I have a broken 1995 SC400 and really need some help. Our main dealer Lexus is out of ideas and I don’t know what to do!

Context:

• Valve head gasket leaked onto alternator. Alternator grenaded. It went to the dealer sounding like a four cylinder car.
• Discovered that the leads and spark plugs are originals from 1995 (!!) and replaced them. Put new alternator on. Still sounded like a four cylinder car.
• Tried several second hand MAFs (they’re no longer available new, we search for part # 22204-42011). Still no difference. The assumption is always that any MAF I buy and that we try is broken. I’ve bought EBay crap and I have bought used used Fuji OEM.
• Discovered today (after two months of being in the dealer) that the heater control valve is leaking anti-freeze - not sure if connected to this problem.
• Lexus did a leak down test and a compression test and it is in great shape. It’s only done 80k miles.

Questions:

• Do we keep buying MAFs until we find a good one?
• Is it the ECU computer that’s broken maybe?
• Idle control aka ‘IAC’?
• Our car is a 1995, is there a different part number depending on when it was built in 1995?
• Any other ideas? I have no clue what I am talking about and, it seems, neither does Lexus.

I could really use some help here. The car is great but if Lexus can’t fix it then it’s no use to me. Thank you so much in advance!

 

Hello,

So, again, what appears to be the problem specifically? A Video of the car running would be helpful.

By the Alternator getting "grenaded", what exactly do you mean?
What else, other than the MAF Sensor, Ignition System and Compression, if anything, was checked during the car's stay at the Dealership?

So far the description of the issue is quite lacking, it would be very difficult to come up with any definitive answer. As mentioned earlier, if the Engine Runs, a video of the way it runs would be quite helpful, while at it, the Dealership *should* have the equipment to pull Engine Live Data out of it when the Engine is running, a Snapshot of the Readouts with the Engine Fully Warmed Up and at Idle, and Transmission in Park would also help a lot.

In the meantime, here is a thread describing the .. numerous issues that plague a number of ECUs used in older LS and SC models. Do keep in mind, however, that even if all the symptoms match, it does not necessarily mean that it's immediately time to replace the ECU, at least take the time to take the Covers off and inspect it, as a guaranteed working example can run you a few pennies, so you would be a lot better off making sure that it does need a replacement before pulling the trigger, unless the Dealership would be willing to reimburse you the costs if it doesn't help.

Hope this helps and best of luck!

 

If I knew what the problem is specifically then we would all be able to fix it, wouldn’t we?

The alternator was bathed in oil coming from a leaky valve cover gasket and we believe surged. The brand new battery was destroyed, for example. As I said, the engine sounds like it’s running very rough and not on all cylinders. The car is at the dealer and it’s not easy for me to get a video but you know what a four cylinder engine sounds like when it’s running rough, don’t you?

Can the dealer run a diagnostic when there is no OBD2?

 

Your dealer has no idea what they are doing. Take your SC to a qualified shop.

Apart from that, are you sure it was a leaking valve cover gasket that drowned your alternator? I would double-check, as the most common side effect of a bad alternator on these cars is the notorious power steering pump leak, as it sits right above the alternator and will drown it when leaking. Furthermore, a bad alternator will not cause your car to surge in idle or misfire or anything apart from displaying a battery light on your gauge cluster and eventually allowing the battery to drain, and thus, causing the car to die.

As for the MAF, why are you convinced that the MAF is bad? I'm having a very hard time believing that the problem persists because a bad MAF was used several times. This should point to the fact that your original MAF is, in fact, operating fine; I recommend putting the original one back on and replacing the paper gasket.

Next: That's good that the spark plugs and wires were replaced; however, it sounds like you are experiencing a misfire as it "runs like a 4 cylinder". I would also replace your distrubutor cap and rotors on both sides using Bosch parts; they are inexpensive, just as important to the rest of the ignition system, and also fairly simple to replace. I also recommend replacing your ignition coils. These can be a little pricey from the Lexus dealer; however, they are the only option, as other brands are made in China. I went with the NGK coils despite them being made in China, and they have served me well for a year so far, though.

Cleaning the idle air control valve is a good idea. I pulled mine at 89k miles and it was dirty. I recommend cleaning it with some throttle body cleaner and also replacing the paper gasket.

