Laco_Papso

930 Euro Spec was stored during winter months and after that some problems appear.

It was almost impossible to start the car. After the start, there was a lot (I mean, really a lot, like old Cummins diesel) of black smoke.
I checked sealing rings on intercooler hoses - 2 were cracked and old - all of them were replaced.
Spark plugs were all black, so we swapped them for a new set.

After that, 930 start with a lot of black smoke again.

Then I checked K-Jet.
WUR was out of spec, one diaphragm was cracked, so I rebuilt, set warm and cold pressure and put it back. Car was running, and it was almost impossible to set CO% correctly. Suddenly the engine stall, and it was not possible to start it again.
Problem was in CDI unit. CDI was making that annoying noise but wont work. CDI is replaced with brand new Classic Retrofit CDI and new ignition coil.
After that, I checked K-Jet pressures again and was able to warm the car up. Then I set the CO% to spec.

Now 930 starts without problem, hot or cold. After I take it on the road, pull on first gear is without problem, but in second gear, the car starts smoking (black). After I reach 3k RPM, it starts misfiring "jumping" and bucking as hell. Then I was driving at +- 2k RPM with a small amount of throttle, to drive back to the garage. The first pull with full throttle and boost is fine in second gear. Another pull is the same, as I was writing above.

What else should I check? Both fuel pumps are working, can there be a problem with the fuel delivery on the boost? I'm stuck right now. This is the first 930 I'm working on - every value that I can check is in spec and still not running as it should.



One more thing - almost none pops from the exhaust during deceleration.

Thanks

fritz k.

A very strange accumulation of failures after just a few months of sitting over the winter, hardly imaginable.

The car has a safety pressure switch at the back of the intercooler that switches off the fuel pumps if the boost pressure becomes too high. Try accelerating slowly and with little gas, if the error doesn't occur then check the switch.
The WUR has a full load enrichment, depending on the type the control pressure is reduced by 0.7 - 0.9 bar at 0.5 bar boost pressure. Has the enrichment also been checked?

Fritz

David Delano

You have a mixture problem on load. If AFR is normal at idle then you need to check it at full load to see if you are way off. Sounds like you are running very rich (black smoke) under load. If the smoke was blue it would indicate oil blow by. I installed a real-time AFR gauge with an O2 sensor on my exhaust to monitor mixture at all times. Its very important in these cars to maintain proper mixture under load as a lean condition could cause overheating and engine detonation. Sounds like you are running very rich so no fear of that but the cause is the challenge. If you have access to a dyno you could recreate this there with an O2 sensor in the tailpipe to prove this theory. Hokey-dokey way is to use some bailing wire and wire the portable O2 sensor into the tailpipe and drive it to cause the issue with a handheld unit (I presume that's what you are using). The WUR controls mixture at all engine speeds and loads so once you prove that it is a mixture problem (AFR) I would start there to go component by component. The fuel distribution unit may be a place to go next after the WUR. If its just cutting out without the black smoke then I agree with Fritz (above) it could be a faulty over boost sensor.

Laco_Papso

Yes, it was really strange. I found the solution somehow. The car was smoking black while it was bucking, but there was not a single pop in the exhaust. This leads me in a different direction. I know a lot of black smoke means running rich, but with this amount of smoke, it has to shoot from the exhaust like an M60 machine gun. So then I looked at the fuel pumps - still factory originals. So I swapped both of them for a new BOSCH. The engine was running a lot better, but it was unstable - one day it was running kinda well, and the other day it was not great but not terrible.
Then I swapped both pump relays (borrowed from 2 SC’s waiting for service), and it works. I hooked it to the CO tester, adjusted the mixture again (I measured pressures, and they were still in spec), and it is running great. Acceleration is smooth from idle to 6k RPM without jumping or spitting. No black smoke, and the exhaust sounds as good as it was before.

The white 930 is the troublemaker. I hope the gray on the lift will be better…

Laco_Papso

Yes, I checked the enrichment a boost as well. The whole problem was in the fuel pumps and their relays - pressure and delivery rate at idle were enough, but there was a lack of fuel on boost. I didn't check the fuel distributor with BOSCH KDEP tester because it was running well before winter. If I did that, I could find the lack of fuel on full throttle.
But thank You for reply, I don't know about the safety pressure switch.

David Delano

Thanks for the update - always helpful to post the solutions. We all learn from them. Those pesky relays are the cause of many lost nights of sleep. Interestingly they control a number of other things like the voltage at the AFR which needs a strong 12v to heat up the internal metal element which opens and closes it. Glad you got it sorted. While you are in there consider direct wiring the fuel pumps to the battery with individual fuses for each pump. It's a standard fix and offers peace of mind.