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4.0 V8 - Misfires only at low RPMs and other related symptoms
So, introductions done it's time to try and start getting the S-type running like new.
The first, and as of now, only major issue (it appears it's all related) I am aware of consists of the following symptoms:
Constant (what seems to be) misfires at idle that are physically felt and heard inside and outside the car.
Car shakes and shudders somewhat violently like it is going to stall and seems to lose power starting at around 80kmh/50mph until around 110kmh/70mph (I assume it's RPM related, not speed related since the violent shakes stop if I speed past or stay below the mentioned speed/RPM combination).
Very strong gas smell as soon as I start the car that seems to remain even as the car is driven.
Extremely excessive fuel consumption at low speed, low gear driving (Average of 48L/100km/5mpg, confirmed with the loss of around 40km/25mi of fuel autonomy in just a few minutes of city driving).
My observations and tests:
Car does not show any codes and the engine light never came on.
Using the OBDII reader what was mostly apparent was that the SPARKADV is all over the place at low RPMs/idling when the symptoms show, going from say, 15 to -3 to 14 to -5 and so on constantly. It, however, becomes stable when I take the car to high RPMs and keep it there.
The OBDII reader also seems to show it's throwing fuel in excess to the cylinders.
All the other values I took from the OBDII reader seem to be normal.
The car seems and feels to act smoothly at high RPMs, either driving or with the car stationary in neutral.
All the symptoms remain with the car in gear, reverse or neutral. As such, a transmission issue seems out of the question.
Fuel consumption is within spec on the highway when the symptoms are not present.
I cleaned the MAF and changed the spark plugs but it made no difference at all.
Since most of you here know this car inside and out, any ideas on what could be causing this? I do not wish to order coils and injectors for the problem to be something completely unrelated and a common problem with the AJ28 that means either something more serious or, on the other hand, that requires just a simple fix.
Connect a mechanical pressure gauge to the test port on the injector rail. Make sure the physical pressure is within specs and agrees with the indication on your scanner.
If that is good, I wonder if a knock sensor could be acting up. IIRC, the computer tries to advance the ignition timing to where knock is first detected, and then backs off slightly. The detection of knock is not seen as a fault, as it’s a normal part of controlling the timing. But if a knock sensor was acting erratically, it could theoretically mess up the timing without actually setting a fault code. There are fault codes for a dead knock sensor, but I don’t know the logic for monitoring one that is putting out an erroneous signal. Might be worth a little more research.
Check LTFTs and STFTs for confirmation of fuelling once you confirm correct fuel pressure. Fuel pressure should be about 3 bar when the ignition is in the ON position prior to engaging the starter motor.
Given the age of the vehicle, it may be possible there is oil fouling the spark plugs and coil units. If so, the cam cover gaskets and spark plug seals must be replaced.
Does this AJ28 have a test port on the injector rail? Just double-checking since I'll have to order a fuel pressure gauge in that case. And regarding the knock sensor, that's an outstanding theory, I would have never reached there myself. What sort test could I do to rule it out? Simply disconnecting the sensor and check if the problem remains?
LTFT was around 8% I believe but I will make a recording of all settings next time I get to the car and post it here.
Regarding oil fouling, both the spark plugs I took off and the coil plugs seemed fine and clean. Here are photos of two of the random spark plugs that were replaced. I do not see anything worrying myself but I lack the proper expertise to do so as well.
Does this AJ28 have a test port on the injector rail? Just double-checking since I'll have to order a fuel pressure gauge in that case. And regarding the knock sensor, that's an outstanding theory, I would have never reached there myself. What sort test could I do to rule it out? Simply disconnecting the sensor and check if the problem remains?
I am pretty sure all of the early models have a fuel pressure test port. Poke around, it looks like a valve stem you’d find on a tire.
The knock sensor? No idea how you’d test one. It’s just another crackpot theory of mine, trying to understand why you’re not getting any fault codes. Maybe just keep that idea on the back burner if nothing else pans out.
One more thought. Some history of the car will help. Is this a derelict you found in a field and are trying to revive? Was it owned by a retired Jaguar mechanic, maintained in showroom condition, and this is a new problem out of the blue? Something in the middle? Any other recent work?
One more thought. Some history of the car will help. Is this a derelict you found in a field and are trying to revive? Was it owned by a retired Jaguar mechanic, maintained in showroom condition, and this is a new problem out of the blue? Something in the middle? Any other recent work?
