'73 450 SL electronic fuel injection

[turbopete]

the ballast resistors should let 12V through on initial start up anyhow, so that shouldnt be the cause of the non start. ford ran with ballast resistor systems on early fiestas and escorts, to give the coil extra power for cold starts so that they started more easily! once running the resistors gradually brought the voltage down, to prevent the coil overheating.

 

[osc]

As i said before i have never had to adjust a fuel regulator, i wonder what other problems you are masking osc. you have found the mixture adjuster on the ecu?

I just checked my fuel pressure with a different gauge and it is smack on 2.2 bar which is 32 psi. Basically the problem was that the car would run very lean and stall - especially when hot idling. I had the correct fuel pressure but no flow in the return line so there was a fuel flow rate issue - basically I think the pump had become inefficient. Unfortunately I found this out after replaceing EVERY SINGLE component in the injection system, so I do have a lot of spares if anyboday is interested!!!

I replaced my pump with another Bosch one I had in the garage, set the ECU knob in the middle and increased the fuel pressure until it was not running lean on hot idle. I have flow of fuel in the return line back to the tank and now the fuel pressure is 32 psi which is what the system specifications indicate and the car is running spot on (small misfire at 4500rpm which i suspect is the dissy cap).

 

[Alex Crow]

the ballast resistors should let 12V through on initial start up anyhow, so that shouldnt be the cause of the non start.

it is correct that there is either a different resistor, or none at all (depending on model) used on startup. the reason for this is that on startup voltage typically drops to 10v -just when you want the best spark! obviously with the engine running there is 13.5v available. the starter motor has an output which is live when cranking, this is wired parallel to the other ballasted circuit.

from memory your sl450 has a set up using two ballast resistors, probably 0.4 and 0.6 or 0.8 ohms, it will be marked on them.

to isdyldan, i would be interested to see the fuel pressure while you are running/cranking. if i had your symptoms in the workshop i would have the gague on permanently and a strobe on the ignition. have you got both temp sensors connected? and better disconnect that cold start injector incase your thermotime switch is u/s, do your plugs get wet/very wet? and have you listened to all the injectors? they can go down in pairs if the pointsa are problematic.

 

[osc]

Alexander: i think you may be able to help me with this quesion and I suspect the answer will be useful for this thread which is why I have not posted a new topic.

At the moment i have set my car for unleaded to 30 BTDC at 3000rpm without vacuum.

Please can you advise on keeping it at 25 BTDC @ 3000rpm vs 30 BTDC @ 3000rpm (without vacuum), or other setting you know works well with this engine.

It has been suggested that it will be smoother and a lot more economical at 25BTDC, and I can use a valve lubricant additive every 5th full tank.

My problem is that I have not seen another early 450 engine so I do not know how smooth a good one will run, and therefore if mine is properly tuned. After fixing the fuel flow rate problem, I think it is pretty good and has loads of grunt but not as silky as the 380 V8.

If there is anyone near me (London area/South East) with one of these I would be keen to meet up.

 

[Isdyldan]

I'm in surrey, if I ever get this thing running!

There is no ignition unit on the inner wing behind the n/s headlight like I had on the '78 450 I had and the '81 380. There is a large ucu mounted in the passenger (n/s) footwell. There is also an aluminium unit mounted near the ballast resistors with nothing connected except a few wires which go into the loom, and it looks like there should be a small pipe connected. There is another smallish unit mounted on the bulkhead which has a large vacuum hose connected from the inlet manifold. The plugs are getting wet, and there is a spark - so why no go?? It will fire occassionaly.

