Jabba
28-09-2014, 11:50 PM
Had the 4.0 for a couple of months and so far have fixed a few 'annoyances' and defects - but there is one I can't get to the bottom of and is probably why the previous owner passed it on.
Does anyone have any idea why a 4.0 would be hard to start when hot, usually after 'motorway' exercise ? If left for 30 minutes it starts, usually on second attempt. Around town and trips to the supermarket etc it tends to start OK, it cranks longer than usual but it does start. The car starts first time every time on the first turn of the key cold. I really need to fix this issue, you don't get many bites at the apple to start this car - three attempts and it is game over for the battery, wouldn't mind but it's a new 110 Ah battery, the charge voltage is OK, the BEMS is properly coded.
There are no errors recorded at all that would indicate a cause for this, I stupidly replaced the crank sensor based on information in a forum - without thinking - if a crank or camshaft sensor was failing the system would throw an 'implausible signal' fault when the two didn't correlate, for there to be no error both must be failing. The replacement made no damn difference, didn't fix it, ordered a camshaft sensor at the same time but can't even find the bugger so no idea how I'm going to replace it when it finally arrives.
I've measured the engine temperature sensors in VCDS and they are OK when hot or cold - the block sensor is a B*****D to change anyhow as it is underneath the AC compressor - 4 hours work, one AC degass and recharge - for a £25 sensor - but this has to be a garage because you can't run the 4.0 AC compressor with no charge in the system - it has no clutch so running it dry is certain death for it. So conservative estimate £300 to fix a pox bottle sensor that could be done in 10 minutes if sensibly located.
I have reproduced the error on the driveway - got it good and hot, real good heat soak then left 10 minutes - temperature sensor at 92 Deg C. I noticed that the fuel pressure didn't want to rise above 50bar - this is bad, it started second turn of the key but I don't know what changed because VCDS loses communication if you turn off the ignition - which you must do in order to try and start again. Fuel pressure at tickover when running is a little over 300bar - which seems low for a common rail - I'm not about to change the high pressure pump on a whim since this requires specialist tools (engine must be lowered on a special bridge).
I have Elsawin but frankly it is useless - contains nowhere near enough information to do sensible diagnosis - no fuel pressures, no dataflows, no startup sequencing, no 'sensor involvement' diagrams nothing. without adequate information it can be very hard to identify the issue even when you can see the sensors - since you don't know what they are 'supposed' to be for any give condition.
This engine is way too complex to go poking around in the dark, and Audi are way too greedy - they want £150 for a 1 hour diagnostic session with no guaranteed resolution which is a right royal p**s take. Then they would probably start playing swap the part 'roulette' at my expense just in the hope of getting lucky - which would be a very expensive exercise.
Sticky fuel pressure regulator (but no fault in system), air in system ? (but why starts first time cold after standing for days), high pressure fuel pump ? (but running pressures no different when cold).
I'm going to replace the fuel filter since the previous owner (or his garage) decided to destroy the fuel pipes by fitting them with jubilee clips - which they then overtightened and seriously deformed the fuel feed and return line (hope I can recover them Audi want £300 for new ones) - looks like a 'no brand' filter too - but if this were bad the cold start would be bad.
Basically I'm out of ideas on the hot start issue, I'm open to ideas, I could also do with a decent label file for the 4.0 engine ECU for VCDS - may sound surprising but Ross Tech don't have one.
Does anyone have any idea why a 4.0 would be hard to start when hot, usually after 'motorway' exercise ? If left for 30 minutes it starts, usually on second attempt. Around town and trips to the supermarket etc it tends to start OK, it cranks longer than usual but it does start. The car starts first time every time on the first turn of the key cold. I really need to fix this issue, you don't get many bites at the apple to start this car - three attempts and it is game over for the battery, wouldn't mind but it's a new 110 Ah battery, the charge voltage is OK, the BEMS is properly coded.
There are no errors recorded at all that would indicate a cause for this, I stupidly replaced the crank sensor based on information in a forum - without thinking - if a crank or camshaft sensor was failing the system would throw an 'implausible signal' fault when the two didn't correlate, for there to be no error both must be failing. The replacement made no damn difference, didn't fix it, ordered a camshaft sensor at the same time but can't even find the bugger so no idea how I'm going to replace it when it finally arrives.
I've measured the engine temperature sensors in VCDS and they are OK when hot or cold - the block sensor is a B*****D to change anyhow as it is underneath the AC compressor - 4 hours work, one AC degass and recharge - for a £25 sensor - but this has to be a garage because you can't run the 4.0 AC compressor with no charge in the system - it has no clutch so running it dry is certain death for it. So conservative estimate £300 to fix a pox bottle sensor that could be done in 10 minutes if sensibly located.
I have reproduced the error on the driveway - got it good and hot, real good heat soak then left 10 minutes - temperature sensor at 92 Deg C. I noticed that the fuel pressure didn't want to rise above 50bar - this is bad, it started second turn of the key but I don't know what changed because VCDS loses communication if you turn off the ignition - which you must do in order to try and start again. Fuel pressure at tickover when running is a little over 300bar - which seems low for a common rail - I'm not about to change the high pressure pump on a whim since this requires specialist tools (engine must be lowered on a special bridge).
I have Elsawin but frankly it is useless - contains nowhere near enough information to do sensible diagnosis - no fuel pressures, no dataflows, no startup sequencing, no 'sensor involvement' diagrams nothing. without adequate information it can be very hard to identify the issue even when you can see the sensors - since you don't know what they are 'supposed' to be for any give condition.
This engine is way too complex to go poking around in the dark, and Audi are way too greedy - they want £150 for a 1 hour diagnostic session with no guaranteed resolution which is a right royal p**s take. Then they would probably start playing swap the part 'roulette' at my expense just in the hope of getting lucky - which would be a very expensive exercise.
Sticky fuel pressure regulator (but no fault in system), air in system ? (but why starts first time cold after standing for days), high pressure fuel pump ? (but running pressures no different when cold).
I'm going to replace the fuel filter since the previous owner (or his garage) decided to destroy the fuel pipes by fitting them with jubilee clips - which they then overtightened and seriously deformed the fuel feed and return line (hope I can recover them Audi want £300 for new ones) - looks like a 'no brand' filter too - but if this were bad the cold start would be bad.
Basically I'm out of ideas on the hot start issue, I'm open to ideas, I could also do with a decent label file for the 4.0 engine ECU for VCDS - may sound surprising but Ross Tech don't have one.