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Hi!
I've searched the forum a while to find some information on this problem but I feel the need for a new thread.
I have a problem with an occasional missfire in my XJR -96. The engine runs fine and smooth when cold, but as soon as the car goes into closed loop I get a missfire/stumble once every 3-5 seconds. I believe the missfire is consistent through the rev scale.
My guess is a problem with one of the sensors the ECU uses during closed loop. Can enyone tell me the difference between closed and open loop regarding the various sensors?
I've owned the car for a few months and I haven't driven it very long, there were a few things wrong with it when I bought it and it's been sitting in the garage most of the time.
So here's what I've fixed so far:
1. New downpipe
2. Changed both O2 sensors (one has been bad for a long time I suspect....)
3. Welded the cracks in the manifold ( I know, mostly temporary)
4. New manifold gasket
5. New Champion RC9YC Spark plugs
6. 6 new ignition coils (Says Lucas made in GB on the box)
7. Cleaned the throttle housing carefully not messing with the TPS (I get a good 0-97% reading)
8. Adjusted the throttle wire
9. Cleaned the MAF sensor (with dedicated cleaning spray)
10. Switched to another Crank sensor that was in the boot when I bought the car, made no difference.
The LFTF is stuck at -11.7 and has been since I bought the car (could be my cheap OBD2 readers fault maybe...).
Now to the strange part, I had negative STFT numbers (around -7 on both banks) and 0,16 g/s for the MAF (x 100?) at 18% throttle, then I unplugged the MAF, the engine hesitated a moment then ran kind of smooth on idle but really bad response when reving.
I plugged it back in and there was no real difference, so I shut the engine off and on again. It started up worse than earlier and had more missfire, and now the STFT was dancing around +10%, and 0,12 g/s at 17,6% throttle.
I unplugged the MAF again and twisted the pins on the MAF just a little for contact. Now the STFT was -25% on both banks with 0,11 g/s at 17,6% throttle.
Something is up with the MAF, is there a way to know definitely that it's bad?
The mass flow rate at 13% should be a little over 4 grams / sec
The 13 % is the lowest it gets
As you throttle up the supply of vacuum overcomes the leak rate and the STFT should come closer too the target value of 0.0
Your EGR error should range around 0 as you throttle around , someone recently found coking of oil vapor deposits on the valve
Thank you for answering!
I don't think it's a vacuum problem, the STFT never gets near 0 even when throttling up.
And 4 g/s at 13% is more than I get, even if I assume my OBD2 reader has moved a decimal....
I can get my hands on a used tested MAF but its still kinda pricey so I want to be sure it's bad. Can anyone tell me how?
It is hard to believe the supercharged and non - supercharged engine have this same reference point values as both MAF sensors are different part #s
Someone in New Zealand with the supercharger has apparently calibrated on up above idle settings that you may find out about
If the EVAP control valve is shorting to ground or the connector this can effect the MAF value . You can try disconnecting the EVAP
Ok, before I started removing the connector from the MAF I had 1,14v at idle (650 rpm). I never checked it again after that, I will look again tomorrow.
I didn't really get the part with calibrating, can you explain more?
I've never looked at the EVAP control valve, does all the cars have this? I don't have an EGR valve for example.
Is the ECU supposed to handle connecting and disconnecting the MAF while running without problem? What happens to yours when you do this? I think mine is acting strange....
In calibrating you would get a higher voltage at each RPM step 1000 , 1500 , 2000 ect
There is a table of these calibration values for the normally asperated MAF in a Jaguar publication on my other computer
The Evap valve is located behind the left headlight and under the air filter box , The EGR valve on yours may be very buried under the blower or not included in Sweden
From my understanding the ECU when it is missing an important sensor like the MAF it will default to a different and less then optimal set of maps or data arrays . There is a lag and adjustment time shifting between the all sensors regulation and the missing and then you have the reverse adjustment when you abtain all your sensors back
This works fine on a new engine but as the sensors degrade or out of factory adjustment the transition can be rough
Have you run the throttle position sensor very slowly though out it's range with a meter , since it is located under the throttle body you can remove some insulation as the ( green / yellow ) center wire again in this case goes over the fuel rail
You would be looking at 0,60 volts DC at idle and climbing with twisting by hand the throttle body . The engine can be not running but the key must be in the run position .
