98 e320 Long Crank on start

[RRC44]

Hi All - this topic has had many suggestions - but no cure yet.

98 E320 97,000 miles when purchased, now 135,000. Have not resolved long cranking since purchase 24months ago! Prior to purchase I had MB dealer do a pre purchse inspection.

Was told changing spark plugs would take care of problem.

The sympotoms are irregular, in that: On Cold starts (first start of the day) sometimes an immediate start (normal), other times, cranks for 5 secs prior to starting. On starts within 10 minutes or more after shut down, almost always a normal start. After 10 minutes, irregular starts, some normal, some not. Car rarely sits from Friday to Monday, but when it does it often has an immediate start.

6 or 8 times across the last 24 months when starting after long (5 sec) crank; a mis-fire on cyl 3 code was thrown, car would ran rough at idle without smoothing out. Shut down car, restart and runs smooth at idle.

Car runs normal through driving power range, and never dies, 23 City MPG, 28+ Hwy Mpg.

What's been done:
Jan 12 Plugs were replace with OME plugs purchased from dealer.
Oct 12 Fuel pump, filter and relay - OME replaced by indy.
Nov 12 Replace No 3 cyl coil with Bosch and new MB spark wires on cyl 3. o
Dec 12 Crank shaft position sensor replaced with Bosch sensor
Apr 13 Ran Seafoam Injector cleaner at double strenght thourgh 4 tanks of gas at indy's recommendation.
May 13 Replaced Mass Air Flow sensor Bosch.
Nov 13 Replace Camshaft sensor - OME.

If the problem is a leaky injector: With cyl 3 always throwing the mis fire code, it seems that would be a likely culpert. Any reason to not to replace one injector rather than all 6?

I witnessed the fuel rail pressure test before and after. Pressure dropped like a rock immediately on shut down. With fuel pump, filter and relay replaced, the rail held pressure.

Out of ideas and money!! &

[engatwork]

You will get more response posting this in tech help. Maybe the mod will be along here shortly and can move it.

[spdrun]

Looks like classic symptoms of a fuel pressure issue.

Fuel pressure regulator bleeding down, rather than keeping fuel in the fuel rail, or a leaky injector doing the same thing intermittently. The fuel pump takes a few seconds to develop enough pressure in the system to inject enough fuel to run the motor. Could also be leaky check-valves in the pump itself, but probably not the pump.

There's a "tire valve" type nipple somewhere on most fuel systems, and you can connect a pressure gauge to it. The system should hold pressure for several minutes after turning the car off.

How the heck could your mechanic have not even thought of the fuel-pressure regulator, rather than throwing other parts at the issue?

[ptoro01]

Agreed with fuel regulator or injector. But it could be a vacuum issue, the fuel pressure regulator is controlled by it.

Does your gas tank hold pressure? I have similar symptoms and my tank often doesn't "hiss" when fueling up, but at times it does.