j2b4o

Like the title says the speedo is inaccurate in my 90'. It reads slow and gets worse the faster you go. For example at 20mph on the dash I am at 30mph and at 60 I am at 80. I replaced one of the speed sensors for the sake of throwing parts at it (works for some ppl lol) and nothing changed. The sensor I changed I believe to be the #2 sensor from what I could glean off the net. It was on the driver side above the rear tranny mount.

Any advice on how to calibrate the gauge or what a possible cause could be would be very helpful. I have slightly larger than OEM diameter tires on the car but when I run it through a tire calculator it says I should only be off about 3mph at 60mph. Thanks for reading!!

LScowboyLS

speed sensors are rarely the problem on LS400, cluster capacitors and ECU capacitors are two good suspects, when was the last time the speedo was accurate?

j2b4o

I have no idea how long. Didn't know until I got pulled over and the cop said I was doing a solid 80 and my dash was solid 60. So I checked it with a few different speedometer apps and it gets worse the faster you go.

Have any idea how to calibrate the speedo?? I know it is often done on other cars. Should be doable on the LS.

I realize that the ecu and dash caps are problematic but ive never heard of them causing this specific symptom before and I don't really have space in my life right now for the downtime the car will need to resolder new caps.

Stereorob

Lol it's called you have a 1990 Ls400 back when I had my 90 it had the same problem. At 60 I was flying past every car on the road. At 80 it was like I was doing warp speed. The faster I went the worse mine was. When I was doing 100 according to my car I was actually doing 150!!!!

xxmariolxx

I have a 90 too just foxed the same issue like yours. Its the capacitors. My dad fixed mine and we changed all of them since if a few are giving out I'm sure the rest wud give out soon? Works perfect now. Cost me $15 in parts. But my dad is a electrical engineer and knows what he's doing. It think it costs around 200 to get it fixed by someone

LScowboyLS

the easiest way to calibrate an LS400 speedo is to use this free app on your android phone!

it is extremely accurate, and it even has this cool way it reverse the image so you can put the phone on the dash and read the reflection in the windshield like an expensive head-up display!

j2b4o

Was it the dash caps or ecu caps?? Or both??

LScowboyLS

dash caps are far more likely as far as speedometer accuracy

xxmariolxx

dash caps. theres 3 mother boards the mains ones and then one for the rpms and one for the mph.

j2b4o

Ok that adds up because my rpm gauge has been dead for a while. So either of you have a thread with a list of the caps needed for a 90'?? Is it in the ecu caps thread??
Just have to find someone locally that is competent enough to do it lol.

LScowboyLS

it can be tricky to know which board has the bad capacitors, they are several boards in the car that affect the tach and speedometer

xxmariolxx

I changed them all in the tach just to be safe. Even if I knew which did what. They would prolly fail sometime soon

xxmariolxx

Nope. I can look tommorow and tell you. I would change all the caps in all 3 boards. Just to he safe, at first I didn't know there's 3 boards. Just changed it on the main one and then the needle started acting differently it wasn't bouncing around anymore. Then I did more research and realized there's 2 more boards. I just opens it and took another car to Fry's. I changed them all with the exception of one cap because it wasnt avalible anywhere but ebay. It also wasn't near the mph so I thought it wouldn't matter much and it didnt. I will list all the caps with the exception of one tommroow morning

xxmariolxx

Here they are with the expetion of one. these are all in the tach
470/ 16v
100/ 25v
33/ 16v
10/16v
33/ 35v
220/16v
47/ 25v
4.7/ 50v
33/35v
10/ 16v
10/15v

LScowboyLS

how many of them are electrolytic type (the ones that look like tiny coke cans)?