You can remove the ECU connector and look at the TPS variable resistance through the range does not spike out or go infinite as you move the throttle with the engine not running
In calibrating you would get a higher voltage at each RPM step 1000 , 1500 , 2000 ect
There is a table of these calibration values for the normally asperated MAF in a Jaguar publication on my other computer
The Evap valve is located behind the left headlight and under the air filter box , The EGR valve on yours may be very buried under the blower or not included in Sweden
From my understanding the ECU when it is missing an important sensor like the MAF it will default to a different and less then optimal set of maps or data arrays . There is a lag and adjustment time shifting between the all sensors regulation and the missing and then you have the reverse adjustment when you abtain all your sensors back
This works fine on a new engine but as the sensors degrade or out of factory adjustment the transition can be rough
Have you run the throttle position sensor very slowly though out it's range with a meter , since it is located under the throttle body you can remove some insulation as the ( green / yellow ) center wire again in this case goes over the fuel rail
You would be looking at 0,60 volts DC at idle and climbing with twisting by hand the throttle body . The engine can be not running but the key must be in the run position .
You can remove the ECU connector and look at the TPS variable resistance through the range does not spike out or go infinite as you move the throttle with the engine not running
OK, I will check the TPS voltage/resistance. I did test the percentage with my obd2 reader and it looked good, but maybe that's not the best way to test it...
The OBD 2 tester may not see a open contact spot on the TPS wound resistor . It may discard a very short timeframe out of range reading and just smooth out the % readout
I found on mine the TPS connector round metal locking feature missing on mine so the connection was questionable
You may still have a bad crankshaft position sensor even the spare that somehow ended up in the trunk , it could have been bad as well
If you open up the TPS wire loom as it goes over the fuel rail there are some wiring splices that have been found corroded
A CEL code for the CKPS does not always show easily on the X300
Any other CEL codes ?
Missing clamping 2nd tabs on the ECU car side connector ? I had 4 on mine . They are considered as sockets but each individual socket is 2 pinching tabs to make good contact / grip
The OBD 2 tester may not see a open contact spot on the TPS wound resistor . It may discard a very short timeframe out of range reading and just smooth out the % readout
I found on mine the TPS connector round metal locking feature missing on mine so the connection was questionable
You may still have a bad crankshaft position sensor even the spare that somehow ended up in the trunk , it could have been bad as well
If you open up the TPS wire loom as it goes over the fuel rail there are some wiring splices that have been found corroded
A CEL code for the CKPS does not always show easily on the X300
Any other CEL codes ?
Missing clamping 2nd tabs on the ECU car side connector ? I had 4 on mine . They are considered as sockets but each individual socket is 2 pinching tabs to make good contact / grip
Yes, sounds like a good idea to check all of the connection points you mentioned. Is it the ECU sockets you mean? Or are there any other sockets on the way?
No not a single CEL code since I bought it, but I've heard that these cars don't throw codes that easy... Nothing to worry about I think, or it's it?
I'm having a friend over tomorrow that will help me out, he's got another obd2 reader so we can compare and stuff to check compression and vacuum leaks. Think I'll know more tomorrow.
Your friend may have the better software on his laptop that can log a test drive in a sensor values graph that you can review and send with time marks on when the engine stumbles
You can post the graph for others to look at
RPM
TPS
MAF
You already know the coolant temp sensor gets you to close loop mode but who knows maybe it pops back and forth the open / closed loop
See if the EGR error PID shows a variance around 0 which would show you have one and it is moving trying to stay on 0
I had a similar issue where my engine would "dip" every 32 seconds. I'd see it on the RPMs, and sometimes would get so bad as to stall my engine out at a stop light.
