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LeeT
27-04-06, 19:03
starting to fault find my suspected stuck injector today. can someone tell me what voltage i should be seeing at the injector plug please?

Wez
27-04-06, 21:47
I guess anything from 10v - 14v as most ECUs have a voltage offset table.

LeeT
27-04-06, 21:54
I guess anything from 10v - 14v as most ECUs have a voltage offset table.
hi Wez, when checking the voltage at the injector plug, would the plug need to be connected to the injector? im asking as i only have 0.3volts across the plug pins when disconnected on two of the six plugs ive tried. i havent really had time today to have a good look around. surely if i had this voltage on all 6 injectors the car wouldnt run? im thinking maybe i forgot to reconnect something when i reinstalled the intake manifold?

Lucifer
27-04-06, 21:55
Should you not be checking resistance? Ohm

LeeT
27-04-06, 21:58
Should you not be checking resistance? Ohm
possibly but if theres no power there in the 1st place whats the point? i'll be having a good look tomorrow and if need be will remove them and get them sent down to you
lee

Digsy
27-04-06, 22:42
You'll need an oscillascope to see the full voltage at the injectors properly, and they'll need to be in circuit (i.e. plugged in).

LeeT
27-04-06, 22:49
You'll need an oscillascope to see the full voltage at the injectors properly, and they'll need to be in circuit (i.e. plugged in).
thanks for that. do you know anything about the injjector ground wire being bolted to the intake manifold? like i said before im going to have a proper look tomorrow but it would be nice to just find that ive forgoten to connect up the injector ground when reinstalling the intake manifold. wishful thinking i know:)

Digsy
27-04-06, 22:52
thanks for that. do you know anything about the injjector ground wire being bolted to the intake manifold? like i said before im going to have a proper look tomorrow but it would be nice to just find that ive forgoten to connect up the injector ground when reinstalling the intake manifold. wishful thinking i know:)

The injectors are switched to gound through the ECU so there should be no connection to the engine or chassis. The 12V feed comes from the resistor pack, if you have the low impednace injectors. If not then I guess it comes direct from the battery.

LeeT
27-04-06, 22:56
The injectors are switched to gound through the ECU so there should be no connection to the engine or chassis. The 12V feed comes from the resistor pack, if you have the low impednace injectors. If not then I guess it comes direct from the battery.
right, thanks again. yep they are low impedance. just hope i can get to the bottom of my problem in the morning. i just remember reading that there are a couple of grounds bolted up to the intake manifold and if they are not connected will leave the injectors with little power. iirc gregsupra from turbofit had the same or similar problem recently and the problem was one of these grounds

Digsy
27-04-06, 22:59
Maybe thet's where the ground ends up after it pops out fo the ECU. Try PMing Ian C. We measured the voltage across his injectors using a scope a year or so back. We used wires attached to pins that you could slide down inside the insulation on the plugs.

LeeT
27-04-06, 23:03
Maybe thet's where the ground ends up after it pops out fo the ECU. Try PMing Ian C. We measured the voltage across his injectors using a scope a year or so back. We used wires attached to pins that you could slide down inside the insulation on the plugs.
ive sent him a pm pointing him in this direction. i know im not going to get a true reading with a multimeter but surely i should be seeing something close to battery voltage?

Digsy
27-04-06, 23:09
ive sent him a pm pointing him in this direction. i know im not going to get a true reading with a multimeter but surely i should be seeing something close to battery voltage?

Depends on how close to 100% duty cycle you are. If you are at idle then probably not.,

Ian C
27-04-06, 23:10
There are two wires to each injector, and one of these will be the same colour on all 6 plugs - that's your +12v feed.

With your ignition on and the car mobilised you should get battery voltage at this wire. You can check with the plug off, put one probe in the +12v pin and the other on the battery negative (*not* the other pin, it's not connected to anything until the ECU grounds it to fire the injector).

The voltage should be the same on all 6, and if you measure resistance between each +12v pin and it's brothers it should be almost zero (ignition off for that one :) ) Again, with the ignition off, check the other pin on each connector against the battery negative - you should have infinite resistance as none of them should be grounded at that point. If one is, it'd be stuck open. Also you could just listen with a long extension bar or something to each injector as the engine idles, they should all sound the same, if one is wildly different then it could be the source of your problem...

The earth you are thinking of is just visible by the dipstick, under the intake runners. If this was missing your car probably wouldn't start and you'd get all sorts of other problems as well, I assure you :)

-Ian

LeeT
27-04-06, 23:16
thanks Ian, thats exactly the kind of reply i was after. Thats given me a good place to start in the morning. i'll report back how i get on
Digsy, thanks for your help also. the injectors will be nowhere near 100% duty cycle, they're 850's :d

Wez
28-04-06, 11:34
There are two wires to each injector, and one of these will be the same colour on all 6 plugs - that's your +12v feed.

With your ignition on and the car mobilised you should get battery voltage at this wire. You can check with the plug off, put one probe in the +12v pin and the other on the battery negative (*not* the other pin, it's not connected to anything until the ECU grounds it to fire the injector).

