running problems

[jim 56]

Hello all sorry to be a pain but I just can't get my 1972 280 SE w/130 engine to run right I hope I can get more help.
Let me tell what I have done.
Checked compression 150 psi with very little difference between between cylinders.

Just rebuilt the short pump rewound by a member on site new brushes and seals.At a gauge on fuel filter I have 14 PSI.
Installed Crane 700 following installation procedures from tech manual.
Installed new plugs NGK BP5 ES gapped at 30.
Checked CSV no leaks manually engage it to start
Put a new thermostat in the WRD device it does shut down air although not completely but after the car warms up I put
     my finger over filter hole and feel a little bit of suction but idle does not change.I read in a few posts that this is OK
I backflushed the injectors (I do not have the equipment to check them)but I assume they are ok as all the plugs look them
     same and the car doesn't really have a miss.
I installed a new fuel filter and bleed the lines all the way to the injectors.
Installed a new cap and rotor.
The coil is new it is PVL 101 400 on the coil it says Bosch 0221122001 I assume this coil is the right one (though I may be wrong
Set up the linkage according to linkage tour throttle closed FIP at stop FIP rod at 233mm
   OK now here is what's happening.
The car starts pretty good when I energise the CSV for 3 seconds it idles rough while warming.It gets to about 175 degrees in a couple of minutes then settles into idle from 750 to 850 or so.It varys but still does not idle too well.
I checked the timing moved it to 6 BTC.
The vacuum at the tap on the intake manifold reads 14hg
When I do the split linkage test moving the throttle the car dies.Moving the FIP rod has no effect.
So according to the split linkage it tells me the car is running lean.Looking at the plugs they look really clean.
I adjusted the full rack screw on the FIP ccw about 6 clicks it is now 24 clicks from its starting position.Still the same.
Adjusted the idle screw cw(with engine off) 8 clicks still the same.This is probaly about 26 clicks from it's all the way in position
I tried turning the BC out as Dr.Benz suggest it has no effect or very little.
So I really don't know what else I should do should I keep turning FIP idle screw.
I can't really time it at 3000 RPM because when I try to bring engine speed up it spits and backfires.
Sorry this is sooooo long but I really need help at this point.Maybe I'm missing something please let me know.

[mrfatboy]

Whew!  That's a lot to read 

Here are my off the cuff remarks.

- I think spark plug gap should be ..032" - 035"

- Timing should be 38 degrees BTDC @3000 rpm.  8 degrees BTDC @ idle. (at least for earlier cars.  The pros here can confirm.)

- Are all the spark plug cables in good shape?  No cracks? Solid core?

- After you did the linkage tour are both the FIP linkage and the throttle body linkage on their stops at rest.  This is the most important thing. Do you have the alignment guide hole for the linkage on the intake manifold?

- Being a later 280 there is much more involved to the linkage than earlier cars.  I have seen one worked on and fixed but it is above my pay grade to explain here🤣 Hopefully pros can help here.

- In general, it sounds like your FIP is way out of whack. Guessing lean.  At this point I would suggest investing in a fuel mixture sensor. See links below. It will save you a lot of aggravation.


Again,  just my 2 cents.  Hopefully pros can zero in on the problem.

Innovate Motorsports (3837) LM-2 (BASIC) Digital Air/Fuel Ratio Wideband Meter incl. Bosch LSU 4.9 https://www.amazon.com/dp/B001S7W836/ref=cm_sw_r_cp_api_i_C-w6Eb0SPH542

Innovate Motorsports 3728 Exhaust Clamp Cast-Stainless https://www.amazon.com/dp/B000CO9MF8/ref=cm_sw_r_cp_api_i_a.w6EbWQBFRQ1

[Pawel66]

Even though I am not a mechanic, let me put my 2 cents for inspiration - why not?

