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Surging on the overrun at around 1800 rpm - 3.0 V6


Lazlo Woodbine
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Hello.

I'm not an expert on engine management but I am aware of "fuel cut" on the overrun in EFI systems. I would expect the system to turn fuelling back up/on (depending on whether it's a partial or total cut) at 1500 - 2000 rpm.

The problem I'm getting is a surge as I slow in gear with a closed throttle and it's reliably as I get to around 1800 rpm. It's not violent as such but it makes driving smoothly very difficult and frustrating, in fact I often end up either having to use the brakes inappropriately to overcome the surge or just using a lower gear than should be necessary. When driving hard it's not an issue (although engine braking is not as good as I'd like) but trickling along in traffic can be quite a task.

I'm thinking that the ecu is a bit to keen in turning the fuel back on/up but further than that I'm not so sure. Is what I'm describing to be expected? I would hope not as coming off the brakes after being on them for a few seconds only to then suddenly gain 5 mph because the revs happened to have dropped below 2k is a bit silly. Has anyone else had a similar issue?
 

 

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I have no fault codes either present or pending and apart from this issue the engine seems to be running well. There is a bit of Oil in the inlet manifold which I will be sorting out soon and I did have some funny tickover issues a year ago when I replaced some ABS sensors but I shan't go into that yet.

I changed the Oil and air filter today, I will be doing the fuel filter tomorrow. Imminent plans include new spark plugs, cam cover gasket and an Oil catch can to stop the inlet manifold filling with gunk.

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Hi Ralph,

I think you, like me, have one of the rarer manual box cars?

Not saying that your car is not at fault, but I understand that Jag built the ECU on the manual to raise revs for smoother gear changes. Someone more knowledgeable will hopefully confirm details or you could research.

I was almost convinced that I had a vacuum leak or something after removing inlet manifold to get at plugs and coil packs, as when revving, it would go up beautifully, then hover around 1800-1500 rather than returning to what I considered normal idle. 

Since being told this is a design feature, rather than a fault, I have found it easier to live with :wink1:

All the best, Russ

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Hi Russ

Yes it's a manual. I have driven a few automatics but never owned one, they're just not for me. I think a manual box suits the 3.0 V6 so well, it really likes to rev and for "making progress" the manual really lets you use that upper end power to full effect.

I thought that what I see as a problem might been a built in "feature" and have searched for information on it but what with manual S-types being so scarce it's difficult to find. It's not a massive issue but if I can stop it happening I will. What bothers me is that in third gear at 30 mph the revs are right at that point where it starts surging and as I like to drive on the throttle not the brakes (if you see what I mean) it makes town driving tedious.

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Hey Ralph,

Same here, I can appreciate wafting around in an auto could be more relaxing, but the manual Sport was my preference. Lighter, faster, more economical and more engaging. I looked for ages before I found mine and then had to travel for it, but I don't regret it!

I've fitted stainless rear silencers plus a few other cheeky mods that have really brought out the 'Sport' nature of the big cat! Helluva car, especially for the money you can pick them up for :yes:

What you describe does seem to be quite extreme though, worth checking all seals, breathers, vacuum pipes etc. Have you had the manifold off yet and done the coil packs and plugs?

I hope you enjoy yours as much as I have mine!

Cheers, Russ :wink1:

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Hi Russ

I can't imagine it having an auto box to be honest. I was actually very lucky with my car as it almost found me! I'd been idly looking at S-types about 18 months ago but knew I couldn't really afford the manual Sport that I really wanted. Then a few months later my father mentioned his friend was selling "the Jag" but didn't know what it was apart from it being a manual. Well I was expecting a diesel X-type but when it turned out to be this I was amazed. It had many faults and 5 minutes MOT but I got for very cheap and fixed it up, it was due to got to the breakers so I'm glad I got to save it. 

I would like to make mine a little louder but not too much. I can't afford the nice stainless exhaust boxes from Adamesh etc. but if I can find a couple of rotten standard ones to use the front pipes off I may well experiment with some generic re-packable straight though boxes.

I have a pile of used spares including an airbox so I have put a few 1" holes in the old one which make a nice growl on WOT. I made sure they're all on the wing end of the box to (hopefully) suck in only cold air and I kept the original pipe in to the wing. I would ideally run a pipe out to the upper grill aperture in front of the radiator but space is amazingly tight around there.

I will have the inlet manifold and breather system apart soon as I want to change the plugs and the RHS cam cover gasket needs replacing. Also there is a fair bit of Oil getting into the manifold so I'm going to fit an Oil catch can in the PCV system to try and stop that. It may be that that Oil being burnt is exacerbating the surging I suppose. I'll double check for any unmetered air that may be getting in then.    

 

IMG_1669.JPG

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Hi Ralph,

I also picked mine up for a song with known faults, and luckily I can do my own mechanics when required, so it didn't take long before having her running well. I've since spent (much) more than the purchase price on parts and maintenance, but she's pretty well set now. New brakes and tyres inc staggered 275/35/18's on the back, Waxolyed and serviced, helluva car!

After some research I picked up the induction system from an STR (eBay £20), which intakes from above the grill and not the wing. This has a better inlet flow, but I haven't had the chance to fit it yet so can't speak to the benefits. The rear silencers, while not being Adamesh, and a 2nd hand eBay purchase at £60 each, have opened her up nicely. And the boot spoiler was a steal, only c£40 painted and delivered, I'll send a link if of interest.

She's not our only car and I hope to have her indefinitely, even if I get another Jag (XKR) as planned. So I've been viewing most expenses as an investment in her future, rather than just unwanted costs. Being a manual, even the fuel is not that bad, especially when driven sensibly. But driving her sensibly all the time would be missing the point I think! 

