JakeS2

Hello,
Little update, coding plug is '89 manual with cats:


I'll be taking off the intake manifold and injectors soon. When we measured fuel pressure it dropped quite quickly when engine was shut down, like 5-6 minutes to zero ; sounds like leaking injector.

edit: GREAT! Flickr has suspended linking of actual images. I'm switching to Picasa, d**n you Yahoo
edit2: hmm.. think I managed a way to hack around that restriction...

JakeS2

More "content" on topic.
Sorry for lame FPR meter. But in nutshell it seems idle frp runs at +3.5bar and when I switch off engine it goes to 3.8. On some of the runs fpr was at 3.8 when engine was running.

In addition after 30 minutes from engine shutdown pressure was still at 3.5bar, is that something to worry about?

John Speake

In that case there may be an intermiitant vacuum leak...

The pressure holding at 3.5 sounds good on the face of it, if the meter isn't sticking... previously you said the pressure dropped quickly ?

JakeS2

John, yes I said so before as the meter was not working as it was not that tight fit. These home-made appliances are of... you know. That is why I wanted to re-test the pressure. There is a buddy of mine doing electrical fuel pressure measurement setup and I'm going on that route - as soon I get feedback of his setup.

Meter is not sticking, but it is shaking like a dog with itch in it's a..e. I'm suspecting vacuum leak under the throttle body myself too. Will be ripping off the intake manifold this week. We'll know more then.

JakeS2

Okay, points (again) to John. There is at least one leak. I did not want to risk burning my car so I went on the cigar route:

but it was a tricky one to find out! I had to cap the maf (see in the picture) until smoke started to come out from that joint (see on the right side of the picture)


Tomorrow I'll switch that hose and find proper tighteners.

JakeS2

Little update. Now there are new hoses from Y-joint to plenum and brake booster plus proper tighteners, sorry no pics this time.

Now it's time to drive - and hard!

fraggle

So it IS all fixed?? right on!!

JakeS2

Okay, this is now me trying to give back to some of (new) 928 owners. If the symptoms like on this thread occur, it's most likely due to vacuum leak somewhere in the system.

In the picture below you can see MAF and plenum output capped. This is to make sure air does not flow out from those places. So if you did not get it yet, the procedure goes : you blow cigar smoke into the attached large pipe and see where it comes out.



In the lower part of the picture you can see the Y-Pipe. This seems a good culptrit to look for leaks as it uses pre-tensioned tighteners that were done like 20 years ago and rubber they are sweezing has dried thus not making the connection tight anymore. My replacing tubes that attach to this pipe and using proper tighteners might fix your problem - like it did with mine. Cheers.

Arnoud

Great outcome, Jake!

So: no more black smoke ("screen") and just the fabulous sound track when you put your foot down?

GregBBRD

I'm a bit confused how a vacuum leak can make an engine run rich at WOT. Really confused.

Can someone explain?

Seems like any vacuum leak would allow unmetered air to be sucked in, after the air flow meter...which would make the car lean. And at WOT, above 5,000 rpms, the vacuum to the FPR should be virtually zero, anyway.....so a small vacuum leak doesn't change the fuel pressures.

At WOT, the O2 sensor is completely "out of the loop".....so any feedback from it is ignored. And the throttle switch has "put" the engine into the WOT map.....that doesn't know intake manifold pressure or leak from the right rear tire.

Where is the additional fuel coming from and what signal is sending it?

JakeS2

I don't know in detail what goes on in there, all I know is that I fixed leaking x-over to exhaust manifold joint and fixed vacuum leak. She has never pulled this strong during time she's been mine.

Arnoud: If I floor it during load she puffs some black smoke but not that much but I really really love the lift-off bang she makes We'll be doing some AFR runs later on this month but MPG has improved and she _really_ pulls strong now so I guess we're on right direction.

JakeS2

Okay, what can I say now... was at track days and before that drove like I stole it to the track event... no issues what so ever - apart from biiiigg grin on my face :-) She does not puff smoke anymore (unless I suddenly drop from 5 to 3 and slam it..) and she pulls pretty good.

What happened in Alastaro Circuit was that I was doing nearly 170 before main turn (called Las Palmas) - was just overtaking a 911 turbo btw when I lost all brakes. With pumping and some steering magic I managed to keep her on track and rear-pusher's driver knew to keep distance. So I boiled my brakes. I have to brake a lot as I had street tires and even those MSPS3's dont have lateral grip at those speeds. But boiling happened also to fact I did not remember that there are TWO bleeding circuits in each caliper, stupid me.

Well, now she's back on her wheels and as there needs to be pics, here's one from today. My 1,6yrs daughter was at garage with me :-)

JakeS2

Okay, little update. Since last summer we did the TB job (woohoo, not a virgin anymore) and changed WP to a new Laso unit (with plastic impeller). I'll write the other findings later on but -- we are back with the idle problem. She pulls strong but now and then idle remains over 1000rpm after driving (standing on lights) or actually well below 700rpm. Usually it's between 700 and 800rpm.

So, I decided to hunt down the failure (not there yet):
- no apparent vacuum leaks, however if I do the cigar trick [see above posting in this thread] I can hear that air is going somewhere slowly but there is no mark. I have done it from fuel regulators' vacuum connection, the Y-pipe and so on - same result always.
- MAF was changed last year, it's a refurbished from JDS so that should be ok.
- Exhaust manifold does not have leaks, I even changed the bolts to X.
- O2 sensor was changed last year.
- Relay panel was rebuilt and cleaned this winter (new fuses but however, with old relays).
- I can hear a clear click when I open the throttle linkage by hand, also returning the linkage results in 'click'.

So what to do next? Before going to take apart the intake I'd like to know if there are things I can try out before doing that. I actually have bought a new set of intake seals and a new ICV but since it's summer I would not like to open the plenum just in case.

JakeS2

Update:
- Soaked the ICV with brakecleaner. Result not tested.
- Ordered : Temp II sensor.

dr bob

The only vacuum-related disassembly for the timing belt project is the little solenoid valve for the intake "flappy" valve. Reversing the hoses accidentally allow air to pass through to the vacuum supply side. If you have a MitiVac or similar handy, verify that the hoses are correct by testing that the supply side connection is actually closed to atmosphere with engine off. Sorry I don't have a picture handy.

Or just reverse the hoses on the solenoid and see if you condition disappears.