Hot starting problems
Discussion
Over the last couple of weeks my 350i has developed a hot starting problem, you have to crank it over for ages to get it to restart. From cold it starts no problem.
It has a rising rate fuel regulator and was hunting at idle when warm, so I adjusting the idle speed using the bleed screw ,which stopped it hunting, but now it has starting problems when warm. Any help/advice would be much appreciated.
Cheers
Tim
It has a rising rate fuel regulator and was hunting at idle when warm, so I adjusting the idle speed using the bleed screw ,which stopped it hunting, but now it has starting problems when warm. Any help/advice would be much appreciated.
Cheers
Tim
Not that it is, but a coil on its way out struggles to provide a good spark when hot.
Put something cold on it and if it then starts without any problems, the coil is suspect.
Think you have made the mixture leaner and that is more difficult to ignite.
Have you checked CO%, because when it is too low it is not good for the engine?
I run 3 - 3.5 vol%CO. For power it seems 4.5% is the best, but don't need it, it is quick enough for me.
Rob
Put something cold on it and if it then starts without any problems, the coil is suspect.
Think you have made the mixture leaner and that is more difficult to ignite.
Have you checked CO%, because when it is too low it is not good for the engine?
I run 3 - 3.5 vol%CO. For power it seems 4.5% is the best, but don't need it, it is quick enough for me.
Rob
active1064 said:
Over the last couple of weeks my 350i has developed a hot starting problem, you have to crank it over for ages to get it to restart. From cold it starts no problem.
mrzigazaga said:
There was a post recently posted up from H. John as regards to a service bulletin that was sent out as regards to a Vapour lock issues surrounding the RV8
Indeed - but this is much better! 
Hot Start Problems occur (typically on the 350i) when a vehicle with the engine
at warm to hot operating temperature is parked (worse in the sun) for a short period and then
cranked.
My interpretation is that our Efi systems can and do suffer from fuel vaporization, all the
more so if there is restricted under bonnet clearance. Think about it this way. When the
engine stops, the latent heat in the block is no longer able to be removed by the
cooling system and the block temperature is very high, more especially in hot weather.
Now, with the car stationary and the cooling system inactive, that latent heat quickly
rises and is collected by all the metal parts surrounding the fuel intake system, including
the aluminium plenum and the fuel rail. This area gets very much hotter a few minutes after stopping than it ever does under normal running and cooling conditions.
This leads to the fuel vaporizing in the fuel rail and upon re-start, despite the pressure
being controlled by the regulator, vapour is an expanded form of liquid, so the resultant
air/fuel mixture will be much weaker than the anticipated stoichiometric ratio of 14.7:1.
Obviously when trying to re-start the car, the pump pushes in new, cooler fuel but it is
still very hot under the bonnet and new fuel may still vaporize until it can carry some of
that latent heat away. A difficult task if you think about it. From our school physics
lessons we learned the amount of heat required to vaporize a liquid is many times more
than required to raise its temperature by just 1 degree (i.e. 1 calorie will raise 1 cc of
water by 1 deg C, but it takes 540 cals to vaporize the same amount into steam at normal
pressure. It’s less for petrol but still significant at about 80 cals depending upon pressure).
With fairly limited fuel flow all that trapped heat is not going anywhere until perhaps, in
desperation, we lift the bonnet, peer suspiciously at the engine, pull at a few wires, suck
our teeth and generally curse our luck for a few minutes. All this while the heat is at last
escaping to the atmosphere very nicely thank you. After a few minutes the vaporization is reduced and, bingo, the engine starts. Relieved to be mobile again off we drive, until it
happens again the next time we stop and the mystery continues to confound us.
To make matters worse, some cars (SD1 Efi for example) have a thick under-bonnet sound deadening blanket which is very effective at retaining heat.
Rover designed a dealership, retro-fit kit to be offered when a customer complained of hot start problems but the kit is NLA and all we have now, are the published details.
