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Post by valhalla on Feb 27, 2015 1:23:51 GMT 1
Does anyone know if a throttle-body adaption (lower stop) DTC will inhibit a start on a VW 1.4 petrol of this vintage? I have an unusual car that refuses point-blank to breakdown on me, yet has been a problem on and off for the long-suffering customer for a year now.
The symptom as I can pinpoint it is that the car cranks, but will not fire, first thing on a cold morning. Once it has been left for 20mins after a non-start, you can go back to it, turn the key, and it starts first-time, and will not play-up again for the rest of the day. It does this only occasionally, maybe once a fortnight after very cold park-up overnight.
My first thoughts are crank-sensor or cam-sensor intermittent breakdown, but I see no codes over VCDS, but I do see a recent couple of codes for throttle lower stop adaption out-of-range (with attendant zero-rpm freeze-frames). Live data on all of the channels during a start for me (i.e. a successful one each time) shows no issues on coolant sensor, engine rpm, throttle voltages. I know the customer is not making this one up, but I cannot keep the car forever! Fuel pressure is good to the engine when cold, and the pump doesn't sound unusual in any way.
The history on this Golf is that it was reported that the starter motor was "grinding" during some cold-starts last Winter, and I eventually put a new motor/solenoid assembly on it, after having previously cleaned all power-distributions and earths around the battery/starter/fusebox/inner-wing areas, when the customer came back after a week to say it was doing it again. I have since then modified the main battery earth lead to connect directly to the starter earth lead terminal, rather than feeding current through the inner wing, and thus earthing the whole battery current through the body-post that would have previously just had the starter lead attached. I am told this has made no difference to the non-starting habit, which comes back after a week or two. The battery has also been tested (it's a recent Bosch Silver unit) and the only thing I can find slightly unusual is that the terminal voltage is showing 11.6v on the ECU at KOEO prior to start, having previously measured 12.7v key-off with the multimeter. No issues with alternator control after start, straight up to 14.1v.
I have cleared all the codes down (there were 5 in total in the ECU, including 3 old codes from near-new) in order to have a clean-slate to work with. The trouble I have is that there is only one chance each day to try this.....and I'm having to leave the vehicle outside in the sleet and snow to best simulate conditions with the customer......
Many thanks for any help anyone can offer.
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Post by jmac200t on Feb 27, 2015 1:48:41 GMT 1
If He has a second key i would just try it to rule it out.
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french crap fanatic
Apprentice
french car specialist based in dagenham east london
Posts: 3,355
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Post by french crap fanatic on Feb 27, 2015 2:32:21 GMT 1
Does this car have a electric distribution board on top of battery? I've seen these go bad and do odd things! I've also had one which had a hairline crack that you could only really see under a magnifying glass! I've also seen Bosch batteries fail and cause low voltage during cranking,car seems to spin ok but won't fire!!! Last of all,some American cars used to fill up at a petrol station which had a phone transmitter nearby! Afterwards they wouldn't fire up,the AA/rac knew about this problem and would tow them a bit further and hey presto! Think they were explorers!
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Post by natedog on Feb 27, 2015 5:14:40 GMT 1
There's 3 parking spaces at my local asda that seem to generate lots of non starts. Rolling the car backwards a few feet gets most of them running. I didn't believe it when I went out to my 1st job there, and was told to push the car out the space before trying anything else.
Does the punter always park in the same place when it has the problem? Can't see it being likely though.
Does this one have an earth under the battery tray like the mk4 and 5 did? Seen a fee with that earth broken which will cause starting problems. Or the fuse box by the battery as already mentioned
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Post by Noberator on Feb 27, 2015 11:23:13 GMT 1
Valhalla I've heard of Skoda having issues with cold start on these engines or a noise when started from cold. Due to this I believe VAG issued an internal TB for all Main Dealers to address this issue.It may be worth a phone call to your local VW Dealer and speak to someone technical . From memory I believe the fix is an ECU reprogramme.
