Rough Running at start up
 

'94 945, non turbo.


When started cold, it runs as if it were missing...then evens out after a little while. Worse when the ambient temperature is cold.

This problem started around labor day after I replaced the head gasket. Started fine before that but was losing coolant out the side.


I've done LOTS of stuff to eliminate the rough running, but the only thing that had any effect AT ALL was re-torquing the head.

So, over the weekend we did an "exploratory" and replaced the HG, AGAIN. No obvious leaks in the gasket, and the most disappointing thing is, IT STILL DOES IT.

Any help out there? You mention something (or tell me how to troubleshoot the problem) and I'll tell you if I did it already.

Atwell "the head gasket specialist" Haines
'94 945
Disgusted in NJ

RE: Rough Running at start up
 

Have you checked the fuel pressure?
Coolant temp sensor?
Fuel pressure regulator?

RE: Rough Running at start up
 

Hi Tech,


Fuel pressure: No, don't have the gauges to check it, would a mechanical tire pressure guage that fits on the fuel rail schrader valve work?

Coolant temp sensor: Yes, replaced the sensor the first time. Compared the resistance of the new one to the old one, they read the same within 100 ohms.

Fuel pressure regulator: no gas smell at the vacuum line, new, tight ends on the vacuum line.

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Is there a way I could have affected the fuel pressure? When I remove the cylinder head I just pull the whole intake away and tie it to the strut tower...no disassembly.

Thanks

RE: Rough Running at start up
 

No the tire guage will not work.

No that would not affect the pressure.

Try to get a fuel pressure guage and connect it and let it sit overnight and then start it and watch the pressure as it runs funny.

RE: Rough Running at start up
 

Ok, I can borrow a fuel pressure gauge I think.

Thanks,

RE: Rough Running at start up
 

Remember that there are two coolant temp sensors one for the gage and one for the fuel injection. You want to chenck the one for the fuel injection. Just thought I would mention that.

RE: Rough Running at start up
 

Another idea: When you pulled the head did you disturb the fuel rail and injectors? When the orings around the injectors get old they crack and give you a vacuum leak and they tend to do it on start up. Once everything gets wet and warms up they seem to quit. Just an idea $4.50 per inj for the seals and plastic end caps fpc groton.com

I changed these on my wifes 740 and it made a world of difference so....I changed them on my 240 and they made absloutely no difference at all. ???

RE: Rough Running at start up
 

Yep, and replaced them both the first time the head was removed. My resistance readings were on the rear one which is for the ECU. Both new & old within 100 ohms.

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And regarding the injectors:

After the problem started I had pulled the injectors and cleaned them as best I could. Put new seals on them at that time, no change (except the idle was better when warm).


Update: Today I was under the hood each time I started the car. I'm getting no change in idle when I unplug #3 injector (during the engine's hissy-fits). So, I'll be trying to find a spare set of injectors then send them all to an injector cleaning/balancing service.

Remember these are REX injectors so they don't have removable end caps.

Thanks all, keep the ideas coming!