Sending your ECU out to get checked is also an excellent idea. It's a matter of WHEN, not IF, when it comes to the ECU needing to be rebuilt on an SC400. I had an intermittent high idle where the car would subsequently die at 93k miles, and it ended up being the ECU. I recommend sending it out to Tanin Auto Electronix, which is located in Wisconsin. They had me taken care of in a little under 2 weeks, including shipping to and from.

If you have any additional questions, please feel free to PM me. I have spent the last 2 years restoring my '92 SC400, and it would be faster to tell you what I didn't replace than what I did. Best of luck!

 

Well if it really does sound like a 4-Cylinder car, and that's all there is to it, just replace the Ignition Coils and Wires, but I would like to believe, for the sake of my already thin grasp on reality, that if the issue was indeed this simple, it would already be solved by now after so much time at the Dealership. The reason I am looking for a Video is that I am trying to hear something in that sound that you may not, which could potentially give a clue as to what causes it beyond a list of components that were mentioned earlier, and likely already checked.

At this point, I don't think that coming upfront and asking the mechanics to record a video of the car running would be too big of an issue, and if they refuse, then seeing their lack of success so far, I would strongly suggest to get the car away from them, and to find a more qualified repair facility, even if it is another dealership.

Again, by "destroyed", do you mean it got exploded, the acid boiled over, or it just stopped accepting charge? This is important to know as if it was the Voltage Regulator inside the Alternator that failed first, causing the Voltage to raise uncontrollably until the rest of the Alternator followed suit, it could affect a number of other electrical systems in the car, especially when the Capacitors used in those systems are already on their last legs from 30 years of service, yes, I am talking about the ECU again. Here is a thread that goes in a bit more detail on how the Alternator works, and the consequences of the Voltage Regulator Failure.

One of the reasons I wanted to get the Engine Live Data is that it could be a good pointer to the ECU issues, but what I keep forgetting is that, even though LS got OBD2 Protocol way back in 1994, SC has only gotten it when it became mandatory in 1996, which makes the process a bit more tricky. That said, you still have several options, the most obvious one, as mentioned earlier, would be to take the Covers off the ECU that is currently in the car and inspect it for any potential damage, which should be more or less obvious, considering the circumstances. If that doesn't work, here is a thread on how to get the Fuel Trim Parameters using an Oscilloscope, even if the Dealership that the car is currently at already got rid of the OBD1 Diagnostics Equipment, they really should at least have an Oscilloscope.

As mentioned by AlanSC400, however, the question of rebuilding the ECU for those cars will come up again sooner or later, it's just an unfortunate reality of those older Lexus models, though the good news is that it's only a one-time investment, provided the job is done right, and you won't have to come back to this subject again, so even if the ECU is intact at the moment, I would still suggest looking for a place to send it out to, just in case, if not now, at least you will know who to contact later.

Might be worthwhile seeing how easy it is to access, though I am rather certain that Toyota used a Metal Gasket in there, Part Number is 22278-50011.

That is true, even if the Valve Covers leak, they would have to leak buckets of oil for the Alternator to get affected, seeing how deep it is in the Engine, in most cases it will be a problem with either the Power Steering Pump, or the Lines coming to it, which is worth checking while at it.

While it is a good point to check those components, I am not a huge fan of just throwing parts in the wind without at least the courtesy of checking them first, I have seen cases when both Caps and Rotors last for over 200,000 miles before, and while I am not suggesting that this is how it should be, at least giving those components a look before throwing them out may go a long way.

Hope this helps and best of luck!

 

Sad to read about your car. The best advice above is to find an independent repair shop that has experience and references working on SCs. The Lexus dealership will not be able to fix your car and the bill will be staggering. Not that the independent will be inexpensive, either, but you will have a better result. Find a shop in the area and tow the car to them.

Sending out the main ECU to be tested, repaired, and certified is a must as a failed ECU causes a whole host of gremlins to chase; many shops will spend too much time troubleshooting symptoms that a repaired ECU will resolve.

 

Recommend that you first replace the distributor gasket. That gasket has a tendency to leak onto the distributor and short it out.