Cold start hesitation
 

For about a month now the engine has hesitated a bit when pulling away after first starting. It 's not directly related to either cold or damp weather, and only does it for the first few hundred yards if I go up the hill rather than down.
After that it runs perfectly. The symptoms feel exactly like a carburettor engine that needs a bit more choke for a few seconds.

It's the LH 2.4 system, 1991, with the earlier version that has an additional 5th injector hidden under the injector rail. I've cleaned and replaced fuses 4 and 6, and the fuel pump relay looks OK - no corrosion or apparent damp.
The car starts promptly, runs well at idle, and drives OK if I stay in 1st and don't try to accelerate too soon.

I'm looking for pointers - I presume it's some cold start setting being slow to respond. Is the 5th injector for cold starts? Could this be the engine management temperature sensor failing?

If I'd only just bought the car I'd have guessed it was normal - slight hesitation on a chilly morning before it starts to warm up - but it's never done it before, even on much colder mornings.

I would start by replacing the distributor cap and rotor, and the spark plug leads if these are more than about 5 years old. Rotor arms don't seem to last as long as they used to. If symptoms persist, try cleaning the IAC valve and the throttle body.

I’d replace the ecu temperature sensor under the third runner of the inlet manifold- they don’t last forever and my car had running issues just after starting before replacing it.

Makes sure you buy a Bosch one- the pattern ones don’t last long and sometimes don’t work at all.

Ignore the internet that says you need to remove the inlet manifold to fit one, all you need is a deep socket that fits the sensor and perhaps to move some wiring or of the way.

Cheers

as soon as you let go the starter when starting the cold start injector stops spraying , it's job is done in STARTING the engine , It does not RUN on the fuel from the cold start injector .
I would suspect injector spray pattern , ie atomisation .. pull all the injectors out and watch the spray pattern as someone turns it over ... it should be a fine mist coming out no drips or dribbles ...

Check the spark plugs and if necessary, re-gap them to 0.65-0.7mm - chances are if a previous owner changed them at all they just whacked them in straight out of the box and most plugs (certainly NGK) come with a factory-set 0.9mm gap which would be the equivalent of at least 20k miles use.

On a cold engine any ignition maladies are made more obvious because a weak mixture (even allowing for the cold running enrichment) is harder to fire.

Also check the dizzy cap, particularly the carbon brush inside as these have a habit of breaking off.

May also be worth investing in a new set of HT leads considering the past month or so has been incredibly damp..........

Spark plugs, HT leads, distributor cap and rotor arm were new last year, and I regularly clean the IAV anyway.

I didn't know that about the cold start injector only spraying while turning the starter motor - is that peculiar to the 5th injector, or to all the injectors?
I'd just assumed that the mixture was generally enriched while cold-running.

The ECU temperature sensor seems the best easiest check - it came with the car about 5 years ago, so is of unknown age.

I'm wary of removing injectors, but it may come to that. The last (only) time I've done that was on a previous 240 when I suspected the seals were leaking. I found it a nightmare getting them back in again - they took so much force I was worried I'd damaged the new seals.

What make were the HT leads and did you gap the plugs correctly when fitting?

The main 4 injectors all spray while the engine is being cranked and running, when cold the ECU increases T.inj or injection time to richen the mixture. The cold start injector is arbitrary enrichment purely for cold starting and isn't fitted to all models, even thoe with the same engine management system.

I would check the plug gaps (correct if needed) and also the plugs themselves for any sign of arcing or similar on the porcelain insulator. Also check there is no corrosion (whilte and flaky usually) on the connectors inside the dizzy cap. While yo're under the bonnet, also check the air filter is still clean.

Plugs were new (Denso, as always) and correctly gapped a year ago (2000 miles in present circumstances). The leads and cap came from Brookhouse.

What i'm saying is don't discount them just because they're new. :nah:

There was a thread some time in the past few days with a regular cold start misfire and a new set of HT leads in the past year. Those new leads had failed and the car is now running as it should again apart from a separate fault the the OP of that thread will hopefully be investigating. I've also know plugs to fail a matter of hours after being renewed because they were faulty. It's not worth overlooking the obvious just because they are new/recent parts, you can spend a fortune on other things that you "think" are the fault only to find later it was in fact one of the new parts you'd "overlooked" because they were new.

Regarding the rotor arm:~
If you you need to change it then go for Beru/Bosch- as mentioned even new items can be faulty, had it on a Motorcraft part well under twelve months old.
Beru is just the opposite- same for the distributor cap.
Bob.