I searched this forum and I see the voltage regulator outputs a higher voltage after start-up than in normal operation. Someone previously said the alternator will put out 15.2 Vdc to quickly top off the battery, then it drops to something lower. Someone else mentions the voltage could be "up to 15 V".

I am measuring 15.2 to 15.3 Vdc across the battery as soon as the engine starts. It remains above 15 Vdc for as long as I have watched, about 5 minutes.

Is this normal? Or should I be putting in a new alternator?

Follow up question, any advice on changing the alternator? The manual says the A/C compressor has to come out to remove the alternator. Do I need to get the A/C refrigerant removed before starting the alternator work?

 

dh53, depending on the age of the battery and how long the car has sat, yes, this may be normal. What I would say to do is to start the car, take it for a spin around the block (10 minutes of driving) and then with the engine still running, measure the voltage again. if it is still up at 15 VDC, then yes, you have a problem. This is where I would start by measuring the voltage inside the cabin of the car and seeing what it is there. If the voltage is down around say 13.7 VDC there, then you have a high resistance wire between the battery and the engine bay fuse box or the engine bay fuse box and the passenger cabin fuse box. In short, the ECU is seeing a low voltage (due to the voltage drop in the bad wire) and it is adjusting the alternator output accordingly to bring the voltage up.

If you want to monitor the battery voltage as the ECU sees it, then you can try the following:
-starting with the engine off, depress and hold depressed the TRIP button on the end of the turn signal stalk
-With the Trip button depressed, start the car
-With the Trip button still depressed, watch the information screen in the instrument cluster, when it says "ENGINEERING TEST" or something similar, release the TRIP Button. This will take about 3 seconds from the time the motor is up and running.
-depress the Trip button (about 35 presses) until you see the information screen say "BATT XX.X" where XX.X is going to be the voltage on the system (should say 13.7). If this is saying 15.0 (or something similar), then we have a wiring problem. if it is down around say 12.7 VDC, then we have a high resistance connection in the wiring most likely. Of note, as you get close, you should see the screen say "TRN-0", then on the next press, it will say "IVD 00", then on the next press, it will show you the battery voltage. if you overshoot it, press the Trip button a bunch of times to circle around to go at it a second time. Of note, the first 2 presses are going to test the cluster itself, so, you are going to see all the lights come on and then all the gauges sweep full arcs. This is normal.

As for replacing the alternator, you do not necessarily have to remove the A/C compressor, but it will be something that will be in your way and will make getting the alternator out a bit more difficult. But, many members have left it in. As for getting the system evacuated before starting the work if you are going to pull the A/C compressor, legally speaking, yes, you are supposed to. But a lot of people just pop the lines and let it leak out. With that being said, when you go to refill the system, YOU MUST!!!!!! get it evacuated before new freon is put in or the A/C system will not work right.

To exit out of this condition, you can either simply turn the car off or press and hold the TRIP button for 3 seconds and the information screen will go back to displaying the ODO.

 

Thanks Chris. As soon as I can drive the car for 10 minutes I will try this out but I am still stuck at:

https://www.jaguarforums.com/forum/x...x-type-237742/

New coils, new spark plugs, new battery, new battery cable, pulled and cleaned all the grounds, inspected all the wiring I can see and I cannot drive the car 100 feet without flashing CEL and P0303 code. Not that I need a code to know something is wrong. It takes nearly full throttle to get the car to drive 100 feet, bucking and lurching the whole time. It feels like the car is running on 3 or 4 cylinders, not 6.

You interested in a parts car?? I'm at the edge of giving up.

 

Hello d53, a defective alternator triggers a lot of error messages. These are not real. A Jaguar mechanic knows such things, should know. To change the alternator the air conditioning compressor should be unscrewed. It is not necessary to unscrew the hoses when unscrewing the support frame. Then you can push the A/C compressor to the right side. When unscrewing the support frame, it is necessary to mark the position of the frame so that it can be put back into the old position. At the front the screws can be unscrewed completely, at the back only one part is needed. Please note that when unscrewing the screws at the back, the screws remain tensioned so that the nut is not lifted out of the anti-twist protection. Happens very often when working with the impact wrench. Most of the time it is not enough to unscrew the frame to remove the alternator, then you have to lower the engine. Not too much otherwise the engine will fall down.

 

dh53, lets not give up quite yet. Keep in mind that a misfire can also mean a fuel issue, not just a spark issue. I would try looking at the wiring for the #3 fuel injector. Look for funny bends in the wiring (indicating a broken wire inside the insulation). Probably a good time to look at the wiring for the coil too for the same indications. Talking with another member, he was saying that it may be the fuel injector harness that is having issues. There is a separate harness just for the fuel injectors and you can get one at a wrecking yard for under $50. The hardest part of this job is simply getting the upper half of the intake off.

 

Really appreciate your help Chris. At this point I have the lower intake manifolds off because I spun out one of the cheap-o PEM nut fasteners in the plastic lower intake after removing the upper intake manifold 20 times in 2 months. I drilled and tapped a couple of set screws into the PEM fastener so I can put the car back together without hundreds of dollars in new parts that aren't related to the problems. Will put it together as soon as the rain stops here in Maryland.

The fuel injectors, fuel injector wiring, fuel injector connectors look solid. While I have everything apart I will swap fuel injectors between Cyl 3 that keeps coming up with misfires and any other cylinder.

Cyl 3 coil wiring did have an apparent problem, the green wire on one of the pins had no insulation for about 1/8 inch just before the coil. I cut the wire, cut back the insulation to clean copper, spliced in new wire, and soldered that in with new heat shrink. Made no difference.

I have accessed cylinder 3 coil and plug so many times I can literally take the upper half of the intake off in under 15 minutes now. Wondering how soon I can become Jag certified...

 

I hate to have you take the intake off again but have you checked for injector pulse on cyl 3 ?

 

I would swap spark plug 2, coil pack 2 and cable 2 with spark plug 3. (Or any from the front side of the engine.)

This will tell you if it is in the wiring or the pack/plug. If misfire is still present on 3 then you have eliminated the main causes and narrow the issue down farther.

If the problem moves, then you have defective parts and don't have to remove intake again to address them.

I once spent two weeks troubleshooting an engine misfire to finally find out it was due to a a bad set of brand new OEM points from the mfr.