MoTeC Global Forum

I am having a problem on a Chev LS7 running the standard high impedance injectors. We are seeing random diagnostic errors on the F3 screen. On startup we can see say from cold a few injectors (it is running full sequential) trigger an "error inj 4 combinded Open" ie it goes red and rather than ok saids "open"

I have conducted the following checks: (results below)

- Resistance test from Injector pin to ECU Pin, do this one more than one injector to have a proper base line all went to 0 on ohm meter)
- Resistance test from the 12V+ source to the injectors, do this one more than one injector to have a proper base line. All47.8 ohm
- Resistance test the injectors (probably not needed as you have swapped the injectors around) all 13.4ohm
- Resistance test between the ECU injector pins and ECU Ground All 104.4 ohn

All appeared good on the tests above and I used contact cleaner on all injectors plugs etc.

This error is often isolated to inj4 but others will pop up. I swapped inj 2 and 4 but the error persists on 4 and I haven't seen it on 2.

You can see on this youtube clip what I am talking about when I recorded a short portion
https://www.youtube.com/watch?v=WUJ2Z0dXgog

First time I started today I had a collection of errors on different injectors that cleared quickly. Inj 4 persisted but as that video shows it will clear. At times inj 5 will flash up as well. I had a close look at plugs but I dont think they are an issue. With more rpm on say 2000 odd you tend not to see errors. Also as the idle drops down and it wants to stall out but is still running you will see more of the injectots come up open.

I am hoping this is a setting in ECU manager that I maybe need to adjust. We have run the car at pace on the track and there is no apparent miss but would be good to understand and correct this.

Any ideas much appreciated.

I have injector current set to 0 as I understand thats where it should be for injectors in the 12 to 16 ohm range.

Your second test showing a 47 ohm resistance between the 12V supply and the injectors sounds like the problem to me. I would expect very little resistance so that the total resistance through the injector would be 13 ohms of the injector, not 47 + 13 or 60 ohms.

Does all of your injector power go through a connector, or is spliced at a common point so that corrosion or other cause of a bad connection could be adding the extra resistance. This extra resistance could mean that only 200mA of current is flowing to the injectors, instead of the nearly 1A that I would expect.

Do you have a current probe and an oscilloscope you can use to determine the amount of current flowing to the injectors when they are open?

Many thanks David

That makes very good sense. Should have been obvious when I chekced it but as you might have guess not my area of expertise. These are professionally built looms. There is a large 40 or so pin Autosport bulkhead plug and socket. I suspect that the common joins will be on the engine side of the plug. If I can figure out which pin I can check resistance either side and try to narrow things down.

I have access to an oscilloscope so I can move onto that check as well.

Will advise on progress.

Thanks again

Further on this I had wrongly checked the resistances on the injector supply through the injector and back to the ecu. They only had a very small variance of between 13.9 and 14.1 ohms. So that hopefully rules out the wiring.

Will look to borrow an oscilliscope to check injector current. Does anyone know when "injector current" is set to 0 for 12-16 ohm injectors what the current range would be that would trigger the "open" error.

Was contemplating repinning the injector 4 and one other injector to see if this will move the error.

A Open error cab be caused by the contact bounce on the injector pin.

The Open error is ECU cant measure the +12V supply through the injector when the engine is running.

Thanks. Here ios a screenshot from i2 showing a couple of injector voltages with errors. Other injectors were fine. Not sure if this adds anything to the picture or not. I was told the voltage spikes are not abnormal.

While this is likely less common with the connectors you are using, I had a similar intermittent OPEN injector problem that ended up being the following (see image). The cause was a paper thin piece of broken plastic, approximately 0.5 x 1.0 mm.

Thanks I saw your posts on another thread when I was looking for ideas. I have looked at the plugs but might inspect them even more closely again.