4200 CC : Problem starting when engine hot

tonycharente

Member
Messages
145
I’ve now owned my 2005 (MY2006) 4200 CC for over three years and I still have an intermittent problem starting it from hot. This seems not to be an uncommon problem, but I have yet to find a definitive list of what to do to resolve it.

The car starts immediately from cold or when the engine is still warm, but sometimes (but only sometimes) it won’t restart when the engine is hot. It happens both in the winter and in the summer, and seems to be related to the engine temperature, not the outside temperature.

Returning home on the very day of my purchase (!!!) the car did not want to restart hot. I had stopped for 10 minutes in a service area (not to refuel, this having been done 65 miles previously.) When I wanted to restart (so after 10 minutes) the car did not want to restart. The starter motor spun the engine very quickly with no problem, but the engine refused to start. I left it for another quarter of an hour, and then it started as if nothing had happened.

Once home, plugging in a generic ODBII reader I had a pending P0128 code - "coolant temperature below thermostat regulating temperature". By doing research I found that this could come either from the thermostat, or from the coolant temperature sensor. The temperature indicated on the dashboard remains quite low, rarely exceeding 75°C, but this could come from false information provided by the sensor, which would result in too rich a mixture, and therefore the refusal to restart. From time to time the P0128 code has changed to "active" (therefore with the engine warning light coming on) without in itself creating a starting problem.

The car has not wanted to restart from hot from time to time ever since then, quite rarely and always shortly after stopping with a hot engine. After a few minutes it always restarts as if nothing had happened, albeit sometimes with a higher than normal tickover for a while. The car drives perfectly.

However, still only with the engine hot, I sometimes also had a problem when I reached roundabouts slowing to a stop to give way to other traffic. Letting the system downshift on its own when approaching the roundabout, sometimes the engine has simply stalled, with the impossibility of restarting for 10 minutes / a quarter of an hour. That is to say that once stalled, I found myself with the problem of refusing to hot start without waiting. Doing some further research I found that stalling in these conditions could be the result of too low a "PIS" (the hot clutch slightly touching the flywheel causing the stall). Having bought a “Launch X431 Pros Mini” diagnostic tool a year ago, I increased the "PIS" to 5.2 and it has never stalled while driving since.

It had been months since the car refused restart when hot, but it did it to me again a few weeks ago, so I decided to have the coolant temperature sensor replaced. It has made no difference (temperature gauge still remains quite low, rarely exceeding 75°C, and still the occasional refusal to restart from hot.)

I also increased the PIS to 5.35 in case the clutch was still dragging when hot, but it has still done again it since.

During my three years of ownership, in addition to replacing the coolant temperature sensor, the battery, the clutch and the air filter, inter alia, have been replaced.

The last time it wouldn’t restart from hot I tried switching the ignition on and off several times before using the starter motor as I had read that the problem could come from a problem with fuel pressure not holding up (non-return valve not working) but that achieved nothing. There is no smell of petrol under the bonnet. Opening and closing the petrol cap makes no difference. Ditto the door. The brake light switch is working properly.

I am at my wits end… …all suggestions as to what to try next (and in what order) very welcome.

Thanks in advance

Tony
 
Last edited:

Oneball

Member
Messages
8,522
I’d try to sort the engine temp issue to start with. So I’d check the thermostat is opening and closing and that the cooling fans are cutting in and out.
 

philw696

Moderator
Staff member
Messages
19,580
Using the Launch get some live data and see if that points you in the right direction especially intake air temp.
 

Zep

Moderator
Messages
7,458
Have you done the carbon canister and checked the purge valve? When it will not hot start can you smell fuel from the exhaust tips?

My GS was tricky to start hot because of the canister and I have had other cars that would not start at all when the purge valve was faulty.
 

Gazcw

Member
Messages
6,051
Changed the canister and crank sensor (I think it was) on mine but it still struggles to start hot. It also sometimes struggles when I move it out of the garage cold. Switch it off and then maybe start it a minute or 2 later. Starts but just takes extra turns to get there.
 

