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Discussion Starter · #1 · (Edited)
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 circles slowing to a stop to yield to other traffic. Letting the system downshift on its own when approaching the circle, 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 gas under the hood. Opening and closing the gas 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
 

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Have you replaced the crank sensor? Not a fan of firing the parts cannon but the cranks sensors are know to get flaky and create similar symptoms.

At a guess the low temperature could be caused by a stuck open thermostat......

C
 

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If your engine temp has always been low, why haven't you replaced the thermostat? Funny you mention the coolant temp sensor. Mine crapped on me driving it home after buying it. The next time I cranked it, it was obviously running rich and tripped a code less than a mile up the street. I also just went ahead and replaced my thermostat also, as to me that is cheap insurance.
 

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Discussion Starter · #4 ·
Thank you both for your replies.

RE: "If your engine temp has always been low, why haven't you replaced the thermostat?"

Good question ! The reason was that if the coolant temperature was sending a false to the temperature gauge that would explain my hot starting problem. It looked to be a lot easier to change than the thermostat, so I thought I'd start with that. I don't think that running ar 75°C instead of 90°C would cause a hot start problem.

RE: "Have you replaced the crank sensor? Not a fan of firing the parts cannon but the cranks sensors are know to get flaky and create similar symptoms. "

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?

Many thanks
Tony
 

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What codes do you get when you run a scan?
 

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Maybe you should consider that fuel injected engines are notoriously hard starting when hot. Ask any small aircraft pilot what its like doing a quick turnaround on a summer’s day.

I've had two Maseratis (4.2L and 4.7L) both were/are hard starting when hot, especially in summer.
 

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Both of my 4200's had no problem starting when hot.
 

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Discussion Starter · #12 ·
Maybe you should consider that fuel injected engines are notoriously hard starting when hot. Ask any small aircraft pilot what its like doing a quick turnaround on a summer’s day.

I've had two Maseratis (4.2L and 4.7L) both were/are hard starting when hot, especially in summer.
Then I think they both had a problem :););):(:rolleyes::rolleyes: !!!
 

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I have never had an FI injected engine that was hard to start when hot. Carbs OTOH.....

C
 

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I have never had an FI injected engine that was hard to start when hot. Carbs OTOH.....

C
I've had a couple and they're all 90s to mid 00s cars.

Salut @tonycharente mon ami, ca va? If you are having trouble with the engine temperature, you should replace the thermostat - removing the intake is very easy, it takes less than 20 minutes. This is how I did it
I can't see why this would prevent the car from starting when hot.

A crank sensor is a common issue with a lot of cars, as the sensor ages the wires can form micro cracks which open and close depending on the temperature of wiring. If you keep your launch with you, the next time it happens you should be able to read the crank position sensor to verify it.

Another reason I've had a hot car fail to start is exhaust flowing back into the cylinders. This car was a turbo and stalled while racing so the exhaust blew right through the intake side. I had to crank it until all the gasses had cleared. If you have blocked cats you could also have exhaust reversion. This is an unlikely scenario.

Hope that helps.
 

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Discussion Starter · #16 ·
If you are having trouble with the engine temperature, you should replace the thermostat - removing the intake is very easy, it takes less than 20 minutes. This is how I did it
G'day Lambertius (!!!) Excellent and very instructive video, thank you, but not at all related to replacing the thermostat - wrong video posted ??? Will be very useful if I do end up having to replace the crank sensor though... ...and yes, I now "never leave home without my Launch".

At present though I'm hoping that my hot start problem may be being caused by a stuck open fuel purge valve. The weather here has been around freezing or just over these last couple of days and my garage is not heated but it should warm up by Thursday. I'm planning on testing the purge valve as that looks to be fairly easy to get at.

Thanks again,
Tony
 

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It was just a video to show you that it is easy to remove the intake. I don't have a video of the thermostat being done. I'm sure it will be something simple at the end of it all!
 

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Discussion Starter · #18 ·
At present though I'm hoping that my hot start problem may be being caused by a stuck open fuel purge valve. The weather here has been around freezing or just over these last couple of days and my garage is not heated but it should warm up by Thursday. I'm planning on testing the purge valve as that looks to be fairly easy to get at.
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
 

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My intake air temp is usually 1-2 deg above ambient.
 

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Discussion Starter · #20 ·
Update...
In preparing to plug the purge valve as suggested on the "other" forum I used some rubber hosing with better hose clips and I so thought I'd try measuring the vacuum leakage again, both of my purge valve and of the Mityvac itself, this latter having previously itself been the subject of a slow leak. It turns out that the leakage of the Mityvac itself was down to leaks from the supplied clear plastic tubing (despite my using clamps) - it now only drops 2 or 3 PSI even overnight. So I remeasured the purge valve leakage rate yet again. There is still a small leak, but less than I had thought - a drop of around 10 PSI over 1.5 hours. Could that rate be enough to cause my hot start problem?

Anyway my next step is to try the car with the purge valve and the pipe to the manifold plugged to see whether this resolves my hot start problem. As my hot start problem is very intermittent, and as I only drive the car about once a week, it may be months before I start to feel that this has cured it. I do hope so, but at least if it it hasn't I'll have saved replacing the carbon canister and/or purge valve for nothing.

Watch this space...
 
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