Injector help needed please
Discussion
I’ve been doing some testing on the injection system of my flapper 350i today. I’ve been following the fuel injection maintenance guide PDF from the Wedgepages, checking all the voltages of the potentiometers are correct, and the ecu readings are within limits. It wasn’t because I thought there was any particular fault with it, I just like to keep things tuned up and running correctly. Well, other than a slight misfire at around 3000rpm which I think may be down to the timing. I also haven’t touched the fuel system in 9 years so thought it could do with a service.
When I came to the section on testing the injectors and power resistor, I got a bit confused. I disconnected the power resister and hooked up a multimeter to pin 9 and set about checking pins 1,3,5 & 7 hoping to get a reading of around 6 ohms, however I just got a zero rating on the screen. I must admit to not having done much ohm testing, so wasn’t really sure which setting to have the multimeter on (2k, 20k, 200k, 2M, 20M etc etc_), so I tried them all. None of the settings produced a reading. I also tested pin 2 against 4,6,8 & 10 and again got no reading. Does this suggest a knackered power resistor, bearing in mind that the car has been in regular use?
Incidentally, the multimeter should be working fine as I tested various things on the ecu which all gave the correct ohm reading.
Anyway, I then started with the injectors. It mentions that with the ignition on, the voltage should be within 0.5v of the battery feed (12v I presume). See page 34 of the PDF for all the techy wording. My multimeter displayed just over 12v. Should this feed to the injectors not be 3v due to the power resistor limiting the voltage? I’m certain I had the power resistor plugged in at the time (I had disconnected it earlier to test remember, but I’m sure I connected it again during this test) – if it had been disconnected then I would have got a zero rating at the injectors right?
So, now I’m a bit confused. I have a resistor that doesn’t appear to resist and 12v at the injector multiplugs. All this and the car still runs fine, or did last time I used it a few days ago. Haven’t started it since but no reason to doubt its suddenly broken. Its dark out now hence I’ve come in and started reading some of the previous posts on injectors and stuff, which has made me think there could be a problem.
Anyway, my questions are as follows should anyone who’s reading this fancy a challenge:-
Which setting should my multimeter be on when testing the power resistor? Not being an electronics expert, I couldn’t tell you the difference between 2k and 20M!
When I test the resistor (pins 9 and 3 say), what should my reading be? 6 ohm? What if its zero – is it broken?
Should there be a 12v feed to my injectors like the PDF says? (ignition on, ecu unplugged, multimetre set to volts, grounded on battery, other wire held on terminal of unplugged injector multiplug).
Ok, assuming that the above is all correct, what’s the best way to check the operation on my injectors? Can I remove each one in turn and attach the cold start injector fuel supply to it, and then just “pulse” some voltage into it with a battery to make it operate? With the ignition on and the airflow meter wedged open to run the fuel pump, will the injector fire with every “pulse” I give it? I know I need to block off the hole in the system where I took the injector out off too. I just want to physically see a spray pattern from each one to make sure none of them are blocked.
If its ok to do this, then what voltage needs to be supplied to the injector?
Sorry for rambling on, but I’d rather give all the details instead of missing a load of stuff which could be important. Hopefully going to take them plenum off tomorrow as well since you can’t get to one of the injectors with it on.
Thanks in advance,
Dan
When I came to the section on testing the injectors and power resistor, I got a bit confused. I disconnected the power resister and hooked up a multimeter to pin 9 and set about checking pins 1,3,5 & 7 hoping to get a reading of around 6 ohms, however I just got a zero rating on the screen. I must admit to not having done much ohm testing, so wasn’t really sure which setting to have the multimeter on (2k, 20k, 200k, 2M, 20M etc etc_), so I tried them all. None of the settings produced a reading. I also tested pin 2 against 4,6,8 & 10 and again got no reading. Does this suggest a knackered power resistor, bearing in mind that the car has been in regular use?
Incidentally, the multimeter should be working fine as I tested various things on the ecu which all gave the correct ohm reading.
Anyway, I then started with the injectors. It mentions that with the ignition on, the voltage should be within 0.5v of the battery feed (12v I presume). See page 34 of the PDF for all the techy wording. My multimeter displayed just over 12v. Should this feed to the injectors not be 3v due to the power resistor limiting the voltage? I’m certain I had the power resistor plugged in at the time (I had disconnected it earlier to test remember, but I’m sure I connected it again during this test) – if it had been disconnected then I would have got a zero rating at the injectors right?