Thanks again for being so keen in trying to help me. I will take a look into finding said test port and into getting a pressure tester.
The car had two previous "normal" owners, it was driven but taken care of by the first one since I have official dealer records up to 2011. I have no clear service history for the second owner (a family member) but the car always worked and had periodic standard maintenance at random mechanics (which may have not been up to standard however). What I know for sure is that it has been standing still in a garage for the past 2 years except for an occasional drive and that it came to me with the mentioned problems as soon as I got it. This was a few weeks ago.
Overall, the car seems to be in a reasonable shape, it was never beaten up not had any crashes. It was always stored in a garage. There wasn't a single drop of any fluid on the floor. Superficially, I see no issues with the engine apart from a small oil leak on the driver side (left) cylinder bank. just below the fuel injectors. Oil and coolant levels are normal.
When an X200/X202 sits unused for extended periods, the fuel pump(s) tend to seize.
If you're not able to locate the fuel rail schrader valve, use a smart phone connected to the PCM via the OBD port with a Bluetooth interface and the Torque app. The fuel pressure should be around 3 bar.
@The_Portuguese, the spark plugs shown in your post look normal, however you would need to remove all eight coil units to confirm there is no oil present in the spark plug wells.
@NBCat, thank you again for your help. I have a standalone OBDII reader but I do not recall checking the fuel pressure there. Will double check that next time.
Regarding the spark plugs and the coils, I didn't made myself quite clear perhaps. I removed and replaced all 8 spark plugs, verified both spark plug wells and coils and did not see anything wrong visually.
All of you gave some ideas on what to check and I'll report back as soon as I have updates. If anyone else has more theories, tests or tips I will gladly try them all!
Just read this for the first time. My first thought was a dirty MAF. But you cleaned it and saw no effect. My second thought is maybe a bad throttle position sensor. But if they are out of range usually a CEL / code is set.
My final thought is this... excess fuel is being commanded. Therefore some sensor or combination of sensors or condition (vacuum leak) is causing the computer to command it.
What troubles me is that you can smell the gas. Maybe do a smoke test and look for leaks. Could be a dynamic leak... at higher RPM's it might run ok because the volume of air leaking is small in comparison to lower rpms (actually engine load).
@wydopnthrtl, thank you for your input and do read this post because I believe you will be pleased!
So, dear friends, thanks to all your encouragement and theories I could not put it on hold and went check on the car yesterday and I have updates along with a possible "catastrophic" scenario perhaps. I also took care to record videos for all of you to enjoy.
First things first, I recorded the engine sound, both warm and cold at the tailpipes and in the engine bay. For those of you with a lot more knowledge than myself, perhaps you will find some relevant sound I missed that may lead to some diagnosis.
We also found another leak on the full load breather (on the induction tube side). All the leaks were on the o-rings or rubber seals (that's the proper name?), not on the tubes/lines themselves.
In short:
However, we found something that does worry me a lot more than those leaks mentioned above. When we turn the car off we can hear a VERY worrying noise. It does sound like a massive vacuum leak but we have no idea where it comes from and what sort of mechanism that can cause it when the car shuts down. Do any of you have any pointers to where it can come from?
Even More Crude Vacuum Leak Test (Vacuum Leak On The Back Of The Engine Heard Again) - This vacuum leak test was done by my friend blowing into the induction tube, a very high tech method only reserved to the best of professionals! You can hear the leak again in the back of the engine for a brief moment after my friend stops blowing.
Finally, here is the live data from the OBDII Reader at idle. Fuel pressure is a tiny bit lower than the 300kPa mentioned above but I don't think it's very relevant right? Feel free to pause the video to see any read-out in more details.
As you may have noticed, we used a water sprayer to find vacuum leaks. And guess what, we did!
Nice detective work. For even better results finding leaks, you may have to shift your plan of attack just a little bit. Rather than listen for a change in how the engine is running, watch the short term fuel trims on your scanner. When you momentarily plug a leak (with water spray in this case), the computer instantly adjusts fueling to maintain a steady idle speed. The upshot is you can easily miss leaks that way, especially small ones. Ideally, instead of water, you should try a flammable spray such as electronic cleaner, propane from an unlit torch, etc. When the intake draws in something flammable, even though the idle speed remains steady, the change is fuel trim is much greater and easier to spot. Obviously be careful not to start a fire, but a small amount judiciously applied shouldn't be a problem.
