Wiring Mysteries-94 Ls

[LSPaul]

Hi, all--

Before Christmas I picked up another older LS ('94 5th Anniversary edition) with some minor issues and 80k fewer miles than my '93, a nearly-perfect body and the previous owner's service receipts from 2001-2011 or so from the Lexus dealer in Des Moines. The car has plenty of the usual issues (instrument cluster electrolytic capacitors, split leather on the front seats, broken driver's door handle, needs new tires badly, but has hadlots of money spent maintaining other bits), all for a grand. Why not own two LSes? I plan on getting this car into shape, keeping it garaged and on standby, eventually rotating this one into service and retiring the '93 when it gets past 300k/something big breaks/rust starts breaking out. We'll see.

I have started to revive this, but have run into a challenge; I'll get to that in a moment, as that's where I'll pick the collective's mind on this one, even after spending hours studying the electrical manual and diagrams for the car.

The car was advertised as missing on half the cylinders; I thought, piece of cake--I checked and subsequently replaced the LH coil, which did test out of spec with my DMM. I can hear bits of toasted/broken catalytic converter rattle in the LH exhaust pipe when I close the door, too. The result of putting in the new coil? Nada. Cranked, no spark.

I went back and forth from here to Des Moines few more times while on business in mid-late December/around the holidays, making visits to the car (still in the seller's driveway at that time) to test and try stuff. I made some progress, but I still haven't fully solved the mystery.

Here's the progress, sorta: I had/have the luxury of being able to swap/test parts with my '93. I've been able to eliminate the fuel injection and main relays (swapped around and tested on the bench), fuses, both ignitors (with a swap from my '93, crank position and camshaft sensors (resistance checked in situ), I've pulled the computer down and checked voltages... which at first led me to believe I had a bad ECU, as there's no "Check Engine" light with the key on (checked to make sure the bulb was good, too), no codes pullable when the test pins are jumpered under the hood and no main power to the box with the key on. Before Christmas I pulled the ECU and while visiting family out-of-state for Christmas had my brother (who's an electronic tech) check the boards for damage, the electrolytic caps (for visible leakage, values and ESRs), with no issues noted. For an encore, I plugged the '94's ECU into my '93... which started right up and ran fine. Arrgh! Who knew I would wish for a bad ECU?

I finally had a break in the weather and business a couple weekends back, so I borrowed a neighbor's pickup, rented a car trailer and drove over to Des Moines, where I got it out of the PO's driveway, onto the trailer and home.

Looking at the car further in my driveway (between snows and massive cold blasts), I did notice bits of plastic wiring harness loom that appears to have been chewed and deposited by a mouse or similar creature under/around the brake master/booster. Apparently the car sat outside for several months before I bought it, which would be more than enough time for mice to do their thing.

I pulled the inner fender last week to inspect the harness from the LF side of the cabin to the front junction box, but didn't see any damage to the wiring harness. When I turn the key on, the main relay does operate, but the fuel injection main relay doesn't--there's no voltage at pin 1 (that actuatuates that particular relay, but there IS voltage at pin 2 (where the relay would close, sending power to the ECU.

After all this, some questions:

-Could I get away with jumpering the pins where the FI relay is to see if the car would get power to the ECU and theoretically start? If it actually works, I don't plan on driving the car this way--just need to see if it'll run!

-Any ideas where to look and feel the wiring harness for damage (I have also checked the trunk hinge harness and didn't see anything broken there)

-Is the ignition switch itself something that commonly fails on these cars?

Thanks in advance for your thoughts and input.

Paul

[landar]

I read thru your lengthy post and might have missed it but have a few questions:

1) Does the engine run, if only on half the cylinders...or not at all?

2) You say you put in a new coil and no spark. Did you check for spark at the coil or at a plug? Did you check the rotor and distributor. I don't know how many times I have heard of the rotor being busted. They do get brittle.

[LSPaul]

Hi, Randall--

Thanks for the thought; I was hoping you'd chime in!

The car doesn't run at all. I checked for spark both at the end of the coil leads and at random plugs. I eyeballed the LH side distributor (cap/rotor) when I had the LH timing belt/spark plug wire cover off-looked all right. Caps and rotors certainly do get brittle--I replaced those bits on my '93 during my in-field timing belt change; those were pretty cracked.

Paul

[landar]

You were hoping I would chime in? Am I that infamous now? ^_^

I guess the seller was fibbing when they said it only ran on half the cylinders, huh? Go figure.

The really good news is that you have a 'donor' car that you can use to test various areas. I do not have schematics or I would give you some detailed ideas of where to check. And I do not like the sounds of potentially chewed wires. That would be my main focus at this point. If a furry creature did chew on some wiring, it would need to be fixed of course. You can examine your 93 in that area and make comparisons.

As for the ECU power, I do not see a problem with energizing the relay to supply power to the ECU. But I would want to track down the supply for pin 1. Is it the ignition switch? Although I have not heard of ignition switches being a particular problem on the LS, they do wear out from use so it could very well be bad. I would probably jumper pin 1 to +12v and see if the relay will pull in. Then try to start. Pin 1 would, I assume, be the coil of the relay so I would also ohm that out before applying the voltage. Maybe it is shorted and took out a fuse? I highly doubt it but you never know.

[LSPaul]

I'll go with "famous" over 'infamous', thank you very much!

All the fuses are intact and have continuity, plus I did the relay swap test into the '93. All good there. ^_^

Update: In the "nothing left to lose" department, I did a quick experiment this evening: pulled the FI relay, jumpered pins 2 and 4 at that relay was able to start the car--it ran for a few seconds, enough to turn off the oil pressure light, then I turned it off. *That* alone is real progress. So I'm back to tracking my way through the engine harnesses to figure out where the break in that circuit is located. I was able to download the wiring diagrams for some light reading; there's more of that in my future, me thinks.