So, now I’m a bit confused. I have a resistor that doesn’t appear to resist and 12v at the injector multiplugs. All this and the car still runs fine, or did last time I used it a few days ago. Haven’t started it since but no reason to doubt its suddenly broken. Its dark out now hence I’ve come in and started reading some of the previous posts on injectors and stuff, which has made me think there could be a problem.
Anyway, my questions are as follows should anyone who’s reading this fancy a challenge:-
Which setting should my multimeter be on when testing the power resistor? Not being an electronics expert, I couldn’t tell you the difference between 2k and 20M!
When I test the resistor (pins 9 and 3 say), what should my reading be? 6 ohm? What if its zero – is it broken?
Should there be a 12v feed to my injectors like the PDF says? (ignition on, ecu unplugged, multimetre set to volts, grounded on battery, other wire held on terminal of unplugged injector multiplug).
Ok, assuming that the above is all correct, what’s the best way to check the operation on my injectors? Can I remove each one in turn and attach the cold start injector fuel supply to it, and then just “pulse” some voltage into it with a battery to make it operate? With the ignition on and the airflow meter wedged open to run the fuel pump, will the injector fire with every “pulse” I give it? I know I need to block off the hole in the system where I took the injector out off too. I just want to physically see a spray pattern from each one to make sure none of them are blocked.
If its ok to do this, then what voltage needs to be supplied to the injector?
Sorry for rambling on, but I’d rather give all the details instead of missing a load of stuff which could be important. Hopefully going to take them plenum off tomorrow as well since you can’t get to one of the injectors with it on.
Thanks in advance,
Dan
If I remember correctly, the cold start runs on 12v whilst the normal injectors run on reduced voltage (can't remeber the voltage)
All the reisitances are low I think, so the multi meter should be set on ohms not K ohms.
Hope this helps, if no one else has come along by the time I'm sober and can think straight, I'll post more tomorrow.
All the reisitances are low I think, so the multi meter should be set on ohms not K ohms.
Hope this helps, if no one else has come along by the time I'm sober and can think straight, I'll post more tomorrow.
There is little to service on the fuel side, if it's working leave it alone, unless you're confident you know what you are doing. If you think the misfire is timing, then check that out fully before anything else. It is worth checking the condition of the fuel line rubber hoses around the fuel rail area, as they degrade and leak.
I think the series resistors are on the ground side. So all the feeds to the injectors will be at 12V and the ground side of the injectors at something like 6V. But only when they are being energised of course.
A meter isn't much use measuring this while it's running unless it has a peak hold facility. Better off using an oscilloscope.
A meter isn't much use measuring this while it's running unless it has a peak hold facility. Better off using an oscilloscope.
First off, your multimeter (and resistances). Is it digital or analogue (moving needle type)? I guess from 'screen' it's digital...
The resistor pack doesn't use any resistors as you might expect. Inside there's a piece of fibreglass printed circuit board (PCB) material with copper tracks etched on it. The tracks meander around the board creating a long path of copper that has resistance. There are only two fault conditions with a resistor: short-circuit (or lower resistance) or open-circuit (or higher resistance). Withe etched resistors it's virtually impossible for them to go short-circuit and read less than the rated value. They can however burn out due to excessve current and read higher than they should.
If your meter says 0 ohms then it's telling you there IS continuity, so the resistors are likely to be OK and the meter simply lacks resolution to discriminate between 0 and 6 ohms (though I've never seen even cheap meters be THAT inaccurate).
As to why you're measuring 12v at the injectors: with the injectors closed they draw no current. When the injector fires (it's earthed by the ECU) its low internal resistance causes a lot of current to be drawn. If the resistor wasn't there the injector would act like a fuse and simply melt. The resistor serves to limit the amount of current that the injector can take (the resistor will actually act like a heating element as it does so).
In the process, the current being dissipated causes the 12v rail to drop to a theoretical 3v.
Now with the injector closed 12v is still passing though the resistor as far as the injector. The meter draws a miniscule amount of current in order to feed its measuring circuit and is thus able to read the 12v without pulling it down.
With the engine running the injector is firing that fast that although the supply to it is in effect swapping between 3v and 12v, the change is too fast and too frequent for the meter to follow, so it will either latch on to one or the other or perhaps read an average of the two. You really need an oscilloscope on there to see it happening properly.
Incidentally it's doubtful that an injector WOULD fire if you poked just 3v into it, but we'll leave that for now...
Part two follows shortly...
The resistor pack doesn't use any resistors as you might expect. Inside there's a piece of fibreglass printed circuit board (PCB) material with copper tracks etched on it. The tracks meander around the board creating a long path of copper that has resistance. There are only two fault conditions with a resistor: short-circuit (or lower resistance) or open-circuit (or higher resistance). Withe etched resistors it's virtually impossible for them to go short-circuit and read less than the rated value. They can however burn out due to excessve current and read higher than they should.
