928 rough running.

[dobbo]

    Had to drive to Kulnura to pick up a tyre via Yarramolong valley and Bumble hill, unfortunately at the start of Yarramolong valley road engine started missing under acceleration and was terrible going up Bumble hill witch spoilt the best part of the drive. Stopped a while at Jerrys café  checked plug leads etc (motor cooled down) returned home and car ran ok until it got hot and started missing again .      Was going to change plug leads do these symptoms suggest other problems eg dodgey coil or green wire to dizzy (green wire has been affected by heat) replaced sparkplugs 2000km ago.                        Has anyone here changed out the green wire and did it make any difference also how often should you change coolant in these alloy engines thanks in advance Dobbo. 

[bear924]

 I always find under load problems the most difficult to resolve as it's hard to look around the engine bay while driving. I've never worked on a 928 (or driven one for that matter) however the first thing I would look for is a vacuum leak.  I'm going to pressure you 928 is an older version with CIS as more modern version have electronic fuel (unsure from when .. my guess is S4). If it has a vacuum leak, as you increase load on the engine the fuel ratio leans out and then the engine starts to miss.  It may be a hose that was dislodge while doing the plugs??  

[dobbo]

  Bear924 thanks for the reply and yes your right it is a 1980 with k tronic  fuel injection. I checked for vacuum leaks by disconnecting the hose of the dizzy and sucking on it (maybe not the best way) but it seemed to hold vacuum. About 1 in 20 stops at traffic lights it suffers from poor idling (rough and too slow, below 500rpm) that's why I checked for a vacuum leak. It seemed ok. 

[ANF]

My 928 (CIS) had similar running problems you are talking about, it ran worse at idle the warmer it got. Would clear with mod to high rpm though - it ended up being the WUR pressure was all wrong, and it could not be adjusted back to within normal specs. I had a rebuilt one (changeover) put in and it ran perfectly. I had also replaced every vacuum hose I could find, plus leads, plugs, etc, etc.... my car was running lean, got pretty good economy!! Now (well did....) have power to burn!

Check the fuel pressure and get your WUR checked.
I got mine from here https://k-jet.biz/

I put a new green wire on mine when I bought, made no apparent improvement (or otherwise) in the running, but the old one did look crap. Very expensive to get one now though.....

It can be a process of elimination, I happened to check the WUR last.... I replaced every gasket/ rubber seal/ rubber hose in the intake system plus put new injectors in it. It was all needed but was not the cause of the very bad running.....

[dobbo]

        Thanks ANF just ordered new plug leads quite expensive (misses whinging as they do , could buy some nice handbags with that money) but will try and test fuel pressure after I replace leads. Hope I don't need a WUR as they are a bit pricey as well thanks Dobbo.

[jnr356]

WUR can be adjusted,was common when they were new

always reminds me of "risky business"  when the 928 was hard to start,he needed his done too

[dobbo]

 jnr356 might bite the bullet and get a Porsche mech to check WUR and fuel pressure. Will replace plug leads this week and check for vacuum leaks and plug colour.                                                Took it out today very hard to start and missing under load(seems to be getting worse) the funny thing is i've never seen the accumulator in the fuel circuit however it always started fine when hot. ANF will not worry about changing green wire and hope I get more power when I get this problem sorted.

[dobbo]

    Update checked plug colour looks ok, replaced plug leads ,fixed 3 vacuum leaks and tried to remove filter at FD inlet fitting but seized in. Test run and no more missing and idling much better THANKS ALL Dobbo.