The V8 Owners Forum -

Hello All

The usual GT40 Rover3.9 EFi quite worked 102 cam Hotwire

Runs great pulls well etc.

Now unfortunately some council workers recon it should also stop and put traffic lights all over the place.

So I put my foot on the brake and go down through the gears then finally on the clutch and the engine dies.

Next set of lights brake and come down the gears, but do a "heal and toe" to blip the engine when putting the clutch in for the final time and it and then idles perfectly.

So wht could cause such a symptom? I don't mind the blip on the throtle as it sounds great but sometimes when a bit more rushed the engine dies - starts again first turn of the key and immediately idles.

Idling once up to temp is about 700 rpm - probably not too low. When cold it runs faster as expected.

So any ideas?
Only thing I can think is that the resistor in the "Auto in gear" circuit is not right - would it cause these symptoms??

Ian

Sticky or sluggish idle air control valve?

Ian Anderson wrote:So I put my foot on the brake and go down through the gears then finally on the clutch and the engine dies.

Next set of lights brake and come down the gears, but do a "heal and toe" to blip the engine when putting the clutch in for the final time and it and then idles perfectly.

So wht could cause such a symptom? I don't mind the blip on the throtle as it sounds great but sometimes when a bit more rushed the engine dies - starts again first turn of the key and immediately idles.

Ian,
Coming down thro all the gears will put the engine on overrun for the whole of that period causing continuous vacuum in the manifold.

IF your system has a vacuum controlled overrun valve then it does not switch the fuel back on before the engine dies.

When you blip the throttle the vacuum immediately disappears and the fuel starts flowing again.

What overrun valve? I hear you ask.

Well thats that theory blown to smithereens!

Try again.

Coming down thro all the gears will put the engine on overrun for the whole of that period causing continuous vacuum in the manifold.

With the throttles shut, the airflow meter provides very little fuel which passes right thro the system anyway, mixes with the air in the exhaust system and pops and bangs due top self ignition.

At the same time the very high vacuum in the inlet area during the long period of deceleration causes any residual fuel condensed on the inlet manifold and plenum chamber walls to evaporate and create an over rich mixture.

All this fuel again passes into the exhaust system unburned because the mixture is way off and again ignites in the exhaust sytem with popping and banging.

So there is NO fuel anywhere in the inlet system as the car grinds to a halt.

When you pop the clutch and come out of gear to let the engine idle, there is no fuel condensed on the walls of the inlet system and plenum chamber to pick up the idle state immediately and the time lag from the injectors is too great for the engine to catch, so it dies.

The design idle speed for these engines with Efi is higher than your 700 rpm so the solution would be to raise the idle speed to 900 rpm to see if that gives sufficient fuel to catch the engine before it dies.

However, when you blip it the engine catches because to had an immediate enrichment and the engine catches rather than dies.

If neither of these theories work then come back for more stuff out of left field.

Ok Ramon I try increasing the revs on idle slightly - it should work.

Now on the plenum ther eis a small screw that acts as a stop on the throttle / butterfly mechanism - presuming this needs to be moved out slightly. So how do you do it as the screw doesn't seem to have any slot or hex or anything to allow it to be turned. Is it a pull the plenum apart and do it from inside job? (Or Ian the butcher method or run a saw through it and make a slot for a screwdriver!)

Or I could also just pit constant tension on the accelerator cable - now I getting a bit basic!

Ian

The screw on the butterfly is not the idle screw. It should be set as per the instruction on Ramons site (i'm sure he's got them), that show feeler guages between the butterfly and the plenum. Basically the butterfly should be completely shut at idle, and the idle air flow is going through the bypass passage controlled by the vertical large screw at the opposite end of the butterfly to the throttle position sensor.

Chris.

This is a hotwire system adjusting the throttle bypass shouldnt change the tickover as that's controlled by the ecu via the stepper motor. That said if it isnt setup properly as in the air bypass is closed too much the stepper cant do its job properly. If it idles faster when cold then chances are its set near enough as you obviously have enough headroom.

ChrisJC wrote:The screw on the butterfly is not the idle screw. It should be set as per the instruction on Ramons site (i'm sure he's got them), that show feeler guages between the butterfly and the plenum. Basically the butterfly should be completely shut at idle, and the idle air flow is going through the bypass passage controlled by the vertical large screw at the opposite end of the butterfly to the throttle position sensor.
Chris.

There are bones of contention on the question of butterfly gaps which I have tried to reconcile on pages 2 and 5 of the PDF available here:

http://www.vintagemodelairplane.com/pag ... ing01.html