S Type R Strange Behaviour

[Occulomency]

Hi,

Well my lovely, if a little temperamental STR is acting up again, and it's got me puzzled.
I'm used to the engine warning light telling me my catalytic converters are stuffed (they aren't), and my fuel gauge acting as a purely decorative random semaphore generator, but lately my beloved has taken on a new habit with which to frustrate me.

It started feeling a bit, well, rough at low road speeds, nothing major, but just a bit rough. The trouble really starts when I hit the S button and floor the accelerator. At high revs, above 4,500, the engine sort of coughs and stutters, loses power and won't progress.

I changed the fuel filter, assuming fuel starvation, but to no avail. So I hooked up my ELM and went for a drive logging as I went.

Nothing looks terribly odd to me, fuel pressure stays high, the MAF peaks at near 300 g/s, however the Comm Throttle Actuator Control seems to wobble about a bit when I would have expected it to be full on open.

I am getting no errors from the gear box or the electrical system, so although I would not discount a miss-firing coil, I would have thought that it would log an error if that was occurring.

So, does anyone have any ideas before I spend all of my money at the garage?

The car has covered 60,000 miles, it's an 07 plater.

[Montana5]

Hi Fraser, although your findings are pointing towards the throttle body perhaps sticking and in need of a clean, could I suggest something a bit simpler first off...

Obvious one but is the air filter clean.

Are there any blockages in any of the surrounding air box ducting, both in and out of the box.

I assume your air box is the same as the earlier models, at the bottom of the box there is a flap that opens up by a solonoid under full throttle to allow more air into the box, kinda like... oh oh he has hit the loud pedal again, we need more air to compensate, open flaps unfortunately you might not be able to see if this is working properly, however what you can do to eliminate it from the fault diagnosis is to disconnect and remove the flap completely, its held on by one screw and clip, make sure you get the little spring that should pull the flap back when not needed.( My spring was well corroded so I just removed the whole thing and in my mind the car ran and sounded better )

Might be worth a shot.

Doug.

[Occulomency]

Hi Doug,

Thanks for this advice, I can confirm the air filter is new (it was changed last week as part of the regular servicing schedule) but I can't recall ever having the throttle body cleaned or my ever having heard of this auxiliary air intake.

I shall investigate and report back in due course.

Again, many many thanks.

Fraser.

[Occulomency]

Well, my troublesome STR is back in the garage today.

Mike (my mechanic) didn't really believe there was anything wrong with the car and thought I was being a bit of a fuss-pot. Anyway, after much cajoling he agreed to clean out the throttle bodies and remove the auxiliary air flap and give the car a test drive.

All was fine until he got over 5,500 revs... Now he believes me!

So, first port of call is new plugs, then coil packs I guess.

He did mention that the plugs that have come out are a very strange colour. Now I don't know what he means by that, but when I fetch the car I'll get a photograph of them and post it for interest's sake.

Hopefully we are getting closer to the solution.

I'll keep you updated.

Fraser.

[Occulomency]

Well, I've never had 'Restricted Performance' mode before....

New plug packs it is then...

Onward....

[J44EAG]

Suggest you check to make sure the multiplug, (if you can get to it), on the throttle body is fully home and clear of corrosion. The car can play up something rotten if the plug is not correctly located.

I`d also ensure that the fuel filter is new. You would be quite surprised at what comes out of an old unit. I changed mine recently and the car became much happier. Details on that job in this link.

http://www.jec.org.uk/forums/viewtopic.php?f=199&t=5415

I`m assuming that the STR has the same filter location as the more humble cars.

Mike

[Occulomency]

Mike,

The multi-plug is fine and the fuel filter was changed about 600 miles ago (it was very heavy!).

Sadly I'm now off down the route of a set of 8 on plug coils. Mind you, I did get them for a smidge over £300 delivered, so it's not as awful as I had anticipated. I'm a little sceptical as to my chances of success as I genuinely don't understand why I have no error codes for the miss-fire.

Still, this is my last shot until I pass my car into the tender ministrations of the JLR dealer network.

All fun and games.

Cheers.

Fraser.

[J44EAG]

Coil misfires don`t always flag up as fault codes. A really major "event" has to sometimes occur to record a fault code. Significantly faulted ie cracked coils do however show up quite easily.

I assume you have checked for oil or water tide marks on the rubber coil boots? As we know flooding of the spark plug wells caused by failed cam cover seals or water ingress from the front scuttle panel can cause the wells to fill with liquid and cause coil plug issues.

