The V8 Owners Forum -

Good morning guys and girls, I am new to the site so please bear with me! I have been building a project car for the last two years and now can finally see the light at the end of the tunnel! However I have been stumped with a running fault for the last week and can't seem to get over it.....

I am a confident mechanic but this ones really getting under my skin (I'm used to modern ecus etc and this is all back to basics however I'm probably not thinking straight so I'm calling on you guys to see if anyone recognises the symptoms I'm having....)

Engine originally on carbs ran fine.....now (rightly or wrongly) I fitted the 3.9 efi injection system.....since then I cannot get her to run nicely.

Symptoms are.......will not idle at all
Runs very erratically farts and backfires through induction
Exhaust getting very hot
Gasses coming from exhaust smell so rich your eyes burn
Will not rev more than 4k and gutless....



Originally I thought timing problems......engine condition is good mechanically and cam timing is fine. I have fitted new dizzy cap leads and rotor (all lucas) for serviceable purposes. Replaced the ignition amp as it failed on me and fitted a new vacuum advance as the diaphragm was split. Used a DTC to find tdc on cyl 1 marked the crank pulley and have set timing to 6*btdc and I'm happy that IGN timing is correct.

Still the same however, I then proceeded to set up my air flow meter and throttle pot.... Firstly I found the airflow meter to be faulty so I replaced that.....Set the Co value to 1.0v (tried 1.5v but no different) and the throttle pot to 0.33v at throttle closed (0%)

Fuel pressure is around the 3bar mark just under when running. I removed the rail and pressurised the injectors and none leak etc (however this may not be a valid test but it's all I could do with what I have!)

Still the same......I bought a roverguage lead and software and everything seems ok I have 2 faults
1 neutral position switch (don't have one guessing it's not important)
2 road speed signal (also don't have one but hoping that won't be an issue later anyway)

Oh system is closed loop no lambdas

Also if you guys could clarify.....

Is it ok to use 3.9 efi on a 3.5 engine (guessing the air flow meter would see less air thus inject less fuel)

Also I noticed the inlet manifold had half moon shape cut outs where the injectors sit but my head doesn't match this very we'll??

I will massively appreciate any help you guys give and will be trawling through the forums later to maybe help someone else through my experiences! Thanks again!

I've not got details for the hotwire, but on the flapper, the fuel pressure is more like 36 psi engine stopped, 28 psi idling. So if you are seeing 43 psi with the engine idling, I'd say the reg has failed, or there is no vacuum feed to it. That would result in a rich mixture.

Other things to check:
- Firing order is right, i.e. 18436572, you might have two leads swapped.
- Run it in the dark to see if any of the leads are arcing to an adjacent lead.

The heads should have little cutouts - next time you remove the inlet manifold, you can file them in. But I don't think this is the cause of your woes.

If there are no lambda sensors, it must be open loop, not closed.

Chris.

I have done some checks and the fuel pressure is 44psi all the time so my guess is that's certainly not helping. I cannot seem to find any original regulators around so have bought a universal fuel pressure regulator that is adjustable. Feeling quite happy this will sort my problems! Il keep you guys posted thanks a lot for your help!!

Hi Cliov8;
There should not be any problem with the hotwire injection system on a 3.5 engine.
I have just updated the EFI system on my 3.5 engine from the old Flapper system to the newer Hotwire system and the engine runs fine after carrying out the following adjustments (I did need to buy a new stepper motor, throttle pot and road speed sensor though).
Assume the engine is healthy and timing/plugs etc. are correct.
Do you have the correct tune resistor fitted? Should be the green one at 470R.
Your fuel pressure is too high, set it to 36-38PSI.
You will need the road speed sensor to tell the ECU if the vehicle is moving or not. When it senses that it is not moving it goes into idle mode and the stepper motor controls the idle. If the road speed sensor is not fitted then you may have problems with it stalling when you come to road junctions.
Also fit a 510R resistor between ECU pin 34 and earth. If you do not have one let me know and I will pop one in the post to you.
Set the base idle to 525RPM.
Set the AFM to 0.9 - 1.4v.
Adjust the plenum butterfly so that it is 1mm over centre at the top compared to the bottom.
Reset the throttle pot to 0.32 - 0.34v after you have adjusted the butterfly valve. Is the throttle pot healthy, with a steady reading around the idle position?
If you cannot get it to idle after all this I would suspect the stepper motor.
Hope this is of help to you.
Andy.

How about an update!

Have you now sorted the problem?

Yep! I have fitted carbs! Was fed up with injection issues anyway. Thanks for your help unfortunately we just couldnt get to the bottom of it! I suspect either an internal ECU fault [/b]