Check Engine Light at 2500 RPM 1FZ-FE Auto (1 Viewer)

[KingRat]

Check Engine Light at 2500 RPM
I've a '97 80 Series FZJ 4.5 VX Auto (175k miles) that has started to give the "check engine" light if I accelerate past 2.5k RPM. This has no noticeable effect on general running, it is still a thirsty beast and the light goes off when I stop and switch off.
This makes checking engine codes v. difficult. It has been running perfectly up to this point and does not get beasted, drowned or green-laned but I do use it for field/forest work and towing.
I run on E5 unleaded, have put heavy duty springs, Rancho adjustable shocks, de-catted straight through custom stainless exhaust, new Denso top lambda sensor, removed the charcoal filter (not necessary in the UK) new head gasket and seals and complete ATF change but this was done about 6 months ago and its been running perfectly since. This is new.
I've noticed that there is a new hesitation or increased change gap between 2nd and 3rd on the auto box and the speedometer has stopped working. The gearbox speed sensor is working fine and the loom is in good condition.
Any information or solutions will be greatly appreciated.

 

[ceylonfj40nut]

How did you “de-cat”. Is the ECU tricked? Do have any knock sensor issues?

 

[BuckarooBanzai]

I had a similar issue on a truck. Intermittent check engine light at higher rpm. It ended up being a loose battery connection on the negative side. Might as well pluck the low hanging fruit first.

 

[KingRat]

I had the cat removed with a hammer and long cold chisel then sleeved internally so that it passes the visual exam. It was to add extra beef to the exhaust note and as it's a UK model it only has one pre cat lambda sensor so no ECU tinkering necessary. The emissions always pass the MOT test so long as it is good and hot and a bottle of Redex added to Shell (99 octane) E5 fuel. An 80 series fan at the testing station is also a plus.

Thanks for the suggestion about the negative connection, I'll have a look but as I'm now installing an LPG setup I'm pretty sure that all the electrical under the bonnet is sound. Would the failed speedo cause an ECU problem/stumble? I also no longer have cruise control.