Injectors not working

[Cobber]

Just doing an install of a 1uz in a cobra and it looks like the injectors are not working.

When I put the meter on the injector +ve it reads 12v with the ignition on but when the engine is cranked over this drops down to around 9v. The battery seems to have plenty of cranking power and there is a spark.

Celsior ECU all standard set up. I know the ECU, AFM & igniters are fine as they were running on my engine.

Can I test the injectors by just putting 12v through them?

I think it's something simple Ive missed.

Any ideas?

 

[cribbj]

Andy if they're high impedance injectors (>10 ohms) you can test them by putting 12v directly to them. However, if they're low impedance (~2-4 ohms) you'll fry them. You'll need to put a 5-10 ohm resistor of about 5-10 watts in series with the injector you're testing. Don't leave power on it continuously......

To me this sounds like a dodgy earth in the ECU.

The injectors should have a switched source of +12v on them all the time, and it's the ECU that provides the earth return for each injector to fire it. If the ECU isn't earthed well, then the injectors may not be firing.

 

[Cobber]

Thanks John,

Ran out of time today to do more checks. I will check all earths and powers next.

They are standard 1uz ls400 215 cc injectors.

 

[Cobber]

Just done some more checks, The battery drops down to 9.5 volts when cranking so it looks like the battery may be stuffed. Meter was put directly on the battery terminals.

Strange thing is, it cranks over fast enough and there is a spark but no fuel :-(

Would the injectors still work at 9.5 volts?

 

[cribbj]

It's a long shot, but maybe the IGF or IG (for a dizzy system) signal isn't making it back to the ECU if none of the injectors are firing?

With no IG or IGF, the ECU thinks there's no fire, and it won't trigger the injectors.

It's not the Ne (crankshaft) or G (cam or distributor) signals, because you have spark, but maybe your ignitor isn't giving the confirmation (IGF) that the coil fired?

Still think it's a missing earth somewhere though

 

[gloverman]

Do you have power at all the correct places on the ecu - The one I wired yesterday I forgot the ECU supplies a power supply to switch the main relay and not a earth as most do. A quick check of the power supplies would be a good Idea I think. What are the plug confirations of the ECU? Cheers

 

[Cobber]

Celsior ecu. Powers seem ok and the ecu is switching the power relay ok, the voltage drops to 9.5 volts during cranking on the whole system. Will swap batteries next.

 

[diob]

black/orange wire

running from the engine harness to where your fuse box for the celsor was is a black yellow wire, connect this wire to ignition on relay.

It provides the power for the injectors and ignitors.

hope this helps.

 

[diob]

oops

sorry black/orange

 

[rms]

Strange thing is, it cranks over fast enough and there is a spark but no fuel :-(

What turns the fuel pump on. Is it running ?
The SC400 has a seperate fuel pump computer, there is no switched out from the ecu to the fuel pump.

Don't know about the Celsior, even though I own one, have not looked.

 

[gloverman]

is it the 26-16-22-26 celsior ECU as I have just wired one. Have you tried some engine start, if the ignition system is working correctly them it will run on engine start good enough to idle. - Cheers

 

[Cobber]

Yes it's the celsior ecu, have not tried aero start yet but I think it should work as there is a spark.

Fuel pump is running fine. sta turns fuel pump on and fc -ve switch holds it in when engine is running.

Injectors and igniters are getting 12v power but it drops to 9.5v when cranking. It is a dry cell battery (odesey I think) and will look at swaping to normal wet cell to see if that makes a difference.

I won't be able to get back to the car for another 10 days but then I will check the igf signal, change the battery, check earths again (fibre glass car) and squirt in a bit of aero start and see what happens.

Thanks for the help guys I'm sure it's something simple that has been missed.

 

[LondonBenji]

sorry to be a bit off topic but would you mind if I asked a few questions?

What cobra kit are you running?
Where did you get the engine mounts from?
If its not a FFR kit do you think your engine mounts would fit?
If it is an FFR kit can I get some of your engine mounts

 

[200sx-v8]

Cribbj,
Are you sure that the injectors are fried with direct 12v if they are low impedance?

I always thought that the resistors was there for to save the injector outputs on the ecu.

 

[cribbj]

Can't say I've ever put the 12v directly to a low impedance injector and tried it. That was a warning given by Ross Collins of RC Engineering years ago and it seemed logical to me so I followed it. As you probably know, the low impedance "Peak & Hold" injectors require a 4:1 driver circuit to operate correctly, which "bangs" them open at 4 amperes Peak, before cutting the current back to a Holding current of about 1 ampere. That's why we get faster opening times with these than high impedance injectors.

Now I must admit I don't know whether it's the injector or the driver circuit, or a combination of the two that figures out when to cut back to the Holding current, but I do know that batteries are pretty dumb, so if you connect a 3 ohm P&H injector across a battery, it stands to reason it's going to draw 4 times the current of a 12 ohm high impedance injector, and it will heat up that much faster too, without any fuel going through it.

Note, I was referring to bench testing above. In terms of energising the low impedance injectors from an ECU not built to handle them, I would agree with you, I'll bet it would be the ECU driver circuits that would overheat & fry.

 

[diob]

My little shits, off the topic

dam kids, thought it would be a good idea to drop stones in the inlet manifold.

how much will this one cost me

wait till they buy there first car, I am going to go up and down the side of their cars with a ball pen hammer, chop up the wiring harnesses, put stones on their engine.

the engine goes backfire, backfire, bang
oh well go buy a another motor, good thing 1uz-fe engines are cheap

 

[Mattmannz]

9.5V at cranking is probably okay, anything above 9V should be enough for the ECU to operate okay.

In terms of measuring the voltage at the injectors it's best to use a scope rather than a meter if possible as the meter might make it look like everything is okay when it's not as it will be missing quite a bit of the actual resolution.

Matt.

 

[Cobber]

Will get back onto this in the next week or so and let you know what I find. I know the whole system was working before going into the car so it must be something simple.

Benji it is not FFR, so custom engine mounts.

 

[Muzza_NZ]

BUMP: did you ever get to the bottom of this Cobber?

 

[Cobber]

Yes she is running now, I should have posted ags ago.

The thing that sent me off track was when I first started looking for the problem I found the crank sensor disc had not been put in and the cam belt was miles out from the person who put the engine back together. So after fixing all this up I thought there must be something else a miss.

After a squirt of "start you bastard" it would run so I then traced the fuel lines, swapped them over and bingo she ran.

A lesson in life learned again. Start at the begining with all the basics.

Many thanks for everyones help on this.