[johncc]

I am wondering if I have an injector problem, so I'd like to check them out. I've done this on another car by duct-taping them into milk bottles and cranking the engine... can a similar thing be done on the 9K? How good is the check compared to a proper test on the bench?

I've asked about injector check & cleaning, and I've been told an hour's work at 40 quid an hour (assuming I take them out myself). I'm wondering if that's worth it, really. What do you all think?

Having said that, I don't know what they cost to replace! Are they a Bosch part? Does anyone know the 10 digit code if so?

If they are easy to check yourself, and cheap to replace, then I'd go for check and replace any slightly suspect units...

 

[wherewolfe]

Grab the milk bottle and tape and check them yourself...should have a fine spray coming out each injector. If not replace only those without spray. Very simple to replace and I believe about $50 each last time this was discussed.

Don't have them cleaned or reworked as the cost is only a short term fix.

 

[Dazzel]

I actually test and flow injectors as part of my job, if you are going to test the injectors I think you'll find they have to see a signal from the ecu to trigger them, the only way you can do it is if you take out 1 at a time and run the engine on 3 cyls so that the injectors are all firing, if you can try and time it for the same period of time for each one(use a stopwatch if possible)and measure the amount of fuel injected, a measuring jug of some description should be sufficient, the amount injected should be within about 2ml between the injectors.I hope this has helped.

Cheers Darren.

 

[Dazzel]

Having just thought about it you won't be able to take out 1 injector as they are all fitted into a fuel rail and as the engine won't run with out fuel you won't be able to fire the injectors for a great amount of time,the only thing you may be able to do is take the whole assembly out and crank the engine over for a few seconds, but that won't give you a good representation of spray pattern during running conditions.The injectors themselves aren't really reconditionable it's more cost effective to buy new ones.

 

[johncc]

I've seen some DIY cleaning setups where people use an aerosol of carb cleaner, a plastic tube, some wires, a battery, and a pushbutton switch. The idea is you blast the aerosol spray through the injector while tapping the switch.

What do you reckon on the advisablity of this? I realise that you have to keep the pulses short! I also realise it won't get back a knackered part, but it should get the good ones tip top again, right?

I'm thinking it should be possible to make up (or buy, anyone?) a circuit to generate the pulses to run the injector... basically an oscillator and a MOSFET drive. Not sure about frequency and wave timings though. Guess you must have machines at work to do this, though Darren?

 

[mark e]

If I was trying that method of cleaning John, I would prefer to use a current limited benchtop power supply.

I don't think you need to worry about keep the pulse very short though- remember at max load injectors can be looking at up to 80% duty cycle, so they are designed to be effectively "on" permanently. The point about tapping the button is to cycle the moving parts of the injector to aid dislodging any unwanted deposits.

 

[johncc]

I think you're right Mark. I believe the "short pulse" part is because the current direct from a 12V battery will be too high, and keeping the pulses short should avoid damaging the coil (much)! I'd rather do it properly though.

Do you know, or know where I can find out about, a suitable driver circuit for the injectors, or failing that, what voltage and current they should get?

I figure if I knock a circuit together it will be a useful part of the toolkit for ever more.

I was even wondering about an EZ Bleed (which I could do with anyway), a spare header tank cleaned and filled with cleaning fluid, and suitable tubing, instead of the aerosol.

 

[mark e]

A quick play with my green injectors...

DC resistance 12 ohms
Minimum operating current circa 0.2 amps with a voltage across the terminals of 2V.

HTH

 

[johncc]

Mark, if you've got an injector "on the bench" there, can you tell me if it has a manufacturer's logo on it? Does it have a 10-digit number on it?

 

[mark e]

John,

The injector I've got is an upgraded one- I believe they're commonly known as "Green giants" and were/are fitted to Volvos

There is no manufacturers mark on them that I can see. However the 10 digit ref is 0280155968.

I'll have my standard set back tonight, and will check them...

 

[johncc]

Thanks Mark - I'd love to know, because I have used a Bosch agent in the past - about half the price of a motor factor - but they are mainly maritime stuff, so you have to give them the exact part number.

I've been doing some Googling and reading - found some interesting stuff! I now know more about Darlington vs. MOSFET drives, flyback pulses, peak-and-hold circuits, and more besides, than I ever wanted to know

I'll certainly try and feedback anything i find out via the site - I am sure others would be interested in a cheap injector cleaning setup.

Thanks again

 

[mark e]

I don't reckon you'll need much more than a simple square wave generator driving a bipolar tranny myself. At idle speed of say 900rpm, the injectors are going to be firing 900/4 or 225 times a minute, a frequency of 4Hz or so. You don't need any particularly quick devices to take care of that...

 

[johncc]

I was thinking much the same Mark. I've seen a nice simple circuit using a Darlington pair and a diode to sink the back-emf.

It seems there are two injector types - high-impedance or saturated, and low-impedance. The high-impedance (approx 10-12 ohms apparently, like your green ones) are self limiting in terms of current - in other words, you can just chuck 12V at them.

The low-impedance type (about 2 ohms) require more complex driver set-up. They use an initial peak of about 2 to 4A to open them and then a hold current of about 1 or 2A to keep them open. I'm not sure how necesary this actually is, but at the very least, if you wanted to drive them off 12V you'd need a resistor or a transistor circuit to limit the current!

If the Saab ones are the same as the green ones, then it's pretty simple. The other type of drive is not too hard though - a single IC is available to do it

I've seen some nice designs using microcontrollers to provide a specific pulse width and a specific number of pulses, to do flow testing. I think that's more than I'll need though - I just want something that's a bit better than the wires and switch approach!

I saw a good suggestion too using a spare fuel pump and pressure regulator ripped from a scrapyard to provide the fluid, but I think my idea is easier

 

[Dazzel]

The only problem is for most injectors to work properly you need the pressure in the rail(usually somewhere around 3 bar on most gasoline engines)otherwise the injector wont spray properly, If you are not too far away and you ask me nicely I could run a test matrix on them for you at work,which would also clean them, the equipment we have can simulate any engine speed or injector pulsewidth, plus we can measure the amount delivered quite accurately. If you are interested let me know.
Cheers Darren