1.9tdi Hot start issue
Discussion
Several weeks ago Ebay got the better of me and I "won" an 04 Sharan with the 1.9 tdi engine, manual box.
Starts and runs perfectly from cold but after 20/30 minutes(once fully up to temp) if turned off, it flat out refuses to restart. It has to be left about 2/3 hours to get cold enough to start again. No lights on dash.
There are many vag tdi hot start threads but it's hard to know what to do as the hot start problem exists in many guises, a lot of the time there is missing info on exactly what engine, what problem and what cured the problem.
Anyway.....Previous owner had battery checked and had the starter motor and temp sensor replaced, and I've changed the crank sensor but the problem persists.
I haven't had a deep obd diag scan done yet but would have thought if any faults are logged then the eml would be on.
The problem must be that it's not fuelling.
It seems unlikely this is due to lack of the required crank speed due to: 1. the new starter and 2. because I've tried cranking hooked up with jump leads to boost voltage and current.
Can anyone offer any advice on what to do next?
Starts and runs perfectly from cold but after 20/30 minutes(once fully up to temp) if turned off, it flat out refuses to restart. It has to be left about 2/3 hours to get cold enough to start again. No lights on dash.
There are many vag tdi hot start threads but it's hard to know what to do as the hot start problem exists in many guises, a lot of the time there is missing info on exactly what engine, what problem and what cured the problem.
Anyway.....Previous owner had battery checked and had the starter motor and temp sensor replaced, and I've changed the crank sensor but the problem persists.
I haven't had a deep obd diag scan done yet but would have thought if any faults are logged then the eml would be on.
The problem must be that it's not fuelling.
It seems unlikely this is due to lack of the required crank speed due to: 1. the new starter and 2. because I've tried cranking hooked up with jump leads to boost voltage and current.
Can anyone offer any advice on what to do next?
Does it seem to turn over fast when hot as some replacement cheap starter motors are not the same quality as an oem one, especially when the heat gets in them.
I’d certainly try to look at a crank speed test but you need diagnostic equipment.
Have you read about the disconnecting coolant temperature sensor trick when hot to see if it starts any better?
I’d certainly try to look at a crank speed test but you need diagnostic equipment.
Have you read about the disconnecting coolant temperature sensor trick when hot to see if it starts any better?
Belle427 said:
Does it seem to turn over fast when hot as some replacement cheap starter motors are not the same quality as an oem one, especially when the heat gets in them.
I’d certainly try to look at a crank speed test but you need diagnostic equipment.
Have you read about the disconnecting coolant temperature sensor trick when hot to see if it starts any better?
Yeah it cranks quite fast, hard to believe it's too slow to fuel. I think I have a "foolproof" test to rule out crank speed, I'm going to drive to the top of a hill, get it hot then try n bump start it.I’d certainly try to look at a crank speed test but you need diagnostic equipment.
Have you read about the disconnecting coolant temperature sensor trick when hot to see if it starts any better?
I haven't bothered disconnecting the temp sensor yet as I'm under the impression it's been changed but I may as well check it's new and try that, where is it located?
stevemiller said:
CAM Sensor they start to fail to heat. The sensor is only used on the first turn to sync the fuel engine position. Once the engine cools the sensor will see the first crank.
they fail because of heat? is that a belt and pulley off job?Edited by stevemiller on Sunday 5th April 10:03
sliks said:
Yep agree with cam sensor suggestion, likeliest culprit. They fail with heat. All you have to do is cool it down again.
Since your cold starts are fine that pretty much says your fuel system is in good order
I wanted to test the cam pos sensor theory so today I hooked up a hair dryer right next to the cam pulley where the sensor sits.Since your cold starts are fine that pretty much says your fuel system is in good order
I let it get very hot all the way through and really hoped that the car wouldn't start because that'd pretty much be a definite diagnosis of the hot start problem if it didn't start.
But it did so I'm back to square 1. It's not fuelling for whatever reason when it gets hot.
Am43 said:
Have you read the fault codes ?
Injector loom possibly ? It’s a replaceable item which breaks down and can show problems when hot, it’s under the cam cover !
I have just ordered one for my 1.9tdi runner
I haven't but I think the previous owner had a scan done, No eml on. Not sure about the loom, It would cut out when it got up to temp if it was that(one would think), the car will continue to run until it's turned off then refuses to start again. Injector loom possibly ? It’s a replaceable item which breaks down and can show problems when hot, it’s under the cam cover !
I have just ordered one for my 1.9tdi runner
It runs perfectly both hot and cold.
In theory it has to be something that is needed to start the engine that then doesn't function correctly when it's hot.
It's an interesting case, live data would provide key parameter infomation but if not available then the repair must carry on regardless
Which temp sensor did the previous owner change? There was some models to suffer from intake air temp sensor (built into map sensor) wiring chaffing on the loom. Worth checking that loom but they usually cause a hard to start condition not a complete no start. Can also unplug it when the vehicle is not starting, this will put mil on temporarily but worth it in my opinion
Which temp sensor did the previous owner change? There was some models to suffer from intake air temp sensor (built into map sensor) wiring chaffing on the loom. Worth checking that loom but they usually cause a hard to start condition not a complete no start. Can also unplug it when the vehicle is not starting, this will put mil on temporarily but worth it in my opinion
shtu said:
shtu said:
At hot start, does the glowplug light come on at all?
This is an important detail.The engine power relay is famed for degrading on that era of VW and will give a hot nonstart, but no codes to go on either.
When it fails to hot-start, watch the glowplug light.
But more interestingly I also tried bump starting it down a hill and the bloody thing started! That suggests that the problem is lack of required crank speed after all!
I have an 2003 1.9 TDi Passat
have anyone found the fix i have same issue it started like a month ago i was at every local service and they couldnt find anything. they are amazed how good engine works but the start is making me really mad i removed the temp sensor and first time it started normally when hot when i came home after 30min or an hour it started and shut down like every time then i pluged in the sensor it started and but again it went out but started with the sec try or third
have anyone found the fix i have same issue it started like a month ago i was at every local service and they couldnt find anything. they are amazed how good engine works but the start is making me really mad i removed the temp sensor and first time it started normally when hot when i came home after 30min or an hour it started and shut down like every time then i pluged in the sensor it started and but again it went out but started with the sec try or third
Very difficult to guess at but if it’s proving difficult to track down I’d start by changing the common sensors that fail such as the cam sensor and coolant temp sensor.
Not normally the way to diagnose a vehicle just throwing parts at it but you have to start somewhere if you can’t get a good diagnosis.
Try to buy quality oem sensors if you can and go down that route.
Not normally the way to diagnose a vehicle just throwing parts at it but you have to start somewhere if you can’t get a good diagnosis.
Try to buy quality oem sensors if you can and go down that route.
I had the identical hot start problem on an Audi 80 I'd just bought. Turned out to be the coolant temperature sensor (the blue one in the coolant manifold). If you've got the maintenance manual it'll give you the resistance figures to check its serviceability with a multimeter. A new sensor was only about seven quid.
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