Asiandude

Hi everyone
OK so amethyst might not be the greatest colour for a GTS (and same colour inside!) but this one deserves some love right now. It's sitting in a local workshop and problem is as follows: starts and idles ok, slowly apply throttle and still ok, apply throttle quickly and engine quits. The mechanics have replaced the fuel pump, fpr and both dampeners. I've just checked the temp 2 at the LH plug - ok, however the idle and WOT switches aren't clicking and I'm not getting any ohm reading at the LH plug. I'm suggesting they pull the air inlet plenum and check out the throttle body....but it isn't my car or my invoice (!) am I on the right track for these guys or is there something or a check i've forgotten? You're the guys to ask and thanks for any assistance.
Joe
'87 S4 auto (lovingly restored daily driver)

Nicole

Can't help you with the mechanical problem, but Amethyst is an awesome color! And your matching interior is called "Magenta". You should protect it from too much sun, because burgundy type colors fade quickly from UV exposure.

Best of luck!

SeanR

When you replaced the fuel pump, did you replace both the internal and the external ones? Also, you will only hear a click on the throttle position sensor (TPS) at the idle contact. If you are not getting the correct readings from an Ohm meter, then the TPS is bad and the intake should come off for all the stuff under there. Knock sensors, TPS, et al.

Asiandude

Ha Nicole, beauty is in the eye of the beholder, definitely a lady's car though. You're right about the sun fade, it was one of the Brunei Sultan's (or rather his brother I believe) they recently auctioned off quite a few 928s and 911s and much else. Not sure who owns the car but it could do with some tlc.

Asiandude

Thanks sean, actually this really isn't my car, I was asked to help the workshop who have hit a dead end with this. I drive an S4 and do all my own maint and just try to help these guys, before they do some serious harm! The throttle switches aren't working, would this cause the engine to quit under quick throttle?

Hilton

Is it dying under fast throttle application at low rpms? Or is it only dying once the rpms are high?

Tell them to test the coil resistances - the workshop manual has the specs. Unlikely, as its an uncommon failure on 928's, but could be a load issue on th eignition system.

Also test the fuel pressure with a gauge on the rails, while engine is running - its possible its getting enough fuel to maintain pressure at low rpms, but pressure is dropping off as throttle is applied (applying hard throttle would exacerbate this as jumping to WOT map would increase fuel consumption a lot). Could also test the fuel pressure regulator to see if its holding vacuum (or whether there's fuel in the vacuum line - also a sign of failure).

I think the throttle switch is a red herring - failure to detect WOT wouldn't result in engine dying when rev'ed - just reduced acceleration/power. However the failure of readings may indicate it should be replaced anyway - although I'd first adjust the throttle cable to make sure its slack enough to let the idle switch close, until you do hear the click (the idle microswitch will likely click even if electrical contact is not working). The WOT switch doesn't click.

Fuel pump shouldn't be an issue either - if the in-tank pump is dead, the car will still run in 40 degree celcius ambient temps, and if the external pump is dead, it won't hold idle and will die after a very few engine revolutions.

edit: also, if you're in Brunei, may want to contact Rennlist users A928GTS and Z928328 - both got their 928's in the recent bulk auctions, and have spent time finding 928-capable mechanics. This shop may be able to outsource some of the work to more familiar hands?

Asiandude

Thanks Hilton, it seems that the engine dies on fast throttle from idle. The fpr was leaking and they've replaced that, the knock sensor connections look brittle and that probably goes for the hall effect as well but those wouldn't cause the issue with stalling. If the throttle is opened slowly all seems ok, only quick throttle kills it.

Z928328

Asaindude/Joe,

Are you from Brunei? Welcome...to another Bruneian.- Where do you bring your 928? for service. I know which GTS are you talking- It's starts & will go dead after few mins.

Mine is currently in my garage awaiting parts from USA.Most parts arrive but I'm waiting for Porken tensioner & that's it. Just drive it around near by & start it every 2 days. I'm bringing it RNF workshop once the tensioner arrive.

Z

Hilton

Hmm.. coming back to this after reading up on other non-car stuff for a bit, it occurs to me that a sticking idle contact in the TPS could be the problem. If its sticking in the idle position, and slow to release to cruise, then the lack of fuelling could cause it do die too.

I'd go with this plan of attack:

Test fuel pressure with engine off, and running (WSM gives specs for both conditions), adjust and re-test the TPS, and see where that leaves them.

If TPS is definitely dead, then the owner needs to be aware of the WYAIT's (knock sensors, old hoses, gaskets/o-rings, TPS, ISV, injectors), as paying shop rates to remove the intake more than once would be more than the difference in just doing it all at once.

Might also want to point the shop at one of the 928 vendors in the US - they can get good markup and still come out cheaper than the local dealers.

Best of luck and thanks for trying to help out a random unknown 928 owner!

Wish I could find an Amethyst manual GTS for sale, I think its an awesome colour (although I'd prefer a combination of linen leather/carpets and magenta dash/console).

Mrmerlin

if they are going to try to adjust the TPS it would be best to just replace it since this is usually done on the bench

Hilton

Oops, I wasn't clear - I meant adjust the throttle cable so the TPS idle switch is definitely being activated at closed throttle, and then test the continuity on/off idle.

Replacement is definitely the way to go if its non-functional.

James Bailey

A defective mass air would put the car in limp mode where it will run slowly on a stored program but not revup well at all. How about letting them use your mass air sensor as a easy test ?

Asiandude

Thanks to you all. I'm thinking that the TPS issue must be part of the problem and at least worth replacing or wiring repair. We did pull the MAF and all seems in order, the car is very low mileage so...it should be ok (unless its already been swapped, but there's no history for this car) It's possible the LH may also be on the way out. The mechanics wanted to try my MAF, LH and EZK from my S4....but my car runs really well and it don't want to risk messing with it! Maybe I'll do some wrenching with them today. With the intake off the knocks etc can be replaced anyway, the connectors have crumbled so I doubt that any of that works.

Yes I'm in Brunei, an expat. I bought a junk '87 S4 from Thomas and have slowly got it back to health (as budget allows!) It's marine blue with black leather interior, mostly remade now but not a bad job. These cars are certainly worth the effort and this forum is an amazing source of information, couldn't have got my car on the road without these guys. The car in this thread is in RNF in Bunut, probably your best bet for maintenance if you don't do it yourself.

So i'll let you know how this turns out. many thanks.

Bill Ball

Then try the other car's parts in your car. It's much easier since you don't have to remove your LH & EZK; just unplug them and plug in the others. Also, note the WOT switch does not click; just the idle section clicks if adjusted correctly.

Asiandude

Bill, a good point!! I'll check if they've started the intake yet.
Joe.