Hi all,

I've been having what I think is a misfire for quite some time that I have have been having some trouble diagnosing.

After purchasing three different bluetooth code readers I've finally got one that appears to work.

I have purchased an OBDLINK LX which now works with Torque and other apps and gives some readings and has shown the error codes.

The car has had this misfire issue for months and has not thrown any faults until recently. The fault code is P0172. If I clear the code it does not come back for a very long time, usually a month or so.

What I am feeling is a vibrating, loss of pickup between about 1300 and 1800 rpm. If I rev the car beyond 2000 rpm then the misfire seems to go away or at least seems to ease the vibration and the cars power returns. You can feel the vibration through the pedals and floor etc.

You can also feel the vibration when stationary whilst revving the car. The problem does appear to be when under load, although the idle does not seem quite right either. The idle seems to fluctuate about 20 to 50 rpm when idling so feels a lumpy.

When the car is started from cold, the idle is lumpy and there is a smell of fuel from the exhaust.

The car isn't throwing any misfire fault codes so I can't seem to work out which cylinder is misfiring. I've got readings for fuel trims, temperatures, RPM, Fuel pressures etc.

I've now used the code reader to get some live readings.

All apps that I have tried, do not seem to provide live cylinder misfire readings. I have so far tried Torque, OBDWiz (on Windows) and OBDLink and Car Scanner. They all don't seem to be able to see individual cylinder information. Am I expecting too much from the software?

I'll attach some images of the live readings that I have managed to obtain so far. They are readings from when the car has warmed up and been run for a while.

What do my live readings seem like to you guys and is there any way I can get live sensor readings for each cylinder so I can pinpoint which are misfiring?

Thanks,

Chris

 

Live reading data from Torque and OBDWiz.


From OBDWiz



From OBDWiz


Mode 6 readings From ODBWiz

 

Torque Readings - When vehicle is idle and warm.

 

Torque Readings - When revved and warm.

 

Torque Readings - After revved and whilst warm.

 

Torque readings - Intake Manifold Pressure on idle and when revved.

 

Hi Chris,

I don't know if you are using the free Torque app or the Torque Pro app, which costs USD $4.95, but Torque Pro can definitely read individual cylinder misfire codes as well as the random misfire codes. I believe any generic OBDII should be able to read misfire codes such as P0300, P0301-P0308, P1316, etc. Individual cylinder misfires are probably not your issue.

Your rough running may simply have to do with rich running. P0172 indicates rich running in Bank 1, but both of your banks are running rich according to your Long Term Fuel Trims. Here is the listing for P0172 from the Diagnostic Trouble Code Summaries:




You can download one of the more complete DTC guides here:

Jaguar X350 DTC Summaries

Looking at your screen captures, the first thing I notice is that your Short Term fuel trims seem fine at idle, near 0, but your Long Term Fuel Trims are significantly negative, indicating that over time the ECM is reducing the fuel in the Air-Fuel Ratio because its sensor inputs indicate the AFR is richer than it should be.

The second thing I notice is that in the list from OBDWiz the Engine Coolant Temperature Sensor is reporting the coolant temperature as 194F, but in the Torque scan the temp is reported as only about 60 degrees (presumably Centigrade), or 140 degrees Fahrenheit. With the engine at operating temperature, the coolant temp should probably be in the range of 80C/176F to 100C/210F, so the OBDWiz reading looks plausible, but the Torque reading does not. If the ECTS is intermittently under-reporting the coolant temperature, the ECM will intermittently continue to apply cold-start fuel enrichment even after the engine has reached full operating temperature. I think the ECTS would be the first thing I would pay close attention to to see if its signal is sometimes reading colder than it should.

Another test that might be worthwhile would be to capture readings at full operating temp at idle, 1,500rpm and 2,500rpm and compare the readings of all the sensors listed in the Possible Causes of P0172 to see if any readings appear implausible at any of those engine speeds.

P.S. Please use your User Control Panel to edit your signature to add the year, model and engine details of your Jaguar to help others provide the most accurate replies.

Cheers,

Don

 

Thanks Don. That's all really helpful info.

I do see that I have a minor coolant leak from the thermostat housing that I am going to look at changing. Yes you are correct that Torque is currently in Centigrade. I have not completely configured OBDWiz yet.

The Torque readings were taken after the car had been running for about 20 minutes. The OBDWiz readings were taken the next day after a drive for an hour or so. Apologies if this has confused things but I wasn't happy with what Torque was giving me in terms of readings so I had to install and configure other apps to see if they could provide the extra live data I am looking for.

I just don't want to go changing loads of items if I can prove what the problem is beforehand.

My car details are already in the signatures. I wonder if they are not visible to everyone else for some reason. I will check it's in place.

