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sprinkles08, ASE Certified Technician
Category: Lexus
Satisfied Customers: 22986
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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My Lexus 400 is loosing current to all the 4 injectors on

Customer Question

Hi Don, My Lexus 400 is loosing current to all the 4 injectors on the left bank (RHD) after the car runs 3-4 kms. Can you tell me what the problem could be?
Submitted: 2 years ago.
Category: Lexus
Customer: replied 2 years ago.
Also to note, once when the injectors were not working, we put off the ignition switch and restarted the car and it worked fine for a while.
Expert:  sprinkles08 replied 2 years ago.

Hello and welcome to JustAnswer!

There were two possible fuel systems, port and direct injection. Due to your symptoms I'm assuming you have port injection. If you're losing power to a whole bank of injectors then it's going to be a wiring issue. The injectors all receive power from the ten amp injector fuse and the engine controller pulses ground to actuate the injectors. A loss of power to some injectors only would have to be an open circuit in the wiring.

What fault codes set when this happens?

Customer: replied 2 years ago.
I had the ECU checked, it seems to be ok.
If it is a wiring issue how come in cold start it works ok and only after driving a few kilometers current to all 4 injectors disappears and on switching off the engine and restarting the current comes back for a short while.
It would seem like a relay is cutting off on extended use and switching off the current and restarting it catches again.
Is there any relay in the system between the ECU and the injectors?
I have checked the wires to and from the injectors and they seem intact.
Also to note something that could be related. The Automatic Transmission is not in good shape. The car takes a while to move after starting and when it gets warmed up, the clutches tend to slip more. Could this be related to the Bank1 loosing current to all injectors?
I have checked the fuses and wiring as suggested by you but find no fault in them. Please Help.
Expert:  sprinkles08 replied 2 years ago.

There isn't a relay involved and the ECM isn't what powers the injectors. They all receive power from a fuse. How are you determining that they are losing power?

Customer: replied 2 years ago.
We measure the current going to the injectors with a meter. In cold all 8 injectors have current but in hot the left bank shows no current at all while the right bank continues to run. In the fuse box there are 2 separate fuses for the fuel injection system, both have been checked along with the holders, wiring and sockets and are OK. Why does the current disappear when hot is the question.
Expert:  sprinkles08 replied 2 years ago.

The circuit that powers the injectors is opening. All injectors are powered by the same fuse, a single wire leaves the fuse and it breaks up to go to eight injectors. There has to be an open circuit on the power feed wire.

Customer: replied 2 years ago.
If as you say there is an open circuit in the feed wire, how come it works when the engine is started and upto about 3-4 kms drive? Again if you are right, there has to be some connection between the circuit working when cold and getting open when hot.
Also if one fuse is powering all 8 injectors then current to and from the fuse has to be OK or else the other 4 injectors would also not work.
As I had asked earlier, is there a link between the transmission and the injectors to sort of protect the gears from slipping by over revving, it cuts the current to one bank of injectors. Please explore this possibility as well. Thanks very much.
Expert:  sprinkles08 replied 2 years ago.

No, there is nothing that will shut off injectors to protect the transmission, and if that was the case then all eight would shut off. The injectors are all powered from the same fuse, the same wire leaving it. If some injectors have powre and some don't then you have an open circuit to the ones that don't have power at that time.

Customer: replied 2 years ago.
Okay, so I am going to get into the wiring to check for any defects. The fuse in this car is a 20 Amp one that when removed cuts the current to all 8 injectors. I will trace the wiring and get back to you. Tomorrow is a holiday so I will only be able to work on the car again on Friday the 18th. i will keep you posted.
Expert:  sprinkles08 replied 2 years ago.

You're welcome!

Customer: replied 1 year ago.
Hi Don, I have opened the wiring loom from the fuse to the injectors on the left bank and all checks out ok. All the wire insulation is intact and does not show an open circuit anywhere. What should I do now?
Expert:  sprinkles08 replied 1 year ago.

If only four injectors are losing power there has to be an open circuit to those four. You can hardwire then if your'e unable to find the problem.

Customer: replied 1 year ago.
Hi Don, after refitting the wiring we tested the car again. There was no difference. However, when testing the current with a bulb accross the two terminals of the injectors of the working right bank, the bulb flickerers intermittently. On the left bank, in cold start it also flickers but after a short drive it does not. On testing the main current to ground it shows continuous current. This means this means that in failed condition current is coming to the injectors but breaking contact when hot on the other end. Where does this second wire go from the injector? I tried direct earth, it does not work, I tried hot wiring it to the corresponding wire on the right bank, it does not work. What should I try next? Sorry this dragging on for so long but I must get to the bottom of this. I sincerely ***** ***** the help you are giving me.
Expert:  sprinkles08 replied 1 year ago.

You're actually losing injector pulse rather than power then.

Are any P codes currently setting?

Customer: replied 1 year ago.
The fault codes showing are the same.
P0135 & P1349.
Expert:  sprinkles08 replied 1 year ago.

If you clear the codes does the P1349 reset immediately when you start it? If not, are the injectors only losing pulse when the code sets?

Customer: replied 1 year ago.
Most likely it does but I will have to check that out. After resetting codes, P0135 comes on immediately on starting. I interchanged the O2 sensors from left to right. The car ran well for 10 miles (instead of the usual 4) and then again, left bank was not firing. So the O2sensor is not the cause.
Expert:  sprinkles08 replied 1 year ago.

We need to see if the injector drivers are being shut off as a result of the P1349 setting.

Customer: replied 1 year ago.
How do I test the injector drivers & where would they be located. How do I resolve the P1349 issue.
Expert:  sprinkles08 replied 1 year ago.

Your question thread was about the injectors not working but you don't know if they're actually turning off? Why did you initially believe they were turning off?

Customer: replied 1 year ago.
The injectors do turn off after a short run. We tested them with a test lamp accross the terminals of the wires going to the injectors when cold and the lamp lights up and when hot the lamp does not light up. That's why I thought there was a loss of current to the injectors. But after you told me about there being a common suply to all 8 injectors, even when the test light does not come on when hot, the current to the injectors when tested to ground is there. It would therefore seem that only when hot, something is failing. What should i test now and how.
Expert:  sprinkles08 replied 1 year ago.

Do the injector drivers only turn off when the P1349 is active?

Customer: replied 1 year ago.
When code P1349 is reset, the bank 1 injectors begin working but stop again after a short drive.
Stopping the car with ignition off for 5 minutes when they are not working and then on re starting the injectors begin to work again. I removed,
tested and refitted the oil pressure solenoid on bank 1. It is not stuck. When is it supposed to be energised?
Expert:  sprinkles08 replied 1 year ago.

I'm a full time tech and at work this morning, I'll get back to you as quickly as I can.

Expert:  sprinkles08 replied 1 year ago.

Do you have the VIN?