2001 XC70 hard starting only on warm days Topic is solved

Post by **darrylrobert** » 06 Mar 2020, 07:45

Ive been chasing a hard starting issue on my 2001 v70xc since i purchased it 4 years ago. happens during summer on 30c (think thats about 75-80F) days car starts normal after overnight but after getting to running temp then stope for 10mins it will sometimes crank but not start, always starts after 3 attemps. No codes. When it does start i can drive to a safe place like home and start it numerous times normally but leave it for 20mins and it can often hard start again but not always.

Have got the 'start prevented try again' message once so i switched out the receiver module (pic) hopefully this is the problem. I swapped out a spare ignition key module thinking it wouldnt work but its not as sensitive as my original module and whats strange i can unplug it and the car still starts.

Have also swapped the fuel injectors thinking it could be a leaking injector as after 1hour after shut down on a hot day there is no pressure on the fuel rail. Left overnight when its cool and it still has pressure after 12hours..

: I thought these were programmed to the car

I have a spare fuel tank pump which i am planning to instal when i empty the tank some more, thinking it may be the pressure valve releasing pressure when its hot. I have also heard a screeching noise once coming from the pump area when it was hard starting.again no codes no check engine

now that summer is over probably have to wait 12 months to find out if my fixes worked

Post by **abscate** » 06 Mar 2020, 07:58

Temperature dependent stuff is almost always electronic in nature, but the antenna ring is a really robust device and seldom fails.

The antenna is not coded to the car, its just a pickup.

Is your battery relatively new and gives solid, well over 12 volts reading at rest?

Post by **oragex** » 06 Mar 2020, 10:49

How are the small wires at the coolant temp sensor connector ? Also the dash outside temp is it correct ?

Post by **darrylrobert** » 06 Mar 2020, 20:15

thanks, i will check those wires. both cluster temps appear correct, the outside temp on the cluster is spot on however only one the drivers side sensor works the passenger side isnt communicating with the computer. This hard start issue has been since i purchased the car, i think the previous owner swapped out the mirrors as they are missing the folding motor and i have a folding mirror button. Anyway my scan tool tells me there is a communication missing signal issue with one of the mirrors, i will check this again.

Do both mirror temp sensors need to be working?

Post by **darrylrobert** » 06 Mar 2020, 20:33

i came across this utube video, and its a volvo. they diagnose it to be the coolant sensor but i believe this sensor also controls the cluster temp gauge, so wouldnt i see the gauge saying "cold" rather tahn normal 12 oclock position?

Post by **abscate** » 07 Mar 2020, 06:17

No you won’t. The gauge is really only a cold, normal, overheat indicator, there is very little range on the scale

The fuel injected when cold is about 3x normal, so if the ECT isnt in spec the engine won’t run well.

Post by **E Showell** » 10 May 2020, 05:43

If you floor the gas pedal when you experience the hard starting, and the car starts right up, that's a quick and dirty diagnostic for bad ECT. Reason being: bad engine coolant temperature sensor generally thinks the engine is cold and dumps in extra fuel to enrich the mixture and facilitate a "cold" start. Depressing the gas pedal feeds more air into the mixture, leaning it out for a hot start.

Post by **darrylrobert** » 10 May 2020, 06:08

Thanks , i never tried that. I changed the engine coolant sensor as suggested also the crank sensor, fuel pump, injectors, thermostat, starter motor with problem still persisting.

Last thing i did was update/replace the purge valve from the old style, and also replaces the one way valve under the inlet manifold.

The last warm day 27c i tested the car fairly thoughly, drove it hard then shut it off in the sun and let it sit for 10mins then same test and again sit for 30mins, car performed well.

Time will tell if i fixed the problem...

Post by **darrylrobert** » 10 May 2020, 06:22

There is also another xc70 owner video on youtube who believes the crank sensor wiring running near the starter motor can cause electro magnetic interference. I organised the wiring and placed the plugs back in their holders but re-routing/extending the wires is a big job so left it as is. I think if it where a problem more owners would be complaining.

Post by **oragex** » 10 May 2020, 09:07

Keep us updated, this way others can learn from it