Good luck! :wink1:

Rear_snip.JPG

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Hey Russ

I like the look of your car, a spoiler really does improve them. I would be grateful for the link please. I'll investigate the STR intake, it sounds like a good solution.

I just couldn't run the car if I didn't do all the work myself. I think I've only ever paid for work to be done on a car 3 or 4 times in 20 years, the last one was supplying and fitting a gearbox in a Discovery as I thought I couldn't do it on the drive. It came back with a mis-aligned clutch, leaky slave cylinder unions and leaking transfer box which convinced me that whatever the job I will learn how, and/or get the kit, to do it. Except for big paint jobs maybe.

Tis' a helluva car, especially as mine still stands me at less than that out-of-focus dog...

 

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Here is the link to the spoiler, you'll need your paint code. Mine was all the way from Taiwan in about a week, self adhesive too, don't know how they do it!

I've always been similar and could not have been running the car I have without doing my own mechanics. It's only in the last year or so since our business has got busier that I've subbed out the odd job. Like I let the guy strip back, rust proof and then Waxoly the underside of both the Jag and one of our Discoveries, just easier for them to do it on a 4 post lift than for me to do it on axle stands and ramps. At £200 (each), I thought it a good investment and saved me a couple of filthy weekend (sure there's a joke there somewhere!).

Generally though, if I do it myself, I know it's been done right, and like you, when I've subbed out mechanics, I've had some expensive mistakes! Luckily I have a guy I trust now, so if I can't be arsed or don't have the time, it gives me another option :yes:

 

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Thank you for the link. That is not a lot money when you think about it, I may well get one. 

I would like some R rear lights, they're silly money. But I have a plan to tint my own, not the lens itself but inside. I'll let you know how it goes.

My Discovery is far from ready for rust proofing, learning to weld better is my next task..

Waxoiling/filthy weekend: 5907c0c9aa0c9_jeremypeepshow.thumb.jpeg.e6bbc376dfeb68ba28b532fcddd5bf0c.jpeg

 

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Haha, just seen it! I know the show and bet I'd look like this or worse after grinding, brushing and sorting the underside of the car! Which is why letting someone else do it on a 4 post lift seemed the best bet! So you have a Disco as well? I have a 300TDI, currently SORN'd and a TD5 which is the daily drive. Interesting to think they would've been competing for the same money with the S-Type back in the day, i.e. do you want a rugged 7 seater for your £30K, or sporty, luxury mid size executive etc...

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Good, I'm glad you've seen it, there could of been a big misunderstanding there..

Yes I've got a 1990 V8i manual. I bought it because of the wonderful noise. The first thing I did to it was replace the back box with a straight pipe.

It's kind of in limbo at the moment, the chassis is rusty in awkward-to-repair places. It's been sat for over a year now and I really need to get on and learn to weld properly or get rid of it.

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A V8 does make a nice noise, but so does my V6 S-Type with the stainless tail pipes on on TBH :yes:

I did a stint as a fabricator welder, working with 1-5mm plate and box section, and after that, welding cars is a nightmare, it's like they're made of tin foil! My 94' 300TDI has had a new boot floor and some patching, and will need a bit of welding before I put her back on the road, but I have a guy who can do that on the cheap so it's unlikely I'll try it myself.

Speaking of welding, have you had a look under the sill covers on your S-Type? They're a bit notorious for going there, but if you have welding skills, you should be OK :wink1:

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Yes I'm trying to convince Mrs Woodbine that having louder exhausts won't get us burned at the stake. She still shudders at the thought of some of my old cars.. We did see a CLK today which sounded amazing and she said as much so I may be making progress.

I'm not a good welder. I have stuck some thicker stuff ok though and I did weld an exhaust with a stick once.. My discovery has a couple of rotten outriggers, battery tray, sills, roof edges etc. On the chassis the turret for that tubular cross member that (I think) the A arm hangs off has gone to dust. But also the main rail right next to the turret has 4" of the top edge missing and a crack down the outside edge. There's a body mount at the back that needs work, the body has dropped so far I can't open the back door as it's resting on the bumper. Just reading that back makes me want to reach for the matches..

The boot floor is good though.

 

9 hours ago, Russ68 said:

 

Speaking of welding, have you had a look under the sill covers on your S-Type? They're a bit notorious for going there, but if you have welding skills, you should be OK :wink1:

 

Erm, funny you should say that because the last time I jacked up the o/s/r the jacking point changed shape. I've been ignoring it until I get the suspension sorted as it feels like it's trying to put me in the hedge at the moment.

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  • 7 months later...
On 4/20/2017 at 2:05 AM, Lazlo Woodbine said:

an oil catch can to stop the inlet manifold filling with gunk.

Wow, do the S Types still have an Oil Catch Can? If so', is it only on the manual Box version and if not where is the bl^&^y thing?

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I've certainly minimised it. There was a slight air leak around the control flap unit on the back of the inlet manifold and the rubber end of one vacuum line was perished. There's still a noticeable surge as the revs drop to 1800 but not like before. 

The control flaps have a big O ring to seal them and they're silly money to buy. As both flap units are the same I put the top one in the back where it's awkward to get to then fitted the one with leaky O ring to the top with some instant gasket to seal it.

There's no Oil catch tank as standard. I got an after market one to install but haven't yet. There are a few jobs mounting up that I'll do all at the same time, sometime..

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On 20.4.2017 at 2:53 AM, Lazlo Woodbine said:

The problem I'm getting is a surge as I slow in gear with a closed throttle and it's reliably as I get to around 1800 rpm.

This may not help you at all, since yours is a manual, but for 2002.5 to 2004 with automatic transmission, a surge during warm up while driving at around 40mph may require reconfiguration of the transmission control module.

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