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OBD System on ‘90 Lexus LS400

I have a 1990 Lexus Ls400. Cars that are under the year 1996 don’t have OBD systems & I’m wanting to do a performance tune on my car, but you can’t do that without an OBD system. So I’m wondering if it’s possible to develop/install an OBD system with my stock engine with the year of car I have, is this something I can do, regardless if it’s work that I’d have to do on my own, if a mechanic can’t?

What results are you looking for? What’s the current condition of the engine and the car overall? Any aftermarket stuff on it yet?

28 year old vehicle , just be glad it runs . The amount of money it would take to do what you want would be better spent on a different vehicle . Also since your location is unknown you may have emission problems if you mess with this thing.


Well it does have OBD 1, not 2. Your only hope is to install an aftermarket ECU from someplace like Haltech. Now that will take some serious wiring to install as well as set up to run your car. There may be security systems that may not play well with an aftermarket ECU, or some aftermarket ECU’s. You need a very competent specialty shop to have any hope that this will work.

Cars in literal flawless condition. 28 years old and has 165k on the odometer. Only mods are coilovers and wheels so far.

What results are you looking for? Are the new wheels/tires heavier than the originals? That will decrease acceleration for sure and increase braking distance probably.

I did some research on ECU’s and just for the Firsr gen Ls400 in general, there is hardly any aftermarket parts whatsoever, so I wasn’t able to find anything but stock ECU’s. I mean the money i’d spend to do this is something I really would consider, regardless what work comes with it. I’m all honesty it’s just a matter of looking for what I need when it’s so hard to find.

What is it you want to accomplish?

The weight has hardly a difference & I do have brand new brakes all the way around

Finding an after market ECU that’s compatable with my car to get the OBD II system so I can do a performance chip

What effects do you seek from the chip?

Nothing major really, I’m not expecting to get a performance chip and get an immense increase in power and what not. Just a tad bit better gas mileage and yes, a little bit more power. Just an investment for the long run

I seriously doubt if you would even notice much of an improvement . Again I ask where are you located because this site has mostly US based members.

I’m in the us. I live in Idaho

It sounds like it wouldn’t be a wise investment for me to do which is really what I need to know, so all this will probably have to be a pass, thank you

You might get more out of making sure the suspension is 100%. Struts, shocks, tires, alignment, etc.

I own a 92 Corolla, so the ignition and fuel system and engine computer are probably similar. You have an OBD I connector where you could connect a specialized gadget to monitor the various signals, O2 sensors, distributor sensors, rpm, vehicle speed, MAP, etc. If you want to go beyond that you’ll have to solve the hardware limitations built into that design, such as batch injection (all injectors fire at the same time rather than timed to the camshaft), the lack of direct camshaft and crankshaft sensors (both are probably derived from the distributor shaft), the lack of a mass airflow sensor (you engine may use an MAP instead), and the lack of a precise throttle position sensor. If you can’t solve those limitations then installing another engine computer likely won’t be very effective at improving performance. All those problems (if you have them on your car) can be solved, but it won’t be a simple thing to do. Also any tinkering w/that stuff will likely cause you grief come emissions testing time, if you have that to deal with in Idaho.

To maximize efficiency and power, take care of the basics: valve adjustment, correct spark plugs, cap and rotor in good shape, tires correctly inflated. When it’s time for new tires, look for some with low rolling resistance. Any mod touted as a “performance” enhancer is probably money spent with little or negative payback.

Your car doesn’t have OBD II so hand held tuners are out of the question. You might be able to find a piggy-back chip for the ECU or have a custom PROM burned. That’s how ECU tuning was done before OBD-II. It’s not something that you see much of these days. You cannot effectively retrofit an OBD-II system to an OBD-I compliant vehicle. Also for a stock, N/A V8. Any gains from an aftermarket tune are going to be very minor.