Stalling 328 when slowing down and it's not the clutch...

Dashpot!

 

Rob, they're right, you DID promise a full explanation.

I heard a little about it Saturday night, it's ugly gentlemen....

 

Great.
We are all looking forward to the answer to the mystery question of the stalling.

Clearly, it cost you $2K because it's a Ferrari vibrator.

Good luck!
rt

 

Rob-

Why are you keeping us in suspense??

Sheesh, now I won't be able to sleep tonight!

 

Rob...Your car is running to rich. Stalling or rpms dropping on decel is a dead give away to a rich fuel mixture...over adjustment of the Co adjustment screw in the air flow meter. They more then likely adjusted this to make your car pass the e-test. They probbably tried to lean it out to pass the test and then re-adjusted it too rich. How does the car start when it is warm? Does is take a few extra turns of the starter to get her going? Testarossa's are also very sensitive to this type of thing.

You could very easily adjust this yourself to a point were it won't stall.
All you need is a 3mm allen head tool and a good ear. Then afterwords get it set on a 4 gas analyizer.

One other possablity is the metering valve beside the fuel distributor is not functioning. With the car running that valve(looks like an electronic fuel injector) should be making a buzzing noise. If it is not then you need the protection relay located in the trunk under the carpet on the right hand side.

 

Norwood should know this with all their experiance!! This should be fixed for free because the car was not acting like this when you brought it to them.

 

O.k. Here we go...

O.k. Between the fuel distributor and the air horn on the air flow meter,there is a small plug or screw. Remove the screw. With a 3mm hex head tool instert it down into the hole. Gently and slowly wiggle it until you feel it slip into the adjustment screw in the fuel distributor.

To lean the mixture out you unscrew it like a normal screw. To enrichin it you go the oppisit way. Start the engine

By your description you have to lean it out just a bit. becareful as a little tiny turn goes a long way.

As you are adjusting you will notice an immediate change in the way the engine runs. Too lean and it will start to run poorly. You will know you have it close when the rpms rise to their highest point just before the engine starts to shake.

You may after the adjustment is done turn the idle down with the large bypass screw on the end of the airflow meter.


Remember..only move the adjustment screw a tiny bit at a time.

During the adjustment..move the screw a little at a time and then remove the adjustment tool. Give the engine a good rev (say to 3500rpm) and let it return. You will see that as you adjust, the idle will become more stable on the decel and not drop out and then bounce back up.

After the adjustments are done and the car is running smoothly..shut the car off and let it sit for about five minutes. Then go back and start it. It should start quickly...within the first couple of turns of the starter. If it does not..then you are still a tad to rich.

HTH..if you have aymore qiestions please e-mail me I will be happy to help.

All this should be performed with the car at operateing temp.

 

a) Which emissions numbers were failing, CO, HC, or NOx?

b) While it's idling warm, can you detect a slight miss once in a while?

Have they tried putting a scope on the flywheel sensors? (possibly dislodged during clutch install). If you clamp the vac advance line, does anything change? (bad vac sensor). Ignition scope? (these Marellis are getting old).

 

Could it be something involving the brakes, most notably the vacuum that is drawn off the intake system to power the brake booster, that could be causing this (or contributing with another fault)?

or

Plugged fuel filter or in-tank filter (insufficiant fuel supply, especially while braking, as the fuel in the tank sloshes to the front and away from the pick-up).

or...

 

my thoughts are leaning towards a cracked vacuum line somewhere or a faulty temp sensor for the injection. Something is not telling the injection what is happening and it is lagging when the vacuum should be increasing and going back to idle mode. loss of vacuum to the unit could do this easily.
does teh car seem to idle a little too high? this could also point to a damaged vacuum line allowing air back into plenum.

