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94 LS400 AC Issue

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Old 05-16-11, 04:03 PM   #1
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Default 94 LS400 AC Issue

Hello everyone, new Lexus owner here. I recently purchased a 94 LS4 with 184k miles on it. And after much reading here, and other Lexus related forums, I was able to pull off my first timing belt change. That evolution also included changing the valve cover gaskets, spark plug boot seals, cam seals, crank seal, new water pump, tb idler and tensioner pullies, hydrolic tensioner, serpetine belt tensioner and idler pullies, as well as new distributor caps and rotors. I did manage to install the rotors 180* off, but solved that one the morning after I completed the install. The biggiest issue I had was I didn't initially have a suitable way to remove the bolts of the crank and cam pullies, the purchase of a chain wrench and breaker bar solved that issue. Thank you all very much for all the useful information that I've found.

I have a few more issues to resolve, I think some of the high pressure hoses are leaking, but I'm not certain yet, I have yet to get underneath and do a thorough cleaning of the undercarriage and engine. There are two issues, however, that I have prioritized, namely getting the AC to work, and the transmission to shift into overdrive. Otherwise, it runs great now.

Now, as to the transmission, after much reading of symptoms from various sources, I've come to the conclusion the most likely culprit is the solenoid in the transmission. My next step will be to remove it, and soak it in PB blaster, which may have some success. If not, I have will have to find a source to purchase one. In either case, I went ahead with the purchase of the tranny fluid from my local Toy dealer, type IV, as I recall, so I can drop the pan as soon as I'm ready.

And last, but not least, on to the AC problem. I've gone through this site and the others, trying to find someone's problem that matched mine, and a few did. However, where their problems were solved with the addition of more coolant, mine was not. I've checked the Clutch relay, I even went so far as to swap it with the EFI relay after I checked it. I've put a jumper wire across the relay brass connectors and verified the compressor runs, and also blows ice cold air inside the cabin.

At this point, I'm at a bit of a standstill, while at the Toyota parts department, I was speaking with a service tech over on the Lexus side, as well as a Toyota parts man who was knowledgable about the LS4. I was given exploded diagrams for two more relays to check, one inside the dash located near the blower, and the other inside the engine bay fuse box. I will do that here shortly. The other item I wanted to check, but I'm unable to find an answer about is, the sensor mounted on the back of the compressor, does anyone know the Ohm value for a properly functioning sensor? If I can find any other problems electrically, I'll take the vehicle into the Lexus dealer for diagnostics, but I'd rather avoid such a costly trip.

Any assistance or further insight would be greatly appreciated.

Regards,

Terry
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Last edited by Privateer; 05-16-11 at 04:16 PM..
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Old 05-16-11, 04:15 PM   #2
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Oh, and I forgot to mention, I also repaired the stearing wheel elevator. Popped in a couple of washers behind that gear, and it works like a champ. Repaired the Gauge cluster by soldering in three capacitors, the lights were intermittently coming on and off. As well as the fuel gauge not showing fuel at all. Changed out the LCD in the HVAC controller. Replaced the shifter **** because the old one was shredded. And when I pick up the antenna mast, I'll replace that too. Though I will likely have to pull the unit, and open it up, because when I pulled the mast, the cable was no longer attached to it. Oh, and I Believe my EGR tube is cracked, I can hear what appears to be an exhaust leak coming from that location.
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Old 05-16-11, 05:03 PM   #3
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I really can't help with the others but are you sure about the EGR? Note that its directly behind the engine on the passenger side bank. A real biznatch to get off. I would check the simpler exhaust connections for bad gaskets before the EGR tube.
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Old 05-16-11, 05:13 PM   #4
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I am hoping it isn't, however, you can plainly hear an exhaust sound when standing over the center of the engine, or rather when your ear is over the center. Though at one point, I was standing inside the engine compartment when i had to remove one of the tiny bolts holding the one of the wiring brackets on the backside of the RH valve cover.

I'm not relishing the idea of removing it, and if I have to go that route, I'm considering the EGR delete that I've seen posted. Though I'm a little unclear as to the resister... namely, where does it go, with six connections inside the plug, I don't want to guess.