 

[Alex Crow]

hello osc, the unleaded fuel question, as you know, is a problem in two parts.

firstly valve seat lubrication, there surely would be no harm done in using an appropriate product for this purpose, although how it can still work after 4 tanks of unadulterated fuel i do not know. however i am not convinced of the real need for it, as i understand it the material used by mercedes for valve seats in this era was more than capable of running with unleaded fuel. you would need to consult a specialist to confirm - eg scholar engineering in suffolk.

on the point of knock ratings of fuel, four star was 98 ron and unleaded is 95 ron - not a huge difference when two star was a lowly 92 ron. you can easily buy 99 ron fuel at almost all filling stations these days, so there are a few options. retarding the ignition by 5 degrees will easily allow for the use of 95 ron, and may not even be needed at all.

lets remember though that these old cars have been around the block many times and often these vacuum systems and distributors are wrongly matched. some systems use vacuum advance, and some vacuum retard. i have seen incorrect throttle bodies fitted before causing all sorts of problems (pagoda 230 sl) so i suggest that you double check timing with all pipes connected at 4,000 rpm (to be sure - i think max advance is at 3,000 rpm as you suggest), blipping throttle to make sure that it does not exceed about 38 degrees - off the top of my head. certainly if you do this and see 50 degrees there is a problem somewhere. the real test though is when using full throttle at say 2,500 rpm in top - do you hear pinking?? if no pinking is heard at any engine speeds and you see 38 deg at 4,00rpm and 0 deg at idle with everything connected then happy motoring.

 

[Alex Crow]

I'm in surrey, if I ever get this thing running!

There is no ignition unit on the inner wing behind the n/s headlight like I had on the '78 450 I had and the '81 380. There is a large ucu mounted in the passenger (n/s) footwell. There is also an aluminium unit mounted near the ballast resistors with nothing connected except a few wires which go into the loom, and it looks like there should be a small pipe connected. There is another smallish unit mounted on the bulkhead which has a large vacuum hose connected from the inlet manifold. The plugs are getting wet, and there is a spark - so why no go?? It will fire occassionaly.

the footwell ecu does fuel only, not ignition.

the aluminium device near the resistors/battery should have that vacuum pipe connected - i did mention this already!!!!!!!!!!!!!!

 

[Alex Crow]

on a separate point, does that large dia manifold vacuum pipe connect to the manifold pressure sensor? (large aluminium electronic component on inner wing near battery) the vacuum comes from the rear of the manifold.

there, i knew i had mentioned it already, i spotted it in your picture. :lol: what does that vacuum pipe connect to currently?? ie the one seen in the picture coming from the rear center of the manifold, draping over the fuel regulator, and exiting stage bottom left.

 

[osc]

there should be a "transistorized switching unit" mounted underneath the wing with 4 wires.....

*brown wire to earth
*green/yellow wire to distributer contact bresker
*black wire to 0.6ohm ballast resistor then goes to coil +ve
*red/black wire to 0.4ohm ballast resistor (and in parallel to starter motor red-violet wire). the other side of the ballast resistor to ignition switch (red/black wire)

 

[osc]

there, i knew i had mentioned it already, i spotted it in your picture. :lol: what does that vacuum pipe connect to currently?? ie the one seen in the picture coming from the rear center of the manifold, draping over the fuel regulator, and exiting stage bottom left.

alexander: top spot. god knows where this is connected....i hope its not to the windscreen washers!!!

connect this pipe to the manifold pressure sensor (the unit on the inside of the wing with a 4 wire socket going into the loom) If you the check the resistance on the connector the inner two should be about 90ohms and the outer approx 250 or 350 ohms i think. it doesnt matter which was around this plug connects.

just to be clear, this is NOT the transistor switching unit with the 4 coloured wires i described earlier and you will need to make sure you find and connect this as described else you will not start...

