That would make me want to do a compression test even more. If one pot is running poorly due to low compression it can soot up the spark plug and cause a misfire. Rev the engine hard at a lean mixture (3/4 throttle would do it) and the soot gets burnt off; the misfire disappears for a while usually only to return after a gentle drive at light throttle.

 

Oh you mean a cylinder balance test! That could work. If he has the equipment for it, it is worth a try. Then if it reveals an imbalance it would be an indication that it would be worth doing a physical compression test.

 

balance is shut off the injector watch it drop

ford relative comp test uses crank speed variation. if you go in as lincoln ls with any decent scanner you can probably do it

otherwise high amp clamp and the cheap pico..takes 2 minutes

 

My scanner is pretty basic and has no such provision. I do have an inductive ammeter probe I could connect to my oscilloscope. I could disable the injectors and then record the starter amp draw as a waveform. If compression is relatively even, I should see 6 fairly similar peaks.

As Kent Dorfman would say:



Wish me luck. The weather is supposed to be cooperative tomorrow and my wife has made no plans for me (yet).

I pulled the trigger and ordered a set of reman OEM injectors but they won’t be here for at least a week. In the meantime, I’d like to continue troubleshooting without tearing things apart too far. The car is still drivable.

 

buy a thinkdiag it’s like 80 a year all makes all models put that junky scanner aside

 

I see. I’m not familiar with that. A novel idea.

 

Had a little free time to continue troubleshooting towards my predetermined conclusion (bad injector).

Realized I forgot to change the fuel filter after replacing the pump. Had a little trepidation upon seeing the plastic hose connectors, but no problems there. Much to my surprise, the filter was nasty. The old fuel I poured out was rust colored. Not sure where that came from, as the tank is plastic and was very clean inside when I had the pump out. Fuel pressure has been good, so I don't believe fuel flow had been restricted to any great extent. Just like previous faults, I think I corrected A problem, but not THE problem.




Next task was to analyze starter amp draw to look for low compression compared to the other cylinders. I used an inductive amp clamp on the battery ground cable. The clamp output was connected to my tablet oscilloscope. The results weren't entirely conclusive. When I increased the vertical scale to show higher peaks, I'd get all sorts of weird spikes. Seems I was trying to over-amplify a fairly weak signal from the clamp, and those results became useless. At a lower resolution, I did show consistent peaks, so that's a little encouraging. I do plan to run a proper compression check next week when I have the plenum off for the injectors.

 

New fuel filter made no difference. Starting to have my doubts about the injectors being the source of trouble. Have been driving the car every day and have had zero codes. That, and the fairly consistent starter amp pattern has me optimistic I'm not dealing with a compression problem. When I have the plenum off, I'll run a compression test to be sure.

Had a little time yesterday to check for vacuum leaks. I did the test twice, once with propane and a second time with carb spray. Not a budge in fuel trims, so that's encouraging.

I'm still planning to replace the injectors, if for age alone. Hard to imagine multiple injectors being just bad enough to cause rough running but without setting misfire codes. Since I had been previously getting P0301, I will swap #1 plug and coil with known-good units from the easily accessible side.

Got to wondering some more about the PCV and Full Load Ventilation system. Details at post #21 in this thread:

https://www.jaguarforums.com/forum/s...2/#post2591435


I was thinking the Full Load Ventilation system was the filtered air supply for the PCV system, but now I'm thoroughly confused. Jaguar treats the systems as two separate things, so perhaps my thinking is less correct than usual. The part that has me really confused is Jaguar's description of the PCV valve:

"The PCV valve has a spring-loaded plunger which opens under the intake vacuum created at low throttle settings."

This is 180 degrees backwards from a conventional PCV valve. In a typical PCV system, the valve is closed (or nearly so) with high vacuum (throttle closed) so as not to affect idle quality. Yet Jaguar is saying this is when the valve is fully open. Still trying to get my head around this, but the intake system could be calibrated for this extra source of air. From what I can extrapolate, the Jaguar PCV valve kinda seems more like a fixed orifice with a check valve to prevent reverse flow, but don't quote me on that.

