3.9 V8 Cold Starting Problems

[Budgie]

Hi All,

I need a little assistance to locate a problem on my 1995 3.9 V8.
I had the fuel pump go a couple of weeks ago, just stopped and never went again. That's been replaced and the motor runs but when you start it from cold you need to give is some thottle when it initially fires otherwise it won't keep going, like there's no choke. Now I know the 3.5 had a cold start injector in the plenum chamber but what does the 3.9 have?
Any other ideas what could be causing this?

Another wee problem is the fuel gauge. A couple of days before the pump gave up the fuel gauge started doing all sorts of things. One minute it was reading full to the brim and then it fall to below the red and the warning light would come on. I thought this was part of the pump problem but it still does it with the new pump fitted. Has the gauge gone south or is there something else I could look at?

Cheer for any input. ;)

[mentalmoshio sophs V8i]

mite be a poor connection around the fuel tank where the pumps is mines not the best ive ever seen, or a bad earth wire along one of the senders

[Range Rover Blues]

The 3.9 uses multiple fuel maps depending on temperature, it's not just hot or cold.  Ity also uses an idle stepper motor on the rear of the plenum to control idle speed, the throttle plate almost suts completely and without the steeper the "base idle" spped is less than 500RPM.

[Budgie]

Thanks for that, I've got a spare stepper motor so I'll swap that over and see if it make any difference.
I don't think it's a bad earth as I would have expected it to show the right fuel leave at some point, which it hasn't. Worth checking anyway.  ;)

[Budgie]

Well the cold start problem was the stepper motor.
I took it out today, reconnected the wires and turned the ignition on & off once to reset the stepper motor, the plunger should withdraw fully but this one juddered a couple of times and didn't move, remaining about half way out.

So I replaced it with the spare I have and the engine fired first time, as normal. The tickover is very high now but I think that's cos I sealed the plenum chamber properly before swapping the stepper motor and I put new exhaust manifold gasket in as a couple were leaking, so I'll have sort that out.
But before I can do that I have a wee wiring fault to sort out as when I started the motor for the second time it only ran for about 30 seconds, then the fuel pump fuse blew.
I replaced the fuse and as soon as I turn the ignition on the fuse blows again so there's something not right in there.  :roll:

[Range Rover Blues]

I've had the wires snap before now right by the tank, could be shorting to earth or could be a faulty pump.

Don't worry about the fast idle, it's just the ECU getting it's thing together.  It'll do that sometimes if it sees the battery voltage go down during cranking to put a bit of life back into the battery.

[Budgie]

The pump's new so there shouldn't be any problems with that and the fuse was blowing prior to the new pump going in, I though I'd got the blown fuse thing fixed by replacing the pump.
The wires on the pump are OK, I just need to trace then back.
There are a few strange wiring problems on this vehicle though. When first got it there were a lot of fuses missing in the main fuse box, when I got the sunroofs working the fornt one opened but itself when I went over a bump and wouldn't close (yes it was raining at the time and I didn't have the allen key to close it manually  :roll:) so these are now disconnected at the ECU. The fornt nearside healight' connector at the bulb was also melted and needed replacing.
No wonder I got it cheap.  :D

The fast idle was coming down on the second start-up when the fuse blow and the battery does need a good charge so I think you're right about that one.

[Range Rover Blues]

I can't remember off the top of my head but something else runs from the fuel pump relay, the MAF perhaps :-k

[Budgie]

I'm going to sit down with the workshop electrical manual tonight and have a scan through it.  ;)

[Range Rover Blues]

It's a great read :-.