Alex Sol

I may have incorrect springs in my dizzy and hence some hesitation on the build up of revs. when considering fuel, air, spark and timing i have:

1. good fuel - 91 octane
2. clean air filter
3. working afm - rebuilt from California shop
4. spark - fresh wires, coils, caps, rotors,
5. timing - perfectly in spec 40 thou spin around twice and check the needle gauge job... i'm forgetting all the correct terms
6. distributor - rebuilt by some hack.. most likely incorrect springs
7. dizzy belt - newish and car runs and idles fine on either primary, secondary (or both) with some lumpy idle (i can see the afm quivering with the small opening from the vacuum during idle)
8. valves - adjusted a month ago... bang on .1 mm gaps all around
9. voltage regulator - old / original about 390,000 kms guessing, and got really hot from engine fire in march
10. ignition leads - new msd on primary and older original beru with about 50,000 kms on it


Can anyone suggest where to purchase the correct springs that go inside the distributor?

main issue is that the revs do not build up the way i like (feels like i'm slightly starved of air or that there is hesitation when the engine should be just absolutely screaming all the way through the rev range) and some back fire and i can hear the barn door slap on the afm at certain revs and not always able to reproduce the conditions though quite consistent when... on gear change with high revs (over 5-6,000 rpms) so i'm looking at checking timing and starting at the distributor...

could it be i'm so used to driving my daily e46 m3??? nah! it's a tune issue with the 964.

Steve Weiner-Rennsport Systems

Alex,

The distributor springs have no affect on ignition timing, thats ALL done in the Motronic's software (chip).

Those springs are there for rotor phasing that ensures the rotor tip is lined up with the distributor cap's contacts at all engine speeds.

If you have some driveability problems, you need to look elsewhere.

Alex Sol

daaam... thanks Steve!!

if i have incorrect spring(s), wouldn't that affect how and when the contact is made with the cap and rotor as the rpms increase. ie the rotors fling outward with the increasing speed of the engine? similar to if the spring was busted, missing or incorrectly sprung?

Assuming it's not the springs in the distributor, where is the most obvious place where the motor stutters just off idle and the afm slaps? or where the revs hesitate while building up revs around 4,000rpm and again at 5,500 rpm... to the point where it feels like the motor is not making any more power above 5,500 rpm?

Spyerx

How’s your resonance flap functioning?
Have you smoke tested for vacuum leaks in all hoses and induction?

Alex Sol

resonance flap just kinda sits in the car under the intake... i replaced original intake with cone. i'll check the vacuum leak and look to replace some of the lines.. i did this with my bmw 335d vacuum lines that were brittle and snappy.in a 10 yr old bmw so.... i could only imagine i may have some original rubber lines in the 964. suggest to go with the 3.5 mm rubber fuel line? 2.5 time the price of silicone... or about a dollar per foot..

Spyerx

So you’re not sure if your resonance flap is functioning correctly? If it’s stuck open, or if it’s not opening right, you will feel a performance difference. It is supposed to open about 5k

Stock tune or aftermarket?

see this post
https://rennlist.com/forums/964-foru...eave-open.html

Goughary

Resonance flap doesnt open basis rpm.
It opens basis throttle pedal position- as the plenum shaft rotated around toward wide open throttle, the wot switch gets hit,- and this then opens the vacuum line to suck the lever for the resonance flap, and thereby it opens the flap.

But yes the issue here sounds a bit like the wot switch isn't being activated (check the wot cam) and also look for vacuum leaks. If you don't have enough vacuum to open the resonance flap you will lose power as per that link above.

wallra

when I was setting up my stand alone setup I wanted to know when the flap opened and a couple of months back their was an article on intakes in excellence and It said the flap opened at 5500 RPM's so this is where I set mine to.

JasonAndreas

dutchcrunch

I’m Leary of a rebuilt arm. That might be your problem, you can source a good used one on eBay, just confirm it’s never been open. Have you confirmed each ignition circuit can run the car independently.

dutchcrunch

You already confirmed ignition operation, still think that arm might be a problem.

Alex Sol

@dutchcrunch i have been looking at the 993 coil, lead and distributor setup - used on ebay. i'll consider to swap it all out ...

as far as resonance flap goes, my performance issues start around 2k rpm ie: afm door slaps (back fire) on mid to high rpm changes such as 5000 rpm or under full throttle runs. Also there are times it feels like the engine is starved of air then hesitates, then opens wide...

the ignition does run on just primary or secondary or both..

Alex Sol

@jason wasn't clear what the resonance flap is and now i get it... very possible the culprit. i thought the 'flap' was the canister that sits in the intake. now i get it is more like a throttle butterfly valve...

how to test?

Alex Sol

@spyrex i'll check the options on how to smoke test the intake. i did a simple test with a can of brake cleaner and juiced all the vacuum lines that I could see. any quick tips on the smoke test?

Alex Sol

https://www.pelicanparts.com/techart..._Leak_Test.htm

get a 'smoke pro'...