So I gets to thinking, could the present symptoms be caused by a partially clogged valve, not flowing enough air under high vacuum (throttle closed) conditions? Or maybe too much airflow? I can't really increase the airflow easily, but I could fit a temporary restrictor for troubleshooting. The line from the PCV valve (through the infamous elbow) to the throttle body is 3/8" diameter. I fitted a restrictor with an 1/8' hole in it to see what would happen. This immediately made the chugging and poor idle much worse. Even though my test didn't make things better, it seemed encouraging that I actually made things worse, strange as that may sound. Am I on the right path? Can't say for sure, but I hope a new PCV valve will be the actual fix.

Thoughts? Maybe something else is causing all this? Remember, I'm no longer getting the P0301 or any code for that matter.

 

The saga continues. The drive to work this morning had been the same as usual, with an erratic idle and occasional chugging at part throttle. Pulling away from a stop light, the chugging was a little worse than normal. Normally I don't get chugging on acceleration, only at part throttle or idle. And then lo and behold, the CEL starts flashing! Normally this would induce a sense of dread, but I was excited to know there'd be a fault code stored. I eased off the gas and the light turned off within 20 seconds. A quick scan showed the P0301 had returned and was pending. This is the only code I've seen in a week.

So now my thoughts pivot to some fault specific to #1 cylinder. I'm already planning to replace all 6 injectors, and swap a known good coil and plug to #1 cylinder. I'm also planning to run a compression check and replace the PCV valve. But thinking ahead, what if the problem continues? Anything else I should consider while I have that big annoying intake plenum out of the way? I really need to get this whole mess cleaned up soon.

Had another thought: Could the P0301 be a red herring? Consider this scenario - There's some minor problem with #1, such as compression slightly low relative to the others, but still within limits. Under normal circumstances, you wouldn't even realize it. But when the engine runs roughly for some other reason, #1 cylinder gets flagged because it had been making a smidge less power than the others, but it wasn't really the root cause. I ask because there don't seem to be a lot of possible faults specific to one cylinder other than plug, coil, injector, or compression. On previous occasions, I've had misfire codes due to bad coils, but the loss of power was so slight I never noticed it. I mention this because the P0301 I'm getting now is only showing up on rare occasions, nothing consistent.

More thoughts: Could a clogged cat cause the symptoms I'm seeing? Last summer, I changed the left cat due to a recurring P0430 code. The new cat took care of that. I plan to replace the right side (same bank as cylinder #1) but that's been on the back burner with other HPCs (Higher Priority Crises). A new cat for the right side has been sitting in my garage for several months, taunting me.

 

Clogged cat may be making the number 1 cyl problem magnified. If you have the cat i would replace it before tearing too much apart. Depends on your workload my friend and weather cooperation

 

You can test to see if a clogged cat may be contributing to the P0301 in a few ways:

1. With the engine hot and running, use an infrared thermometer to measure the temperatures at the inlet and outlet ends of the cat itself (not the exhaust manifold or connection flanges). The oulet temperature should be considerably higher than the inlet temp (ideally at least 100 degrees Fahrenheit hotter). If the outlet temp is cooler than the inlet temp, the cat is not lighting up and may be internally obstructed.

2. Loosen the cat flange at the exhaust manifold to create an air gap, or remove the upstream O2S. Test drive to see if the engine performance improves and if the P0301 recurs (O2S DTCs may occur but can be cleared after the test drive).

3. Connect a vacuum gauge to the air intake manifold/system and measure vacuum at idle, then rev to 2,500 rpm and hold at this speed. When the engine is revved, the vacuum should dip momentarily, then climb back to nearly the same reading as at idle. If it takes several seconds for the vacuum to return to near the idle reading, the exhaust may be obstructed. Hold the engine at about 2,500 rpm and continue to watch the vacuum gauge. If the vacuum remains low or falls, the exhaust may be obstructed.