Tedwud

Junior Member
Messages
25
Identical to the issues I had. I replaced the coolant temp sensor too but no change. I ended up replacing the thermostat. Upon removal, I found it was stuck open. With the new thermostat, the temperature has been absolutely spot on, and I’ve had no issues with the hot start or stalling. I also had the same fault code prior to the thermostat replacement.
 

philw696

Moderator
Staff member
Messages
19,580
Changed the canister and crank sensor (I think it was) on mine but it still struggles to start hot. It also sometimes struggles when I move it out of the garage cold. Switch it off and then maybe start it a minute or 2 later. Starts but just takes extra turns to get there.
That's not a great thing to do as you are over fueling the combustion chambers.
Fuel can wash the bores of oil and excessive wear can occur.
Better to leave the engine running honk the horn for someone else to close the garage door.
 

Gazcw

Member
Messages
6,051
That's not a great thing to do as you are over fueling the combustion chambers.
Fuel can wash the bores of oil and excessive wear can occur.
Better to leave the engine running honk the horn for someone else to close the garage door.
Yeah. It's more when I get it out, leave running until secondary air is off whilst I shut the garage door and then no sign of kids so have etc go and give them a kick. Not a regular occurrence as I just tend to say screw it and leave them behind.
 

tonycharente

Member
Messages
145
Have you done the carbon canister and checked the purge valve? When it will not hot start can you smell fuel from the exhaust tips?

My GS was tricky to start hot because of the canister and I have had other cars that would not start at all when the purge valve was faulty.
I'm hesitant to change the crank sensor in the immediate, given the amount of work required to remove the inlet manifold to gain access to it.

I've also posted my query on a French Maserati website. One suggestion has been that it might be caused by the immobilser. Next time it happens I'll try locking and opening the car with the remote and also try my spare key.

If that doesn't work it's been suggested I use my Launch to measure the engine revs whilst trying to start the car. If it reads "0" that would confirm the chances that it's the crank sensor. What do you think, please?

Changing the carbon canister looks less of a PITA than changing the crank sensor though...
 

Zep

Moderator
Messages
7,458
I'm hesitant to change the crank sensor in the immediate, given the amount of work required to remove the inlet manifold to gain access to it.

I've also posted my query on a French Maserati website. One suggestion has been that it might be caused by the immobilser. Next time it happens I'll try locking and opening the car with the remote and also try my spare key.

If that doesn't work it's been suggested I use my Launch to measure the engine revs whilst trying to start the car. If it reads "0" that would confirm the chances that it's the crank sensor. What do you think, please?

Changing the carbon canister looks less of a PITA than changing the crank sensor though...
I guess you have a choice of where to start, my experience is one of a few different potential causes.

You could remove the pipe to the inlet from the purge valve and block it to see if it makes a difference before trying.
 

tonycharente

Member
Messages
145
Using the Launch get some live data and see if that points you in the right direction especially intake air temp.
Hello Phil,
Thank you for your suggestion. Next time I take the car out I'll certainly try to read the intake air temp. Presumably this should should rise from ambient (currently very cold even down here in the Charente !!!) but what should I expect it to rise to once the engine itself is hot, say with an outside temperature of around 4°C?

Also, what other live data should I be reading (there are so many) please?

Many thanks
Tony
 

tonycharente

Member
Messages
145
You could remove the pipe to the inlet from the purge valve and block it to see if it makes a difference before trying.
Thanks for this. What's the function of the purge valve; could it, itself, be faulty and if so how; and how do I get to it, please?
(I assume it's somewhere under the bonnet (?) but I couldn't spot it without removing any of the covers).
Many thanks
Tony
 

Zep

Moderator
Messages
7,458
Thanks for this. What's the function of the purge valve; could it, itself, be faulty and if so how; and how do I get to it, please?
(I assume it's somewhere under the bonnet (?) but I couldn't spot it without removing any of the covers).
Many thanks
Tony
The system works to prevent petrol vapour being released into the atmosphere. When you fill up with fuel (or it gets a bit hotter and some vaporises) the vapour is captured in the carbon canister. This is then released through the purge valve by the ECU to burn off the vapour.

If the purge valve is stuck, it lets vapour into the engine at the wrong time, giving a rich mixture. Ok when cold but not when hot, when it effectively floods the engine.

