230SL idles great but no power and sputters after a few minutes!

[AllenF]

Hi Folks,

I finally got to drive the SL after the rebuild / restoration.  The car starts and idles beautifully but I was having some trouble establishing the mixture settings and I needed to wait until I could get it on the road (seats, tags) to begin the testing.   The car has a 250SE engine in it from the previous owner, and ran reasonably well before but it had the usual leaking valve guides and such and the main bearings weren't very pretty so I decided to just go through it. 

I installed a crane ignition and an AEM  UEGO 02 sensor so to assist in the mixture settings.  I checked fuel flow at the back  ( about 1 L / 15 sec) and the timing is set at 30 at 3k.   If I am sitting in the garage at idle, it idles great, mixture looks perfect.  If I rev it up to 3k in the drive, runs great, smooth, and the mixture is perfect according to the tester.   But when I take it out on the road, it will pull up to 5k 'ish but it feels weak (my 230SL was much faster) and after a few minutes it bogs down as if it's starving for fuel and sputters home.   The sensor shows that it goes way lean under acceleration.   I checked the injectors to see what the pattern looked like and they all did work, or at least they were not just dripping away.  Any suggestions on where to start are welcome.   I would have sent the pump in for a rebuild during the resto but as I mentioned, the car ran well before I tore it down, so I didn't think it was necessary.   

Thoughts?

Thanks in advance...

Allen

[Cees Klumper]

Sounds like fuel starvation due to, probably, dirt/rust in the fuel tank or fuel lines. Maybe start with a new fuel filter and then check the fuel flow for volume and pressure.

[Benz Dr.]

Bump your ignition timing up to 38 degrees at 3,000 RPM.

[AllenF]

The fuel injection lines were replated, is there a chance they could be corroded or restricted?   How do folks clean these out if this was the case? 

I did replace the fuel filter, and I think I need to replace the fuel tank as the fuel looked like unfiltered home brew beer.   The tank does have rust in it from sitting, just not sure how much rust is too much.    But at this point, when I run the fuel flow test (disconnect the return line at the tank and run it for 15 seconds into a container) I get pretty close to 1 liter.  Not sure if there's a way to test if I am getting proper flow between the injection pump and the injection nozzles?   I tried moving the timing but she doesn't run well very far off the factory settings. 

[rgafitanu@gmail.com]

Plumb a cheap fuel pressure gauge at the fuel line that goes to the CSS. I chased this issue for a year. The tank had surface rust from sitting 20 years. It clogs the screen filter in the fuel pump intake. What is difficult about diagnosing this is the fact that when the fuel pump is working and the engine is sucking at high revs the rust particles spread over the entire surface of that screen effectively clogging it. The engine stalls. You stop the car and it starts almost immediately apparently without problems. With the pump off the rust particles fall allowing for fuel to flow again for a short time. Unless you plumb the gauge it is very difficult to pinpoint this. If you see the gauge fall under 6 PSI it will stall.
Unscrew the intake fitting from the fuel pump and pull the screen. If there is anything coming out of it you have a problem.

[Benz Dr.]

Plumb a cheap fuel pressure gauge at the fuel line that goes to the CSS. I chased this issue for a year. The tank had surface rust from sitting 20 years. It clogs the screen filter in the fuel pump intake. What is difficult about diagnosing this is the fact that when the fuel pump is working and the engine is sucking at high revs the rust particles spread over the entire surface of that screen effectively clogging it. The engine stalls. You stop the car and it starts almost immediately apparently without problems. With the pump off the rust particles fall allowing for fuel to flow again for a short time. Unless you plumb the gauge it is very difficult to pinpoint this. If you see the gauge fall under 6 PSI it will stall.
Unscrew the intake fitting from the fuel pump and pull the screen. If there is anything coming out of it you have a problem.

38 degrees BTDC is the factory settings. 30 degrees @ 3,000 RPM is how much your distributor advances and then you need to add idle timing of 8 degrees to get any real power.

[AllenF]

That sounds a lot like what I am encountering.  I put a modern Bosh fuel pump in, so there's no screen at the back end.   The fuel filter had a awful lot of crap and it was definitely restricting things, but driving it immediately after replacing it delivered no change.   I guess the next stop is a new fuel tank to be safe.   

Thanks for the guidance so far. 

Allen

[Cees Klumper]

Maybe the new 'modern' Bosch pump does not produce sufficient pressure. But I would also see what happens at 38 degrees advance at 3,000 rpm as Dan suggests.

[AllenF]

Thanks for the tip on the timing. Should I disconnect the vacuum advance at 3000 or is the vacuum essentially gone at this rpm anyway?

[ja17]

Having a fuel pressure gauge temporarily plumbed in will verify the problem when it occurs. Guessing can be expensive!

[AllenF]

Thanks Joe.  Where exactly would I plumb that in?   And I assume I would need to extend it so I could see it while under way?   

Thanks again.   Looks like everyone is out of stock on fuel tanks at the moment. 

[vande17941]

Did you ever set your timing to 38 degrees like dr. Benz said? It will fix it.

[AllenF]

I will test the timing and report back.   Looks like everyone is out of stock on the Dansk tank, so I will need to make a go at de rusting it.   

Allen

[AllenF]

Well the fuel tank was definitely a major part of the problem.  While the pump would deliver 1 liter/ 15 seconds in the first 15 seconds, over time the rust and debris in the tank settled around the screen and choked it off.  I thought the tank looked acceptable (compared to other tanks i have used over the years) but clearly this one was nasty.  New tank on the way and I will update later.  I did adjust the timing up to 38 degrees, but until I get the fuel sorted out I can't comment on the results. 

Allen

[AllenF]

Success. 

New 250/280 SL fuel tank installed and all of the sputtering woes are gone.   The AEM fuel sensor is a godsend.  It was still running a bit lean at speed but I enriched it a bit and I will check it out on the next drive, but it is running fantastic even at this lean setting.     

I did set the timing to 38 degrees and it seems to run fine at that setting, but I haven't compared it to the 30 degree setting with the car running properly on the fuel side.   But all is well. 

Now it's time to move on to my mushy brakes and finding someone who understands how to do an alignment. 

Thanks for all the help.