Another poor mpg thread. (1 Viewer)

[LS1FJ40]

I know. Beat the dead horse.

Just want to make sure I'm not missing anything obvious.

My 93 smells like unburned fuel. I suspect the charcoal canister but also am wondering what else it could be that might be negatively impacting fuel economy.

I'm getting 11ish on the highway. 9-10 in town.

New plugs, new wires, new cap, new rotor.

She seems sluggish still. Like slower than my 3FE sluggish. I know she's a tired 325k mile truck but she still seems lacking.

She's always been like this. I thought new plugs and such might help. No dice.

Timing? Any sensors?

Only code I get is for the EGR which I have deleted and need to jump. Symptoms existed prior.

1993, 325k, 285 BFG ATKO2s, sliders, fridge, no second or third row.

Thanks

 

[jonheld]

Clogged air filter?

 

[suadero]

Injectors?

 

[Douglas S]

Test compression if you are worried about a tired high-mileage engine.

 

[bloc]

Clogged exhaust? Tire pressure?

I don't automatically buy that a 325k mile engine is wearing out, though you don't know the full history of yours.
I have 290k on mine and consistently hit 14.5-15mpg on the freeway at 70.. 40psi in my 315s, stock gears, and part-time kit. As far as I can tell it was maintained well for the first 150, the second? not so much.

 

[Seth_O]

I've done a pretty extensive overhaul of maintenance items on my '93 (including cleaning the injectors, air filter, plugs, etc) and am UP to ~12mpg mixed driving (started at ~11mpg before all the maintenance work). And I have a LIGHT foot on the pedal. No extra weight, no towing, no crazy burn-outs.

I figure mileage is the trade-off for not having to deal with OBDII

296k & 33" BFG KM2's @ 35 psi.

 

[gandrimp]

I have a "93" ,285 BFG ko2's,35 psi, stock gears 180,000 miles. We just did nearly 5000 miles loaded what I would call heavy, built rear bumper spare hanging behind with jack and 5 gal water jug. 50, yes fifty gallon of fuel when full (that doesn't take long to change). NO rear seats but had storage on 2 levels, 2 coolers, 4 plano 1819 size and 3 cheap walmart style totes. We had 2 bikes with a DIY swing out bike rack. I run the 2.5 inch OME lift and lets say I had no stinkbug effect. 2 adults if you count me. Nothing on top, stock front bumper.

I like to drive 55-65 mph, we were going much faster. I once saw 89 by the gps. A lot of 70 - 80 mph. When we got west of Denver I was pretty proud of the LC, in the mountain's I actually passed a loaded semi and a huge older motorhome. For a while (seemed like a full day) we were in cross winds where the steering wheel was probably close to 20 degrees to the right to go straight while traveling 60 plus (white knuckle).

All this to say 11.5 average, never saw 12 mpg. I know it would have been better at my normal speed, but 13 is about all I can get around here.

 

[LS1FJ40]

Clogged air filter?

This is on my list. The PO replaced it at some point with a WIX air filter. It doesn't appear clogged but that doesn't mean a whole lot.

Injectors?

That is kind of where I was leaning but when I pulled the old plugs I couldn't really tell. They were horrible. Didn't appear to be leaned out or burnt out. But they appeared to be OLD. I'm sure it wouldn't hurt any to pull them and have them serviced or whatever it is they do when you send them off.

Test compression if you are worried about a tired high-mileage engine.

Tested compression after I got it home in March and was within spec.

Clogged exhaust? Tire pressure?

Tire pressure might be a possibility. I'm taking it on Saturday to pick up my spare to match and have them rotated.

I don't automatically buy that a 325k mile engine is wearing out, though you don't know the full history of yours.
I have 290k on mine and consistently hit 14.5-15mpg on the freeway at 70.. 40psi in my 315s, stock gears, and part-time kit. As far as I can tell it was maintained well for the first 150, the second? not so much.

Mine sounds strong as hell. Purrs like a kitten. Nothing bad sounding about her. She just seems a little bit sluggish.

 

[LS1FJ40]

I've done a pretty extensive overhaul of maintenance items on my '93 (including cleaning the injectors, air filter, plugs, etc) and am UP to ~12mpg mixed driving (started at ~11mpg before all the maintenance work). And I have a LIGHT foot on the pedal. No extra weight, no towing, no crazy burn-outs.

