem with its electrical connector or wiring, the ECM doesn't know whether the engine is cold or hot and will apply an incorrect fuel mixture.

A few things you could check:

1. Carefully check for any leaks in the air intake plumbing between the MAF and the throttle body, and in any vacuum hoses and crankcase breather hoses.

2. Check for proper operation of the EGR valve;

3. Check for proper operation of the carbon canister purge valve (if equipped - it's near the canister ahead of the front left wheel behind the wheel arch liner).

4. Check the spark plug leads to confirm they are in the correct firing order and the cylinder 1 lead is correctly positioned at the distributor cap;

5. Clean the electrical connectors at the ECM (behind the glovebox on LHD cars);

6. Clean the ground points associated with the engine management system (EMS), in particular the two on the intake manifold and the one on the firewall/bulkhead behind the cylinder head;

7. Clean both ends of the engine ground strap;

8. Perform a compression test on all six cylinders;

6. Remove the cam cover and carefully inspect the timing chain and upper tensioners. If the chain is loose, it is possible it has skipped a tooth on one or both cam sprockets. This is uncommon on an XJ40 but not impossible.

Have to run again but will try to think of more possibilities.

Cheers,

Don

 

Update

1 Fuel system is ok.
- The pump works ok and lots of fuel shoots out at cranking and when on open loop.
- The diaphragm in the return valve is ok, no fuel leaking in through the vacuum hose.
- Fuel filter does not seem clogged, plenty of flow. Replaced anyway.

2 Leads and ignition
- Leads checked and all good.
- Leads in the correct order too.
- Plenty of spark.

3 Timing chain
- Rocker cover removed, timing marks line up with the original tool I made up.
- Not loose and all good.
- Engine timing is not effected by the fault.
- Reflected in running at idle, the engine's physical timing is not altered.

4 MAF
Removing the cables to the MAF caused the engine to die.
Inconclusive until cleaned.


To do list;
Clean the MAF and Throttle body.
Check the intake body itself for leaks.
Check the EGR valve and intake body for excessing oil/grit.

Can not get under the car at the moment to check the catalytic converter.
Likewise removing the o2 sensor down there to check it would be advantageous, but can't get under there today.

-

Notes;

Car still starts fine.
Engine runs fine at idle speed.
Any throttle applied causes rough running.
The term 'plinking' comes to mind. As the engine does not necessarily backfire through the intake manifold, but more so the excess noise can be heard through the exhaust. No loud bangs occur, but the engine does run really bad with the throttle applied. I am happy to conclude it is either a fuel mix problem at this stage. Physical timing is ok, so it is down to the EFI system's timing and management based on its sensors.
The engine does not improve with warming up, any throttle causes rough running.
Engine runs ok at idle but much more is to be desired here too.

-

Overall I am still quite as stumped as I originally was. No conclusive finds as of yet.

The engine is still acting up with any applied throttle in a very consistent manner.

Still ongoing.

 

Update.

After cleaning the MAF, there was a hesitation in starting.

It eventually did, but it might be safe to assume that the MAF is dead.

A replacement has been ordered, so will see how it goes once it arrives.

At this stage; it is just going to be a game of replacing things until we are back to normal.

-

 

Update.

After checking over the EGR system.
- EGR idle solenoid is good, and it works ok.
- Crankcase Hose has some gunk in it, which was quickly cleaned.
- Not sure about the sensor on the crankcase hose, might need an OHM reading from that tomorrow. Not sure where you can buy these either?
- The system seems to be ok, no visible problems need fixing.

-

Still a hunch on the MAF and probably the TPS too.

-

 

Update; Pinpointed the problem.

Following through with some extra diagnostics, having removed all the sensors on the car I have found a few faults. No idea how the car was actually running so well previously!

MAF was out by a few OHMs, same for the CTS, and so was the ITS, but only by a bit by the factory specifications. Replacing these will help with fuel economy in the long run and I am happy to keep the old ones as spares.

However, the worst offender in the EFI system was the 02 or Lambada sensor. Is was completely dead. Made no difference to the running condition of the car when unplugged as a backup test. When unplugged the check engine light came on, and whent away just as it did a few days prior to the engine running rough too.

Next update will be in a few days when all the sensors have arrived in the mail.

Let's hope it fixes the problem, and the car runs better than it ever has before.

----

 

Update.

So the ignition [spark system] parts have arrived today. I spend less than an hour putting in a new engine control module (ECM) replacing various parts of the wiring loom as well. Car starts up better, but it does not run better yet.

Next week coming in the mail, will be the EFI seneors.I will see which was the one causing the difficulties in particular with regards to running rough above 1k RPM.

Renewing everything in one hit was relatively cheap, so I hope that the overkill helps keep it on the road longer.

 

Update: not good.

Everything was fitted today as it arrived in the mail yesterday.
MAF
O2 sensor on the intake.
O2 LAMBADA sensor changed on the exhaust. [With great difficulty ].

-

The car still runs just as poorly.

Which has got me stumped completely now?

-

 

So the engine on this car is the 3.2l version. The engine starts and idles well, however with even the slightest touch of the throttle, the engine will run poorly and if you push too hard it will choke, spit, or backfire. It has been quite a persistent fault that is now very concerning.

I have done my best to update and fix the problem by replacing parts with new ones. However, I have been completely left stumped because there is nothing left to replace now. The only thing left would be the TPS throttle positioning sesnor. There is nothing to suggest the one in there may be faulty right now, and I may need to troubleshoot symptoms of that anyway, but I assume it is working fine.

List of parts replaced.

-Plugs
-Leads
-Distributor cap
-Rotor
-Coil
-Condensor
-ECM Engine control module
-Crank Positioning Sensor
-MAF Mass Air Flow Meter
-O2 sensor on the intake.
-O2 LAMBADA sensor changed on the exhaust. [With great difficulty].
-Air Filter too just in case.

If anyone has any advice or wisdom, it would be greatly appreciated.

One day the car woke up with the fault and it has been this way ever since.

 

Hi Terry,

That is truly frustrating! The one thing on my original list that comes to mind is a compression test of all six cylinders. Perhaps you have one or more valves that are caked with carbon and not closing properly, or worn or sticking piston rings in one or more cylinders.

In the U.S. we can borrow or rent a compression gauge from local auto parts stores - don't know if that is true in your area.

Cheers,

Don

 

Didn't someone else have the same problem recently that turned out to be water in the gas?

Larry

 

Hi Larry

Will give that a check to day, new thoughts are the fuel pump, and I picked up the fuel filter today for it was well.

Also going to check the exhaust pressure in front of the cat today. Calling in some mechanic friends with some special tools to narrow it down further.

Cheers