If your meter says 0 ohms then it's telling you there IS continuity, so the resistors are likely to be OK and the meter simply lacks resolution to discriminate between 0 and 6 ohms (though I've never seen even cheap meters be THAT inaccurate).
As to why you're measuring 12v at the injectors: with the injectors closed they draw no current. When the injector fires (it's earthed by the ECU) its low internal resistance causes a lot of current to be drawn. If the resistor wasn't there the injector would act like a fuse and simply melt. The resistor serves to limit the amount of current that the injector can take (the resistor will actually act like a heating element as it does so).
In the process, the current being dissipated causes the 12v rail to drop to a theoretical 3v.
Now with the injector closed 12v is still passing though the resistor as far as the injector. The meter draws a miniscule amount of current in order to feed its measuring circuit and is thus able to read the 12v without pulling it down.
With the engine running the injector is firing that fast that although the supply to it is in effect swapping between 3v and 12v, the change is too fast and too frequent for the meter to follow, so it will either latch on to one or the other or perhaps read an average of the two. You really need an oscilloscope on there to see it happening properly.
Incidentally it's doubtful that an injector WOULD fire if you poked just 3v into it, but we'll leave that for now...
Part two follows shortly...
Thanks for the input so far guys!
Just to answer a couple of points. The reason for testing all this is partly to get to the bottom of the misfire, but also as the system hasn't been touched since I've owned the car. Its got 155,000 miles on it now, and whilst the engine was apparently rebuilt at 130,000, I'm not sure which parts were replaced etc. The performance has been down recently I feel, so I want to check everything thoroughly this time. I would also like to see the spray pattern from the injectors too as a couple of the sparks were inconsistent to the others. One seemed a bit wet even though the car hasn't been run for a few days, and another was totally clean perhaps sugesting that no fuel was getting through to the bore?
Good point about the cold start being 12v - hadn't thought of that!
Also, getting 12v on the live feed to the injectors makes sense too if the resistor is on the ground side of the system.
I'm still a bit worried about the resistor as I would like to see an ohm reading for this. Just want to make sure it is actually restricting the voltage.
Just to answer a couple of points. The reason for testing all this is partly to get to the bottom of the misfire, but also as the system hasn't been touched since I've owned the car. Its got 155,000 miles on it now, and whilst the engine was apparently rebuilt at 130,000, I'm not sure which parts were replaced etc. The performance has been down recently I feel, so I want to check everything thoroughly this time. I would also like to see the spray pattern from the injectors too as a couple of the sparks were inconsistent to the others. One seemed a bit wet even though the car hasn't been run for a few days, and another was totally clean perhaps sugesting that no fuel was getting through to the bore?
Good point about the cold start being 12v - hadn't thought of that!
Also, getting 12v on the live feed to the injectors makes sense too if the resistor is on the ground side of the system.
I'm still a bit worried about the resistor as I would like to see an ohm reading for this. Just want to make sure it is actually restricting the voltage.
Ahhh, fantastic! Thanks Wedgie! It took me so long to write my last response that you'd posted in the meantime.
That really does make sense now and explains the voltage at the injectors.
With regards to the multimeter I'm using, its quite a comprehensive digital one, Draper or Sealey I think. When in one of the ohm modes, it just says 0.00 on the screen when I have it on 2 pins of the resistor. When I remove it, the screen displays a load of numbers before erroring. So, it suggests that the meter is working ok and really is detecting zero ohms when in place. I'm not sure what the ohn range of it is, but goes from somehting like 2k to 20M - again, that means nothing to me!
Perhaps I will just leave the injectors in place and treat the fuel tank to a bottle of cleaner instead. I know you can have them "sonic blasted" etc, but I don't really have the means to be able to do that.
Anyway, I shall wait eagerly for part 2! Will it have a section on how to double the power for 50 quid? ;-)
Thanks again all,
Dan.
That really does make sense now and explains the voltage at the injectors.
With regards to the multimeter I'm using, its quite a comprehensive digital one, Draper or Sealey I think. When in one of the ohm modes, it just says 0.00 on the screen when I have it on 2 pins of the resistor. When I remove it, the screen displays a load of numbers before erroring. So, it suggests that the meter is working ok and really is detecting zero ohms when in place. I'm not sure what the ohn range of it is, but goes from somehting like 2k to 20M - again, that means nothing to me!
Perhaps I will just leave the injectors in place and treat the fuel tank to a bottle of cleaner instead. I know you can have them "sonic blasted" etc, but I don't really have the means to be able to do that.
