ALFAGTV6.COM

[Al_Cam]

I haven't had one, if you were hoping for an exciting story, but have been tempting the gods.

I have had an occasional starting problem with my '83 GTV6. If I stall the car after starting when cold, I struggle to get it to fire again. It will turn over, but no ignition. Checked for spark, fuel pump going, all sorts of stuff to no avail. Thought it may be an intermittent electrical fault. Happened the other morning and while poking around under the bonnet I noticed petrol on the top of the seal of plug number 2. I guessed with all the cranking I'd been doing, I'd flooded the Plenum to the point where petrol was leaking out of the throttle body. So I used the standard flooded motor method and held the accelerator pedal on the floor and turned it over, after a few seconds it started and ran beautifully!

I recounted this story on an Australian web-site and horrified one poor bloke (Hi Shane).

When having problems starting, I occasionally use the accelerator, which is supposed to be a good way of causing Plenum Pop. But… what are the chances? If starting from cold, the Cold Start Injector fills the plenum with good, rich Air/Fuel mix. That’s its purpose. Wouldn’t that be setting up the conditions for Pop? Wouldn’t opening the throttle let in more air, which would reduce the chances of ignition? And what is the mechanism for igniting fuel in the intake? What is the source of ignition? Timing way out so that you’ve got spark while an intake vale is open?

Any thoughts or like to share your experiences please.

AL.

[patzo_3l]

on these v6s pressing the throttle while cranking the car is a sure fire way to blowing the plenum off. it is very very common. i have found disconnecting the fuel vapour lines to the intake helps, but this is more of a case when hot starting. apart from looking at differnt things id say you have 2 options, 1, learn to live with cranking it over without pressing the throttle till it starts, i know this is embaressing but after a while youll get used to the people staring at you in car park, belive me. 2,learn to start the car without pressing the throttle lol

unless you have leaking injecters, im pretty sure your car isnt flodded. its more a problem of either vapour block, and/or lean cold start mixtures.

[Greg Gordon]

I am going to offer a different viewpoint here. This may go against convention, but then again, I have done a lot of experimenting with this issue and I can assure you that if everything under the hood is OK, the plenum will not pop as a result of throttle position.

If fuel was leaking out of the throttle body, it's a certainty that the cold start injector flooded the engine. This is quite common after multiple unsuccessful start attempts. The L-Jet system has no flooding protection under these circumstances. It only protects against flooding during a single really long (like over 7 seconds of cranking) start attempt. Multiple unsuccessful attempts will usually flood the engine.

Now, the only way to clear this from the driver's seat is to crank the engine over with the throttle fully open. This is a standard procedure in most fuel injected cars and it works perfectly in the GTV6 provided the plenum doesn't pop.

The dreaded plenum pop is not really caused by starting with the throttle open, however holding the throttle open will greatly increase the chances of a plenum pop. I will explain. The plenum pop is actually caused by air leaks upstream of the throttle body. However during a normal start, the closed throttle largely blocks the cylinders' access to these leaks. As soon as you open the throttle unmetered air can rush in from the leak between the AFM and the throttle and bang, plenum pop.

The most likely leak point in this case is on the underside of the accordion section of the main air intake tube, just after the AFM, however it could be somewhere else.

I know what I am writing here goes against the convention regarding plenum pop. When I first bought my GTV6 it had a horrible plenum pop problem. Once I fixed all the air leaks the problem went away. In fact I have experimented with this quite a bit. With all leaks fixed I can't make the plenum pop, no matter what I do, multiple start attempts, throttle position, nothing makes it pop. However, if I introduce a leak, flood it and start with the throttle open it will pop as often as not.

Greg Gordon

[patzo_3l]

i understand what you are saying greg and completely agree. however im nost cases our over 20 year old cars and bang for time/buck value, are better spent fixing more major issues, therefore , imo id say most cars have some slight leak or crack in that area of hoses. youd actually be hard pressed finding a perfect leak free gtv6 by now id say. just that some leaks are bigger and affect more then others may.

[Greg Gordon]

I agree completely. Most GTV6 and Milanos have an air leak somewhere in the vacuum system. It's a lot of effort to fix them all.

Greg

[Al_Cam]

Thanks Guys,

All makes sense. I realise now that if I’ve not started after 2 or 3 attempts, I probably should unplug the cold start injector. I've put a LED on the CSI to see when it's firing (to help diagnose this problem). So I know that it does eventually stop firing if you keep trying to start enough times, but long after it'll be througly flooded.

It's only a couple of months since I checked the hose for leaks. Didn't appear to have any that went all the way through, but put a bit of shoo-goo here & there (the Greg Gordon look) and I've done the clamps up way to tight. I've still got to have a look at the AFM, so maybe time to check intake tube again and see if my fiddling caused a new crack.

The fuel was dripping onto the top of the middle plug boot. If you have a look at the photo below, it may have been coming from the tube or the throttle body and running down the throttle cable bracket or linkage. I'll check slop in the throttle, gaskets &c...

Alfa 2008 003.jpg (178.23 KiB) Viewed 4417 times

- By the way that was a shot to help me replace all the old tubes, so there is a new set now, except for the intake runner couplers.

If there are leaks that allow fuel to leak out under gravity only, then air can certainly leak back in.

Mixture could be an issue. AFM has been opened and the AAV neither fully opens or closes. I had the idle turned up to get over the AAV, but that was causing hunting when warmed up. I'll have to do something about the AAV before winter as it barely runs when cold at the moment, less than 500rpm.

We've had three days over 44 C / 111 F Down Under, so I spent the weekend putting a relay on the starter solenoid and getting the heater valve to close all the way and didn't have time to check the tube.

Thanks,

AL.