'73 450 SL electronic fuel injection

[meanie]

Here's a couple of decent multimeters that will help measure the pulse signal.
http://www.sealey.co.uk/PLPageBuilder.asp?gotonode=ViewProduct&method=mViewProduct&productid=12537
http://www.beta-tools.co.uk/store/1...1.html?zenid=120ea51fdf78ae29e8ee2074599df8fb
I'd personally go for the Beta one (I have actually).

 

[osc]

I'm not going to read 24 pages (!!!) so going on recent/last post here's couple of thoughts.
It's been a long time, but as I recall the ECU sends 12v signal to the injector to operate it (double check by removing all injector plugs & the ECU plug - if I'm correct one terminal on each injector plug will have good continuity to earth. They should also be equal). Assuming that you have a good earth, check the continuity between each Injector & the ECU - should be a matter of m/ohms. If possible check the pulse of each injector - 10/20 milliseconds roughly.
Gaining a cylinder today leads me to think that you may have a harness issue.
Maybe OSC might allow you to take some resistance & voltage measurements from his system.
A short in the loom may explain the ECU issues, if that were the case.
Forgive me if you've already gone through these thoughts - 24 (!!!) pages is too much for me right now!

i dont think the injectors are 12V RMS, more like 2 or 3 max. 12V will blow them. i am building a test rig....

 

[Number_Cruncher]

>>RMS

The injectors will be fed with a pulse that approximates to a square pulse, and petrol injectors on cars in general are switched on using either 5volts or 12volts. Sometimes the injectors have one side earthed and are given a positive pulse by the ECU, however, on modern cars, the opposite is most likely, in the injectors are switched on the earth side.

In thise case, meanie is suggesting these injectors are switched with 12 volts, and are supplied with a positive pulse from the ECU, and a constant earth.

AC measurements, and RMS isn't a brilliant way to see what's going on with injectors - it's far better to watch the pulse on an oscilloscope. However, it is true to say that an RMS measurement would give you some vague idea of both the supply voltage and the ratio of the on / off time. If your meter has a dwell or mark / space function, that would be better than AC voltage.

 

[Isdyldan]

OSC, this is an interesting site you may find useful when building your test rig:
http://www.diy-efi.org/diy_efi/projects/inj_flow/

I've ordered the set of yellow injectors and will report back when they're fitted and tested, but this probably won't be for a few days. Some articles I've read say that there is a difference between the colours of the injectors, others say there isn't. I'll see what happens. If it works at all I can at least let you know!

 

[Isdyldan]

The replacement injectors arrived and I installed 4 in the drivers side bank. Before, I had cylinders 1 & 4 firing. Now I have 2 & 4 firing. So either half the replacement injectors are dud too (unlikely), or there is possibly a flow rate issue as there seems to be only enough fuel available to run 3 or 4 cylinders at once. Is this feasible?

 

[osc]

this is a very crude way to test but are you getting a big squirt of fuel if you pull one of the rubber lines BEFORE the regulator?

better to test BOTH pressure and flow rate

 

[Isdyldan]

Hi OSC - yes, loads of fuel squirts everywhere if I pull a pipe off (which I've had to quite a lot lately!)

 

[osc]

when my flow rate was low due to a weak pump i was not getting the fuel squirting everywhere so my guess would be that yours sounds ok. you should have all the gear to test it properly.

do you have a trickle of fuel in you return line?

 

[Isdyldan]

Yes there is. I see what you're saying - there must be enough fuel. I'm out of ideas.

 

[osc]

come over to mine with your ECU and MPS...

 

[Isdyldan]

Yes - that would be good. I'll give you a call.

 

[Isdyldan]

It works! It works! It works!!! Sounds fantastic too - running on all 8 - I can't believe it after all this time.
Well, what did I do I hear you ask........not much is the answer. I was just thinking of any possible things left to try, so I wondered if there may be a blockage in the vacuum pipe to the MPS. I just pulled of the pipe at the MPS end and it started perfectly. Very odd. There must have been a combination of faults as I'm sure that had been done before.
At last I can start putting her back together. Many thanks to everyone who has given me help and advise on this one. I'm sure I'll have plenty more questions as I get reassembling!

 

[osc]

YAY!!!

Make sure the pipe to the MPS is not collapsing internally under a vacuum. You will need the MPS to do its thing when you accelerate under part and full load i.e. drive the car

Check the resistance values and make sure you have the correct MPS for your engine size and Euro (American is adjusted different for tighter emmission control)

WELL DONE!!!!!!!!!!!

 

[mtinlin]

Congratulations! What a relief. Good luck with the rest of it.

 

[Myros]

yeeeeeehaaaaaaa

as i'm sure i can hear dylan yell. Now for the book of the film.

 

[Alex Crow]

Now for the book of the film.

i've got the t-shirt, does that count?

 

[Isdyldan]

The MPS I have is the one that I bought with the 350SE ECU and hence the wrong size engine. (the original was leaking). Stupid of me to think they would be the same - a larger engine is bound to produce a different vacuum (be it more or less - I don't know!). I think I'll try and get mine fixed or repair it myself - there is some good reading on this if you Google 'Manifold Pressure Sensor'.

 

[Isdyldan]

On second thoughts, fixing it is not a realistic option. OSC, could you possibly read the Bosch number off the side of yours please if you get a chance?

Thanks, Dylan

 

[steve--o]

i really fancied an old 450 sl till i read this you have all freightend mi to death wil this fuel injection lark

im going to buy an mg instead

Steve

 

[Isdyldan]

Hang fire Steve! It's not that complicated when you get you head round it - I think I was just a bit dim not to realise that the manifold sensors arn't interchangeable. You need to drive an old SL and an MG of the same era (or any other old car) just to see how fantastic the SL is to drive. The only real problem is that the cost of the parts can be quite expensive if you buy them from the wrong place - just look at certain SL breakers selling on ebay (not all) charging ridiculous money for some bits. Most bits are available from Mercman in Southampton at reasonable costs, or you can just hunt around & be lucky. I picked up my replacement fuel ecu for £60, although still haven't checked that my original was ok or not. You also get great help and support from guys on this excellent forum!