 

[osc]

hello osc, the unleaded fuel question, as you know, is a problem in two parts.

firstly valve seat lubrication, there surely would be no harm done in using an appropriate product for this purpose, although how it can still work after 4 tanks of unadulterated fuel i do not know. however i am not convinced of the real need for it, as i understand it the material used by mercedes for valve seats in this era was more than capable of running with unleaded fuel. you would need to consult a specialist to confirm - eg scholar engineering in suffolk.

on the point of knock ratings of fuel, four star was 98 ron and unleaded is 95 ron - not a huge difference when two star was a lowly 92 ron. you can easily buy 99 ron fuel at almost all filling stations these days, so there are a few options. retarding the ignition by 5 degrees will easily allow for the use of 95 ron, and may not even be needed at all.

lets remember though that these old cars have been around the block many times and often these vacuum systems and distributors are wrongly matched. some systems use vacuum advance, and some vacuum retard. i have seen incorrect throttle bodies fitted before causing all sorts of problems (pagoda 230 sl) so i suggest that you double check timing with all pipes connected at 4,000 rpm (to be sure - i think max advance is at 3,000 rpm as you suggest), blipping throttle to make sure that it does not exceed about 38 degrees - off the top of my head. certainly if you do this and see 50 degrees there is a problem somewhere. the real test though is when using full throttle at say 2,500 rpm in top - do you hear pinking?? if no pinking is heard at any engine speeds and you see 38 deg at 4,00rpm and 0 deg at idle with everything connected then happy motoring.

thanks for this, i think everything is properly matched since i've spent a few years finding the right parts! i will have a play with the timing range but i think it does not exceed 38deg. We will continue in another thread if more detail is required.

Nice to have someone that has practical experience of having tinkered with these. thanks for the response.

 

[Alex Crow]

i'd love to say i have had many happy days finding other peoples bodges and mistakes, and getting these old cars to run just right. i really would love to.............

 

[television]

i'd love to say i have had many happy days finding other peoples bodges and mistakes, and getting these old cars to run just right. i really would love to.............

And when the customer says " it has not run so well in years" Yes that does make for a good day

 

[Alex Crow]

And when the customer says " it has not run so well in years" Yes that does make for a good day

true enough, although i rarely enjoy the older cars, the customers tend to be very appreciative and often make my day, yes.

 

[Isdyldan]

Hi - That hose goes to the radiator expansion tank onto the little pipe just below the filler cap. (I am waiting for hysterical laughter at this point, but I don't know - is it definately vacuum??) There is no sign of a transistorised ignition unit as I've see on later cars. There are wires coming from the loom towards the coil/ballast resistors - red/black and green/black. There is another wire (purple/red) from the starter 'block' near the battery which I assume is the 12V feed direct to the coil which is live when the engine is cranked. There is another green/black wire going from the coil -ve to the points.
It looks to me that the car does not have electronic ignition....Is this possible please?

 

[television]

Could it have been removed,,I thought that they all had it

http://www.detali.ru/cat/oem_mb2.as...&L=765.701&CT=F&cat=048&SID=54&SGR=315&SGN=07

http://www.detali.ru/cat/oem_mb2.as....701&VIN=*&CT=M&cat=043&SID=15&SGR=060&SGN=04

It would seem that 1973 was the last year with points, but not in all markets

If you remove the dizzy cap there will either be the module or points with the cap on the top

 

[Isdyldan]

There are points under the distributer cap, and no sign of anything relating to electronic ignition.

 

[television]

There are points under the distributer cap, and no sign of anything relating to electronic ignition.

Yes you will not have it,, it was dropped in the USA during 1973 when they went over to electronic ignition, other countries followed later.

 

[Isdyldan]

So then could there be some injection timing out of adjustment? It looks like a fuel problem still to me. The ignition part seems too simple to go wrong.

 

[television]

The coil is wired to the ballast resistor on the Plus side of the coil, and as you say the - goes to the contact breaker. There must be a condenser wired across the points, and this should be 3.3 mfd for an 8v coil,, if there is no balast resistor and its a 12v coil, then it should be 2,2mfd.

Leaking dizzy caps and rotor arms is always a problem, they must be clean with no tracking marks on the inside or outside, if the rotor arm tracks down to the center spindle, then the car will miss