Anyway, I shall wait eagerly for part 2! Will it have a section on how to double the power for 50 quid? ;-)
Thanks again all,
Dan.
Just measured what voltage an injector will fire at - 1.5 Volts (calibrated Fluke DMM) d.c. power supply. The injector is 2 Ohm the power resistor is 6.X Ohms, in series its a voltage divider circuit ratio 3:1. One side if the injector will be 12v to earth, otherside will be 9v to earth, therfore the injector will only see 3volts across it. You need the injector in circuit (or a load resistor of 2 Ohms) to check it.
sadbloke said:
Just measured what voltage an injector will fire at - 1.5 Volts (calibrated Fluke DMM) d.c. power supply. The injector is 2 Ohm the power resistor is 6.X Ohms, in series its a voltage divider circuit ratio 3:1. One side if the injector will be 12v to earth, otherside will be 9v to earth, therfore the injector will only see 3volts across it. You need the injector in circuit (or a load resistor of 2 Ohms) to check it.
Blimey ok!!! Lol! Whilst I'm not electronics expert I can understand what youre saying. Years of building pc's taught me about volts etc, but ohms has always been a mystery to me.
I think I now know why I've not been getting a reading from my multimetre. Its just dawned on me that 2k, 20k, 200k, 2M etc etc probably stands for thousand and million of ohms. Well, I'm assuming it does anyway. The lowest ohm setting my metre has is 200, so I'm guessing if I use this I should get a readout of around 0.06 or something hopefully. Its also the setting that has an audible signal on it too.
Judging by what you've said, I should be able to use a DC power adapter to fire each injector, given that it produces enough current to operate the internal solonoid. Thats what I'm hoping anyway. Do you think 5 volts would hurt an injector? A PC power pack runs at both 12 and 5 volts - handy to remember when testing automotive stuff.
I think they were pulling around 500 mA at 3 volts. I don't think I would use that type of power supply, P.C. power supply's are switch mode and need to be running with quite a bit of load to work at all and/or be stable at the rated voltage. I will try later with a couple of 1.5 v alkaline bats.
AA size cells will fire them, fully charged Nimh re-chargable- single cell @1.3v sometimes works, but 2 in series to get around 2.5 volts works every time (current around 400 mA ?). When testing with injectors in-situ, if the fuel rail is still under pressure you will be putting fuel in!!!!!
OK I'm back... Sadbloke, ta for that: I'd not tried it but I assumed you'd need a certain amount of juice to overcome the spring resistance of the injector, 500mA doesn't seem much... 
anyway...
Yes, just to confirm that using the cold start injector supply to test the main injectors is NOT a good plan! Yes it'lll work, but you risk frying the injectors. So don't
Here's my cunning plan to test the injectors on the car: the first part is just to test for leaky or non-firing injectors.
Disconnect the CS injector and fit a presure gauge instead (0-5 Bar).
Pull the fuel pump relay and remove the distributor cap (so car doesn't try to start).
Disconnect all but one of the injector plugs.
Put a wire link across terminals 30/51 and 87 of the relay socket and turn ignition on. Fuel pump runs and primes the fuel rail (gauge indicates, say 2.5 bar). Remove link.
Now crank engine and watch the gauge: every time the connected injector fires, the rail pressure drops a tad (with the pump relay out the rail is not replenished).
Now switch off, disconnect that injector and reconnect any other one. Prime fuel rail as above, crank and watch gauge.
If all injectors are firing you should see the same 'trend' on the gauge each time.
Next you want to see the spray pattern: obviously you need the injectors and fuel rail out and in a position where you can stick a jar underneath to catch the fuel. Er... do as above but watch the spray pattern Any leaking injectors will also be easy to see.
Incidentally if you prime the fuel rail and don't crank, the gauge should hold at just under 2.5 bar for a good length of time: I've seen half an hour before. This proves (a) no injectors are leaking and (b) the fuel pressure regulator is OK.
Note that I accept no responsibility if you blow yourself and/or your car into the middle of next week...
To make the testing easier I have a hand-held toggle switch with two long leads and 1/4" spades on the end that can be plugged into the pump relay base, that way you can prime the rail from outside the car.
anyway... Yes, just to confirm that using the cold start injector supply to test the main injectors is NOT a good plan! Yes it'lll work, but you risk frying the injectors. So don't
Here's my cunning plan to test the injectors on the car: the first part is just to test for leaky or non-firing injectors.
Disconnect the CS injector and fit a presure gauge instead (0-5 Bar).
Pull the fuel pump relay and remove the distributor cap (so car doesn't try to start).
