Hi everyone

My 89 v12 is hesitant when starting after a run...if you stop and restart within a few mins not a problem, if its hot and leave it n hour it feels like its fired on 4 cyclinders, then 7 and then fires up a bit rough still, blip the throttle and all is well. Any ideas?

Nick Kent UK

 

I wonder if some of the injectors are leaking? A couple drips here, a couple drips there.....and after an hour you have 2 or 3 cylindesr with raw fuel in them?

Just a thought

Cheers
DD

 

Doug may be on it there. Try something to run in your gas to clean the "crud" out of your injector seats (varnish, carbon etc.) Sea Foam works OK, or go to a Yamaha Marine dealer and buy some "Ring Free", AWESOME product, cleans everything. I even use it in my weedeater, lawn mower, truck and chain saw now.

 

Nick
The other ideas may be right, but it also could be fuel evaporation in the rail, so on restart there is not enough fuel pressure for all the injectors ti function properly. Either because of leaking injectors or because of a fuel pressure regulator leaking a bit of pressure, or even because of pressure leak-back to the fuel pump. Try this when you have a chance:

Get her hot and then leave for an hour with the bonnet up. When you switch on, turn the key to ignition on and wait for the fuel pump (which you will hear running) to stop; repeat x 2; then turn the key to actually start the engine. If it fires better, then it is probably just the heat under the bonnet causing the trouble. Even with perfect injectors and FPR it can happen.

If it bothers you, changing the FPR (on the UK passenger side, front of inlet manifold) is where I would start, as that is easiest.

Greg

 

I knew this would bring a load of good ideas from afar! . 🗼🗽

Nick.

 

+1 for Gregs fuel vaporization theory.

I still suffer from that too, even with a new fuel pump (which includes new check valves) and an inline fuel pressure gauge reading 40psi before start, in really hot weather I will get the stuttering start.

I have "engineered" a solution which is the ability to remote control the fuel pump from my aftermarket central locking key fob. This way I can start the fuel pump as I walk up to the car, and by the time I'm strapped in and ready to go, the fuel pump has been running for 20~30 seconds, guaranteeing the fuel in the rail is now nice and cool (and more importantly still a liquid and not a gas). It always starts perfectly using this system.

 

Top class solution, Sarc. I had a carburetted Range Rover once that I dropped a bigger, later model RR V8 fuel injected engine into, and I rigged up a dash button to push fuel through to solve the same problem. Worked great, but not nearly as smart as your version!

Greg

 

Years ago, on my Ser III XJ6, I rigged a "primer" system working off the door lamp circuit and using a timer module from a GM car. Whenever you opened the driver's door the pump woud run for about 10 seconds.

I thought it was pretty cool but in the end I took it out, deciding it was unsafe.

Sarc's idea of using the RKE remote is great :-)

Cheers
DD

 

I was actually thinking of using another 45 second timer to do something similar, but the whole remote control system for the locks and the fuel pump was cheaper :-)

I have tried to keep it as safe as possible. The remote unit is powered through a relay that de-energizes when the ignition is turned on, so when the car is being driven, the fuel pump can only be powered through the EFI system. This keeps the safety of the inertia switch intact and would in theory prevent the fuel pump from being run on by the remote system in the case of an accident.