1. I would check and confirm ignition timing as mrfatboy suggests. Start with idle.
2. No offence - just to be mindful which way you are turning adjusters - you should turn them in opposite direction to enrich mixture (main - left, idle - right).
3. Split linkage - pressing on FIP lever has no effect. Does this really mean it is very lean? In any case - those movements on levers during split linkage test need to be, I think very small and it takes a second or two for engine to react.

[jim 56]

Thank you for your replies.
I will regap plugs to 32 -35
Yes both throttle and FIP are at the stops.
I believe I am turning FIP adjustment screws the right way full rack screw ccw to richen Idle screw cw to richen.There is no alignment hole
The plug wires say copper core on them no cracks that I see.
I cannot race the engine enough to get it to 3000 RPM as it backfires It is at 8 BTDC at idle.
I am thinking it is very lean also.I guess I'll keep turning the FIP idle screw more until I get different results.
Does anybody know if the coil is correct?
Right now I cannot afford a fuel sensor meter.

[Pawel66]

Perhaps it is important to know: how much of shims do you have under the BC?

[mrfatboy]

From the link below,  the correct coil depends on your vin.

https://www.autohausaz.com/catalog/k/mercedes/1972/1193374-280se/coil

Measure the resistance of all the spark plug and coil wires and report back.

[jim 56]

My BC has three shims under it.Not sure of thickness but when the car is running I have marked it and loosened it two full turns
according to Dr Benz this is the same as adding shims thereby enriching fuel mixture.
The spark plug wires have 1000 ohms each wire.I will have to measure coil wire.
As far as the coil I have the crane system installed I am not sure what coil goes with it.

[mrfatboy]

At what rpm does the engine start to backfire?

As a quick and dirty test, can you set the rpms to right where it starts to backfire.  Then dial the BC CW or CCW while it's running to see if you can eliminate the backfire.  Use only slight adjustments.

If you succeed in making the engine run smoother you will have an indication on what your pump needs to be tuned correctly.

Other thoughts.  I know nothing of the crane system.  Is it working properly?

[jim 56]

The crane seems to be working right started right up after installation still wondering if that is the rightcoil for system I will have to call crane.
Starts to backfire around 1400 RPM will try the BC as you suggest.

[mrfatboy]

Around 1200 - 1400rpm is where the idle FIP thumb screw setting has no effect anymore.

Assuming your idle mixture is set correctly and assumimg that the FIP is going lean at 1400rpm you would enrichen the FIP using the full rack screw (or BC).  This would enrichen the FIP at all ranges.  You then would have to use the idle thumb screw to lean out the lower rpm range to compensate.

There are white and black screws that control mid and high rpm ranges but they are a big NO NO to touch.

[jim 56]

Thank you I shall try tomorrow.One thing I did notice is that the idle screw on the FIP is only 10 clicks from being all the way in and yet it is still running lean

[Benz Dr.]

Thank you I shall try tomorrow. One thing I did notice is that the idle screw on the FIP is only 10 clicks from being all the way in and yet it is still running lean

All the way in, or all the way out? Turning it out leans the mixture.

[jim 56]

Thank you for your reply. The big screw on the FIP pup is 10 clicks from all the way in.The rack screw (adjustment for all RPM range) is backed out 22 clicks from all the way in.Which as I understand should be making it richer.Right now I don't know what to do next.I will adjust gap on plugs to between 32 and 35 as suggested by Mrfatboy.I don't know should I keep adjusting rack screw out more but like I said it still doesn't idle all that well.Do you think the shutter gap on the crane should be moved.There seems to be a wide range on movement of distributor shaft where the light is lit.

[jim 56]

I think I may have found out what is going on.When I installed my rebuilt fuel pump I did a flow test and it looked good ! liter 15 sec. I did it again yesterday had about half that waited awhile did it again.Did it three more times sometime it was ok sometimes not.I removed the check valve in FIP found it was hanging up sometimes.I cleaned it and started car when I revved it up was able to get at 3000 RPM.without backfire.I hope to try readjusting idle next week.Does anybody know the part number for this check valve?