Cold Start

[jeffc280sl]

Bob,

Glad Joe sorted out your problem.  How did he determine your injection pump was lean at idle?  CO analyzer?  Vacumm test? Little or no idle speed change when adjusting the idle air screw?

Jeff C.
1970 280SL 4-speed

[Naj ✝︎]

Bob,
 

quote:Memphis-Blacklick-Memphis
1,331 miles round trip
16.25 MPG (average)

Was the fuel consumption any different 'after' the fix?

naj

68 280SL

[bpossel]

Hello Naj,

Was great to meet you and spend some time together at Blacklick.
Looks like you made it back to London?

No real noticeable difference in fuel consumption.  Just a ton of pickup now!  Need to watch my gas foot now or my bill will be higher...

Take care,
Bob

quote:Originally posted by naj

Bob,
 

quote:Memphis-Blacklick-Memphis
1,331 miles round trip
16.25 MPG (average)

Was the fuel consumption any different 'after' the fix?

naj

68 280SL

bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

[rwmastel]

quote:Originally posted by jeffc280sl

Little or no idle speed change when adjusting the idle air screw?

Jeff,

First, it was adjusting the idle screw on the intake manifold while the engine was running.  Regardless of it's position, no change was evident.  So, it was getting way too much or way too little air to the point that the idle screw didn't matter.  A quick disconnect of the linkage to test increase in fuel and air separately with engine running showed a lean condition.  Then with the engine OFF, they started to turn the IP screw.  I was amazed that it took so many turns to get to an air/fuel sweet spot.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[jeffc280sl]

Thanks Rodd,

After the FIP adjustment do you recall how responsive the idle speed was to an air screw change?

Jeff C.
1970 280SL 4-speed

[bpossel]

Hi Jeff,

Sorry, I forgot to respond to your question...
It seemed it could be adjusted by ~200 rpms.

The way Joe tested the fuel/air mix was to disconnect the linkage from the IP to the main cross over rod.  He would then slightly lower the IP rod (fuel) with one hand and then follow with slightly lowering the crossover rod (air) with the other hand.  So, more fuel, less air....  He continued to push down, increasing rpms, until the engine would cough.  This indicated a Lean condition.  He did this many times, each time adjusting the IP pump fuel setting by only a few clicks (CW to increase fuel).  Joe then repeated the procedure, each time increasing the fuel until the engine didnt cough anymore.  Note: Engine was shut off prior to adjusting the IP Pump, then restarted again.

When the fuel/air mix seemed to be ok, Joe then moved to the intake air screw and adjusted +- until the idle was just right ...  ~700 rpms

It was really cool to watch how Joe did this procedure and to see how its done first hand.  Thanks again Joe!!!

Bob

quote:Originally posted by jeffc280sl

Thanks Rodd,

After the FIP adjustment do you recall how responsive the idle speed was to an air screw change?

Jeff C.
1970 280SL 4-speed

bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

[bpossel]

No idle change when adjusting the idle air screw.
No test equipment used, other than a quick timing check with a timing light.
When Joe increased my engine rpms and the engine "coughed", he said right away...  "it's lean".  Thats when he did the fuel/air mix test.

B.

quote:Originally posted by jeffc280sl

Bob,

Glad Joe sorted out your problem.  How did he determine your injection pump was lean at idle?  CO analyzer?  Vacumm test? Little or no idle speed change when adjusting the idle air screw?

Jeff C.
1970 280SL 4-speed

bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

[jeffc280sl]

Thanks so much Bob!

I understand the disconnecting linkage part.  When adding fuel by pushing down on the IP rod he also added air via the crossover rod.  When you say more fuel less air I suppose you mean he pushed the crossover rod (added air) less than it would have been pushed if the linkage were connected.  He continued to push down (the injector rod or crossover?), increasing rpms until the engine coughed. If he pushed the FIP rod down adding fuel then the engine coughed how does this indicate a lean condition? I would think the mixture would be too rich in this case.  Which ever one he pushed down increasing rpms did he leave the other in the first position (slightly pushed down)?

Sorry to ask so many questions.  Being there is better than a 1000 words of explanation.

Thanks

Jeff C.
1970 280SL 4-speed

[bpossel]

quote:Originally posted by jeffc280sl

Thanks so much Bob!

I understand the disconnecting linkage part.  When adding fuel by pushing down on the IP rod he also added air via the crossover rod.  When you say more fuel less air I suppose you mean he pushed the crossover rod (added air) less than it would have been pushed if the linkage were connected.

YES, that is correct.



 He continued to push down (the injector rod or crossover?),

BOTH

increasing rpms until the engine coughed. If he pushed the FIP rod down adding fuel then the engine coughed how does this indicate a lean condition?

Since the IP pump rod was slightly lower than the cross-over rod as he pushed down, and it still coughed, it indicated a lean condition.
Joe then enrichened the IP pump by a few clicks (engine off).  Then repeated the procedure several times until he then reconnected the linkage and pushed them down together, like a normal condition.

I would think the mixture would be too rich in this case.  Which ever one he pushed down increasing rpms did he leave the other in the first position (slightly pushed down)?

Basically, Joe off-set the 2 rods, holding the IP pump rod slightly lower than the cross-over rod.  With the rods slightly off-set, he then lower them increasing the rpms....

Sorry to ask so many questions.  Being there is better than a 1000 words of explanation.

NO PROBLEM!  It was much better to see it in person.  Hard to explain via words....

Thanks

Jeff C.
1970 280SL 4-speed

bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

[jeffc280sl]

Thanks Bob,

Was the offset 1/4 to 1/2 and inch or so?  Also he checked your timing.  What was that set at?

Thanks,

Jeff C.
1970 280SL 4-speed

[bpossel]

Hi Jeff,

Closer to 1/4 inch or less.  Joe said my timing was set ok.  I am running the Pertronix II setup and my timing is set on 0 @ idle (~700rpm).  My engine seems to run best set this way and Joe thought it was ok.  Also...  I am running on Bosch W8DC's and gap set at 0.040
Bob

quote:Originally posted by jeffc280sl

Thanks Bob,

Was the offset 1/4 to 1/2 and inch or so?  Also he checked your timing.  What was that set at?

Thanks,

Jeff C.
1970 280SL 4-speed

bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

[jeffc280sl]

Thanks so much Bob!

Jeff C.
1970 280SL 4-speed