The always frightening electrical problems

[cre]

I suppose it is worth mentioning that there were a number of changes made to the electrical system throughout the '89 model year. Pretty much all of the components are cross compatible but most have different plugs, the wire harness changed, the external HAC sensor was built into the ECU, the ECUs are different (many different models actually but the only significant difference it the redline depending on wether the engine has a 6M or 7M crank). The AFM and TPS connectors are the same as are all of the temp sensors and the oil pressure sender, the CPS is different and you wouldn't be able to plug it in and the wrong TPS will plug in but the interface tabe will be clocked 90? differently than the tabs on the throttlebody. The significant differences in ECU are highlighted by the harness connector colors.... Basically, if plugs and connectors are yellow it'll work and if they're both grey it'll work.

Again, it doesn't sound like any of this is the case with your vehicle.

[supraheelfan]

Actually my oil pressure gauge did not work for a long time until recently my dad and me installed a Prosport oil pressure gauge, but before that it didn't work at all. Still no error codes and the only lead is this new mechanic however I don't know if he is right or just trying to get more work ya know.

This is off topic, however my dad and I have been in an on-going debate about the oil pressure sender; Does the Prosport sender need an adapter to work? The reason I ask is because my dad hooked the sender up (somehow) and now the gauge reading is way off. Just wondering cause the sender was really hard to get into the block and from the search on the internet the sender needed an adapter to go from NPT to BPT or something like that. Any knowledge about this is appreciated.

[cre]

The oil pressure port is a similar standard to BSP it's JIS actually. BUT there may be a bigger issue... the ECU requires an oil pressure signal from the stock sender. There is a port about 6" to 8" forward of the oil pressure sender's port you may use for your aftermarket sender with less worry about distorting the threads.

EDIT: Scratch that... why don't you check if any sensors are unplugged because the harness won't connect and look up the part numbers. If you look in the TEWD you'll find diagrams of what the connectors are supposed to look like for each sensor and in the TSRM you'll find how to measure each one and what the readings should be. A quick glance in Toyota's Electronic Parts Catalog doesn't show any as being specific to the US but the European market did have some which were different than elsewhere... I didn't check if those applications were for Supras though, could have been Cressidas or 4Runners, etc. The year of the sensor is the only issue I've ever had and heard of from others.

Start here:
http://www.cygnusx1.net/Supra/Librar...spx?F=8401&P=1
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/

[supraheelfan]

Uh oh! The TSRM is not loading for me is it down?

[cre]

It does appear to be down. Try searching "turboninja" and "MKIII" on google a friend hosts PDF (and other) versions for a couple different years there. I'm pretty sure he's still got them posted...

[supraheelfan]

Well the mech at the shop said he replaced some plugs and got the car running again but when I went to go pick it up it wouldn't start at first but eventually did.

Then it cut off on me at a stop light and it was really hard to start back up.

If the wiring is shot thru most of the car should I just replace harness or what? What would be the best/affordable route to take?

Now that I think about it would it be easier to just go for a stand alone and start fresh?

[cre]

Going standalone isn't going to be any easier; You'll still have to replace the wiring harness then diagnose and replace any bad sensors (and replace any that are incompatible)... With some setups you'll need to add additional sensors and make modifications to mount them (such as a crank position sensor). Then there's tuning, the cost of adding a wideband (if you want reliability and on-board tuning). The easiest to install standalones use the stock wiring (ie: AEM and Apex'i).

Most wire harness failures are located at or near the connectors or in high heat locations. If you have recurring error codes they'll often point out the most likely suspects. The wiring which passes over the engine (AFM, CPS, oil pressure, temp sensors and O2) are the most susceptible to heat damage. Testing the wiring for voltage drop is a simple procedure once you get the hang of it.

If you opt to get a replacement OEM harness you may find that Toyota no longer has them (probably not too bad as you would then find out they ran around $500)... There is an established wire harness company who has added replacement 7M wiring harnesses to their product line, but I can't remember who and don't know what the pricing is. Personally, I just rebuild them myself, but it's time consuming and getting replacement clips is sometimes a pain.

No error codes coming up?