All that said, I will go over the exhaust with a fine tooth comb this weekend. I just started college, and I have a psychology class that's been crammed into three weeks. Ugh.
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Old 05-17-11, 05:18 AM   #5
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Regarding the transmission not shifting into overdrive,there is a transmission fluid temperature sensor that will prevent the transmission going into overdrive until the fluid has reached normal operating temperature.If this sensor is giving a constant cold signal it could be the cause of the problem.
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Old 05-17-11, 05:27 AM   #6
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Thank you, my research hadn't turned up that result previously. I'll look into it.
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Old 05-18-11, 06:38 PM   #7
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Quote:
Regarding the transmission not shifting into overdrive,there is a transmission fluid temperature sensor that will prevent the transmission going into overdrive until the fluid has reached normal operating temperature.If this sensor is giving a constant cold signal it could be the cause of the problem.
I stopped by my local toyota/lexus dealer today, and they were unable to identify any such creature on the 94 ls4. Also, I've not been able to find any reference to one anywhere, either. Would you happen to have a part number to help pinpoint this elusive sensor?
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Old 05-20-11, 07:31 PM   #8
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Just an update, I followed a troubleshooting guide I located and traced it back to the ECU. Apparently something got a little crispy inside, I opened it up and discovered a number of traces on the pcb that were destroyed. And without knowing what caused it in the first place, I don't know that it would even work when I repaired them. Looked like I'll be in the market for a replacement. bummer
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Old 05-20-11, 08:25 PM   #9
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Another update, I'm not overly patient when it come to electronics, I cleaned off the crispied traces, and while I was at it noticed that one of the electrolytic caps had committed suicide and bled out over those traces. If that's the extent of the damage, I am fairly sure I can remedy it. However, I'm having an issue with the last case screw, it absolutely does not want to budge, and I'm in dange of stripping the philips head out of it trying to get it off. I'm loath to drill the head out, but if I don't, I will be hard pressed to make the repair with the pcb still inside the housing.
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Old 05-21-11, 09:49 AM   #10
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At least you found a problem. It may not be your exact problem but if you repair it, hopefully it is. It sounds like you know what you're doing so just be patient with it, don't get angry with that screw and put a hammer through it. (something I would do) If it is your problem and can't fix it, you could get a used ECU from the junkyard, they're not too much. GL
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Old 05-21-11, 10:55 AM   #11
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I finally did get it, but I had to drill it, nearly made the situation worse, as the first bit decided to snap, and I nearly punched a hole into the pcb. but I did some testing, and found only two of the traces were damaged enough to warrent new wires. I'm attempting to find a source for the caps now. My local Shack didn't have them. There are 4 of the same type of cap, as well as 4 more of differing values. I may just replace all the old electrolytic types, depending on whether or not my initial attempt at a repair works.
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Old 05-21-11, 12:07 PM   #12
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You could try this place. http://www.digikey.com/?curr=USD Some other members have had real good luck with them.
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Old 05-21-11, 12:53 PM   #13
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Thank you, I'll give them a shout monday.

Meanwhile, back on the tranny front, I've removed the pan, and both solenoids, and presently have them both soaking in PB blaster. The fluid was markedly brownish in color, but I didn't detect any smell of burnt fluid. I'll do a fluid change in the near future. Hopefully that will solve the not shifting into overdrive issue I'm having.

On a side note, I attemped the tutorial that outlines how to read the diagnostic codes, but when I switch the ignition to ON, I get nothing. Even though when I shut it down after getting the O/D OFF light to blink when driving. I've tried wire, and paperclips, both to no avail.
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Old 05-21-11, 08:46 PM   #14
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Ok, end of day update. I reinstalled the Solenoids back in the tranny, put in a new filter, buttoned it back up, and added a couple of quarts of tranny fluid. I also finished up with my attempt at repairing the ECU, got it put back together and reinstalled. AC still doesn't work, and it doesn't pass the diag sheet I have. Sooo, I have an ECU enroute from a yard in TN, but I don't know if it is working, they said they were pulling it from a newly arrived wreck... but I got it for 75 with shipping.

So, I put a jumper across the clutch relay, got the AC fired up manually, hopped in and went for a spin. Took it up to 70mph, and no blinking O/D OFF light to be seen. Seems the PB blaster soak had a good effect on the solenoid. Thanks to JamesTN ( think that was his username) for his post about this cleaning technique. AC blew nice and cold for my ten minute test drive, but as soon as I got back home, I pulled the jumper out. I heard no strange noises coming from the compressor, but even so, I didn't feel comfortable leaving that jumper in, while the car wasn't on. If the new ECU doesn't solve the issue, I may just wire a switch to the relay and activate the compressor manually till I figure it out.
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Old 05-22-11, 12:25 PM   #15
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So, I was impatient again, I located the wire that feeds the other half of the circuit that powers the magnetic clutch relay. With the ignition off, neither pin has power. But with the ignition on,, one side has +12v. Well, since my ECU provides the other side (-), there was nothing present, consider it an open. Since I had already determined the compressor was functioning, and after taking the time to take voltage readings from the connection points, I felt I could put a switch in, to manually trigger the magnetic clutch relay.

I had a switch still in its package, that I hadn't used. One of those little rocker types with the LED in it. I tapped into the wire from the ECU that provided the circuit, and ran it to the switch. And by tapping in, I mean, I cut the wire that lead into the ECU before hooking my switch up to it. I left it in a state where I can reconnect it once my replacement ECU comes in. Now, my initial wiring had power going to this wire (+12v), and I quickly discovered that if you have +12v on both sides of the relay, the only thing it will do is look at you funny, and otherwise do absolutly nothing. Once I took the switch to provide a ground loop, the relay began working in its normal fashion.

So it is possible to remotely trigger the relay for the AC without having to breach the firewall with any new wiring. The downsides are, you've effectively bypassed all the safeguards for running the compressor, and if you will experience higher fuel consumption since the compressor will be running full time, unless you manually cycle it.

As for me, I'll risk it for the few days it takes the new ECU to get here. And, since I have the covers removed for the passenger side firewall, I'll see where I can get a 2 gauge power wire through it.
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Old 05-22-11, 12:25 PM
 
 
 
 
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94, ac, air, clutch, compressor, condition, hose, jumper, jumpering, lexus, ls400, magnetic, picture, pressure, relay, sc400, temp, vent

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