As far as one can tell, there are few, if any, cars on the road today with a retro-fitted
'Kit' in place so:
How might we deal with the problem when it occurs?
• Lift the bonnet and wait.
• Give the accelerator some heavy boots-full when re-starting to make the fuel flow
faster and give a richer mixture.
• Run the fuel pump for a few minutes without starting the engine. This can be done
on both auto and manual SD1's (dunno about TVR). On an auto try to crank the engine in drive, the pump runs but the engine does not turn. On a manual, disconnect the engine
harness and try to crank the engine, the pump runs but the engine does not turn.
• One can’t very well relocate the fuel rail but it might be possible to lag it - but
thinking about that, it would probably work against the problem when everything
is piping hot!
• Fit thermostatic electric cooling fans that continue to run after the engine has
stopped to try and remove latent heat from the engine whilst the car is stationary.
However, with no circulating coolant this would be a marginal solution.
The Underlying Problem
The 350 injection system should be able to cope with this condition but it sometimes does
not - Why? Well one issue is that if the manufacturer put a large blanket under the bonnet as a noise insulator, it perversely also acts as a heat insulator yet the cars, as originally sold from 1982 through 1985, did not unduly suffer this problem.
Only after some years, from new, when these problems became manifest did Rover
design and issue the after-sale, dealer fitted, Hot Start Kits to solve the problem.
I believe the main reason the problem occurred after a few years service is because the
Efi system is probably not functioning correctly in other areas such as mixture, set-up, air
leaks, electrical connection problems, component faults, etc. i.e. poor maintenance of the
system in general (not surprising, as anyone who used franchised dealers for servicing
will know, even today). When this happens it makes it more difficult to cope with the fuel
vaporization abnormality.
The real answer would be to check the system out thoroughly along with the electrical
connections. Whilst it is entirely possible to solve inherent problems using a scatter-gun
approach, in the end a thorough analysis of the system is the best route to follow which
can be achieved using clear guidelines, simple instruments and boring techniques.
My full analysis of the Rover Efi Hot Start problem can be found on the PDF available from this link:
http://www.vintagemodelairplane.com/pages/Download...
Also available from the same link, are the original Technical Bulletins found in Australia, one of the very hot countries where the Efi system had most problems.
Edited by honestjohntoo on Friday 6th June 12:14
July 2025 from New Zealand - my 400SE 1989 has suffered from hot start problems for quite a few years.
We have solved collateral problems: cooling problems, fuelling problems. So now the actual hotstart problem has re-emerged, and finally been solved.
It turns out that the the ignition module (amplifier) being mounted too near the heat of the engine is the issue. Swapping it for a cool one, even a formerly failed and swapped out module, is a fix, until it too overheats.
I am confident this is our fix: It needs to be removed from the distributer, and put somewhere cooler.
I shall report further after a bit of road testing. This has been a mystery and a long process of analysis by experts. But I can at least see the logic in this analysis.
It has been helpful that the car could always be crash started from hot on little slope.
We have solved collateral problems: cooling problems, fuelling problems. So now the actual hotstart problem has re-emerged, and finally been solved.
It turns out that the the ignition module (amplifier) being mounted too near the heat of the engine is the issue. Swapping it for a cool one, even a formerly failed and swapped out module, is a fix, until it too overheats.
I am confident this is our fix: It needs to be removed from the distributer, and put somewhere cooler.
I shall report further after a bit of road testing. This has been a mystery and a long process of analysis by experts. But I can at least see the logic in this analysis.
It has been helpful that the car could always be crash started from hot on little slope.
Had similar issues with my ignition amp(s) which started out as a failure to rev beyond 4k. I put it down to heat and a drip from the swan neck filler cap. I relocated my amp to under the coil using a Lucas relocation kit from ebay which I can't find anymore but it's very similar to this:
https://www.ebay.co.uk/itm/364073400180?_trkparms=...
https://www.ebay.co.uk/itm/364073400180?_trkparms=...
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