Paul

[landar]

That's really good news, Paul. At least you know it will 'come alive'. Very encouraging.

I found an electrical diagram on a 93 which is probably about the same as the 94. It looks to me that the EFI main relay (to which I believe you are referring) and powers the Fuel Pump ECU and Engine ECU, gets initial relay coil power or signal from the stop light switch. If I am reading that correctly, that would mean that you have to be stepping on the brake pedal to get the relay to operate. Wondering if the stop light switch is bad or wires chewed or ?

Do the brakes lights come on when you step on the pedal?

Here is the link -> http://www.yotatech.com/f161/1993-ls400-1uz-fe-wiring-diagram-227080/

[LSPaul]

Good morning and thanks for the link! The Russian site that I had found took their TIS pages down... At least I was able to download nearly all of the '94 electrical stuff. The '93 diagram's pretty much identical to the '94.

From my reading of it, the relay gets power from the M-REL pin of the engine ECU... So I'm trying to figure where to look--upstream power sources to the ECU or a break in the downstream power (between the ECU and the relay pin).

The brake lights and shift interlock both work, no problem.

Thanks again-
Paul

[landar]

I see that pin 13A(MREL) energizes the EFI relay and that is controlled by the ECM. So, what signal is missing such that the ECM is unhappy? Thats the question.

I see on page 68, look at item (9). It says that constant voltage is supplied to terminal batt of the engine control module. When the ignition switch is turned to 'on', the EFI relay is to pull in and supply additional power to the ECM. It makes sense that the ECM would need some primary power to run the relay to give it more direct power.

So, it would seem like a good idea to track down the ignition switch power to the ECM and make sure that the "constant voltage" is there on the terminal "batt".

[steve2006]

As you mention the EFI relay pull in coil is supplied with 12 volts from pin 13 of the engine ECU so you need to check for this with the ignition on at that pin on the ECU then if present check for the same voltage at pin 1 of the EFI relay, no voltage here would indicate a break in the wiring between the 2 points.

If the 12 volts is present on pin 1 then check if pin 3 of the EFI relay is connected to ground as if the ground is not connected the circuit will not be completed and the relay will not operate.

[LSPaul]

After a year, it's time to post an epilogue on this particular thread: I'm pleased to say that I was ultimately able to find the answer to my own challenge with this '94 5th Anniversary LS.

Executive summary: The connector/connection inside the car between the power/fuse block and the interior wiring harness wasn't making full contact, for whatever reason. Cleaning the connector appears to have done the trick.

Detail:

Since I was able to get the FI relay to engage and the car to fire off by adding a 12v external source, I was able to determine that I had power to the fuse block/junction panel under the dash. My first attempt at getting the car back up and running was to run a fused bypass lead from the circuit that supplies power to the ECU to the appropriate circuit of the ECU and one side of the battery light circuit. Some success there, as I was able to get the car running on the crummy gas on board and start assessing the rest of it. I ran into further challenges... The blower fan, AC compressor, return circuit for the alternator and most of the instrument cluster lights (including the charging bulb and thus, the alternator) weren't working!

I started to dig back into wiring during the fall and early winter months here, spending many hours studying the wiring diagrams. I pulled the the LF tire and inner fender, then carefully opened up the body wiring harness that goes from the inside power block to the under-hood junction block. I didn't see any obvious physical issues, and started checking continuity with my DMM... which was present between the two ends of the wiring harness for the alternator return lead!! Huh?! I started moving wires around under the dash, since I had things pretty well torn apart in the lower half of the dashboard... the battery light and the rest of the dash lights came on with the key on! So, I focused attention to that connection-- I unbolted the interior wiring harness from the junction block, sprayed DeOxIt on the contacts of the junction block and interior wiring harness connector, worked it in and out and reconnected the harness to the junction block. Success! Time to put the car back together! From there I retaped and plastic loomed the wiring harness to the front of the car, put the inner fender back in, re-installed the tire, followed by the dashboard--both right and left lower sides.

Now that the car runs, I've moved forward with the majority of the mini-projects on the list from earlier posts (cleaning, fresh gas, replaced front seats with a pair I had here with good leather skins on both halves, replacing the broken LF door handle (found one in the correct color, no less!), fluid changes, etc). I got the car registered and on the road Friday, putting a couple hundred miles on it since yesterday! There's still more maintenance and upgrades that need to be done, but those things will come in time. I currently have the chance to pick up a somewhat rough LS430 locally (and cheap!!) right now, but I'm seriously considering taking a pass on it, now that this LS is back on the road.

Paul

[landar]

Congrats on your fix.

Glad to hear that you got to the root cause, Paul. And thanks for reporting back one year later.

Intermittent connections are a real bugger to find and require a lot of patience and digging as you found out.

Just wondering if you applied a little contact grease to the connection to keep it from future oxidation?

[LSPaul]

Randall,

I fiddled with the car on and off through the year (mostly off), so real progress was slow in coming.

Instead of contact grease, the DeOxIt product I used (CAIG DeoxIT Pro Gold) gently cleans, conditions and lubricates electrical contacts--it's stuff one would normally use on relays, noisy controls, connectors and switches in electronic equipment. I've used it for years in repairing vintage audio and vintage amateur radio gear. Good stuff and spendy, too ($25+ for a 140g aerosal can of the stuff--which will last years).

Paul

[sha4000]

Wow now that's dedication that I can appreciate. I hate when there is something that I can't figure out. I went almost a whole year trying to figure out an issue with my sun roof. I practically removed the whole interior in the process but it was well worth it in the end.

[Exhaustgases]

This is what makes these cars kinda fun, is all the systems and wires. Too bad a bunch of us don't all live in the same area, could we have a great Lexus shop or what.