Cheers,

Chris

 

That's the whole point of computer diagnosis, so I hope your studies will expose the root cause of the issues.


I see them now - I think sometimes the forum glitches and doesn't display signatures for some reason. You're good!

Cheers,

Don

 

Finally got around to getting some more readings from the car at different points in the rev range.

What I have noticed by doing this is that if I have been driving the car on the motorway at motorway speeds for some time and then exit, the car seems not be very smooth for about 10 or 15 minutes and then starts to vibrate again at the rev range between about 1400 RPM to 1800 RPM.

Below are some further readings.

 

At idle:

 

At approx 1400 RPM when the vibration is the worst.

 

At 1800 RPM when there is still some vibration:

 

At approx 2600 RPM when the vibration can be slightly felt:

 

When travelling at approx 60 mph:




Coolant temp versus Intake temp

Not sure why the intake temp drops here. I don't think I slowed down dramatically here.

 

At 70 MPH when the engine does not vibrate:




Coolant temp versus intake temp

Again I'm not sure if the intake temp is correct or within normal tolerance.

 

MAF rate versus TPS reading to see if there could be a problem with the MAF. This is just when the car is stationary and revving the car.


TPS versus MAF rate

 

Well I recently got fault code P0121. So I replaced my TPS (kind of - there is another thread about that nightmare) and replaced my thermostat housing that was leaking really badly. I also replaced my water pump and the new thermostat housing came with a new thermostat and coolant temp sensor. So my leak is now fixed. However, I still have this rough idle, engine vibration at about 1400 RPM and now I get fault codes P0172 and P0175 whilst the car is idleing. If I clear the fault code and drive the car then it does not throw the fault until I stop the car and let the car idle for a few minutes. As soon as I do that then the car throws the rich codes.

I've noticed that when I drive the car and take my foot off the throttle and the RPM's drop to idle the short term fuel trim drops to lower than -18 on both banks. It does that for a few seconds and then returns to about -3 but then throws the rich fault codes and displays 'restricted performance' on the dash for about 5 minutes and then it goes off but leaves the fault codes present.

When the fault codes are present the car drives great and the vibration is almost gone and I can drive the car at speed without issue. Once the codes are cleared then the vibration comes back and it vibrates at the 1400 to 1800 RPM range again.

My RPM also bounces around still even when the car is fully warmed and running at idle. It bounces between about 640 and 670 RPM. I'm now going to see how I can test the MAF to see if it's providing the correct readings.

Thanks,

Chris

 

Hi Chris!

I recently acquired a 2004 XJR and it appears to be having the same problem. Did you ever find a solution? I get codes P0174 and P0171 from time to time. I’m thinking it could be the MAF but not sure because cleaning it didn’t help. Any help would be greatly appreciated!

Thanks!
Cody Cameron

 

Hi Cody,

Your problem is different from Chris' in that his engine was running rich, and yours is running lean. The most common cause of P0171 and P0174 is unmetered air entering the system somewhere between the MAFS and the intake manifold gaskets. Here are the definition and possible causes from the DTC Summaries:


There are lots of places where air leaks can form on an XJR in the air intake, crankcase breathing system, EGR system, brake booster vacuum pipe, oil filler cap, etc. The fastest method for finding all the leaks is a smoke machine, which must be connected at various points to test the entire system. I usually start by removing the MAFS and sealing its port with duct tape. I then connect my smoke machine's large cone attachment to the main air intake pipe where it meets the air filter housing. I turn on the smoke machine and look for leaks around the various Helmholtz resonators molded into or ultrasonically welded to the main intake pipe. I also look for leaks where the aluminum intake pipe meets the throttle body and where the crankcase breather hoses and brake booster vacuum pipe meet the induction elbow below the throttle body. If you see any smoke leaking back there near the firewall, you may need to remove the windshield wipers, wiper cowl and false bulkhead to gain sufficient access to determine where exactly the leaks are.

Next I disconnect the corrugated part-load breather pipe from the air intake and inject smoke into the breather pipe to test its connection to the left cam cover and to test the cam cover gaskets and oil filler tube gasket(s). On normally-aspirated engines or later supercharged engines with variable valve timing, look for oil leaking from the VVT solenoid seals. If oil can get out, air can be sucked in. Replacing the seals is easy.

Then I disconnect the full-load breather pipe from the front of the right cam cover and inject smoke into the pipe. Look for leaks anywhere along the length of the breather pipe, and at its other end where it connects to the lower left rear side of the induction elbow.

Inject smoke into the right cam cover via the breather hose port to test the right cam cover gaskets and the crankcase vent/oil separator O-rings (the round part that looks like a PCV valve).

You may or may not find leaks at all of those joints, but it's a great idea to just replace every O-ring you encounter.

Cheers,

Don