RX400h miss fire after new battery fitted.

Keeling54 · April 13, 2020

As the title suggested, old Battery beyond recovery, bought anew one of exactly the same spec, fitted it yesterday, everything was ok when I started it, had to reset the windows and seats, but didn't drive it.

Went to the wholesalers this morning to pick up the shopping, only a 5 minute drive, was ok going but started miss firing on the way back, it was intermittent, very slight to begin with and then got steadily worse, the engine management light started flashing as I pulled onto the drive.

it was up to temp and had a full tank of fuel, I have a code reader somewhere I'll start with that, any other obvious issues I should be looking at.

EDIT - Just put my code reader on it and it's not showing and recorded codes. May need to take it for a spin again later and see if it re occurs.

ColinBarber · April 13, 2020

have you used this code reader before on the RX? Is it capable of reading from Toyota/Lexus vehicles of that age?

Keeling54 · April 13, 2020

Not sure to be honest, it's an icar soft unit I had for my old merc.

It has a generic code reader built in which is showing no fault codes. It connects OK and gives me a load of readings from the Ecu so I'm hoping it'll pick up codes.

Keeling54 · April 13, 2020

Assuming my new miss fire and Battery swap are not related where should I start looking. Could it be coil pack related, if so where is the best place to get one so I can try and fix it.

I did a bit more testing earlier and the miss fire is really random, it happens and then stops and then starts again, makes the engine sound and feel like a bag of spanners.

ColinBarber · April 13, 2020

You need the error code to know which cylinder has the problem - then you can look at the plug / coil pack (move from one cylinder to another to see if the fault moves with them). If the misfire is random cylinder error then it could be a fuel injector rather than ignition.

You could try disconnecting the Battery to reset the ECU and giving it a run - seems a coincidence that this happened at the same time as changing the Battery.

Delphius1 · April 14, 2020

Random misfires can be hard to pinpoint and may actually be the car working as normal, which just confuses the issue.If the engine management light was illuminated you'll have codes stored in the ECU.

The engine is coil on plug, so you'll have 6 coil packs, not just one coil pack. If one misfires, the engine management is intelligent to know which cylinder is misfiring, so you should get a misfire code to a specific cylinder. That's why you mover the coil packs around to see if the misfire moves with a coil pack. But you should get a code for a cylinder misfire on the code reader.

However, if you have an issue that trips the traction control into working, then that can give you symptoms like a misfire and won't give you a code because it's the engine management cutting the spark deliberately. Basically if the sensors think a wheel is skidding then it will cut the spark to cut power. A usual culprit for that is changing a single tyre and having a wheel rotate at a different speed, or faulty ABS, VSC or steering sensors.

ColinBarber · April 14, 2020

4 hours ago, Delphius1 said:

However, if you have an issue that trips the traction control into working, then that can give you symptoms like a misfire and won't give you a code because it's the engine management cutting the spark deliberately. Basically if the sensors think a wheel is skidding then it will cut the spark to cut power. A usual culprit for that is changing a single tyre and having a wheel rotate at a different speed, or faulty ABS, VSC or steering sensors.

A flashing engine management light is normally because of a major issue (e.g. misfire), and not an issue with the ABS or VSC system (which would throw the VSC light on).

Keeling54 · April 15, 2020

On 4/13/2020 at 9:57 PM, ColinBarber said:

You need the error code to know which cylinder has the problem - then you can look at the plug / coil pack (move from one cylinder to another to see if the fault moves with them). If the misfire is random cylinder error then it could be a fuel injector rather than ignition.

You could try disconnecting the battery to reset the ECU and giving it a run - seems a coincidence that this happened at the same time as changing the battery.

I had a guy round today with a proper code reader, it appears that more than one cylinder is misfiring, his diagnosis was plugs or coil packs, I was very surprised that three were causing a problem and had failed all at the same time. There were no errors stored on the ECU either which I thought strange.

The missfire happens while the car is stationary so not traction control related.

I left the Battery disconnected over night and it still had problems.

I took a photo of the guys code reader screen, if it can get it onto my laptop I'll upload it.

Keeling54 · April 15, 2020

Looks like No2 had quite a few issues, is cylinder No2 at the front or the back?

Apologies for the quality.

ColinBarber · April 15, 2020

I'll just say that multiple coil packs don't all fail at once and you shouldn't blindly accept an error code as definite - it is a starting point for diagnosing the issue.

This is the cylinder layout of your engine

Keeling54 · April 15, 2020

My thoughts as well, i don't see three coil packs failing at the same time, the graph shows most of the missfires appear on No2, The guy was convincing me to replace the rear plugs and coil packs, to be honest I may invest in a Lexus specific code reader, swap out No2 and see if it improves.

Thats my plan at the moment if I can get hold of a coil pack...

ColinBarber · April 16, 2020

just swap coil pack 2 and 6 to see if the fault moves.

Keeling54 · April 16, 2020

13 hours ago, ColinBarber said:

just swap coil pack 2 and 6 to see if the fault moves.

Will try that, any suggestions for a decent scanner, code reader.

Herbie · April 17, 2020

10 hours ago, Keeling54 said:

any suggestions for a decent scanner, code reader.

If you have a laptop then your best bet is to get a miniVCI cable from eBay or amazon.

These almost invariably come with a pirated copy of Techstream, which is the official diagnostic software that Toyota/Lexus technicians use in main dealer workshops. Alternatively, you can legitimately download a free copy of the software from here https://www.toyota-tech.eu/GTS/Wizard/Step5-Software.aspx and pay for a block of time to use it here.

Of course, I'm not condoning the use of pirated software, that's a matter for your own conscience, but either way you'll need that miniVCI cable anyway so that the car and the laptop can talk to each other.

Keeling54 · April 17, 2020

3 hours ago, Herbie said:

If you have a laptop then your best bet is to get a miniVCI cable from eBay or Amazon.

These almost invariably come with a pirated copy of Techstream, which is the official diagnostic software that Toyota/Lexus technicians use in main dealer workshops. Alternatively, you can legitimately download a free copy of the software from here https://www.toyota-tech.eu/GTS/Wizard/Step5-Software.aspx and pay for a block of time to use it here.

Of course, I'm not condoning the use of pirated software, that's a matter for your own conscience, but either way you'll need that miniVCI cable anyway so that the car and the laptop can talk to each other.

Perfect thanks, will give it a go, I'd rather pay for something that's actually going to work.

ColinBarber · April 17, 2020

doing a bit of research on other forums, it seems this engine is known for a single coil pack producing misfires across multiple cylinders, so you should concentrate on the one showing the most misfires. Not sure if the others are actual misfires or just the ECU detecting the misfire at a point in time where another cylinder is due for firing and therefore it triggers against the wrong cylinder - I suspect the latter.

Keeling54 · April 17, 2020

1 hour ago, ColinBarber said:

doing a bit of research on other forums, it seems this engine is known for a single coil pack producing misfires across multiple cylinders, so you should concentrate on the one showing the most misfires. Not sure if the others are actual misfires or just the ECU detecting the misfire at a point in time where another cylinder is due for firing and therefore it triggers against the wrong cylinder - I suspect the latter.

Cylinder 2 has over 50 missfires so that's the one i'll concentrate on.

Just waiting now for the OBD cable to turn up so I can read any stored codes, the guy that did the original check for me didn't show me the fault code list.

Thanks to everyone that has posted on this thread so far.

Keeling54 · April 22, 2020

All fixed now, fitted a new coil pack and spark plug and it runs like a dream, wasn't an original denso coil pack but will try and get one of those as a spare. Luckily I took a snap of the diagnostics otherwise those guys would have been swapping out the rear packs.