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Post by valhalla on Feb 27, 2015 12:13:28 GMT 1
Thanks for all of the tips, guys. I'll try and answer the points you raised in reverse order;
Nobster - The ECU re-program might well be the answer; one of the really old faults logged in the ECU, around the time the car was in its first year, was an internal processor checksum failure. I had assumed that this was due to a dealer re-flash, but the thought is now seeded in my mind that this could be the root of the problem. I think I will exhaust all the other possibilities first, as I hoped it would be a simple case of power-distribution and/or voltage drop at the ECU during crank. I have seen some controllers (not Bosch) that have quite high voltage thresholds for cut-off in the software by-default, easily surpassed on a cold crank, and have had to have a revised voltage threshold re-flashed to cure during engine development.
Natedog - My thoughts all along, exactly the reason why I thought it might be a good idea to take-out the silly bit of VW design that feeds the whole battery -ve into a single post on the inner wing, then feeds the starter current out of a second post on the other side of the fusebox on the inner-wing near the starter-motor. By putting a large battery -ve lead straight to the starter motor body-post, the cranking current plus whatever the car needs to power it up can both flow through the new lead, then the starter post only needs to carry the current to keep ther car powered-up. This doesn't seem to have made things any better in this case, but I'm leaving it on until the problem is solved.
FCF - The Bosch battery is still a concern, especially with the point Nobster makes above. I'm going to get this car into the workshop tonight, so I can leave the Pico leads on the battery and ECU, for a cold-start tomorrow morning. The battery does appear quite new, but this would not be the first time I have had trouble with this make....
Natedog / FCF - The customer always parks in the same place, at the top of their drive, when the problem occurs. However, I'm told it did it once away from home, so I have discounted that problem for a time-being. I'm also sure that he told me that it did the problem with both of the keys, but I think in this case it would be worth my while to try a second key myself. Is there any outward sign on the dash that the engine is imobilised, in case I need to get the customer to look out for this?
FCF - The battery does not have that old distribution board on top of it. It looks like VW worked-out why the design was a bit iffy, and re-positioned the board alongside the battery with the fuse/relay box integral. I have checked inside the box for any signs of cracking on the strips of conductor - none to be seen, but now you mention it, I'm going to have a better look with a magnifying glass, just to be sure....... I have also stripped and cleaned all of the main terminals that come off the front of the +ve buss-bar, twice now, with no effect. All in all, that bit of the car looks good.
So I'm going to chip away at this one, but a call to the VW dealer may well be imminent!
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Post by Noberator on Feb 27, 2015 15:15:45 GMT 1
Can you let us know the outcome Valhalla please.
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Post by Karl on Feb 27, 2015 19:18:44 GMT 1
Don't these TSI engines suffer from carbon build up on valves giving cold start mis fires etc....
Not the cause on this more a question
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Post by Noberator on Feb 27, 2015 21:58:49 GMT 1
Don't these TSI engines suffer from carbon build up on valves giving cold start mis fires etc.... Not the cause on this more a question Yes if it's the twincharge version. :- There's two versions of these ones a 120 bhp turbo charge the other is a supercharger as well as a turbocharger with about 160 bhp. The twincharge engine has gained a reputation for problems with the timing chain and is being replaced in several models by a different engine. The twincharge engine needs to have the oil and filter changed according to the service schedule and using the recommended grade of oil is a major cause.
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Post by Dragon on Feb 27, 2015 22:59:10 GMT 1
Internal check sum errors = screwed control unit, I've changed plenty of them for this fault, also don't be surprised if once it's replaced the real reason it's gone pear shaped shows up i.e. shorted lambda heater circuits or egr faults or problem setting idle stops i.e. stiff throttle butterfly, they can als go south if they have been jumped started.
