flooded or starved?

[enochbell]

I have the dreaded "5-cylinder startup mode" on hot starts with my '64 230sl.  Engine runs great, hot or cold, and it starts easily hot or cold.  But for the first 10 seconds or so after hot start it is definately running on 5...maybe 4 cylinders until the other(s)catch.  I allow the fuel pump to run for at least 10 seconds before starting, either hot or cold.  Don't know if it really does anything, I have always just thought it was logical.  So why do I get only 5 cylinders on hot start?  Fouling?  Starvation?
Engine rebuilt 10k miles ago, everything new (from pistons to ball studs) except the injectors, which I could not find (they are the old style).

As usual, any suggestions would be welcomed.

Best,
g

'64 230sl, fully sorted out...ooops, spoke too soon

[Cees Klumper]

I would try new spark plugs for starters (pun intended). Maybe try new spark plug wires too. Could also be one or two of the return check valves in the FI pump are not that good anymore? Just guessing there; actually I have the same issue, only in my case it occurs cold or hot, and lasts only a few seconds and only if I try to rev the engine; so if I let it idle after it starts, it will run on all 6, while if I give it gas, it will start missing until the few seconds have passed. I have been planning to replace the check valves but have still too many other little projects that are higher on the priority list ...

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[philmas]

Is this the so-called "return check valve"?
Would it be a tough job replacing?
Do you need to replace the whole set?
If not, how could I know which is the faulty one ?

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Btw, I'm no professional, but an intuitive approach to these "misfiring" issues let me think they are most of the time related to the FI system.
At the time, there is no doubt that mechanical fuel injection was a great improvement compared to carbs.And MB, as usual, has been a pioneer.These systems worked incredibly well, at the expense of an increased complexity ,considering there was  no electronic regulation device to help contol the whole thing!
Well, it did work well until some "sensitive" parts begin to wear out....(nowadays, wear out is not a concern any more, they just replace some electronic stuff, and that's it!)

[enochbell]

cees, philmas,

Thanks for the help,

The 230sl does not have the check valve at the IP listed, as for the 250 or 280.  Would the latter part be compatible?  The wires are all new, and the plugs are replaced within the last 3k (non-resistor, of course).  Is there a check valve at the injector as well?

Thanks for your assistance,
g

'64 230sl, fully sorted out...ooops, spoke too soon

[ja17]

Hello Greg,

The later check valves will not work on the early injection pumps.  They are completely different.

Sometimes dirty injectors will cause this. They allow the fuel in the lines to leak out of the injector when the car sits.   You may want to have the injectors tested before having any other work done. Was your injector pump rebuilt?

Joe Alexander
Blacklick, Ohio

[enochbell]

Joe,

The pump was bench tested and calibrated at Pacific, no need for rebuild. Sounds like cleaning the injectors is in order, is there a recommended shop for this?

Thanks,
g

'64 230sl, fully sorted out...ooops, spoke too soon

[Joe]

Before I would go to the trouble and expense of cleaning the injectors, I would put in a can of BG44K fuel injector cleaner. You can get it at NAPA; just pour it into the fuel tank and drive.

Joe

[enochbell]

Thanks, Joe, I'll try that first,

g

'64 230sl, fully sorted out...ooops, spoke too soon

[J. Huber]

Hi Joe, I asked a couple local auto places if they had BG44K. First guy (NAPA) had no idea what it was. He sold me on Lucas something or another. Then I tried our import place -- he'd heard of it and good things but didn't carry it. Said it is one of those "shop" items that mechanics get direct from distributors... Question: are there other injector cleaners that are on a par with the BG -- or would it be worth it to keep searching? Thanks.

James
63 230SL

[philmas]

I found this link on google http://http://www.autobahnpower.com/main.asp?category=BG+44K+and+BG+Productshttp://

Maybe you could order it online?

[hands_aus]

Greg
Does your car have the one second Time relay?
It fires a burst of fuel in the inlet manifold via the CSV, hot or cold.
Try disconnecting the time relay when the engine is hot and restarting the car.
It could be that too much fuel is being injected by the cold start valve.
Maybe the Time relay is operating for longer than one second?

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[enochbell]

Thanks for the advice, just ordered a can of the magical elixer, I will report back on how it works (shipping is expensive from Kansas, $7.99, but I would burn that much in gas searching for this stuff, I think).  

