W201 strands me again. Need Help. '91 2.6
 

I have searched and searched. My problem seems to have been described many times but I have tried the offered soultions except one with no success.

Description: When cold it starts and runs like it always has. Idle is smooth as silk. If I let it idle until good and hot, it will begin to stutter periodically and finally die a seemingly violent, jerky death. It must cool to below about 50C before it will start again. When running at idle, if I gradually open the throttle, it will rev as high as I'm comfortable spinning an unloaded piston engine. However, if I stab the throttle it will die instantly. If below the magic temp, it'll start right back up. If hot; I must wait.

Things I've done based on the great info found here:
1) Tested crank angle sensor (980 Ohms so OK) Cleaned for good measure.
2) Replaced OVP. No change.
3) Tested fuel pumps. Can shoot fuel from end of driveway to street. (Not recommended!)
4) Checked plugs, wires, and dizzy. Seem fine. Pretty new even.

What I have not been able to check is the fuel pump relay. All info I can find puts this relay behind the battery. Not so in my case. The OVP, EZL, ABS, and MAS boxes reside there but no fuel pump relay. Actually, I cannot find a relay anywhere on the vehicle with the "6 zyl" markings. Where else might one look?

I'm open to any and all suggestions as I'm pretty much in situ until I get the old girl running properly.

Thanks,

Sam

The Fuel pump relay is a combination relay with your MAS on your car I believe.

Have you tested the coolant sensor?

I have not checked out the coolant temp sensor. I think there are two located on the head. Is there a simple way to check these?

As for the combo MAS/Fuel Pump relay, there is a knob of sorts on top. Kind of strange.(Function?)

Is this the unit that can be opened to resolder the joints at the connector?

Thanks for the tip, yal.

Sam

Unfortunately I have not heard of anybody resoldering the MAS. Most people just replace it at a cost with a rebuilt unit :(

With regard to the coolant sensor here is a good thread...

http://www.peachparts.com/shopforum/tech-help/184859-mixture-suddenly-super-rich-checking-coolant-temp-sensor.html?highlight=coolant+temp+sensor+ohms