Hey clublexus, I've been lurking through the forums since I bought my 1991 LS400. Its an amazing car, super comfortable and I've always liked oldschool lexus especially since my brother had one.

A little background on the car:

145k Miles
Timing belt done at 114k

Recent tune up to try and address the bad gas mileage:

New NGK Iridiums
New OEM Denso Wires
New upstream o2 sensors
New ECT sensor
Coilpacks x2 on the way

Only code I have is 71 EGR which just popped up today after like a month of not having it. Mind you I replaced the spark plugs and wires today as well.

My question is, is it possible the gas smell is coming from the EGR? Or maybe a split in the manifold, or cat? I do not have any exhaust leaks that are audible.

Could a clogged EGR cause such bad gas mileage?

EDIT: Gas smell was coming from a fuel line connected by a bracket to the side of the shock tower, its a rubber line and then a hardline that goes down and under the car with a bunch of others. No noticeable leaks or anything just smells.

 

Welcome to Club Lexus.

The 2-LS FAQ covers much of the discussions and is applicable to the earlier generation LS.

https://www.clublexus.com/forums/ls4...questions.html

In particular this thread and similar ones regarding the ECT sensor:
https://www.clublexus.com/forums/ls4...read-this.html

 

I appreciate your response, RA40. I have gone through those threads multiple times already before posting. I guess maybe my car is just a gas guzzler.

I have another question maybe you can help with though:

There is a connector by the left bank that I believe is part of the driver side coil because I disconnected it and the car wouldn't stay on and got a code 14.

This connector has 4 wires on the coil(?) side and 2 wires on the harness side with 2 other wires cut off. Is this okay to be run like this? What were the other 2 wires for? I searched for the missing 2 cut wires on the harness side and cannot find any.

Here is a picture:

 

Good pic. If you've replaced the ECT sensor, the next is vacuum leaks. There may be other contributing factors and cut wires that are related to the ignition and fuel injection are potentially big issues. Glad you are getting an error code. In the event you haven't seen this thread:
https://www.clublexus.com/forums/ls4...code-14-a.html

The 1-LS isn't great in MPG though it still should turn 21-22 highway and 14-16 in the stop go.

 

I checked out the thread. I do not have any ignition or spark issues. The connector in the picture has 2 wires cut off so i simply disconnected it and tried to start the car to see what it was connected to. This in turn gave me a code 14 which told me the connector is part of the ignition system (coil, igniter).

As far as leaks I do not have any. The car idles at 650 with the a/c off at operating temp and 800 with it on.

My question was, those 2 cut off wires on the connector, what are they for? Seeing as how the car only runs with the 2 wires and not the 4. I would like to find out if they affect anything for not being there.

 

First off I would check it on an exhaust gas analyzer, you may have problems with things like cold start valve, injectors, fuel pressure regulator etc. As far as the wires I'll have to check mine out when I can.

 

I popped the hood on my '91 just now, removed the two plastic covers and took these photos.

My car is almost certainly original here. My father in law was the original owner.

So it looks like your wiring has been messed with. The plug you're asking about, where it appears to have 4 wires with 2 cut off ... My plug there just has two wires, with the brown sleeve covering it. The other end of the plug is screwed down somehow.

So my guess is that 2 wires is correct. Something may have gone wrong and they salvaged a 4-wire connector, using 2 of the 4 wires and cutting off the other two.

If there's something else you want me to look at, let me know. I did not put the plastic covers back yet.

 

I'd follow that lead if I were you. If you can smell gas, gas is being lost, even if it's just in vapor form. And there's a good chance that if the system is breaking down and leaking in one section, it will be doing that in another place too.

So the theory here is that you might be losing gas at a slow, steady rate, whether you drive it or not. To test that, you can fill it up, take it on as long a trip as you need to, then fill it up again and calculate your MPG ... all this while minimizing the _time_ between fill-ups.

 

I really appreciate you taking the time, oldskewel. The other side of the plug has the 4 wires intact. I'm not quite sure where exactly it leads to but trying to figure out where it went, I found this other plug that wasn't even connected to anything! As well as this unconnected plug, I found a plug connected right next to the driver coil that has only 1 wire coming out of it. I think maybe that one is for the A/C.

pic:


Apart from this, I have a question: at what rpm does the car switch to 2nd gear? Mine always changes at 1800 and above no matter what. I was wondering if my TPS set all the way counterclockwise have anything to do with it? Car idles completely fine and goes through all the gears smooth. Except sometimes when I'm on the highway around 50 mph it keeps doing this weird downshifting/stuttering thing.

pic:

 

I know this thread is old...but look...I had the same exact question about the same exact plug - a four wire plug with two wires connected (twisted, until I get that fixed) and two (green and black) just hanging unconnected. I traced the two that are connected and they lead to the LH Coil, as one might expect. Did anyone ever figure out what the unattached two wires represent? I did...and they lead to the Fan Pump Solenoid (discontinued on my car, which explains why they were disconnected.).

 

So what are you calling a "Fan Pump" ? The only things I know that have a fan pump would be an industrial engine application. And it may not be a dedicated fan pump, but just part of a hydraulic system, since some of those fans can be operated by hydraulic pressure.
The fan on these cars are a viscous fan driven by a serpentine belt and require no pump. There are pumps that are also driven by the serpentine belt, they are the power steering pump and the air conditioning pump or compressor. So what the heck is a fan pump solenoid??????

 

Dicer ~ you might refer to it as 'Fan Bracket'. It occupies the same location and mounts the idler just like the 'Fan Bracket', but on models with the hydraulic fan system, it's referred to as the 'Fan Pump'. The Solenoid is that tubular device noted in this picture.

Here it is on the front of the engine

 

Hmmm "on models with the hydraulic fan system" Okay what models? And remember this is a thread on a 1991, and since my 92 does not have that feature I'm sure the 91 doesn't either.
And yes now I can see that it is a pump. So where is the fan mounted ? And what year has that? And what would that plug and mess of wires have to do with a 91?

 

I've seen this fan on Celsiors. My Celsior has this fan. From the inside, the pump is almost like the pump for power steering. The pump generates hydraulic pressure which is sent to the fan via rubber pipes. The fan spins with this hydraulic pressure. As the engine rpm goes up, the fan speeds up.

The solenoid is there to switch between high speed and low speed. In my car, whenever the A/C is turned on, the fan switches to high speed. It is also dependant on engine temperature.

 

That's a great explanation, Najeeh. Thanks!. My 92 LS400 and I appreciate it.
I posted this bit in case the original thread creator still hadn't identified the two wires...(the mess)....and now we know that they lead to the Fan Pump Solenoid.