Mechanical Fuel Injectors - cleaning

[early 911]

Posted by Robin in Technical FAQ's . . . more likely to be answered here . . .

Has anyone any ideas on how many miles a set of mechanical fuel injectors would be expected to last before they become worn out by the fuel passing through them?
Is there any benefit in replacing them, or having them cleaned?

Don't know much about MFI, but can see it might be worth while cleaning the injectors (if only so you can report back here saying it's made no difference[]). As for how long they last . . . I haven't a clue.

Phil

Phil

 

[bones]

Fitted new injectors to my CIS fitted SC at 150,000 miles, they improved the smooth running of the engine at tickover and on the move but that's about it, if the injectors have many miles on them it just might give you peace of mind if you suspected a leaky one, plus you have the knowledge that the new ones are delivering the correct spray pattern.

 

[bernard tester]

Try injecter cleaner use 1 can to about 35lts I use the Wurth product helps slow runing and prevents stalling. Regards Berny.

 

[Guest]

Hi

MFI Injectors don't wear in the same way as modern electro-mech ones do (which are fouled by deposits), they are like a diesel injector with a low (hundreds of PSI not thousands opening pressure), To clean find someone with an ultrsonic bath I should expect them to last at least 100K Miles

HTh

 

[Robin]

The Mechanical injectors have already done over 170000 miles and the car runs reasonably well, but with each injector having had around 7000 litres of fuel pass through each one! That is 35 barrels of petrol per injector! there must be some sort of wearing of the holes, or weakening of the springs. I just wondered if anyone else had the experience of changing them for new injectors @ £65 each and what changing them did to the mechanical fuel pump settings, fuel consumption, performance etc.

 

[Guest]

Robin

All the statistics aside, The two operating parameters for the injectoras are opening pressure and visual inspection of the spray pattern, If these are within spec the injector is ok. As I said they are incomarable to diesel or electro-mech injectors, for exapmle they have no quiescent ressure against them (like an electromech one) nor the opening pressure of a diesel injector. To clean I'd soak in injection system cleaner and use an ultrasonic bath if available but only after testing them, I am of the opinion if they aren't broke don't touch them


.

 

[ian cox]

Robin,
You may remember that I once owned chassis number 1295 on a 2.7 RS and I did the following with great effect.
My MFI system was running fine when warm and cold starting was okish. What would happen is that the car would start immediatley and then die. I then had to crank the engine for 5/6 seconds and then it would start and run ok.
So what i did was first take off the MFI pump and send it to Tower Bridge Diesels in London. They are a diesel engine specialist but have all the kit to clean and recalibrate the MFI pump. Normally the only thing that is wrong with the pump is that the choke circuit gets full off muck and does not close off properly. These leads to a smell of petrol and rubbish fuel economy. Price for this work is around £300. The MFI pump came back as good as new.
The odometer said 80kms so i guessed at least 180kms. The reason for the strange starting problem was that the injectors could not close and seat properly to shut off the fuel when the engine was not running .Over several weeks of inactivity the fuel would leak out and air would get into the first few inches of the fuel lines. This led to instant start but instant stop as described above.
So I replaced all the injectors by buying the Bosch part code, much cheaper than Porsche, replaced the sealing washers as well and the car ran like a dream. Russel Lewis of RSR reset the pump and did tune up and the car ran perfectly.
With this and replacing the plug leads, spark plugs, rotor and points I got 219bhp on JZ Mactechs dyno. Steve McHale said that this was the best one he had seen.
So in my opinion get the pump cleaned and recalibrated, change the injectors get a proper tune up and the car will put like a train.

Kind regards Ian

 

[jamescharnley]

ORIGINAL: Robin

The Mechanical injectors have already done over 170000 miles and the car runs reasonably well, but with each injector having had around 7000 litres of fuel pass through each one! That is 35 barrels of petrol per injector! there must be some sort of wearing of the holes, or weakening of the springs. I just wondered if anyone else had the experience of changing them for new injectors @ £65 each and what changing them did to the mechanical fuel pump settings, fuel consumption, performance etc.

Robin, what symptoms was your car showing to prompt the question re. the injectors?

I have a problem with the car running rich at high rpm's ( causing those following to have stinging eyes) . I'm going to clean out the choke mech on teh injection pump ( I'm not convinced this is the problem) and check for air leaks around my inlet manifolds. I am worried my injectors might not be closing properly