I took it to several shops, including one jag specific shop that had me change coils, sensors, including EVERYTHING on your list, but the dip prevailed. Finally found a different fantastic jag-specialized shop and it turned out to be a failing intake manifold gasket. I couldn't find it looking for a vacuum leak, either could three other shops.
If you end up getting the intake manifold gaskets replaced, make sure you do the ******* hose.
By the way, you should be using RC12YC spark plugs, and for future reference, your coils should be Made in Japan, by Diamond, OR QYL branded from Amazon. Everything else seems to cause trouble in less than a year.
Lastly, what is the throttle body % open at idle? Should be around 12-13% give or take. (You can read it using an OBD scanner)
I had a similar issue where my engine would "dip" every 32 seconds. I'd see it on the RPMs, and sometimes would get so bad as to stall my engine out at a stop light.
I took it to several shops, including a jag specific shop that had me change coils, sensors, etc, and it turned out to be a failing intake manifold gasket. I couldn't find it looking for a vacuum leak, either could three other shops.
If you end up getting the intake manifold gaskets replaced, make sure you do the ******* hose.
I see, my engine doesn't loose revs it just missfires, and my intake manifold gasket is new I changed it myself. I did not do the b****** hose, it looked good and my plan is to lift the engine out once it runs good, I'll do the scary hose then.
I really think it's a sensor of sorts giving me trouble, but I'm open for other suggestions of course!
[/QUOTE]By the way, you should be using RC12YC spark plugs, and for future reference, your coils should be Made in Japan, by Diamond, OR QYL branded from Amazon. Everything else seems to cause trouble in less than a year.
Lastly, what is the throttle body % open at idle? Should be around 12-13% give or take. (You can read it using an OBD scanner)[/QUOTE]
Okay, I really looked around the forum for the right spark plugs, guess I listened to the wrong guy.
Yes I can see why the coils give problems, I had to "fix" them with using the original connection rod (don't know what it's called) between the coil and the plugs, the one's that were in the new coils wasn't even near touching the plugs. The car ran really bad before I fixed it.
The reason I don't think it's the coils is that it runs fine when cold.
The coils as current flows through them will heat up and expand and that is where the troubles with them show up . You can have a bad new coil as well . some coils will arc as a short to the wall of the spark plug well . This arcing sets up stray electrical signals through the sensors package , in theory
Cleaned the O2 sensors return wire shielding grounds which are the upper 2 small terminal post on the firewall ? You will see them as the dashed lines in the picture at PIG153L
The large ground strap from the starter bottom mound bolt to car frame if bad can cause weird things that defy logic
13 mm socket with a 12 inch extension for the starter lower mount bolt and 10 or 8 mm on the car frame , has to be done from underneath
What is the coolant sensor showing you? You can bypass that sensor by shorting the two harness contacts. That’s a quick and easy way to cross that off the list.
Have you ever tried to monkey with the harness connector at the MAF. Sometimes that gets wonky. If you can get any response by fooling around with the harness connection at the MAF, while running and warm, that can indicate a problem there. I’m not crossing off the MAF just yet.
I believe the oxygen sensors are ok....assuming your engine only has two. If you have four, you really should change the other two.
You mentioned replacing the crankshaft sensor. The camshaft position sensor must be considered. I don’t know how to diagnose it unfortunately.
