Intermittent starting issue
- Thread starter skahigh
- Start date
i plugged in Carista today and graphed some nice plots on the Torque APP . . .
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of Engine RPM vs Engine LOAD, vs Fuel Rail Pressure.
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from these we can see, . . .
Engine tick over @ 900rpm we get about 30,000Kpa rail pressure.
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accelerating with engine load we can see upto 170,000Kpa,
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during stop / start SHUT DOWNS rail pressure bleeds down to 0Kpa ( 300Kpa)
so NO Rail pressure.
.....
during stop / start RESTARTS. - rail pressure rises to over 30,000Kpa almost instantly
.
++++++++++++++++++++
additional graphs showing instant rise of rail pressure. . . .
.
++++++++++
of Engine RPM vs Engine LOAD, vs Fuel Rail Pressure.
+++++
+++++
from these we can see, . . .
Engine tick over @ 900rpm we get about 30,000Kpa rail pressure.
+++
accelerating with engine load we can see upto 170,000Kpa,
+++++
during stop / start SHUT DOWNS rail pressure bleeds down to 0Kpa ( 300Kpa)
so NO Rail pressure.
.....
during stop / start RESTARTS. - rail pressure rises to over 30,000Kpa almost instantly
.
++++++++++++++++++++
additional graphs showing instant rise of rail pressure. . . .
.
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charting your data the plot looks similar . . .
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tick over rail pressure about 30,000Kpa
Load acceleration > 90,000Kpa or higher
shutdown event - <900Kpa
++++
+++++++++++++++++
As an interested observer of this discussion, and trying to understand the interlinking of the 100s/1000's of lines of IDE values that the ECU and all the other control units are looking at to keep these vehicles running! So, thinking aloud -
The numbers in "IDE00416 Starter control: terminal 50 feedback" appear to confirm that the starter is operating as shown by the rise in engine rpm.
However, I am curious as to why "IDE00412 Starter control: terminal 50" remains "active" in the above known good start, but is "not active" during cranking in skahigh's original no start data, shown in Dellmassive's post #12 - except for one line, presumably when the key was turned to start position?
What controls the "active/not active" flag?
Does the ECU interpret the Starter control Terminal 50 "active/not active" flag as a cross check that the starter is operating?
Could the ECU see the starter as "not active" and therefore doesn't command the fuel rail pressure control valve to operate?
Have I missed something obvious?
Looking forward to my further education on our beloved ECU's!
Cheers
Simon
My assumption is IDE00412 is indeed only a recording of the key in start position. In the snippet below the key was very briefly flipped into start position - just to catch the timing of events following it.
There are quite a number of parameters available - unfortunately only 12 can be recorded simultaneously - thus several recordings are needed to catch them all. Below a recording of glow plugs, starter relays, etc. trying to understand/document what's going on at startup (cold engine at +24 ℃ ambient temperature)
In the above IGNition was turned off from 25.22 to 26.14 seconds to initiate engine starting sequence from the beginning.
Not at all since I took the passenger seat out and cleaned those contacts.
In the interim, the van has been serviced including a new fuel filter and fuel system cleaner (I had pondered whether the latter might help to fix a sticky valve). The weather has also warmed up.
Very annoying, I'm actually wanting it to happen again now so I can do a bit more debugging! I'm carrying the laptop and VCDS cable around at all times just in case.
Bit of an update. The issue finally reoccurred after an evening spent parked at an angle on a slope on my mother in laws drive. About a quarter of a tank of fuel remaining.
I whipped the laptop out and ran the fuel pump test. At first it made a rhythmic clicking sound (solenoid?) from the rear and then after two or three goes the usual loud rhythmic pump whirring sound began. After that the van started straight away.
This suggests to me:
- Not a wiring issue as there was activity from the rear when running the pump test
- faulty pump or an issue with the fuel pickup leaving it dry initially?
I whipped the laptop out and ran the fuel pump test. At first it made a rhythmic clicking sound (solenoid?) from the rear and then after two or three goes the usual loud rhythmic pump whirring sound began. After that the van started straight away.
This suggests to me:
- Not a wiring issue as there was activity from the rear when running the pump test
- faulty pump or an issue with the fuel pickup leaving it dry initially?
sounds interesting. . .
Hi there, I have not resolved my issue yet but, I do believe I have narrowed it down to a problem with the lift pump since the usual pump sound is different when running the fuel electronics test when the issue occurs.
I wouldn't have had a chance of narrowing it down without buying a vcds cable.
jordanL
Member
What's a vcds cable? Is it a diagnostic machine? How would I use it and make sure its used at the right time etc?
I have a strange situation. Noticed sometimes if I leave the ignition on for a few mins without starting first thing in the morning it’ll take few cranks to start like the battery is low almost but it’ll start. If I start straight away after ignition on it’ll start ok. I’ve been monitoring fuel pressures in obd11 and after I shut off the van the pressure goes from 30,000kpa to 0kpa. Im not overly convinced with OBD11 as an advanced diagnostics tool as it’s limited on the T6 and I can’t see injector values. so I have VCDS on the way. I’m thinking it’s either pressure regulator or possibly injectors letting by. TBC……
Sounds like the van turns glow plugs off during that few minutes if you don't start the van, hence there will not be enough heat when you actually do.
Glow plugs do eat lot of power, it makes sense to not run them too long. Would be better to cycle the ignition if you have to keep it on for some time before starting.
Ah makes sense. I was thinking glow plug issue but maybe I’m causing the issue.
I have been monitoring for rail pressure today and when start stop kicks in the rail pressure drops in about 15 seconds to 200kps from 32000kpa. Could it be the fuel pressure regulator or an injector leaking off?
the fuel rail bleeds down pressure quickly after key off - thats normal.
Oh right, maybe I’m mistaken. I thought I read that the rail pressure should stay pressurised and even rise due to heat soak?
Correct - for petrol engines.
