'88 528e Starting Problems

New to this forum.

Car has been cutting out while driving on side streets, freeway speeds or idling.

Sometimes it will resume while coasting, with no more interruptions, other times it must be re-started.

Has always started when cold, except after last time it ran, ~7 days ago.

Yesterday changed in-tank fuel pump and sender to no avail. Will change fuel filter today.

Timing belt not broken.

Not being familiar with the results of various parts not working, I have made a novice's list of possible suspect parts.

Could it be any of these that are causing the problem?

-Fuel Pump Relay

-Fuel Injection Relay

-Non-Return Valve

-Throttle Switch

-Electric Fuel Pump (next to fuel filter)

-Fuel Pressure Regulator

Thanks for your opinions.

Nice list so here's my 2 cents worth. the most common cause of your symptoms is the DME 'Main Relay'. the 3 relays clipped onto the fuse box are for the DME [injection] the 'Main' is a 5 pin relay with 2 large red and 2 large red/white wires. the 'Fuel Pump' relay is one of the 4 pin relays, LOOK FOR 2 green/violet wires coming off one pin. the other relay is for the 'Purge Control' valve [don't worry about this one].......repalce the MAIN & FUEL PUMP relays and see what happens, chances are that you'll have fixed your problem. as to the rest of your list here's a short list of symptoms they'd cause when they fail or faulter.
+Non-return Valve [fuel pump check valve?]
^long hot restart cranking time
+Throttle Switch
^odd idle problems, racing, etc...NOTE: you can test the idle switch by driving the car and watching your MPG gauge; cruising @ say 3,000 RPM, release the throttle completely. if the MPG gauge swings ALL the way to the left while decel'ing [until ~ 1,800 RPM] the Idle Switch is good. This is the 'Fuel Cut' mode of the injection on decelleration.
+Fuel Pump
^syptoms are similar to what your experiencing
+Fuel Press. Reg.
^won't 'kill' the engine but you'll notice rough running, black smoke & possibily a fuel smell. the Press. Reg's. fail by sticking closed, dead heading pressure [+125 psi] and can cause leaks at slightly loose fuel hose clamps.
+Intank Pump & Fuel Filter
^usually causes 'starvation' @ cruising speeds, esp. in hot weather or high altitudes

HOPE THIS HELPS ! ! !....................................jb.

jb,

Thanks for taking the time to post such a comprehensive explanation.
Tomorrow I will try the Main and Fuel Pump relays as you suggested. Hopefully that will solve the problem.