1993 Ls400 Over Heated...ran But Started Skipping

[Bruno Molly]

93LS400, 1UZ. Drove the Family to the beach in North Carolina, 2.5 hrs. Rolled like a top. The next day, while waiting on wifey to come out of a sandwich shop, we sat and idled with the AC on for about 10-15 mins. Didn't pay attention to the temp gauge as there were many Bikinis in motion around the venue. When she returned, put the car in Reverse, and the whole car started shaking like 1/2 the engine wasn't running.Mashed the gas pedal and engine started spark knocking like an old high compression engine that needs Hi Octane fuel. Whoa!! looked at the gauges and the temp was 1 hash mark from being pegged. Usually runs about 1/2 way to a little under 1/2. Drove to some shade, Hardly any power like it was running on 4 cylinders. Stopped under a tree and checked the coolant. It was low. Put some water in the res, let it sit for 20 mins. Restarted, still skipping. So I left the key on, engine off, AC fans running for about 5 mins. checked the coolant again. It had sucked in what we put in and was down to the "Low" mark on the coolant tank. Sat another 15 mins, Fans off, Key off. Restarted and car ran fine again. Ran fine all the way home and never had anymore trouble from it. A couple of time I floored it and it didn't want to just Ball out. At that point I figure it needs a new fuel filter which i haven't changed yet.On my to do list. But Expert opinions needed here... What could have happened? Do the Coils over heat? If felt like a Fuel issue. Could the engine be so hot that the fuel pre-ignites before the spark plugs fire? Pre-detonation for lack of a better term? The Fuel pump is only a year old. Previous owner changed it. Has this ever happened to anyone? I have a long standing bond with this car since I brought it back from the Grave. New timing belt, WP, CRank sensor, Caps Rotors, Plugs..all with about 5k miles on them.

This is what the car used to look like when I saved it.

Donor car...now being rebuilt with new rear clip:

After repair: Frame machined showed Front of frame was bent 13mm. Tech School Students pulled frame back to within .5mm of 100% perfect ..for FREE! Body shop quoted me $1600.

Mission accomplished!!! this is why I love this car!

[lexfourcam]

Could possibly be one of the ignition coils, has the radiator been flushed lately? is it leaking anti-freeze from anywhere? It could be running lean, i replaced my fuel filter a month or two ago, and i noticed the car ran much better.

[RDM]

If the engine is overheating, fuel can ignite early and cause the car to feel low on power, but if it continues after it's cooled down then you've got another problem. I wouldn't think a fuel filter would do anything unless it's already clogged, but it's not a symptom of overheating for certain.

[Bruno Molly]

If the engine is overheating, fuel can ignite early and cause the car to feel low on power, but if it continues after it's cooled down then you've got another problem. I wouldn't think a fuel filter would do anything unless it's already clogged, but it's not a symptom of overheating for certain.

Actually it only did it that one time. Never boiled or steamed over but didn't regain its normal power until the engine cooled off in approx 30 45 minutes. I was damn lucky it didn't blow a head gasket...I thought that's what had happened to it. But it wasn't. I flushed the radiator back in December when i was putting it back together. Not sure if its running lean. Could the O2 sensor overheat and cause it to run rough?

[RDM]

A bad O2 sensor just runs in open loop, not rough, just in a 'limp mode' where it's slightly down on power. It would still idle flat and rev fine, just with a little decrease in performance.

[curiousB]

Sounds like maybe two different symptoms. The hard running and missing sounds like one bank of cylinders (4 of them) dropped out due to faulty coil or wiring to it. Common problem discussed in this forum.

The second is more troubling in my mind. Engine overheating and coolant loss can be sign of blown head gasket. Portion of gasket cracks and gets blown out causing coolant to leak out block or into the cylinder. When it leaks into cylinder it is a mystery coolant loss as there are no puddles on the ground. Costly repair as it means removing the head an putting in new gasket and perhaps other parts or machining.

[Mile_High_Flyer]

Another thought as to the overheating. My 1999 LS400 recently did this, and at the time, it only had 80,000 kilometres on the clock. It was okay on flat land driving, but in traffic, or in the hills, it would get very hot. I checked all sorts of things, and of course, cracked head, or faulty gasket were top thoughts. Eventually, I took the top covers over the radiator off, and felt the radiator. The central area was cold, just a few inches down both sides were hot. Obviously the radiator was blocked, even though I had reverse flushed it. I removed it and took it to a local radiator specialist, who took off the tank, and "rodded" it clean. He said he sees a lot of this, and it's caused by mixing different types, or brands, of Anti-freeze. You must stick to one brand. I don't know what the previous owner had used. I got the car at 45,000 kilometres.

Is it possible your overheating may be caused by a similar blockage? Cheers, Keith.

[VBdenny]

Sound like the thermostat might be sticking. Just last weekend before we headed to the Syracuse Nationals my friends SS-454 Chevelle was running hot. Next morning we replaced the thermostat even though it looked okay. Ran the engine up to temperature with radiator cap off and heater on high until it burped and developed a steady flow. Added water to bring it to about 1" under the cap. I stuck my digital AC thermometer in the flow and it was at 159.8F steady. Ran great all weekend and other than excessive rear wheel spin on acceleration, the car runs perfect.

[Bruno Molly]

**** UPDATE and FIX *******

After 4 months of on and off overheating, finally got the problem solved. The overheating was due to the fact that 1st gen fans were used (90-92) and the connector plugs aren't the same as 93-94. So, i had wired one of the condenser fans wrong and it was rotating the wrong direction. Corrected that and the cooling problem went away for a while...the Sluggish performance and stuttering, no power issue was the result of a faulty ENGINE TEMPERATURE SENSOR behind and just below and slightly to the left of the center ignition coil. Green plug, 2 conductor. The Temp gauge sender / sensor is a small single conductor directly behind the center ignition coil and should not be confused with the Engine temp sensor that tells the ECU the engine temp.

Not sure why this causes the engine to not have power when you need it, but it solved my problem. Everything else has been replaced i.e. plug wires, plugs, dizzy cap, rotors etc.... start with the simple things. Maybe this can save you some time if you are reading this. Chances are you just bought a used LS400 and it runs great!!! Until you dump the pedal and it dies. The sensors under your hood are 15-20 years old in most cases!!! Changing the Engine temp sensor fixed the "Engine Death on pedal stomp" problem...

Hope this was helpful.

BM