Start up problems

[carob]

I have a problem with my 1984 350i. First start up of the day no problem at all, but after running for a while then stopping say to fill up it is taking a while on the key to start up again, almost to the point of flattening the battery. I have changed the leads for Magnecor ones new NGK plugs Lucas cap and Rotor arm. It does start but as i say it is as though it is going to flatten out.

[GV]

Try following diagnostics.

1. Check for fuel in the tank - if there's fuel check fuel pump
2. Check for spark at the coil - no spark check & test ignition amplier on dizzy
3. Check for spark at the plugs - no spark check coil/ignition amplifier
4. Are the plugs getting flooded? - remove cold start injector crank engine - check thermatime switch
5. Check fuses for injection, ignition & fuel pump
6. Check & Test ECU - disconnect wait 10 mins then reconnect and crank engine.
7. Check all wiring and connections especially Earths...
8. If the engine is dead when you crank it - check the negative eart strap from the battery.
9 Check starter solenoid - give it a tap.

That's all for now - I hope one of the above may be the solution to your problem as I have had them all!!

Edited by GV on Sunday 17th June 20:19

[carob]

I will try these things out.

Cheers

[honestjohntoo]

carob said:

after running for a while then stopping say to fill up it is taking a while on the key to start up again, almost to the point of flattening the battery.

If the usual solutions dont work, with restricted under bonnet clearance the efi system can suffer from fuel vaporization. When the engine stops, latent heat in the block is no longer removed by the cooling system, the block temperature is very high, more so in in hot weather, latent heat quickly rises to collect in the intake manifold and plenum which get much hotter a few minutes after stopping than they ever do under normal cooling conditions leading to fuel vaporizing in the fuel rail. Upon re-start, the vapor being an expanded form of liquid, causes the air/fuel mixture to be much weaker than the required ratio of 14.7:1. The pump pushes in cooler fuel which will continue to vaporize until it can carry some latent heat away. School physics explained the amount of heat required to vaporize a liquid is much more than required to raise its temperature by just 1 degree (latent heats of vaporisation - water 540, petrol 80). With limited fuel flow, trapped heat is retained until the bonnet is lifted, peering suspiciously at engine, pulling a few wires, sucking teeth and cursing luck for a few minutes, enough time for the trapped heat to escape to atmosphere, vaporization is reduced, the engine starts. Possible solutions, • Lift the bonnet and wait. • Give the accelerator heavy boots-full when re-starting to give a richer mixture. • Run the pump for a few minutes without starting the engine. • Fit electric cooling fans that continue to run after engine has stopped to remove latent heat whilst the car is stationary (with no circulating coolant this is marginal).