Disconnect all but one of the injector plugs.
Put a wire link across terminals 30/51 and 87 of the relay socket and turn ignition on. Fuel pump runs and primes the fuel rail (gauge indicates, say 2.5 bar). Remove link.
Now crank engine and watch the gauge: every time the connected injector fires, the rail pressure drops a tad (with the pump relay out the rail is not replenished).
Now switch off, disconnect that injector and reconnect any other one. Prime fuel rail as above, crank and watch gauge.
If all injectors are firing you should see the same 'trend' on the gauge each time.
Next you want to see the spray pattern: obviously you need the injectors and fuel rail out and in a position where you can stick a jar underneath to catch the fuel. Er... do as above but watch the spray pattern
Any leaking injectors will also be easy to see. Incidentally if you prime the fuel rail and don't crank, the gauge should hold at just under 2.5 bar for a good length of time: I've seen half an hour before. This proves (a) no injectors are leaking and (b) the fuel pressure regulator is OK.
Note that I accept no responsibility if you blow yourself and/or your car into the middle of next week...
To make the testing easier I have a hand-held toggle switch with two long leads and 1/4" spades on the end that can be plugged into the pump relay base, that way you can prime the rail from outside the car.
dickymint said:
Wedg1e knows the trick to fire them with a DMM (so do i but am drunk and cant explain at the mo
Well... all you do is unplug the ECU, identify which pin of the connector goes to which injector and use the DMM on a current range to earth to fire each injector in turn.
I've got a
as well but I'm in and out of the workshop polishing Esprit valves on the mill Once again, thank you for all your help!
I don't have a pressue gauge but I just found this on ebay - should do the trick I reckon.
[url]http://cgi.ebay.co.uk/ws/eBayISAPI.dl[/url]
Just one more thing - instead of removing the fuel pump rely, can I not charge the fuel rails by operating the air flow meter instead? I have the flapper type. I don't want to cut corners but just wondered if there would be any difference doing it this way.
Thanks again for all the help. Happy polishing and drinking to all Wedgers!
I don't have a pressue gauge but I just found this on ebay - should do the trick I reckon.
[url]http://cgi.ebay.co.uk/ws/eBayISAPI.dl[/url]
Just one more thing - instead of removing the fuel pump rely, can I not charge the fuel rails by operating the air flow meter instead? I have the flapper type. I don't want to cut corners but just wondered if there would be any difference doing it this way.
Thanks again for all the help. Happy polishing and drinking to all Wedgers!
digga951 said:
Once again, thank you for all your help!
I don't have a pressue gauge but I just found this on ebay - should do the trick I reckon.
[url]http://cgi.ebay.co.uk/ws/eBayISAPI.dl[/url]
Just one more thing - instead of removing the fuel pump rely, can I not charge the fuel rails by operating the air flow meter instead? I have the flapper type. I don't want to cut corners but just wondered if there would be any difference doing it this way.
Thanks again for all the help. Happy polishing and drinking to all Wedgers!
Yes, except that when you crank, the AFM moves and the fuel pump refills the fuel rail....
Ah yes, I meant for the spray test side if things actually! I should have said.
Will get a pressure gauge on order and go from there I think. Quite looking forward to getting this engine running sweetly for the first time ever. Its always pinked like mad.
Tomorrows job will be measuring how much fuel is in the tanks too. The last time I used the car, I managed to get home with the fuel gauge bang on the zero mark. So now I'm going to drain all the fuel out and measure how much it holds. Then I will know how much I have in "reserve" when my gauge reaches empty. I always fill it up way before it gets anywhere near empty, but sometimes when youre in convoy its not always possible to just stop and do that.
Will get a pressure gauge on order and go from there I think. Quite looking forward to getting this engine running sweetly for the first time ever. Its always pinked like mad.
Tomorrows job will be measuring how much fuel is in the tanks too. The last time I used the car, I managed to get home with the fuel gauge bang on the zero mark. So now I'm going to drain all the fuel out and measure how much it holds. Then I will know how much I have in "reserve" when my gauge reaches empty. I always fill it up way before it gets anywhere near empty, but sometimes when youre in convoy its not always possible to just stop and do that.
digga951 said:
Ah yes, I meant for the spray test side if things actually! I should have said.
Will get a pressure gauge on order and go from there I think. Quite looking forward to getting this engine running sweetly for the first time ever. Its always pinked like mad.
No probs then, that would work! Gauge doesn't have to be anything special: I use old gas pressure gauges from scrapped x-ray sets, they have a threaded inlet on the back that can be pushed into the CS injector hose and secured with a jubbly clip.
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