Rob--laughing at the panties in the car--brings back memories of Spring breaks long ago

 

Rob -- Do you know anything about the "Damper for metering valve" gizmo (item G in Fig 57 page 66 of the USA 328 OM 396/85)? They don't describe it's operation, but it might cause the symptom you report (if everything else checks out OK). I believe all these K-Jet and KE-Jet systems have some provision to prevent the fuel system from overshooting lean when you let off the gas quickly under warm, closed-loop conditions -- i.e., high intake manifold vacuum conditions and decreasing RPM -- and the name "damper" (in the sense of preventing quick changes) just seems to fit with that IMO.
Have you tried something as simple as measuring the O2 sensor output during the "stall" event? If it goes down to ~0V during the stall, I believe that would indicate a lean condition.

 

What's her friend's name?! []

 

Sounds like another happy Norwood customer story! LOL

 

I'm guessing control pressure regulator, since the 328's fuel distributor is specific to an 8 cyl, and I think the Porsche turbos are 6 cyl.

I've been following this discussion, because I was getting similar symptoms (wandering idle) on my '88, but my regulator pressure seems to be okay. (You can get a CIS fuel pressure gauge from NAPA for about $120 to check this.)

On mine, I'm currently thinking either ignition issues (as I started seeing burned extenders) or a vacuum leak somewhere in the billyuns and billyuns of vac lines -- which would be a gold plated b*tch to find. (I guess I need to find a reasonably priced o'scope.)

 

I had a very similar experience this year with my 328. I did the natural thing of lifting the idle to try and compensate but it still did not sound right.I knew i had a problem when i turned the a/c on which is belt driven from the engine and the revs sank to zero. Problem turned out to be a bad gasket around the plenum chamber and the fact that the timing was out on the front bank was obviously not helping.

 

If it was ok before, then SURELY there has been no sudden component failure??

I'd suggest a mixture adjustment has been made badly. The little screw that you remove to gain access to the adjuster, must be in place, or a bung, or your finger tip, while reading the emissions, as it creates it's own air leak when missing.

If you can get your long 3mm allen key in the adjuster, then the screw and plug is missing entirely.....seen a few mechanics do that.

Too rich would seem the likely cause, but too lean is also possible. Some kind of air leak anywhere in the manifold could cause it....maybe around the injectors??? Possibly the plenum rubber gaskets on top of the inlet manifold??

Be sure the aux air valve is working....clamp the hose when the engine is fully warm, and there should be no change in idle speed. When cold, it should almost stall.

Maybe a bad crank sensor, or damaged cable to one....it's easy to trap the cables when doing a clutch.........Or the vacuum line that goes from the manifold to the ECU can get disturbed or trapped when doing a clutch too, it goes through the oil cooler and is easily forgotten or severed up inside the wheelarch. Diconnect it at the ECU and feel for good vacuum with the engine running. If not, there may be an air leak there.

 

So what's the diagnosis?

(And you thought we forgot about it.)

 

Rob read mine and Ferrarfixers previous posts regarding the incorrectly set co mixture screw on the airflow meter. The mixture is too rich causing the car to stall out when you slow down. By adjusting the idel up they have introduced more air in the the intake,semi offsetting the rich mixture setting.

If the car was running fine when you brought it too them... and when you picked it up from them it was not...then they need to undo what ever they did FIRST,, before they start throwing parts at it,with no cost to you.

I also posted in this thread how you could attempt to do the adjustment your self if your so inclined,but if you don't feel comfortable doing it the just leave it and alllow them to do it. But I would definatly get them to undo what ever they adjusted,and get it to the point as if you never brought it in for an e-test. I beleive that this is the shops fault not anything you should be paying for.

 

I'm still betting on a mis-set airmass sensor plate action/position.
Which would be overcome by a higher idle setting.
Which would cause the car to poop out at idle.

Did it cut off suddenly? A fuel pump relay microswitch would do that....

It could be as simple as just set way lean as suggested, but hard to believe that the mechs at Norwoods would not have done that first.

High idle won't hurt it, just will use more fuel and be loud. But it's not right. Should look at your mixture richness /CO through a sniffer to ensure not too far lean.

Good luck!
rt