4. If you can gain access to an exhaust back pressure gauge, you can remove the upstream O2S and connect the gauge hose at that port and then test the back pressure at idle and 2,500 rpm (or whatever rpm the gauge markings indicate should be tested).

Cheers,

Don

 

Your car is pretty high miles, no? Have the value clearances ever been checked? Inquiring minds want to know...

 

Blame has been assigned. You could have talked me out of replacing the cat, but N-O-O-O-O!!!



It just sorta happened. Got home, jacked up on Mountain Dew again. The weather was somewhat cooperative, a rarity for this time of year, and one thing led to another. Initially I was only planning to measure the temperature at the cat inlet and exhaust. But the cats are tucked up at an angle, so the only way to get a good reading is to get the car up on jackstands. And well, if I was going to be doing that much work anyway...

As you may have surmised, the new RH cat didn't make much difference. Maybe helped a little, but not much. Oh well, one more item crossed off the list of suspects.

Next step is to quit messing around and work the P0301. I'll need to grease the sides of the car and shoehorn it into the garage for new injectors, etc.

 

Only 380k miles. Just getting broken in.


Not since I've owned it, going back to 2008.

If possible, I'd like to avoid pulling the valve covers again. If a valve was causing this problem, wouldn't that show up on a compression check?

 

Yes. You'd get low compression in cylinder 1. You could then add a little engine oil to cylinder 1 and repeat the compression test. If the compression goes up, suspect the piston rings. If the compression does not go up, suspect one or more valves are not sealing.

 

Some progress today. Moved the Jeep out into the cold and shoehorned the Jag inside. Talk about a tight fit!




The compression check passed with flying colors. Lowest was 175# and highest was 185#. Phew! I was afraid what I might find. Curiously, the suspect #1 cylinder was the highest.

All spark plugs looked similar. No heavy sooting or anything like that. I was annoyed to find oil had already collected in the 4-5-6 plug wells. It hadn't reached the coil boots yet. Still way too much for only a few hundred miles on new gaskets. Was hoping I could leave the valve covers alone, but oh well.

Each injector looked clean as a whistle inside and out. Was hoping to find a smoking gun like a carbon ball on the nozzle, but nothing. I ran a quick resistance check on each injector. Five of them measured about 14 ohms, maybe +/- 0.5. But #2 injector was way different, around 65 ohms. Never had any codes for anything but #1 cylinder, though. Strange...

All injector connectors looked good and were on tight.

The backs of the intake valves looked nice and clean. No major soot buildup.

Time to call it a night. More fun tomorrow.

 

I know this might sound dumb but maybe your injector #2 is really injector #1?

Regardless that injector will need to be swapped out and might be your smoking gun...

 

Good work, Karl!

I'm sure you know which are cylinders 1 and 2 on your engine, but for the rest of us, here is the diagram from the Vehicle Specification Booklet. Which diagram applies to your car depends on when it was built:



65 ohms is definitely too high for that fuel injector, so it is possible you have found the cause of your P0301. But if the injector came from cylinder 2, we have to ponder why it was triggering a misfire code for cylinder 1 and not a fuel injector code for cylinder 2 such as P0202...

Cheers,

Don

 

Karl, what kind of classic of car is parked next to the Jaguar?

 

The suspect injector is the middle one on the US passenger side bank. The car is pre-facelift so that is #2. I was very careful to label them as I removed them one at a time.

I’m very confused about the ohm reading, but maybe it was still operating, at least to some extent. Could be #1 was clogged internally and was the primary fault, even though its resistance was okay. #2 could have been weak, but not as bad as #1 so it was never flagged. Just guessing.

I’m replacing the whole set. Got me thinking I should check the new ones before installation.