Northern Auto Tech - ECU and Blue & Me Repairs

Technical Unusual JTD hot starting problem

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Technical Unusual JTD hot starting problem

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Davethewave

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Hello everyone,
My punto 1.9 JTD starts first time from cold. 100% reliable and good mpg. Very different starting when hot, when I sometimes have to turn it over for many seconds, several times, until it eventually fires and keeps running. It seems to keep almost firing whilst cranking but never quite getting going. I thought it might be fuel starvation and changed the filter - no difference. I have changed the Crank sensor for a good new one - and checked that it's seated properly. (I definitely took out the old rubber seal).
I cleaned the egr valve - no difference. Blanked it off - no difference. Leak test at local garage gives all 4 injectors the same.
I thought it might be a fuel pressure problem so used multiecuscan to check. Fuel pressure looks ok, but if I record a graph of graph total fuel quantity while trying to start it sometimes stays at zero (not starting) and sometimes jumps up and down from zero to 20-25mg/i (spluttering) until it starts and then idles at around 8-10mg/i.
What could be stopping the ecu from opening the injectors?
No fault codes are recorded.
Any ideas? If I don't resolve this soon then it's going to have to go on ebay for spares or repair!
 
Davethewave said:
Hello everyone,
My punto 1.9 JTD starts first time from cold. 100% reliable and good mpg. Very different starting when hot, when I sometimes have to turn it over for many seconds, several times, until it eventually fires and keeps running. It seems to keep almost firing whilst cranking but never quite getting going. I thought it might be fuel starvation and changed the filter - no difference. I have changed the Crank sensor for a good new one - and checked that it's seated properly. (I definitely took out the old rubber seal).
I cleaned the egr valve - no difference. Blanked it off - no difference. Leak test at local garage gives all 4 injectors the same.
I thought it might be a fuel pressure problem so used multiecuscan to check. Fuel pressure looks ok, but if I record a graph of graph total fuel quantity while trying to start it sometimes stays at zero (not starting) and sometimes jumps up and down from zero to 20-25mg/i (spluttering) until it starts and then idles at around 8-10mg/i.
What could be stopping the ecu from opening the injectors?
No fault codes are recorded.
Any ideas? If I don't resolve this soon then it's going to have to go on ebay for spares or repair!
Click to expand...


Disconnect the Mass Air Flow Sensor and see if its easier to start then

Ziggy
 
Thanks Ziggy,
I tried unplugging the MAF sensor, and immediately the cold starting became difficult (felt very similar to my problematic hot start), and hot starting was fine, so I'm guessing that for some reason a 'bad' maf reading has little effect on a cold start but a significant effect on a hot start.

Is it worth ~£8 for a can of maf cleaner or should I get a new one (I've seen them from £24 to £150!)?
Anyone had experience of cheap new ones?
 
its hard to say which route i'd follow personally

try the cleaner if you wish - but i dunno if that'd actually help?

The car should revert back to a base setting - knowing the sensor isn't working
the car wont perform like 100%
it'll be more like 75%

But its weird it's affecting cold now and not hot

Ziggy
 
I spoke too soon - just been out for a slightly longer run, and without the maf sensor connected it is still really difficult to start hot. Once the engine catches, it runs perfectly smoothly but if I switch off and then immediately try to re-start, it still needs a lot of cranking before it will finally get going.
Does that rule out the MAF sensor?
Thanks.
 
Davethewave said:
I spoke too soon - just been out for a slightly longer run, and without the maf sensor connected it is still really difficult to start hot. Once the engine catches, it runs perfectly smoothly but if I switch off and then immediately try to re-start, it still needs a lot of cranking before it will finally get going.
Does that rule out the MAF sensor?
Thanks.
Click to expand...

the problem hasn't changed then
It rules out the MAF in my eyes

Ziggy
 
Conduct an injector leak off test, probably one or more of them are duff. A diesel purge might rectify that.
 
Last edited:
Local garage has already done a leak-off test and all 4 injectors give identical figures.
I have used multiecuscan to produce a graph showing total fuel quantity (per injection) during cranking, and when hot this either stays at zero or jumps from zero to 28mg or so and back again. I take it from this that the ecu is only giving intermittent signals for the injectors to 'fire' during hot cranking, even though the fuel pressure is ok and engine rpm is 5-600.

Is it worth disconnecting the coolant temp sender - will this fool the ecu into thinking it's a cold engine?
 
Davethewave said:
Hello everyone,
My punto 1.9 JTD starts first time from cold. 100% reliable and good mpg. Very different starting when hot, when I sometimes have to turn it over for many seconds, several times, until it eventually fires and keeps running. It seems to keep almost firing whilst cranking but never quite getting going. I thought it might be fuel starvation and changed the filter - no difference. I have changed the Crank sensor for a good new one - and checked that it's seated properly. (I definitely took out the old rubber seal).
[...]
No fault codes are recorded.
Any ideas? If I don't resolve this soon then it's going to have to go on ebay for spares or repair!
Click to expand...
I'd put a lot of money for the crank sensor. Or at least the wire and/or connection to it.
It's very uncommon but you could have received a bad new crank sensor...

Hope you'll check this out.
 
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