Saturday morning, I was taking my XJS to a car show, but it wouldn’t start so, forget about the car show. It acted like a discharged battery, only making a “click-click-click” sound. I tried my nice portable starter that I’ve successfully used before to start the larger-engine on my XJR, but it would only do the same clicks it did with the car battery. I should add that, since I do not drive this car much, I had the battery charger/maintainer connected until the day before and the green LED was ON, which indicates a fully charged battery, yet the engine wouldn’t crank.

So then I pulled out the big guy, my old Sears charger (50 amp) / engine starter (170 amp) on wheels. I tried to start the car and it did the same “clicks”. Tried again and this time -like totally against its will- it started to crank and finally started out, however immediately after this the rpm’s went up to almost 2000 rpm’s, then came down to about 1000, but here it began to surge up and down like back up to 1500 rpm’s then down to like 900, doing it every 2 seconds. like booom – booom - booom, or like if I was pushing the gas pedal every a couple of seconds. I tried to make it behave by flooring the gas pedal and it would raise the rpm’s accordingly but when I released the gas it’d go back to its booom-booom again. Then I turned the ignition off and tried to restart it again and…believe it or not, it started right out and no booom-booom anymore. I’ve re-started the engine again, several times and it starts like nothing ever happened.

I could just blame it on a bad battery, but the one jump starter could not crank the engine either and even the big jump starter device was very close to incapable to crank that engine. Also, I cannot blame the engine idle surge on the battery. Something is wrong, something is causing those 2 incidents (no start and the surge) but it appears to have resolved itself, which I hate because I need to know what’s wrong. I just hope that somebody here has heard something similar because I have no idea what happened, or worse yet, what IS happening. Why so difficult to crank the engine and with different, proven devices and then why that rpm surge up and down. There may have been a message on the trip computer, but disconnecting and connecting back the battery I forgot that doing that I could erase a message, or do messages remain in memory regardless? Dunno. Right now there’s no message. Feedback is most welcome.

Cheers,

 

Non cranking could be down to a poor earth on the starter motor.
You will need a hefty jump starter to turn the engine over (I presume that it is a V12?); I've had smoke coming out of ones that aren't up to the job.
Hunting is often down to a failing AAV (Auxiliary Air Valve); there are loads of posts about it on here.
Does the hunting ease off as the engine comes up to temperature?

 

could be the starter solenoid not throwing in the pinion I had the same years ago and fitted a high torque starter motor to it, sound proper as well and weighs a lot less,

 

Just a thought.....For a while all I got was the click on trying to start the car, traced it down to the start relay, one of the 3 blue relays on the right wing/fender under a cover.

 

This starting problem sounds like a possible earth (ground) fault. A good idea to very carefully clean up the engine earths that go via the subframe, and a very good plan is to add an extra one direct from the alternator bracket to the chassis frame.


As to the hunting, are you sure there is no pool of No2 lying around??!!

 

Rex
Which model did you buy, please, from which source?
Greg

 

Hi Greg

That Hi Torque Starter Motor looks like Model RAC404A from motorsport-tools.com

(UK) Company https://www.motorsport-tools.com/pow...ter-motor.html

 

I think it was this lot
https://www.autoelectricsupplies.co....5/category/242
or
https://www.autoelectricsupplies.co....3/category/242


they appear to have changed the look of them

 

404 rings a bell but not 404a I think its all about pinion size

 

Oh, it seems that I forgot to indicate that this is an AJ6 car, not a V12. The car has never given me the slightest hint of a bad connection problem, or any lazy engine starting, but then, the rpm surge will have nothing to do with a poor ground connection, or with a suspect starter motor. They are totally different in nature and it'll be one heck of a coincidence that both different problems happened at the very same time, so they must be related. I wonder if all those unsuccessful attempts to crank/start the engine, all that click-click may have caused an odd reaction from the ECU that triggered an rpm surge that later resolved itself? --- I didn't have a chance to check if the problem persisted as it warmed up because it didn't run much through this incident in the garage. When the rpm surge stopped and I got it to start out normally and repeatedly, I just shut it down. -- I do like your hint in regards to the AAV, but were you talking V12?

Cheers,

 

You know, I have actually been wondering if, with 110,000 miles, some items may begin to break down anytime, but so far I've been lucky with most only soft problems with a couple of exceptions with exhaust items. Maybe the starter motor is beginning to kick the bucket, so I'll be paying good attention to engine starting quality. I was actually suspecting the blue start relay from the very beginning and I guess that it could still be that, so if the no-start repeats I'll replace that blue relay first, but the problem is that this would have nothing to do with the possible re-occurring of the rpm surge problem, so I'll have to dig some more on what did cause that problem.

Cheers,

 

Not sure what you mean by "pool of NO2" (nitrogen oxide). At first I thought you were kidding me meaning "N2O", since you may know that this car has nitrous injection... although it is impossible to have "a pool" of N2O because at ambient it quickly evaporates. So, No2?

 

Yes, I'm aware of that blue relay and I will replace it anyway, although is now working just fine, but just in case. However, most responses are only about the no-start problem, but the engine surge concerns me more because it's not just a soft surge like with vacuum leaks, but rather like a firm acceleration like if I was doing it with my foot.

Well, I've been reading a little about the motorized idle speed control valve and its interface with the ECM. Not easy to fully figure it out, but enough to tell me that it doesn't appear possible that this function can generate a fast rpm increase to 1500 rpm and to repeat it over. However, the actual idle speed function of the ECM depends on input from just about every possible condition, or sensor/device in the system and who knows what happens when one of those devices fails to send a (correct) signal. It may be that some false condition temporarily presented to the ECM from my various attempts to crank the engine and with connecting and disconnecting various power sources that induced a temporary erratic ECM response and then, maybe after I finally got it to start right and to idle normal, the ECM recovered from that and began again to work as it normally does, which tends to be a typical car processor behavior.

 

Well, to add insult to injury, today when I reconnected the battery my little digital voltmeter on the cigar lighter receptacle (have it rewired for always-hot) indicated 10.63 volts. Then, I connected the battery to my big charger and the charge needle shows no charging, even after an hour. Yet, only 3 days ago, the other charger/maintainer device LED was green, indicating full charge and the little volt meter was then indicating 12.4 volts. And, since the battery never did crank the engine (only relay clicking sound) hardly any electrical current has been drawn from its supposed fully charged state. It seems that just those "clicks" were enough to kill it. It's only 3 years old with five more pro-rate years left, so back it goes. Was it the battery all along? But then, why my strong portable jump starter wasn't enough to crank it either? And even the big guy really struggled to finally get it to crank. Good reason to check those ground connections, although right now starting current flow seems to be hunky-dory.

Cheers,

 

Try and substitute the battery for another, known good one.
Sometimes, if a battery is too goosed it won't pass current through properly even from a jump starter.

 

I think you'll find it was a joke!

 

I agree, pull the battery. A bad battery can make starting even harder.

 

From afar:


Two issues, possibly related.


1. Starter and or it's circuits have a flaw.


2. Over fueled. Nitrous or petrol or both!!!


Carl

 

Here I'd tend to agree because I've seen similar before. The battery behaves like a low resistance/high amp resistor and it overloads the jump starter.
Another thing that I was beginning to suspect was whether it may be possible that these charger/maintainers that we keep plugged to the battery for fairly long periods may somehow be upsetting the proper charge/discharge cycles of the battery, kind of like it happens when charging to soon a rechargeable battery that creates a "memory" and it will no longer fully charge. I use these battery maintainers on my two Jags and the wife's Z3, but no problem with the other batteries, so far.