Injection pump rebuild

[mauro12]

Hi guys , finally I have rebuilt my inj pump after years of black smoke and huge fuel consumption. First impressions , the car is running very smooth with no stumbling or hesitation. Power is also more and there is no black smoke any more .
I have noticed only 1 thing , during hard acceleration and release of pedal , I hear the exaust popping a bit . Maybe is too lean ? Apart from that the car is running like a dream . I prefer not to touch anymore the pump or any other components . Thank you

[Raymond]

Try depressing the clutch when you jump off of the gas and see if it does it then.  I vaguely recall a circuit on the 4-speed manual that was supposed to cut the fuel to reduce pops & pollution in the exhaust.  I don't have that on my Tremec 5-speed and haven't missed it.

[roymil]

Sounds like the lower solenoid may not be working, or possibly not hooked up after the rebuilt FIP was installed.  Here's a link to description of how that solenoid is supposed to shut off fuel to the system when lifting off the peddle when in 3rd, or 4th gears.   I see you have a ZF-5sp so wondering if it is setup to do that for 5th.    Either way its not a big problem other that wasting a bit a fuel, oh wait, yeah it is at these prices!  Enjoy that new pump...I have been so happy after rebuilding mine.

https://www.sl113.org/forums/index.php?topic=3277.msg46440#msg46440

[Benz Dr.]

5 speed cars were never equipped with any switches on the transmission needed to make that system work. This is why they quit producing cars with 5 speeds for the US market after mid '69.

[mdsalemi]

5 speed cars were never equipped with any switches on the transmission needed to make that system work. This is why they quit producing cars with 5 speeds for the US market after mid '69.

Great information...Mauro's car is an Italian delivery 5-Speed 250SL. So, how can he stop the popping/backfiring? Is it fuel or timing?

[Benz Dr.]

Not likely timing and it may be too rich. Go through the linkage tour and make sure your throttle plate is closing properly. Air entering the exhaust system is causing it to pop from unburned fuel. I would check spark plugs to see if there's a rich running condition.

[mdsalemi]

Now if he can just understand all that, translate to Italian and then explain to the mechanic who put it all together for him…🤔

[mauro12]

I understood very well thank you . I guess there is a small delay in the linkage connected to the butterfly. By the way Hans fritzsche did a fanstastic job . He tuned my r22 pump for my 250sl by changing the space cam nr 22 to a space cam nr 8 . He has a special technology to equalize the amount of fuel in each cylinder with a mistake rate lower than 0.001 % . The engine is very smooth

[Runale]

Would it make sense to have a look at the cold start valve too for any leakages..?

[mauro12]

I guess I will not touch anything . The car is running great and I’m curious to check the fuel mileage now . Before I was getting about 4km /l which is around 10miles per gallon .
Now after the perfect calibration done by Hans fritzsche , I believe should be around 20miles per gallon . He replaced the fuel delivery valves 1 and 4 , both bearings of the cam shaft , a new cam shaft , all seals and the calibration . Total amount was about 2700€. All done in 3 weeks time .

[whittakerturbeville]

Yes. It's an absolutely mind-blowing setup.

[RobSirg]

My auto 280SL runs great, but l can readily make it pop/burble on deceleration……. especially when driving hard through the hills and shifting manually.

I guess it might be running too rich, but l kind of like it (esp. when the roof is down ☺️).

Rob

[Benz Dr.]

My auto 280SL runs great, but l can readily make it pop/burble on deceleration……. especially when driving hard through the hills and shifting manually.

I guess it might be running too rich, but l kind of like it (esp. when the roof is down ☺️).

Rob

More likely a small exhaust leak. Air enters the exhaust and ignites the mixture inside the hot pipes when lifting off and coasting from higher RPM's.

[mauro12]

How to fix this exhaust leak ?

[Lorsar]

Mauro, first you have to identify where it it leaking.

https://www.sl113.org/forums/index.php?topic=35384.msg258587#msg258587

[Bonnyboy]

I had a popping on deceleration and found a small hole on the top of the exhaust where the two pipes are joined after leaving the engine. I bought a new pipe and as I was preparing to replace the pipe I decided to make sure that was the cause of the popping so I put a bit of muffler cement on to seal the hole and tried the car -  the popping on deceleration went away.   So maybe this winter I will put the new pipe on. 

Worth a shot.