Iamwilliam

I have an 82 with 4.7L in it. Was put it into storage for 14 years. I’ve been slowly restoring this car over the last 2 years. Car takes 5-8 seconds of cranking when cold and starts weakly. Once started it runs fine and feels great. If car is warmed up it will start immediately if started again within an hour. After the hour it feels vapor locked, fires up and dies, like no fuel. After a few attempts and very low idle, feathering gas pedal it will come back to life and eventually run fine again.

Iamwilliam

Wanted to mention everything has been refreshed and still have this problem. fuel pump relay, fuel pump (already tried 3 different new check valves) fuel filter, in tank filter, all injectors refreshed and balanced as well as cold start valve, both fuel pressure regulators and dampers, all rubber fuel lines. I have a fuel pressure gauge at the end of the rail and it goes to 36 psi with fuel pump relay jumped, and then drops down to 20 psi within 5 minutes, then slowly drops to 5 psi over 30 minutes, then to zero after about an hour. Everything is new why does it leak down so fast. Where else to check? Not enough pressure causing vapor lock? I hate throwing parts at it but I’ve gotten desperate and still having the same issue

Petza914

To lose pressure like that I think the fuel is either dripping through the injectors or returning to the tank. Since you've tried 3 new check valves, probably not the latter, so one or more injectors must be leaking and flooding the engine, which is also why it's not running right when first started. Does the oil on your dipstick seem runnier than it should be or smell like gas at all?

Iamwilliam

Just brought the injectors back to Rc fuel injection in torrance ca. They were the shop that originally refreshed my injectors last year. I brought them the rails with injectors attached and had them pressurize the rails and test. The tech said they are holding pressure just fine and their printout said each injector had passed all the tests. Unless the shop missed the leaking injector. I’ll go sniff the dipstick when I get home and let you know if it smells like gas.

Iamwilliam

No fuel smell on dipstick. Just smells like oil. I’m out of ideas. I have a new green wire coming in on Monday. Could that be it? Ignition switch? Maybe this car isn’t supposed to hold fuel pressure as long as others since there’s no accumulator?

Ladeef

cold start valve? blue plug at back of engine. Apply 12v to it and see if it clicks. Mine was frozen up and I had the same issue. A few squirts of carb cleaner and applying 12v to it like an injector cleared it up.

Iamwilliam

sent it in for cleaning and got it flow and pattern tested. Just reinstalled it last week with no change in starting behavior. Also aux air valve was sticking so I drilled out rivets and cleaned it all out now it moves as it should but still no change.

GerritD

Hi William,
I have exactly the same issue as you do. Mine is 928S euro kjet of 1980.
Coldstart only works with gaspedal fully down and coldstart valve connector disconnected.
Warmstart only goes well within the hour.
Car runs fine once started.
I have the impression that my engine is getting too much fuel during start, that’s why I disconnected the coldstart valve, and when pressing gaspedal fully down,
I let extract air to the mixture.

You can try the same approach as I did for coldstarting the car . I bet it will fire up immediately

I also renewed everything in the kjet system from the back to the front of the car…

Iamwilliam

Thank you I will try this, disconnect cold start and hold down pedal while cranking. If this works.. what’s the actual fix?

GerritD

I have not yet found a fix, nor the real root cause. One would say the mixture is too rich but then I would also have mixture issues during driving.
And I checked the CO : it was about 1,8% which is between 1,5 - 2,5
Also the colortune was blue which is good.
Possibly there is an issue with either the air metering unit or the WUR itself.
Remember : I need the push gaspedal down to let more air in the system which gives the impression that the metering plate is not letting
sufficient air during start.

GerritD

Any update ? Did the solution I proposed for cold starting the engine work ?

Iamwilliam

I haven’t tried it yet. I started messing with other stuff during the week.. got some nice used bilstein/eibachs from 928 intl and put those on while refreshing some suspension parts, also installed new green wire, and replaced fuel injection relay, will get the car back on the ground and buttoned up tomorrow. I’ll try your method if the little things I’m doing now don’t fix the problem. Will report back tomorrow

Zirconocene

I suggested these videos to @GerritD but I don't know if he looked at them. In parts 2 and 3 of this revival of a BMW 320, M539Restorations goes through the fuel system on this car to address exactly these kinds of issues. On part 2, it's near the 25 minute mark that he starts looking at the fuel system, but he only really gets it fully sorted in part 3. The whole thing is worth watching, IMHO, and part 3 can be found from part 2.

Here's part 2:

Good luck

hacker-pschorr

With L-Jet, these typically have cold start issues due to the cold start injector not working or the thermo time switch has failed. This sensor / switch is what triggers the cold start injector. Without its function. the 9th injector will never fire and the L-Jet system won't be spraying enough fuel during cold cranking.

See this thread:
https://rennlist.com/forums/928-foru...h-testing.html

Iamwilliam

The cold start injector has been cleaned and tested alongside the injectors and with noid light on cold start connector it lights up bright during cranking for like 5 seconds. Thermotime switch is new and also tested for correct resistances at hot and cold temps. I'm leaning towards a faulty new fpr. Sounds like there's air or vapor lock in the fuel system when fuel pump jumpered I can hear a squeal from one of the fpr for a few seconds (air/vapor passing thru?) Not enough pressure in lines causing vapor lock (fuel boiling in rails?) I'm running out of ideas