start problems when car is hot.

[Tomguy]

AFAIK, there isn't a "0" position for the ECU. It should be set to where idle speed/emissions are correct and there are neither cold nor hot starting or idling issues. It will change every time you adjust the MAP and/or the air speed screw (the large screw where the hose from the left valve cover leads to). It's like the MAP - there isn't really a position where you can say "This is default, anywhere from here is a setting not at default" or whatever (although you really can't stall the car out by changing the ECU screw, you can with the MAP if you go too far).

[mbz72]

Thank you,

the car runs better now.

Is it normal that black stuff is lightly building up inside the rear exhaust pipes? The chrome outside is not black only inside.

cK

[Captain Scott]

This is a 2004 thread, but perhaps you all can guide me here to not throw too many parts at it. I searched for the info but didn't find what I hoped for.

My car has a similar problem of fuel pressure dropping after shut down. The initial indications were slow to start on cranking and then slightly sluggish running until she warms up. Then while starting/stopping around town she runs perfect. The next day after sitting overnight, it repeats. Over the past month or so, it has worsened.

It happens gradually over a few hours so that running it is 28 PSI and the next AM it is zero. I measured by placing a guage at the Cold Start Valve. In fact, after the first few minutes after shut down it drops a few pounds and continues. It isn't a leak cuz there is no fuel smell at all. She doesn't smoke on start or run either.

It sounds like a classic fuel pressure reg issue, but does anyone have other ideas to be sure I hit all sides of this problem?

By the way, I havn't been on this forum for over a year because the help I received before had helped me square my girl away so well! Thanks to all of you, then and now.

Scott

Originally Posted by erubin

mbz72,

If your car has fuel injection read on, if it is carburated ignore the following:

I had the same problem with my fuel injected 1972 4.5L engine. After replacing the fuel regulator the problem went away. I trouble shot by putting a pressure gauge with a "T" on the line. Sure enough the pressure would bleed down to 0 psi pretty quickly evn though it should remain pressurized for many hours. No problem starting cold because the auxiliary valve injector pumps in additional gas and masks the defective regulator on cold start up. it would also start up fine within 5 minutes of shutting down the engine because the pressure would not dissapear immediately. the pressure reg is not too $$. I recal something around $60.

[northshore]

Originally Posted by mbz72

Help,

If my 1972 SE 4.5 is hot and you let it sit for 5 minutes and you try to start it it will take 5-8 seconds. Is that normal?

Whats the problem and the fix?

Put a fuel pressure gauge in line and watch and see if it maintains 28 lbs to 30 lbs of pressure over night if not replace the check valve in the fuel pump.

[Adenauer]

I had the exact symptom in a 3.5. This thread from Arthur Dalton clears things up. Well, the guidance does, anyhow. The BOSCH manuals call the swirl pot the "header tank." The header tank inlet was being starved but the after sitting for several hours, the header tank would refill itself and the car would run fine - until the header tank was drawn down.

This was a few years ago for me but Arthur's post is the best gouge on the topic.

http://www.peachparts.com/shopforum/showthread.php?t=198008&highlight=swirl

[Captain Scott]

OK, I think I need some more skooling. My car is a 1974 107, the mechanical FI kind. I did test it and the pressure began to fall off as soon as she was shut off. In a few minutes, it fell a few pounds and kept going to zero eventually.

It was my assumption (probably wrong) that the fuel pressure regulator was to blame for this bleed down. From what you mentioned, could it be either the fuel pump check valve or the FPR? If so, how do you rule out one or the other??

Scott

Originally Posted by northshore

Put a fuel pressure gauge in line and watch and see if it maintains 28 lbs to 30 lbs of pressure over night if not replace the check valve in the fuel pump.

[Tomguy]

Originally Posted by Captain Scott

OK, I think I need some more skooling. My car is a 1974 107, the mechanical FI kind. I did test it and the pressure began to fall off as soon as she was shut off. In a few minutes, it fell a few pounds and kept going to zero eventually.

Either your year is incorrect or your assessment of your fuel system is. MB used D-Jet through 75 and 76 was the changeover year.

Either way, your fuel pump's check valve sounds at fault.

[Captain Scott]

Yep, Tom, that was a bad word-error, no!? As a closet mechanic, I'll probably recover...

On this 74, the fuel pump has been humming noticably on and off for the past 2 years, but I only put a few hundred miles per year. Although I believe the pump is doing it's job, should I just change out the pump or start with the check valve and wait for the pump to worsen? Do new pumps include a built in check valve system or is it extra?

Cost-wise, the check valve is much easier to swallow if the pump will last.

What do you think?

Originally Posted by Tomguy

Either your year is incorrect or your assessment of your fuel system is. MB used D-Jet through 75 and 76 was the changeover year.

Either way, your fuel pump's check valve sounds at fault.

[bill4247]

Tom, if you're lying under the car looking up at the mixture control screw you would turn it countercockwise to lean the mixture, correct?