If the carbon canister is saturated, this means that the release of vapour is much higher for a given valve opening as the carbon controls the speed of vapour release.

The valve is item 17 in the pic below.

94551
 

tonycharente

Member
Messages
145
The system works to prevent petrol vapour being released into the atmosphere. When you fill up with fuel (or it gets a bit hotter and some vaporises) the vapour is captured in the carbon canister. This is then released through the purge valve by the ECU to burn off the vapour.

If the purge valve is stuck, it lets vapour into the engine at the wrong time, giving a rich mixture. Ok when cold but not when hot, when it effectively floods the engine.

If the carbon canister is saturated, this means that the release of vapour is much higher for a given valve opening as the carbon controls the speed of vapour release.

The valve is item 17 in the pic below.
Thanks again. I've reading up on purge valves since I posted my question, and can see that a stuck-open one could be the cause of my hot start problem.

Please could you give me a clue as to just where it is.

Many thanks
Tony
 

Zep

Moderator
Messages
7,458
It will be in the engine bay on the bulkhead. You can follow the hose back from the inlet manifold.
 

tonycharente

Member
Messages
145
It will be in the engine bay on the bulkhead. You can follow the hose back from the inlet manifold.
Many thanks again. I've been watching videos about how to test purge valves - praying that mine will be stuck open !!! It may be Thursday before it's warm enough to work in my garage though... ...will then report back, promised.
 

tonycharente

Member
Messages
145
Many thanks again. I've been watching videos about how to test purge valves - praying that mine will be stuck open !!! It may be Thursday before it's warm enough to work in my garage though... ...will then report back, promised.
Firstly, a VERY HAPPY CHRISTMAS to everyone - Covid not withstanding...
Now my update. The purge valve is indeed located close to te engine bulkhead - on the left (facing direction of travel) on my LHD - the complete left-hand engine cover and the rear middle engine cover removed to gain decent access. Hardest part was getting the tube going to the inlet manifold off the purge valve without damaging the purge valve, which I left in situ.. I then spent hours (over several days) testing the purge valve's ability to hold vacuum using a basic model (plastic) Mityvac vacuum pump. It took me ages as I had a hard time trying to ensure no leaks at the tubes, but also because I discovered that sometimes (but strangely not every time) the Mityvac itself doesn't retain vacuum for very long. This made interpretation of my results rather difficult. However the bottom line is that my purge valve does lose vacuum but only very slowly - it takes many minutes to lose all the vacuum.
It thus most certainly was not stuck wide open. Which is a real shame as it would have meant I'd found the likely cause of my hot starting problem. Could a slow leak still cause a hot start problem?

I also tested that the solenoid was working (using an external battery) and that resulted in the instant release of the vacuum, as it should.

All thoughts welcome, please.

This also leads me ask whether it's worth my while changing the carbon canister right away or should I wait until the car won't hot start again so as to do the other tests first? According to the service schedule the carbon canister is supposed to be replaced at 130,000 kms (my car has only done less than 77,000 kms) but also every four years. I have all the service records and can find no trace of its ever having been replaced. But is it really likely to cause my hot starting problem?

Finally next time I take the car out I'll certainly try to read the intake air temp. Presumably this should should rise from ambient (currently very cold even down here in the Charente !!!) but what should I expect it to rise to once the engine itself is hot, say with an outside temperature of around 4°C?

Many thanks to all,
Tony
 

Oneball

Member
Messages
8,522
Id suggest sorting the running cold first, fan, thermostat, temp sender are the likely culprits. Then see if you still have a hot start issue.
 

Zep

Moderator
Messages
7,458
I would disconnect the tube from the purge valve as you have done and plug both the valve and the tube.

If your hot start issue disappears, then you will know. If not, it rules it out.

Oh. Merry Christmas!
 

tonycharente

Member
Messages
145
Id suggest sorting the running cold first, fan, thermostat, temp sender are the likely culprits. Then see if you still have a hot start issue.
Thank you Oneball. I already replaced the temp sender, to no avail. If my thermostat is not closing properly, causing the running at 75°C instead of 90°C, why would this cause my difficulty in hot starting? Higher fuel consumption yes, but why a problem hot starting?