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Post by valhalla on Feb 28, 2015 1:02:47 GMT 1
Thanks Dragon, I'm trying to tackle the car from the basics, so hopefully should have investigated the throttle motor before a new ECU is fitted. The Lambda heaters seem plausible, if VCDS is to be believed. I got a couple of good resistance measurements yesterday when I whizzed through the live data.
At present, using the above advice as clues to problems, I'm going to plump for the battery being the culprit. I hope to get some decent voltage drop measures tomorrow lunchtime, if nothing else it will back-up the internal voltages that I'm seeing during cold crank at the ECU. Conversely enough, by making the starter motor high-current circuit as efficient as possible, I might have exacerbated the whole issue at the ECU, i.e. the starter motor is capable of pulling-down the battery voltage much worse as the engine starts to turn. Part-warm repeated cranks (allowing for the surface charge to disipate between each for 3mins) at around 20celcius coolant temperature can occasionally show a minimum ECU voltage of 8.1volts over VCDS, which means that the Pico measures at a decent logging rate should be interesting. Allowing for the rotten update rate on VCDS data, sometimes there genuinely seems to be more voltage drop at the ECU than others. The blasted thing still starts though......
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Post by Rhubarb on Feb 28, 2015 1:11:44 GMT 1
I notice you now have a volt drop, so methinks you may need to run in a better/additional earth? It does sound like the cranksensor to me... Old fashioned way, resistance check, a/c or scope check whilst running.
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Post by Dragon on Feb 28, 2015 13:13:28 GMT 1
Does this have a ecu relay ? might be worth checking or by passing?
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Post by Deleted on Feb 28, 2015 13:29:16 GMT 1
Have you considered an intermittant compression problem ,
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Post by valhalla on Feb 28, 2015 18:43:34 GMT 1
Have you considered an intermittant compression problem , Mac, Good point, and the answer is "no", that's something that didn't occur to me, but it's something I'm going to look into now. I have a confession to make, and that is I have made a mistake over the engine code, this is not a TSI, just a bog-standard 59kW engine. That might obviate the risks of dodgy valve-seating a bit? I have tried to get some history on this car, but everything from AutoData onwards cannot recognise the registration, certainly nothing of any use. In fact, AD seems to have nothing of any use on the Mk.6 Golf for the engine management system whatsoever. I lifted the boot carpet this afternoon to reveal that the car is a basic Golf 1.4 Trend (5K1_2B1), which I believe was a "student" edition of the Mk.6 Golf? Cetainly I was surprised to see that the engine code was CGGA, which makes it a 59kW. Serves me right for not peering down the side of the engine for the turbo..... I did a battery drop test this afternoon, and although the Pico Diags analysis of the whole thing was OK, albeit battery discharged, I wasn't happy at all with what I saw from the battery. I repeated the test with a part-warm engine in a manual oscilloscope configuration (battery voltage, starter current, starter + terminal volts, starter casing earth voltage) and considering that the battery had warmed slightly alongside the engine, the drop across it at 500A was not great, not much more voltage than 7v at this stage of the crank, so perilously close to injection shut-off. The voltage drops elsewhere in the system were fine, around .8v battery earth to starter motor casing, and not much at all between the battery +ve post and the starter main terminal. I'm leaving all the gear on the car tonight, with the battery on charge, then I'm going to repeat the test tomorrow, probably just in "manual" oscilloscope mode, as I'm a bit suspicious of the Pico analysis at this stage, and its aquisition/display of data has just got in the way today. The customer tells me that the battery has not been changed recently, but I'm not sure that the car left the factory with a Bosch S3 on it. Either way, if there is any doubt in the matter, the battery is going to be changed, and probably I'll seek out the best that will fit in the tray. I'm not a big fan of these Bosch batteries (whether they're OEM or not), and I've seen too many "conventional" cars have trouble on cold mornings with them, let alone a design that seems as sensitive as this Golf. If anyone has direct experience of other makes on this sort of application, I would be much appreciative of advice. My personal preference would have been to go to Varta (OEM to so many Landrover products) or Yuasa (never had any trouble with these).
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