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Old 14th February 2020, 08:33   #1
StewartIngram
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Default KV6 petrol poor starting from cold

Although generally my KV6 is fine, I have a couple of issues that are bugging me. With the warmer weather not far round the corner, I am thinking ahead of fixing these but could do with some help.
The car is a petrol model mk1 53 plate, in very good condition at around 90k miles, purchased around 14 months ago. I have since converted it to lpg - not my first - and would add that it always starts on petrol, switching automatically over to gas about 1/2 mile later.
1 - When starting first thing in the morning, it takes about 15 seconds or more of turning over to fire. Sometimes, as it initially fires, it almost stops then picks up ok. I would describe it as a faulty "choke", though obviously there is no choke as it is fuel injection! Once started it runs ok, though there is a bit of a "burbly growl" (hard to describe) until fully warmed up. During this time it will (un-noticeably) switch to gas with no change in performance. Once warmed up it purrs as normal. I would add that the temperature gauge, and heater, perform as I would expect (having lived with a KV6 since 2007).
2 - the second fault is probably unrelated, but I mention it just in case.
If I am following a lorry at say 50mph, and accelerate to overtake, normally no problem. But if I use a touch more throttle, I get the engine warning light flash. If I throttle back a tad, it goes off. But if I don't, the light then stays on. Probably a consistent 3500+ rpm. Bear in mind that I will normally be on lpg! When I check with my code reader, it always refers to a cylinder 6 problem; I have checked/replaced the plug & ignition coil there. I suspect that this is a fault with the tuning of the lpg, and when it turns warmer I'll give it a go with the laptop. But as the gas computer reads off the petrol computer, it just might be showing up a fault connected with fault 1? Yesterday I did a quick test on the open road, changing down to 3rd and switching back to petrol, with the revs kept up it seemed ok. This does point to the lpg needing a remap I reckon.

My gut feeling is that fault 1 is related to the petrol mixture available when cold - it is perfect when warm - possibly sensor related?

Stewart
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Old 14th February 2020, 16:33   #2
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The choke, I believe, is that the injectors stay open that fraction longer to let more fuel into the engine.

I expect somebody on the forum will know for certain.---
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Old 15th February 2020, 10:19   #3
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I have since converted it to lpg .... and would add that it always starts on petrol ....
1 - When starting first thing in the morning, it takes about 15 seconds or more of turning over to fire. Sometimes, as it initially fires, it almost stops then picks up ok.
Hi Stewart,

That is clearly abnormal and I would say is more likely to be ignition related than petrol. I would begin with a full engine service, looking out for poor electrical connections and paying particular attention to the sparking plugs.

Since we are in the middle of winter, check that your battery is fully charged by putting it on a smart charger for 24 hours.

The other possibility is that the fault is a result of the LPG conversion but I cannot help you with that.

Simon
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Old 15th February 2020, 14:32   #4
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Thanks for the reply, I'm open to all suggestions!
Just to give a little more background:
I've owned 3x 75, all KV6 auto and all converted to lpg by me. I'm not a trained mechanic, but my late grandad helped me when I started driving in 1967. Since then I have done 99.9% of my own maintenance.
The 3x 75 are as follows:
Gold 2007-2017. Heavily refurbished over the years. Following a brake pipe failure, stripped for spares.
Blue 2017-2018. More refurbishment on this one, many new parts fitted ready for the future. Following a minor scrape on a wheel arch, (not my fault) the insurance wrote it off, but I intended to keep it and get it repaired; whilst awaiting the payment I lost all the engine oil. Once again, stripped for spares. Some are already fitted to the present one.
Silver 2018-present. I can't believe my luck in finding this one, in such excellent condition. Again now has lpg fitted.

OK, what have I done that could be relevant?
Because of fault 2, I have checked and changed cyl 6 plug and coil. No problems found. Going back to fault 1; as the same components are used on petrol and lpg, I wouldn't expect an ignition fault unless the symptoms occurred on both fuels. (Although a worn plug can show a misfire on lpg before petrol). No 6 plug was clean and perfect; as I put new iridium ones in when I did the conversion I expected that. Incidentally, on the gold car, iridiums lasted the life of the car - and also the blue one - never had a problem with them on lpg (and yes I did check them). They last well.
I suspect petrol related, under starting conditions only. Everything is fine once the initial warm-up is done.
I have started simple part swops, nothing dramatic until the weather improves!
On the throttle body, the fuel purge valve has been changed, along with the
IAT/MAP sensor, both from the other cars and easy to change.
The IACV was stripped and cleaned soon after I got the car. I do wonder if this could be the problem, it is on the to-do list again.
Reading the blurb on RAVE, when cold starting there are temp sensors and valves such as this one which might be relevant, I will eventually go through the lot! I'm lucky to have plenty of (known good) spares, just need the right weather! A little advice from the good guys on here wouldn't come amiss though. If I do find anything, I will certainly post it.

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Old 15th February 2020, 19:30   #5
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The car is a petrol model mk1 53 plate, - - and would add that it always starts on petrol, switching automatically over to gas about 1/2 mile later. - - - When starting first thing in the morning, it takes about 15 seconds or more of turning over to fire.
Maybe a fuel delivery pressure issue? Does the in-tank filter have the Fabled Orange Clip (FOC) in place? If not, fit one and eliminate that problem.


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Old 15th February 2020, 20:39   #6
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Get help to spray some cold start into the air inlet. If the engine starts immediately you will know it's fuel related.
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Old 15th February 2020, 21:42   #7
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Maybe a fuel delivery pressure issue? Does the in-tank filter have the Fabled Orange Clip (FOC) in place? If not, fit one and eliminate that problem.


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OK this orange clip is new to me? How do I check it.
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Old 15th February 2020, 21:57   #8
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The MIL light is down to the LPG tricking the sensors (thinking they are running lean) I have had this on a couple of lpg 75's, nothing to worry about, just slightly annoying.

You might be lucky enough to download a map that will clear the light, I wasn't! and I tried for about a year
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Old 16th February 2020, 09:17   #9
StewartIngram
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The other 2 75s were ok on lpg. If anything this one is better - I now get about 250 miles per tank, the others started off at 200, with best at 220. However this one does have the MIL come on. I still have to try a remap, but that requires a second driver as I have to do it on the road. A roundtoit methinks.
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Old 16th February 2020, 15:15   #10
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OK this orange clip is new to me? How do I check it.
The Fabled Orange Clip (FOC) is MGR's fix for the later (2001-on) fuel filter module, which tends to separate. This is called 'FFS' (Fuel Filter Syndrome). The module has a body/housing for the filter and a 'screw-on' cap. To check for or fit the clip, you need to access the fuel tank. This means lifting the rear seat cushion and removing the floor hatch on the left hand side.

HowTo: https://the75andztclub.co.uk/forum/s...ad.php?t=58868

There's a HowTo remove the seat cushion (saloon) if you need it.

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