Misfire on acceleration

Keith Bolton · April 10

Hi , I have a lexus SC400 1993 , it is sluggish when I accelerate (this is an intermittent fault ) but soon goes into full running mode , this only happens when the engine is in drive mode , but doesn't appear to happen in neutral or parking mode ,and it doesn't come up with an engine managment warning light ?,I have had all oxygen sensors replaced and the ECU tested which came back fine ,is there anybody whom have had a similar problem

Malc1 · April 10

Can you put up some photos of your rare 1993 SC400 …… not thinking I’ve ever seen this car 🤔

Malc

Neil E · April 10

This could be many things but I would start with the very common fuel pump ecu fault. It has a 9V mode and also 12V mode when it needs to deliver more fuel. I recall this can also prevent the car from starting when hot.

There is a bypass that you can do with a bridging wire on the diagnostic port on top of the engine to test it. Bridge FP and B+ to put it into 12V mode. If that fixes the problem it's a faulty fuel pump ecu in the nearside rear passenger side panel. In my experience, it can be run in 12V mode without issue and replace the ECU as soon as you can.

Just for you Malc, here is a pic of one of my old Soarers (SC400 in the US) They look a bit like this.

Malc1 · April 10

Ah right, it’s the Soarer
Looks good 👍

it’ll get sorted ok I’m sure 👌

Malc

Tomtit · April 11

I assume the spark plugs are all OK? A coil pack could be breaking down. Could it be down to an inlet manifold leak or an exhaust leak? Just general questions as i am not familiar with the SC400 engine.

Neil E · April 11

22 hours ago, Malc1 said:

Ah right, it’s the Soarer
Looks good 👍

it’ll get sorted ok I’m sure 👌

Malc

Yes it's a 1UZ-FE LS coupe - almost bullet-proof.

2 minutes ago, Tomtit said:

I assume the spark plugs are all OK? A coil pack could be breaking down. Could it be down to an inlet manifold leak or an exhaust leak? Just general questions as i am not familiar with the SC400 engine.

Yes the coils can fail and the leads can arc out with age but that's more obvious and it probably wouldn't be revving well at all. The fuel pump ecu is a known common failure.