dan928

Hi everyone,
Bought a 928 s Auto 1982 4.7 16v with head gasket damage.
When I bought the car started the engine and it run very rough at idle as well as when accelerating it.
Done the head gasket job after reading some very helpful threads on this forum and got all the parts from 928srus (thanks Roger).
Put new spark plugs in and cleaned the distributor cap and rotor arm.
Started the engine but it run very rough at idle and when accelerating it was a bit better but still not right.
Read some threads about cleaning the mechanical injectors and decided to replace with new ones.
New injectors in, engine starts and idles better but noticed it's a bit lumpy when cold.
After a few minutes when it warms up it idles ok.
Driving it in the town, keeping the revs up to about 2000-2500 is fine but if I put my foot down engine dies and then it idles very rough. Five minutes later engine runs fine again untill I go above 2500 revs.
I know there's a lot of things to check or change but I don't know where to start. Thinking about changing all the leads, rotor and distributor cap, but what else should I look for and add on my shopping list? Any help will be much appreciated.

Dan

Ducman82

how is your fuel pressure? check for vac leaks.

Lizard928

This car uses CIS.
Also known as K-Jetronic.

You really need to get a proper set of CIS guages.
I would bet the WUR needs to be replaced/rebuilt.
Its also possible that the distributor has some gunk build up inside of it.

However, first things first is to replace the green wire and check timing.

soontobered84

What is your engine number? M28- 9/10/11/or 12?

Imo000

Are you sure the original problem was the head gaskets and not something else?

dan928

The engine number is M 28/12
It definitely had a blown head gasket as I done the work myself, but it may also have other problems that I'm not aware of. Engine was in a pretty rough condition when I got it and I'm trying to bring it back to life.
I changed the injectors, old ones being rusty and leaking after stopping the engine.
Checked the timing but didn't change the green wire (Is it the one coming out of the distributor?)
Will measure the fuel pressure but need to buy the test gauges first.

Dave928S

Sounds like you're off to a good start and you're getting there.

Yes .. the green wire is the shielded green coloured signal wire coming from the distributor and going to the ignition unit. Expensive ... be sure it's had it before you replace.

Check you have good spark to each plug and coil is OK. Also check there's no light show in the dark under the hood, to do a basic check of all the leads and the cap.

Read up on the K Jetronic system and go hunting for problems after that. Here's a link to a K Jetronic videos thread posted recently which will help with the detective work.
https://rennlist.com/forums/928-foru...ng-videos.html
Check your fuel pressures first and then go from there.

Check every single hose in the engine compartment and replace where necessary ... you can count on some being stuffed.

Does sound a bit like a K Jet system problem.

Eliminate possibilities one at a time and you'll get there.

Where are you located?

dan928

Hi Dave, thanks for the link

I'm located in Worthing, UK

I've checked the leads and the cap, they seem ok but I'll change them anyway

I intend to look into WUR next but have to buy the fuel injection tester first.

Cheers,

Dan

Dave928S

If I'd known you were from the UK with the steering wheel on the correct side of the car I would have referred to the 'bonnet' instead of the 'hood'

Even though my old original leads weren't breaking down a great deal, new ones gave the engine a new lease of life. I don't think you can go wrong getting some of those basics up to scratch first.

Roger has a pressure test kit with all the adapters you need for K Jet.

kinda5150

i'm guessing fuel filter and/or strainer (can't remember if there's an in-tank strainer). replace/check the fuel lines--don't need another 928 going up in flames! if your injectors were that gummed up, then the whole fuel system delivery would be suspect.

dan928

Still waiting for the injection tester but after reading some threads decided to have a look at the Auxiliary air valve.
Took it out, at about 25 Celsius is half opened. Connected it to 12v and it shuts but leaves a small opening about 2 or 3 mm square.Put it in the freezer and after 15 min still not completely open. I understand that it has to open and shut fully so I'll take it apart and adjust it.
Interesting part is that I checked the plug with ignition on (engine not started) and there's no 12V feed.
Checked the WUR plug and again, no power. It must be a bad connection or a relay or something?
Anyone can advice where to look next?
Cheers,
Dan

smiffypr

AAV only affects one thing, the idle speed. It doesn't affect the mixture at idle or at any other speed.
Your problem sounds like lack of sufficient fuel. Have you checked the fuel flow rate yet? Check at the return to the top of the tank. This test covers the pump, and any restriction in the filter, the pipes, the gauze in the fuel distributor, and the pressure regulator in the fuel distributor. Fuel flow should be over a 1120cc in 30 seconds (with the engine running or the fuel pump relay bridged).

Dave928S

Smiffy knows a LOT about 928's and is a wizard with problem solving, particularly on early K Jet cars .. you can't go wrong following his advice. He posted those YT videos that I linked to in my earlier post.

dan928

Connected the AAV after adjusting it and also disconnected the bypass valve for air conditioning ( mine don't work).
I've noticed a good change in idle: at cold start it revs to about 1200 then goes down to normal as it warms up, which didn't happen before.
I'm still waiting for the pressure tester, as soon as it comes will follow Smiffy's advice.
I've looked for a k-jetronic specialist around me but no luck, and to be honest I prefer to do it myself, don't quite trust mechanics. I also ordered Watson's book from Amazon which I understand from other posts is very useful.
Cheers,
Dan
'82 Euro

smiffypr

You don't need the gauges for the flow test, just a measuring jug and a bit of hose.
Smiffy