Engine Power-loss/Stall after warmed up

[Driven]

Hoping the forum can point me in the right direction. Thank you in advance!

Background:'65 230SL
Newly rebuilt engine and FIP by MM, dialed in, run in and normal performance for couple thousand kms over past 6months.

Problem:
Cold starts perfectly, stable idle, warms up, stable temps, drives normally as expected until it does not. Symptoms develop in the following sequence: loss of stable idle, misfiring, unable to accelerate from standstill, and eventually loss of idle & unable to restart.

Notes:
When symptoms are present, but engine rpm is above 2k rpm, engine makes sufficient power to drive. For example, carrying highway speeds and RPM above 2k the car feels normal until come to a stop. if manage to build rpm up past 2k rpm, the engine makes power and it is possible to drive the car at city speeds in low gear (until the next stop). As i understand, the FIP off idle mode starts at 1700rpm.

Resting the engine for as little as 10mins, performance improves, & it is possible to drive distance of a few blocks before performance reverts. this cycle can be repeated over and over again.

Tests/Diagnostics (with symptoms present):
lean/rich test by detaching linkage, to add fuel via FIP and air via throttle plate, independently. Neither adding air, nor actuating the FIP increase idle.
With results of the linkage test, and fact performance reverts after resting just 10mins - coolant is still hot... ruled out the warm up device. From what i understand this device will reduce fuel/air according to coolant temp, but is it capable of shutting down the FIP's idle function mechanically below 1700 RPM? 
Tried adjusting idle mixture richer with the adjustment knob, no change.
Cracked open the return line just before the regulator and confirmed fuel flow.
Confirmed spark and swapped in a new ignition coil, no change.

Could it be vapor lock? Cracked open one of the lines at FIP, and saw bubbles come out where the pipe slots into union joint but wasn't sure if that's indicative of anything.
Would a failing fuel pump behave in this manner?


 


 

[Driven]

Couple of videos:

Accel/throttle problem
https://youtu.be/iW_Cy7-XjPw

Linkage test
https://youtube.com/shorts/pWMVW5mUtKs?feature=share

thanks

[ja17]

Check your fuel pressure while the problem is going on.

[MarkCan]

I use the cold start line feed right by the injection pump to connect my gauge. It can be attached with the proper piece of fuel hose and placed and secured higher up for the test drive.

Check your fuel pressure while the problem is going on.

[rwmastel]

Yes, if you can set yourself up to test roadside during the problem, that would be best.
Test fuel pressure (10 to 15 psi??)
Test fuel flow rate (1 liter in 15 seconds??)

[Driven]

Thank you for replies

Fuel pressure @ cold start line. gauge maxes out at 15psi. It remained pegged out during normal and problem present.
Fuel flow nearly 1.5 liters in 30 seconds, with problem present.

Notes:
Tests above should rule out the fuel pump, regulator and blocked return(vapor lock).

Don't see black smoke or smell unburnt fuel. Plan to use a wideband AFR at the tailpipe to determine change in mixture, when problem is present. If the result is lack of fuel, plan is to bypass the warm up device, with the purpose to keep the thermostat from leaning out the FIP.

What do you all think?




 

[ja17]

Make sure your ignition contacts are good and adjusted correctly. Off brand ignition contacts are notorious for not lasting.

[rwmastel]

Fuel flow nearly 1.5 liters in 30 seconds, with problem present.

What do you all think?

See fuel pump test section here.
https://www.sl113.org/wiki/Fuel/Pump
You should have 1 liter per 15 seconds.  Your pressure is fine, but the amount is insufficient.

[Driven]

Make sure your ignition contacts are good and adjusted correctly. Off brand ignition contacts are notorious for not lasting.

thank you. converted to 123 electronic distributor. that said, intermittent issue with chipboard is a possibility.

See fuel pump test section here.
https://www.sl113.org/wiki/Fuel/Pump
You should have 1 liter per 15 seconds.  Your pressure is fine, but the amount is insufficient.

thanks for pointing this out.
Re-tested volume, both cold engine and with problem. Result is 700ml / 15 seconds cold and 750ml /15 seconds with problem present.

This car has already been retrofitted with modern wet pump so will go with a similar replacement. Hope this solves the problem.

Using an online converter: 67ml per second = 241L per hour.

Can i confirm that a pump with 15psi and up rating, volume between 250-280 LPH should work?

thank you!

[Sal]

I have the exact problem on my 1970 Pagoda! Runs great for about 30 minutes freeway/ City then😱 starts to acing up with the symptoms you described! The mechanic has changed some parts to do with the fuel but have not replaced the fuel pump! Did you find out the specific problem yet? I’m still searching for a mechanic in the San Diego/Chula Vista Ca. Area HELP!!

[rwmastel]

I’m still searching for a mechanic in the San Diego/Chula Vista Ca. Area HELP!!

Sal,
I recommend you start a thread on this topic in the General Discussion forum.  You can search the Vendor Experiences forum for "San Diego".