Bob, my ancient 230sl has a different mapping for the CSV (I think Joe sent me the exact schema) and it does not have a 1 second squirt on hot start.  This feature was added in later models.  So I have installed a manual activator and have calibrated my left index finger to hit the momentary switch for exactly 1 second when I need to.  But the car was behaving the same way (badly) before I installed the manual switch, it would hot-start on 5 cylinders, albeit with more difficulty than I now experience using the manual switch.

Thanks,
g

'64 230sl, fully sorted out...ooops, spoke too soon

[enochbell]

$30 in BG44k later, I think the car idles a tiny bit smoother but, alas, no improvement in hot starts.  It seems as though at least one cylinder is being starved for about 10-15 seconds after hot starting.  Is there some kind of check valve that might have frozen?  Something that makes it necessary to re-prime one (or maybe two) of the injector lines?

Any suggestions would be welcomed,

Best,
g

'64 230sl, fully sorted out...ooops, spoke too soon

[philmas]

I asked my mechanic about replacing the so-called "check valves".
He said it's better replacing both injectors and check valves at the same time.

[Naj ✝︎]

Code: [Select]

quote:Is there some kind of check valve that might have frozen? Something that makes it necessary to re-prime one (or maybe two) of the injector lines?

The 230 Inj pump never had the check valves I believe but it could be that one or two injectors are dripping and lose the fuel in the line when the engine is off. Worth checking - I think...

naj

68 280SL

[enochbell]

Thanks all for the advice.  Some research shows that yes, the ball-check valve on the IP did not appear until the 250.  So I need to replace the offending injector(s)?  Does anyone have a way for me to test the injectors to figure out which are bad?

Thanks, I appreciate it,
g

'64 230sl, fully sorted out...ooops, spoke too soon

[waqas]

During my on-going IP debug, I simply exchanged the suspect injector with a known-good injector to see if the problem moved to the other cylinder or not. My air compressor doesn't go as high as the 15bars needed to test the injector itself.

WAQAS in Austin, Texas

[Naj ✝︎]

g,
 

quote:Does anyone have a way for me to test the injectors to figure out which are bad?

I would look for a diesel injection repair shop. They should have an injector tester. I believe they 'pop' at around 150 psi and you should get a conical spray pattern.

Or:
You could rig up your own  




naj

[glennard]

Is that a variable speed drive?

quote:Originally posted by naj

g,
 

quote:Does anyone have a way for me to test the injectors to figure out which are bad?

I would look for a diesel injection repair shop. They should have an injector tester. I believe they 'pop' at around 150 psi and you should get a conical spray pattern.

Or:
You could rig up your own  




naj

[Naj ✝︎]

quote:Originally posted by glennard

Is that a variable speed drive?

Yeah  

How fast can you crank  :|

naj

68 280SL

[Joe]

Is that an Ohio license plate with the "JA 17"? Hmmm. The setting looks more like rural Georgia.
Joe

[enochbell]

That picture is priceless, I grin every time I see it.  The composition is superb, for a photograph, and the irony is both in-your-face and subtle at the same time.  Thanks for sharing it.

g

'64 230sl, fully sorted out...ooops, spoke too soon

[enochbell]

Just finished a full tank of gas with the BG44k (took me 2 months to burn a tank of petrol, evidence of profoundly screwed-up priorities!) and I am back to report long-term outcome:

Absolutely no help with the hot start issue.  Still starts easy enough, but only 5 cylinders for the first 10 seconds or so.  I assume that one of the injectors is leaking/not holding gas in the line and that I will just have to wait until I find some spare injectors.  They are scarce, though, as from what I gather the early injectors are no longer available anywhere.

The good news:  There is a HUGE difference in performance at low RPMs going from closed throttle to open (clutch fully engaged, first or second gear).  I used to experience a "bucking" in the drive train unless I opened the throttle either full-on or very gently.  Middle ground was an invitation for anoying jerky acceleration.  After a tank full of this stuff the "bucking" is gone.  Don't know how, assume this cleaned up the spray pattern?, just happy to have a smooth launch.

Best,
g

'64 230sl, fully sorted out...ooops, spoke too soon

[Benz Dr.]

Any fuel injector that breaks pressure at 150 PSI is junk. You want at least 200 min. 220 to 250 is even better. I put all new injectors in my car a few years ago which is another reason it will pull high mileage.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061