86 930 turbo ex USA spec dead cylinder

[Bagofspanners]

Hi, to everyone, I have read many of the threads in this forum over the last couple of years and I found it a great source of information and help, however I've come across a problem with my 86 turbo and I was hoping for some suggestions, so here goes.

Earlier this year the car was running but not quite right, with an oil leak on number 4. The gear change was getting a little gritty and the clutch very heavy, so I bit the bullet and dropped the engine and gearbox, with the lump removed I set about looking for the leak, cam box cover removed I discovered 2 snapped cylinder studs!! So this changed my plans a little, I have ripped these motors down before but had acces to a full workshop and all the necessary tools, this time I decided to turn the job over to a local technician, the motor was torn down, inspected and rebuilt, new piston rings, all gaskets, a full set of engine cylinder studs, nuts, new exhaust studs, etc.... In the meantime the gearbox was fully rebuilt and a complete new clutch kit fitted then the lump refitted to the car.
The car was retuned running, but only 5 cylinders, I couldn't reason with the rebuilder he said he doesn't have the diagnosis kit required to trace the problem, blaming fuel or ignition problems. The car was fitted with new rear fuel pump, new plugs, new set of ignition leads, distributor cap and rotor, the car starts on ½ a turn and all 6 cylinders are firing but after 1 min number 4 stops firing and floods, pumping fuel into the exhaust.
Any suggestions? Thanks for reading paul.

[Jeff NJ]

I would make the rebuilder pay to have a professional troubleshoot it. It is his responsibility to deliver a fully functioning rebuilt motor to you and he didn't. If he cant figure it out, he should pay someone else to. In no way should you accept that his delivering a non-functioning motor to you is OK.
I am also a little concerned that the guy that completely tore down and rebuilt the motor is incapable of figuring out what seems to be an electrical issue.

As for your issue, you state that it is still getting fuel, so does that plug have spark when that cylinder stops firing?

[vintagecarlover]

Was the builder motor meister? Ok. Bad sense of humor. Swap a known good distributor or firing system.

[djpateman]

Originally Posted by Bagofspanners

The car was fitted with ***, new plugs, new set of ignition leads, distributor cap,***.

One of these could be the cause. Swap plug & lead to different cylinders and see if the problem follows. Try another cap. It could be a heat related electrical fault. Never assume a new part cannot be faulty these days.

[turbo owner]

Replace plug 4 or the wire, if it runs on all 6 for a minute then 4 quits firing almost has to be electrical. Something is getting hot and breaking down, start with the plug.

[Bagofspanners]

Thanks for your replies to date, I have done all these swaps with known working plugs, leads, injectors, dizzy cap, rotor, I don't know if there's anything I can do with trigger mechanism? But everything sparks with the plug external to the cylinder and when I start the car for a minute runs on all 6 cylinders then number 4 floods and petrol leakers from the exhaust header. The motor builder is suggesting this is nothing to do with his work and I've lost confidence in him now so I'm looking for a good diagnostic outfit in the north east, however I can't see how a fuel problem can be isolated to 1 cylinder.

[LuftWaffle]

Pull the injector on that cylinder and see if the pintle is stuck open.

[Bagofspanners]

Appreciate all suggestions, already done, also swapped injectors 4 and 5 then I eventually replaced with brand new Porsche part, still no change. I think I need to eliminate the spark first, for this I need a method using basic tools, checking volts, resistance, trigger clearance etc.
Please keep the suggestion coming.

[356911930]

^^^^^ This sounds most probable to me.


Rahl

[Bagofspanners]

Originally Posted by 356911930

^^^^^ This sounds most probable to me.


Rahl

I've swapped injectors from other cylinders, tested them in bottle, then I replaced number 4 with a new Porsche injector and again with the same result. I didn't check flow rate with othe cylinders as I thought the fuel was metered in the distributer unit.

[356911930]

Only one cylinder affected... have you done a compression check on this cylinder? Could a sticky intake valve cause this?

Rahl

[LuftWaffle]

You're correct in that the metering happens in the fuel head. I always viewed the spring loaded pintle in the injector as more of a check valve than anything but there may be more to it than that. It sounds like checking flow/volume might be in order. Does it run OK at higher RPMs under load?

John

Originally Posted by Bagofspanners

I've swapped injectors from other cylinders, tested them in bottle, then I replaced number 4 with a new Porsche injector and again with the same result. I didn't check flow rate with othe cylinders as I thought the fuel was metered in the distributer unit.

[pkabush]

Originally Posted by 356911930

Only one cylinder affected... have you done a compression check on this cylinder? Could a sticky intake valve cause this?

Rahl

This was my thought as well. Regardless of the cause though, your mechanic should be the one to diagnose it. Is he an independent Porsche only guy, or....

[Bagofspanners]

Originally Posted by pkabush

This was my thought as well. Regardless of the cause though, your mechanic should be the one to diagnose it. Is he an independent Porsche only guy, or....

I agree but I've lost confidence in his ability so will concentrate on getting it fixed then deal with his poor service. On a positive note I pulled all the injection pipe off and turned the ignition on and 5 pipes remain dry but number 4 was poring fuel out, this suggests to that the distributor diaphragm? Any thoughts please.

[Bagofspanners]

Originally Posted by pkabush

This was my thought as well. Regardless of the cause though, your mechanic should be the one to diagnose it. Is he an independent Porsche only guy, or....

After more checks and with all injector pipes remover and the ignition on, number 4 was pooring out fuel while the other 5 remained dry, after speaking with David who sells Salvox repair kits on eBay, I've ordered a repair kit for the fuel distributor and the WUR, any tips appreciated.

[kenikh]

Rebuilding a fuel head is more complicated than you might think. I don't recall anyone on this forum completing a rebuild successfully. Perhaps you can be the first!

[jpnovak]

Originally Posted by Bagofspanners

After more checks and with all injector pipes remover and the ignition on, number 4 was pooring out fuel while the other 5 remained dry, after speaking with David who sells Salvox repair kits on eBay, I've ordered a repair kit for the fuel distributor and the WUR, any tips appreciated.

This usually means a bad injector. Not fuel head. The pressure to each injector is equal. If one is spraying/dumping fuel then the injector is bad.

Of course, it never hurts to clean the fuel head.

[Bagofspanners]

Originally Posted by jpnovak

This usually means a bad injector. Not fuel head. The pressure to each injector is equal. If one is spraying/dumping fuel then the injector is bad.

Of course, it never hurts to clean the fuel head.

No injectors fitted just the pipes into a cup, ignition on for 30 seconds, although the pumps are not kicked in the residual pressure was bleeding off through number 4 only. I don't know sufficient to say what it is for definite but I'm chasing the problem and advised by others that know more, they say that in this condition I should have no fuel, so check fuel distributor diaphragm, I'm told this is a simple job, any advise?

[JFairman]

When assembling a 930 fuel head a set of 6 alignment pins like these will keep the o-rings from possibly being damaged.

Assembly Tools for Bosch Fuel Distributor 6 Cylinders Jetronic W900100890606 | eBay

[Bagofspanners]

Originally Posted by JFairman

When assembling a 930 fuel head a set of 6 alignment pins like these will keep the o-rings from possibly being damaged.

Assembly Tools for Bosch Fuel Distributor 6 Cylinders Jetronic W900100890606 | eBay

Great tip thanks, I will make these dummy studs from a bolt with the head ground off and a slot cut for a screwdriver blade.
I also dismantled the WUR for a clean and found it was incorrectly assembly,end!mthe actuation pin was not located in the metering plunger, thus no metering , hot, cold, boost.