AJ198T
Member Since: 24 Jul 2015
Location: Sheffield
Posts: 62
  
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Strange and stubborn issue and getting nowhere so far diagnosing.
No error codes, no check engine light, no LPG fitted. 180k
On first start of the day it fires up no problem and the revs settle and are smooth but if you blip the throttle it seems to not want to respond much to the pedal and stumbles/misfires unless you press down and the revs climb higher. A minute or so later you can't replicate this. But the car feels a bit short on low end power most of the time, fine after 3000 or so revs.
No difference either side of new spark plugs, new air filter, different MAF, can of BG44k through the tank, cleaned throttle body. Handed over to mechanic who has done some deep level diagnostics with various machines, he said readings indicate possible lean condition on startup and maybe (but less certain) under initial acceleration, suggestive of air or fuel issue. Did a smoke test for vacuum leaks and found PCV valve and EGR leaking which we thought was bound to be it, but nope, new ones on and no difference. Fuel pressure seems fine. Compression test fine. Coils seem fine.
I'm going to get a new fuel cap just in case original is leaking air, but i believe there would likely be an info message on the dash if this were the case.
Only things seemingly left are either something injector wise which he's leaning towards (although in-situ readings are even across all) or, less likely, exhaust valve leaking under combustion pressure. I seriously hope it's not the latter.
I'm going to have the injectors tested and cleaned but it'll have to wait for a couple of weeks so thought I'd check on here in the meantime in case this rang any bells with anyone...
Cheers, AJ
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 23rd Nov 2020 6:26 pm |
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pagoda
Member Since: 13 Aug 2009
Location: Not London Anymore (or the US for that matter)
Posts: 1923
  
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You seem to have done most of the things that one would go to. Have you checked the oil filler cap is seated correctly? PAGODA
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| 23rd Nov 2020 7:32 pm |
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MintyHit
Member Since: 25 Jul 2017
Location: Bradford on Avon
Posts: 227
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Do you have an IID tool? Perhaps check the fuel trim to see if you have an air leak somewhere... might also indentify if you have a injector issue.
What was the results of your compression test?
Best
James
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| 23rd Nov 2020 8:39 pm |
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AJ198T
Member Since: 24 Jul 2015
Location: Sheffield
Posts: 62
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He said the compression test was fine. I'll hopefully get an IID for Xmas but I think the mechanic's system will do the same and more so I'm not sure I could find anything he hasn't on that front.
Prior to him looking at it I did hook it up to a kind forum member's IID but no codes were present apart form the usual body control stuff and a knock sensor which was replaced (wiring to it was pinched in the inlet manifold) and made no difference. Same for mechanic, no error codes. He said the fuel trims were indicating lean condition (bank 1 I think), and thought addressing the leaking EGR and PCV would do it but no joy. He did reset the adaptations too.
I've wondered if something to do with the throttle body e.g. a misread of the pedal or butterfly position with it being fly by wire. The issue is only when pressing the throttle, not on tickover. But I don't know enough about how that all works and the mechanic hasn't mentioned it as a possible culprit so it's probably a dead end.
I'll get the readouts when I pick the car up later this week. And I'll check the oil filler cap too.
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| 24th Nov 2020 7:34 pm |
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Discoveringcomfort
Member Since: 16 Sep 2015
Location: Berkshire
Posts: 637
 
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I noticed this on mine this afternoon after a week of non use. It cleared petty quickly but will check tomorrow morning. Series 1 V8
Series 2 Hibrid V8
Discovery 3 HSE V8
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| 25th Nov 2020 7:39 pm |
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AJ198T
Member Since: 24 Jul 2015
Location: Sheffield
Posts: 62
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Well, now you've said that, there is a chance the origin of this may have been a rough start after a week of non-use a while back. I can't remember exactly when I first noticed the slight lack of power when driving as it's not super obvious nor the throttle issue but it could well have been from then. It's never struggled to start since though, even when left for a week, so I hadn't thought about the connection.
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| 25th Nov 2020 7:51 pm |
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Discoveringcomfort
Member Since: 16 Sep 2015
Location: Berkshire
Posts: 637
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Mine runs fine in tickover with the cold start raising the RPM, after a short time the RPM drops back to normal but it stumbles a bit on tickover until it warms up a bit more. It is as if the cold start has been turned off to early? Series 1 V8
Series 2 Hibrid V8
Discovery 3 HSE V8
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| 27th Nov 2020 6:01 pm |
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