The voltage should be the same on all 6, and if you measure resistance between each +12v pin and it's brothers it should be almost zero (ignition off for that one :) ) Again, with the ignition off, check the other pin on each connector against the battery negative - you should have infinite resistance as none of them should be grounded at that point. If one is, it'd be stuck open. Also you could just listen with a long extension bar or something to each injector as the engine idles, they should all sound the same, if one is wildly different then it could be the source of your problem...

The earth you are thinking of is just visible by the dipstick, under the intake runners. If this was missing your car probably wouldn't start and you'd get all sorts of other problems as well, I assure you :)

-Ian

Great info Ian.

Can a mod add this to the FAQ or make it a sticky :cool:

Usmann A
28-04-06, 11:44
Hands up, another victim of the "forgot the damn earth straps" saga, a while back.HEHE

Hope you find the cause Lee, sounds like you got some investigating todo, and when it comes to lecy problems, Ians only had a few. ;) :p :D

Time to get out the Mulit and Snap on Power Probe ... that thing is a godsend for wiring numpties.... LOL

Let usk now how you get on.

ps, had my fair share of wiring troubleshooting, but it was mechanical in the end. hahah :search:

Ian C
28-04-06, 12:05
I'll see how the thread pans out and bung it in the FAQs when it's done if you like :)

-Ian

LeeT
28-04-06, 12:37
I'll see how the thread pans out and bung it in the FAQs when it's done if you like :)

-Ian

my wiring checks out perfectly. ive taken out the suspect injector now to check o rings. is it safe to blow the injector through with an airline? i'll clean up the contacts refit and see how that goes
agreed, should be made a sticky, great info

Terry S
28-04-06, 12:50
what injectors are they Lee??

LeeT
28-04-06, 13:05
what injectors are they Lee??
dare i say it? "cough" venoms "cough" 850 side feeds. if they turn out to be the problem i'll just have to replace them but im willing to give them a go first. moneys a bit tight at the moment after the 6spd conversion so if i can get these to run properly, i'll be very happy

Terry S
28-04-06, 13:08
OK thought they may have been Blitz and I was gonna say check the impedance.

Ian C
28-04-06, 14:33
I did a search and found your initial problem description. The other plugs would have shown leaness as the narrowband O2 sensor would have been picking up the unburnt fuel from the overfuelling cylinder and causing the ECU to lean the mix off to all the cylinders.

If you know which injector it is from your plug testing, then you have a few tests you can do:

1. Swap the suspect injector with another one and see if the wet plug effect moves with it
2. Unplug the injector and see if the idle cleans up as the closed loop puts fuel back into the remaining cylinders (it'll still be rough of course as one cylinder is missing and it might overfuel to compensate for all the fresh air being pumped through by one cylinder :) )
3. Send the injector off for flow testing and cleaning. A few days downtime and about 15 plus postage.

-Ian

LeeT
28-04-06, 14:38
thanks ian, im going to go and unplug the injector now and try it. ive put the car back together at the moment after fiddling about this morning and i must say it does seem to be running a bit better but this could be down to the new plugs ive just put in . its now backfiring badly on decelleration too. back soon

LeeT
28-04-06, 15:16
take a look at these plugs. they have been in there 4 miles. one is the plug from the suspect injector cylinder and the other is the neighbouring plug from the same coilpack.

Ian C
28-04-06, 15:22
OK, clean that plug up, put them back where you got them from, swap the suspect injector with another one and do the same 4 mile test. Same plug = wiring problem or spark issue, if the problem follows the injector, it's the injector...

-Ian

LeeT
28-04-06, 15:32
i'll swap them over now but the test drive will have to wait untill tomorrow as ive been drinking :d

LeeT
28-04-06, 17:10
right, ive swapped them over, run the car up to temp and let idle for 20 mins and the problem has moved with the injector. Thanks Ian, your help has been much appreciated. as much as i would like to get all the injectors cleaned/flow tested im just going to get the suspect one done for now just to be 100% sure. does anyone know anywhere that might be able to do this while i wait tomorrow. im happy to travel a reasonable distance.

Ian C
28-04-06, 21:20
Unless you wait for 48 hours, no :) That's how long a good ultrasonic clean takes. Send it to Chris Wilson and he'll turn it around in the time he says it will, but it'll be 4 working days minimum due to transit time and the testing/cleaning.

It's good news you've found the problem :thumbs:

-Ian

LeeT
29-04-06, 11:35
injectors gone off to mkivstore.com for cleaning. i could actually blow through this one and not the others so im almost positive this has to be the problem. i'll keep this thread updated how i get on. Thanks for all help on this, its done my head in.

LeeT
08-05-06, 21:43
just to reiterate. i think this bit of fault finding advice from ianc should be made a sticky.
the injector was indeed jammed open. martin (lucifer) cleaned it and after some messing around with it managed to get it to seal. it failed the flowtest too but its back in the car untill my new injector arrives. This is the first time the car has driven like stock off boost since upgrading the fuel system months ago
so thanks Ianc your advice was spot on

Ian C
08-05-06, 22:03
I rock :thanku: :D

Definitely getting FAQ'd now ;)

-Ian