The near side back plug can be difficult to remove and install and I was quite concious when I changed plugs recently that it would be easy to crack a plug insulator if I was heavy handed with the extension bar and ratchet ie not keeping the extension dead vertical to the plug.

Dying throttle pedal potentiometer units, throttle plate position pot and a broken throttle body TAC module socket can also cause issues. If any one of those three units goes out of limits, then engine mismanagement can occur. However that sort of failure is usually flagged as a "fail safe mode" message. The car drives like a slug when that occurs.

Shame you are not down here in Portsmouth. I`d have had a go at fixing with you.

Mike

[Occulomency]

Profanity isn't allowed under forum rules is it?

Shame, I need to vent. Well, £300 of coils later and the problem is worse! Miss fire on 2-4-6-8, logged as fault codes.

So, I'm guessing loose connection or broken wire. The question is, which one? Anyone have any ideas?

I'm so disappointed, I' thought it'd be back on form today...

Rats.

Fraser.

[J44EAG]

I think perhaps the throttle body plug and socket needs a look see now, Fraser.

Remember the issue I had on J44 at one point? That was eventually pinned down to the throttle internal socket to TAC module pc board connection. The throttle body can be opened for inspection. Use of a magnifying glass may reveal a dry joint or broken connection. A repair might be possible. I eventually lost patience and was fortunate to obtain an excellent second hand throttle from eBay for £20 inc p&p. Throttle body failure is not unknown. BBA Reman in Rochester recon throttles so might be worth a word with them. There might be a common fault.

I`d suggest the throttle, MAF, airflow meter connections/cables/plugs be looked at closely. Recently I blamed plugs for a misfire problem I had. Turned out to be a bad connection throttle multiplug to socket once again. Fixed with a cable tie. Problem gone.

Keep at it. There is a cause and effect for every fault. Finding it is the nause. Once you have it, you will wonder how you missed it in the first place.

Mike

[Occulomency]

Thought I'd post a quick update here as to how my STR is going, or rather not going.

So far I have changed the plugs, points and fuel filter, however the miss-fire caused the supercharger to fail, so a new one of those had to be fitted. The miss-fire is the result of the left bank running very lean. It was assumed at that point that the timing chain had jumped a sprocket, but upon inspection that was not the case.

The throttle body appears to be performing properly, however as the left side has been running very hot, there is a slight concern that I've fried one of my cats.

On the plus side, two major intake leaks has been discovered and fixed, so hopefully my P0420 & 0430 codes will be a thing of the past.

It's been in with my mechanic and his specialist mates for three weeks now, and there is no sign of it returning to me any time soon.

I am enjoying the delights of driving my XJS every day, which is great but a swine to keep clean and the fuel bills are starting to make my teeth itch.

Woe, woe and thrice woe.....

Fraser.

[J44EAG]

This is becoming a saga, Fraser.

Sorry to hear you still have problems. Would have been good to have your car on the STR display at Weston.

Mike

[Occulomency]

It's home!

As ever, some good news, some not so good.

The timing chain hadn't jumped a sprocket, huge sigh of relief all round on that one.

The current thinking is that a tiny little flaw in an intake manifold gasket caused the left bank to run lean, probably since the car was new. As the air leak became worse, the left bank ran leaner and leaner, causing the chain of failures culminating in the loss of the supercharger and left hand catalytic converter.

Had I known that the P0430 code (Left Cat under performance) that I have lived with for two years was actually due to lean running caused by air leaks, I would have got this stuff fixed sooner and avoided myself this huge bill. My fault and a hard and expensive lesson learned.

On the plus side, the repair has transformed the car. It is so responsive, so gut-wrenchingly fast, so smooth, I'm delighted with it again.

I have to compliment the guys at Neil Harrod's in Mansfield for their perseverance. Six weeks of not giving up and logically and systematically diagnosing the issues have saved me a shed load of cash. I'm very impressed with them.

So, all I need to do now is replace the Cats and the car will be back to it's wonderful best.

I'm so glad to have it back.

Fraser.

[J44EAG]

Glad to hear the happy ending, Fraser.

A lesson there for all V engined cars then. Keep those inlet manifolds tightened down. I`ll be having a go at mine when I get back from Weston Park.

Always good to have a recommendation for technical service guys. Worth their weight in gold.

I don`t know if it is worth trying to source secondhand cats to keep costs down. Might be worth giving Eurojag a call. Their parts come with a warranty, all be it a short one.

Good result, Fraser.

Mike

[Montana5]

Glad you are all sorted Fraser, an interesting conclusion.

Doug.