One caveat: Some modern cleaner sprays are eco-friendly and non-flammable, both the liquid itself and/or the propellant. They won't have the desired effect. You can test the spray's suitability by purposely creating a vacuum leak by removing the oil dipstick. The crankcase ventilation system will draw in some extra air now, and if you spray a quick shot there you can see if this deliberate leak affects the fuel trim.
Originally Posted by The_Portuguese
However, we found something that does worry me a lot more than those leaks mentioned above. When we turn the car off we can hear a VERY worrying noise. It does sound like a massive vacuum leak but we have no idea where it comes from and what sort of mechanism that can cause it when the car shuts down. Do any of you have any pointers to where it can come from?
Hard to tell from the video, but could that be caused by refrigerant pressures equalizing within the AC system? My pickup makes a similar noise at engine shutdown if the AC has been running. Try shutting off the HVAC system and see if that makes any difference.
You can purchase replacement parts from SNG Barratt either directly from the UK, or through one of their European locations in France, Germany or the Nederlands.
Nice detective work. For even better results finding leaks, you may have to shift your plan of attack just a little bit. Rather than listen for a change in how the engine is running, watch the short term fuel trims on your scanner. When you momentarily plug a leak (with water spray in this case), the computer instantly adjusts fueling to maintain a steady idle speed. The upshot is you can easily miss leaks that way, especially small ones. Ideally, instead of water, you should try a flammable spray such as electronic cleaner, propane from an unlit torch, etc. When the intake draws in something flammable, even though the idle speed remains steady, the change is fuel trim is much greater and easier to spot. Obviously be careful not to start a fire, but a small amount judiciously applied shouldn't be a problem.
One caveat: Some modern cleaner sprays are eco-friendly and non-flammable, both the liquid itself and/or the propellant. They won't have the desired effect. You can test the spray's suitability by purposely creating a vacuum leak by removing the oil dipstick. The crankcase ventilation system will draw in some extra air now, and if you spray a quick shot there you can see if this deliberate leak affects the fuel trim.
Thank you for you words. I will use the method you describe next time. As you saw, we tried to use MAF cleaner to do just that but apparently it made no clear difference even tho the bottle mentions it's flammable. When I get to the car I'll check for more leaks using the tips you describe in combination with a live read-out on the OBDII reader.
Originally Posted by kr98664
Hard to tell from the video, but could that be caused by refrigerant pressures equalizing within the AC system? My pickup makes a similar noise at engine shutdown if the AC has been running. Try shutting off the HVAC system and see if that makes any difference.
Funny enough, the AC is not working at all. As such, it was off. I have no idea why and as you can imagine, with the engine issues that was not on my list of priorities at all at the moment. Besides, if you notice in the video where my friend blows into the intake, you can hear the leak on the back of the engine for a split second so I don't think it's related.
Originally Posted by NBCat
You can purchase replacement parts from SNG Barratt either directly from the UK, or through one of their European locations in France, Germany or the Nederlands.
Thank you very much for the links. As soon as I know what to order, I'll do a bulk purchase. And thanks for the tip, I will definitely switch to the aluminium housing. Any other must have improvements for the AJ28, do let me know.
But before any of that I really need to know exactly where that "leak" from the back of the engine is coming from since it sounds fairly severe. If any of you have any remote idea on what it can be, go ahead on giving your opinion. I will have to take things apart to reach it regardless but I want to know what I am looking for, at least in theory.
I am thinking the leak could be coming from the brake booster itself or the tube feeding it if not already ruled out....maybe the check valve has failed
I really need to know exactly where that "leak" from the back of the engine is coming from since it sounds fairly severe.
Sounds like it's time for a smoke test to find the leak. Here's one low-buck method from Scotty Kilmer, mechanic extraordinaire and personal favorite of mine:
Whilst the inlet manifold is removed, replace the return hose to the throttle body as they tend to fail at the large to small hose joint.
Check the brake servo hose as the seals can perish causing an air leak.
Another important item that hasn't been mentioned is the primary and secondary timing chains, guides and tensioners. If their replacement with the latest version is not documented in the vehicle history, remove the cam cover(s) to confirm the secondary tensioners are the metal bodied and not plastic bodied type. Failure of the secondary tensioners can potentially cause catastrophic engine damage if the secondary timing chain jumps more than two teeth.
09-27-2020, 03:09 AM
4.0 V8 - Misfires only at low RPMs and other related symptoms
