The V8 Owners Forum -

Hi All,

BACKGROUND
Engine is a 3.5, originally from a 1977 SD1, pretty standard other than having 3.9 Hotwire Fuel Injection. It has run lovely for years, v v sweet. Great economy, starts first time, very fast car. But now it doesn't.

THE SYMPTOMS
1 - Wont start.
2 - Starter turns lovely, but no sign of firing up
3 - There is spark, there is fuel, and the air filter is beautiful
4 - Plugs are black and sooty, and stink of petrol.
5 - If I clean all the plugs it will start, hooray! (albeit lumpy)
6 - If I flick the throttle it dies, boo!
7 - If I gently increase throttle, the revs rise, hooray!
8 - It will run poorly, spluttering for 5ish mins, then "pass out". Return to symptom 1, boo!

PLUS, symptom 8 - PETROL IN THE OIL! yikes.


THINGS I HAVE DONE
- swapped ECU (14CUX) for a spare, no different
- changed CTS (coolant temp sensor)
- swapped AFM for a spare
- changed plug leads
- cleaned & renewed battery earth point
- cleaned the earth at the coil
- swapped new Lumenition elec ignition & new coil
- checked timing; TDC is fine, and timing has been tweaked to be BTDC (have tried all sorts of positions)


OTHER INFO
- 3.5 SD1 lump
- hotwire injection from a 1993 3.9 Range Rover
- Been lovely for years in this form, short trips, long trips (+100 miles) and the odd race at Santa Pod.
- About a year ago, I had the same problem, but went away when I cleaned all electrical contacts everywhere. never really been the same since, and the symptoms have returned.


I am now thinking last years "fix" only hid the problem; perhaps the problem was amplified by poor electrical connections, and swept back under the carpet when I cleaned everything up..


I am not an expert, but I have a little knowledge!

Any ideas what else to do next?

Thanks for your help.

Jim

Usual cause of excessive fuelling is the CTS which commonly fails open circuit. Or the wiring to it causing the same effect.

Unplug the ECU and measure the resistance of the CTS and wiring between pins 7 and 25. At an ambient temp of about 10C it should be about 3000 ohms.

Great, I will check that now.

What should the resistance be at 70ish degress? Cos I will stick it in a cup of hot water and check (I assume I can do that) ?

Since you've already tried another sensor, the intention was to check the wiring as well. If they're right at one temp, they are usually ok at others. Assuming you have fitted the correct spare. At normal running temp, they're usually down to about 200 ohms.

CTS and wiring between pins 7 and 25 - 3810 ohms. About right?

Fuel pressure at startup is about 2bar and remains stable around 2 when running. A bit low perhaps? Could low fuel pressure cause the symptons above...even though the symptoms point to over fuelling?

It would also be worth checking the fuel rail pressure and check that the return to the tank is clear.

I "think" I've cracked it.

It now starts first twist, and ticks over sweet, and can be revved like a V8 should.

Things I did,
- coolant was v v low!! (I know, v v naughty, it needed about 6-8 pints...about half full...why did I not check that? I have now tightened all jubilee clips, we shall see)
- cleaned the breathers
- had a cup of tea


What do you reckon? Low coolant, causing bad CTS readings, causing overfuelling and fouled plugs which in turn caused all sorts of other red herring symptoms?


I assume I should now get a few tins of cheap oil and change it a few times over the coming weeks to flush any petrol out. Followed by some good quality oil once done?


Jim