After having replaced the alternator in my 93 convertible, I noticed what may have turned out to be a bonus. Since I bought the car 2.5 years ago, I was constantly plagued by the CEL lighting up on a regular basis, by which I mean almost every time I started the car. It was almost always little annoying things like the TPS and/or the purge solenoid. After spending way too much time checking, cleaning and searching for replacements for these items I began taking the advice I found on this forum. If it doesn’t affect performance, don’t really worry about it. Consensus was it was caused by a slight voltage drop in the system while starting.
My point is this. I checked the alternator output when I first got the car and it was supposedly putting out the proper amount of voltage to the system, so I didn’t think any more about that item. One morning my alternator wasn’t working right according to the dash gauge. Out comes the tester. Sure enough now it was only putting out 12 to 12.5 volts. So I order a new alternator and install it. This was almost a month ago. Since that time I have not had the CEL come on for any reason.
I am not certain that the old alternator, being marginal at the time, was the cause of the light coming on but it is food for thought. I personally have come to the conclusion, as others have stated, that the electrical systems in our cars are very sensitive to ANY and ALL drops or minor surges of even a very minor amount.
Overall just glad the light hasn’t come one since replacement and was wondering if anyone else had noticed anything similar with their vehicles.
Is not the CEL supposed to light u on starting, and if all is well, go out? If it stays dark, one does not know if it works??
Carl
Yes that’s true. But it was constantly lighting up at random times. Trip computer would show code indicating TPS problem or Purge control valve code or both. Never a real problem with them, just voltage drops or surges that were out of range and tripped the light and code. This was happening for most of the time I have had the car. I tested the old alternator and it was fine until it blew a diode and was only putting out 11.5 to 12 volts, so I had to replace it.
The surges or drops causing this have disappeared since installing a new alternator. I was pointing this out in hopes that others may have had the same thing going on and to give another possibility for their CELs lighting and these codes happening in their vehicles.
I never suspected the alternator because it tested good. and I have no idea why it happened only to those 2 items and circuits.
To clarify a bit more, it wasn’t happening on start up. Sometimes within a minute or two of starting but more often than not in stop and go traffic, especially if the idle dipped a tad to low when I took my foot of the accelerator as I was coming to a stop.
Quite surprising you’ve bought new alternator these days, guessing it’s reproduction with replacement voltage regulator. You should rebuild your genuine one, much cheaper and gives loads of fun!
Replacement voltage regulator is nothing close to original ans usually causing varistions within the system. Mind if I’ll ask whst type of alternator have you got installed??? Your aim is Bosch 115amp…
Actually it was a rebuilt nippondenso 120 amp. It matched what was on there, the pulley being the most important part as well as the connections. I actually had to go with one for the 1995 4.0 to get the right pulley and output. No trouble at all getting it but the price difference from suppliers was considerable. Anywhere from about $110.00 to $289.00. Was in a local alt/gen shop asking about rebuilding it and was told according to their computer, they had one on the shelf that was brought in 6yrs ago and never picked up. It matched mine and I got it for $112. including the tax. They did take mine and said they would rebuild it and put it back on the shelf.since it was a Jag part. It will probably still be there in another 6 yrs. should I need it.
120amp sounds strange. I could swear biggest installed in your engine by factory was Bosch 115amp:
https://www.xjsbanger.co.uk/jaguar-xjs/xj6/xj40-alternator-renovation---bosch-115a
What’s the set voltage on the regulator? Good thing to start from… Your AJ6 should work on 14.0 volts, have a look if the regulator is not Chinese no-name.
I have both, the Jag repair manual as well as the parts book. I always refer to the parts book when ordering or buying parts. It does show both 115 and 120 amp alternators for the 4.0 The one on my car matched the 120 amp, OEM # DBC 5819… No exterior rectifier and a ribbed belt as well as a plug in connector. So I went with what was on it. I tested the charging system thoroughly when I bought the car. I spent 3 days going over it and compiling a list of things that would need to be done over time when I got it home. Being a Jag she decided which of those things got done when. Her basic signal being something goes bad and announces itself in the worst ways and places. Therefore when she acts up I do the best thing and replace or rebuild everything in that area, IRS completely rebuilt when brakes locked and caught fire. Collapsed flex line 2 weeks before I was to replace all 3 and replace brake fluid. C’est La Vie.