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700/900 Series General Forum for the Volvo 740, 760, 780, 940, 960 & S/V90 cars |
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200FT Hard cold start. Pulls like a train when warm.Views : 4152 Replies : 67Users Viewing This Thread : |
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Jul 10th, 2018, 18:14 | #61 |
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Jul 10th, 2018, 21:01 | #62 | |
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Remember sometime back in this thread i commented to someone that no matter what the fault is, the evidence has been there from the start? I genuinely thought you'd already tried refitting the "old" sensor as well. The bit that caused the problem was that you changed the dizzy as well - gave yourself two possibles as being the cause of the non-start. Old engineering rule of thumb when playing "parts-substitution" diagnosis is if adding a different part doesn't fix it, refit the original so as not to confuse the situation. I can only summise that with the dodgy signal from the new sensor, the ECU first saw a cold engine (with resistance) then a hot engine (lower resistance) then a failed sensor (open circuit) that then fixed itself but reported "hot". The older ECUs aren't sophisticated enough to implement a strategy whereby it would try a few different fueling options until the engine started, not sure even that the new ones are! It would seem you've found the fault though! Fingers crossed!
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Jul 20th, 2018, 12:50 | #63 |
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To draw a line under this; the car is sweet now, running fine.
Temperature sensor was the problem - it must have been deteriorating in some way which caused incorrect fuelling, but could be trimmed out by the lambda when warm. If you have similar problems, check the resistance across each pin on the temp sensor, each individually to ground. I found its easily replaced with coolant still in, if you're quick. Also, it helps if you have a deep socket to reach over the eceltrical connector(I used a sparkplug socket with the rubber grommet removed). Thanks again for your help all. Andy |
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Jul 20th, 2018, 13:36 | #64 |
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Glad it's all sorted for you Andy - why did you change the CTS in the first place?
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Jul 20th, 2018, 14:22 | #65 | |
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Glad you got it sorted, wish you many trouble free miles!
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Jul 20th, 2018, 15:27 | #66 | |
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Whilst posting, I say credit to Dave for posting what one should expect re siberia type info in different scenarios. The CTS was already suspect in my ignorant thoughts because disconnecting it allowed the engine to start. But that info from Dave sort of underlined the point. That CTS failed differently from usual failures....moral is be prepared for the unexpected. Above all .... great that it is sorted Andy. Cushti. . Last edited by Stephen Edwin; Jul 20th, 2018 at 16:04. Reason: .... what one SHOULD expect ... that's a better word :) |
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Jul 26th, 2018, 13:24 | #67 |
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Hi all. Was an ebay special. Item 283051494976.
The reason for changing in the first place (seems so long ago..) was just after some googling and forum reading. I didn't actually test the old sensor before just popping the new in. Lesson learnt. It was the parts cannon approach early on. It was always a hunch also that it was running too rich - when I pulled the plugs they were clearly wet with fuel and I was pretty confident spark was good. Temperature sensor, for a few quid seemed like a good place to start, especially as others had seen issues with it, with similar symptoms. |
Jul 26th, 2018, 15:28 | #68 |
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That's a Parts Monster own brand special - normally they dish out pretty good stuff so i'd say you were just unlucky this time.
Also unlucky in your diagnosis, for the same reason medical doctors don't like people "googling" symptoms of illnesses online as very often they come up with a worst case scenario, it seems you may have done the same and instead of curing the problem, made it worse. Engines are designed to run rich when cold, there's no Lambda feedback as the sensors don't work until they reach a certain temperature so it's somewhat arbitrary enrichment - this can also lead to misdiagnosis by reading the plugs in a cold engine. Judging whether a spark is good can also be difficult. If it jumps 1/2" in free air you've got at least 25kV which should be enough to jump 0.6mm in an engine where the pressure is up to about 160-180psi but it needs to be blue in colour to have some strength behind it. If it's more orange and only jumping say 1/4", you're down to about 5-6kV with not much grunt behind it - unlikely to "make the journey" across the plug gap.
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