Recently Acquired 400i GT: Questions about random hesitation

Hello!
Won't be abble to help with your technical issue but
welcome and congratulations for your new toy!

 

Is it the correct MSD coil or is it still the original Marelli coil?
The distributor drive and advance mechanism is indeed something to check / repair.
Do you have any possibility to check the functionality of the VR-sensor inside the distributor (when it starts hesitating).
Maybe someone knows if there is a shared relay for both fuel pumps? If that is the case it would be something I would check as well in your case.

 

This is a result of losing a complete bank for either fuel or spark -- you'll have to determine which (spark or fuel) and which bank to know which system to fix.

This o-ring in the K-Jet fuel distributor can cause the warm shutoff fuel pressure to wrongly fall to zero immediately, which would make warm restarting difficult, but it can't cause your "smooth even loss of power" problem. However, a bad accumulator or a bad check valve on the fuel pumps can also cause the warm shutoff fuel pressure to fall to zero. With that said, the CIS injected 12 cyls will usually start warm on one bank even if the other bank has a fuel pressure problem -- so that almost indicates you have a problem on both banks. I'd suggest you have a Bosch CIS shop (which includes MB and Volvo options) measure the warm shutoff fuel pressure on both banks to first confirm/deny if that is the cause of the trouble. If so, then it becomes an issue of checking each of those three possible causes.

You don't indicate your location -- is your 400i an unmodified euro version, a euro version modified to be US legal, a euro version previously modified to be US legal but now unmodified, etc.?

 

Single distributor and one coil on an injected 400 so losing a bank is fuel related only and sounds like thats probably whats happening as you suggested.

 

Yes, outwardly that's true, but they went to the crazy double-ended, two-level distributor rotor so it's still possible to lose just one bank due to ignition on a 400i -- for example, if one end of the rotor breaks off . Although I would agree with you that (since the problem comes and goes, and doesn't have any non-smooth symptom) it is more likely a fuel problem.

 

most time it is a burned relay box in the passenger food weell. Check the white contact housings for yellow or brown stains, there is then your problem

 

I was going to suggest this as well. Check the relays for the fuel injection. There are a total of three, one for each side and one for something else to do with the FI. It is not uncommon for a bad connection to intermittently shut off one bank of cylinders, resulting in a loss of power. The car will still drive but will be somewhat rough and obviously down on power.

 

For the pump, do a search on "Bosch 69523 69532" for prior threads. Your 400i would've originally come with 69523, but may have been modified to use 69532 (when 69523 wasn't available for a few years) -- you'll just have look to see which you have.

Only the fuel pump relays (or the local connections) can disable one pump. There is another relay involved, but that one would disable both pumps. But usually a V12 K/KE-Jet will fire up and try to run on one bank (although at low RPM) -- are you saying it's now completely dead during starter motor cranking and never even "coughs"?

Have you tried unplugging the safety switch and turning the key "on" to listen for the fuel pump(s) running?

 

Also check the fuses for the fuel pumps. I had one fuse fall out so the engine was running only on one bank. I cleaned and tightened up the prongs and haven't had the problem since.