The camshaft sensor is a hall effect sensor different then the crankshaft inductance sensor . It will read 600 ohms as a fundamental meter reading vs. 1300 for the crankshaft
From my understanding if you have to hold the starter for a couple of engine revolutions before you get a " smooth " combustion start up the camshaft sensor is not doing it's job of aiding in a immediate combustion start up with barely one engine revolution
The camshaft sensor can also be good but not adjusted correctly
I had a CEL code of P0340 but I suspect it was from the pervious owner tinkering around with the connector off trying to start the engine
The camshaft sensor connector can be remove and the engine after the start sequence will run fine
The start sequence is that the ECU only looks at the camshaft at first and once the crankshaft position sensor is on the " true " top center of the # 1 cylinder The ECU will revert to the crankshaft sensor for the duration of your drive , the crankshaft timing gap comes around twice in the 4 cycle and the camshaft turns only once and knows which TDC cylinder it is on because of the gap width dimension difference between each 1 , 2 , 3 , 4 , 5 , 6 cylinder top dead center
I have heard from other post that the camshaft sensor is still looked at by the ECU but I don't have a understanding of that
I do remember someone recently had 2 missing teeth on the flywheel instead of the only one by one breaking off , but this would give you a very noticeable misfire
Did you place the crush washers on the O2 sensors before installing them , others have seen a difference
O2 sensor change take a little run in time to smooth out the engine regulation
The coils as current flows through them will heat up and expand and that is where the troubles with them show up . You can have a bad new coil as well . some coils will arc as a short to the wall of the spark plug well . This arcing sets up stray electrical signals through the sensors package , in theory
Cleaned the O2 sensors return wire shielding grounds which are the upper 2 small terminal post on the firewall ? You will see them as the dashed lines in the picture at PIG153L
The large ground strap from the starter bottom mound bolt to car frame if bad can cause weird things that defy logic
13 mm socket with a 12 inch extension for the starter lower mount bolt and 10 or 8 mm on the car frame , has to be done from underneath
I haven't checked any ground points yet, I will do that, thanks!
What is the coolant sensor showing you? You can bypass that sensor by shorting the two harness contacts. That’s a quick and easy way to cross that off the list.
Have you ever tried to monkey with the harness connector at the MAF. Sometimes that gets wonky. If you can get any response by fooling around with the harness connection at the MAF, while running and warm, that can indicate a problem there. I’m not crossing off the MAF just yet.
I believe the oxygen sensors are ok....assuming your engine only has two. If you have four, you really should change the other two.
You mentioned replacing the crankshaft sensor. The camshaft position sensor must be considered. I don’t know how to diagnose it unfortunately.
The coolant sensor lookes fine in the OBD, but it sounds like good thing to do anyways.
Yes the connector on the MAF is acting strange, or the MAF itself. If you read an earlier post I explain what I did and what happened.
I only have two O2 sensors and their new. I haven't driven the car more than a few miles since the change, could that be the problem??!
The camshaft sensor is a hall effect sensor different then the crankshaft inductance sensor . It will read 600 ohms as a fundamental meter reading vs. 1300 for the crankshaft
From my understanding if you have to hold the starter for a couple of engine revolutions before you get a " smooth " combustion start up the camshaft sensor is not doing it's job of aiding in a immediate combustion start up with barely one engine revolution
The camshaft sensor can also be good but not adjusted correctly
I had a CEL code of P0340 but I suspect it was from the pervious owner tinkering around with the connector off trying to start the engine
The camshaft sensor connector can be remove and the engine after the start sequence will run fine
The start sequence is that the ECU only looks at the camshaft at first and once the crankshaft position sensor is on the " true " top center of the # 1 cylinder The ECU will revert to the crankshaft sensor for the duration of your drive , the crankshaft timing gap comes around twice in the 4 cycle and the camshaft turns only once and knows which TDC cylinder it is on because of the gap width dimension difference between each 1 , 2 , 3 , 4 , 5 , 6 cylinder top dead center
I have heard from other post that the camshaft sensor is still looked at by the ECU but I don't have a understanding of that
I do remember someone recently had 2 missing teeth on the flywheel instead of the only one by one breaking off , but this would give you a very noticeable misfire
Did you place the crush washers on the O2 sensors before installing them , others have seen a difference
O2 sensor change take a little run in time to smooth out the engine regulation
Well the car doesn't start as good as my previous x300, and a bit different every time, maybe I should look into that!
And I see evidence of the camshaft sensor being fiddled with...
I will check the flywheel.
Yes I used the washers! But the car haven't been driven more than a few miles since I changed the O2 sensors, could that be my problem?
Occasional misfire in closed loop.