I figure mileage is the trade-off for not having to deal with OBDII

296k & 33" BFG KM2's @ 35 psi.

I have a very light foot. I'm used to driving my 3FE. Maybe I'm not far off. The smell of fuel is bugging me a bit though. But that could be the charcoal canister...

I swear I smell unburned fuel at the tailpipe though.

I have a "93" ,285 BFG ko2's,35 psi, stock gears 180,000 miles. We just did nearly 5000 miles loaded what I would call heavy, built rear bumper spare hanging behind with jack and 5 gal water jug. 50, yes fifty gallon of fuel when full (that doesn't take long to change). NO rear seats but had storage on 2 levels, 2 coolers, 4 plano 1819 size and 3 cheap walmart style totes. We had 2 bikes with a DIY swing out bike rack. I run the 2.5 inch OME lift and lets say I had no stinkbug effect. 2 adults if you count me. Nothing on top, stock front bumper.

I like to drive 55-65 mph, we were going much faster. I once saw 89 by the gps. A lot of 70 - 80 mph. When we got west of Denver I was pretty proud of the LC, in the mountain's I actually passed a loaded semi and a huge older motorhome. For a while (seemed like a full day) we were in cross winds where the steering wheel was probably close to 20 degrees to the right to go straight while traveling 60 plus (white knuckle).

All this to say 11.5 average, never saw 12 mpg. I know it would have been better at my normal speed, but 13 is about all I can get around here.

My son and I are taking a 4500-5000 mile trip in December. That is part of my motivation on this. If I was pulling 12.5mpg I wouldn't even be thinking about it. Crazy how 1.5 mpg makes me worry!

 

[SUMMIT CRUISERS]

Original Cats restricting exhaust flow? Just a thought.

 

[Timpanogos Slim]

Make sure that all of the sensors and their associated harnesses are in good shape.

There was a recall for 93/94 o2 sensors so you should check with the dealer - you might be able to get new o2 sensors installed for nothing. And that's a good thing because they are a royal pain in the ass to remove. And unusually expensive because the 93/94 sensors are different and the only trusted parts are denso and toyota - which are denso.

The EGR delete may actually be a factor. The code may be causing the ecu to retard dynamic timing.

How heavy is your right foot? My mpg sucks, but i suspect it is because i try to drive it like it were a vehicle with a much better power to weight ratio.

I also don't find it to be sluggish. I drive it like i stole it, and it doesn't have the same get up and go as my GTI, but i have no difficulty merging onto a freeway, overtaking more powerful vehicles, etc, and it feels great cruising at 80+mph, with bursts over 90. I've been a bad boy.

But basically the problem with early efi systems is that they are just smart enough to protect the engine from knocking itself to death but not smart enough to keep you informed about what it is doing.

And they err on the side of caution. By retarding the timing.

There's a procedure in the FSM for checking and adjusting the static timing (it's more than you think - you have to tell the ecu that you are setting the timing), and you should probably go through it, but without a happy ECU your dynamic timing will be retarded regardless, and that will murder performance.

The best mpg i ever got was Orem to St. George pulling an empty dolly - 14.5mpg. St. George with a 1984 jetta coupe on the dolly i got 13.5mpg.

Flogging it like a rented mule from Orem to SLC and back i get like 11. Sometimes as little as 9. But performance is much better than it was when i bought it, with bad o2 sensors, damaged o2 sensor harness, and a broken knock sensor.

 

[scottryana]

How long are your trips and does the truck get up to operating temp? On the later trucks they run very rich until they get up to 160 degrees or so, then they lean out. I don't know about the 93's but if you're making a lot of shorter trips even if you get on the hwy I would imagine Toyota still ran them rich when cold.

I know. Beat the dead horse.

Just want to make sure I'm not missing anything obvious.

My 93 smells like unburned fuel. I suspect the charcoal canister but also am wondering what else it could be that might be negatively impacting fuel economy.

I'm getting 11ish on the highway. 9-10 in town.

New plugs, new wires, new cap, new rotor.

She seems sluggish still. Like slower than my 3FE sluggish. I know she's a tired 325k mile truck but she still seems lacking.

She's always been like this. I thought new plugs and such might help. No dice.

Timing? Any sensors?

Only code I get is for the EGR which I have deleted and need to jump. Symptoms existed prior.

1993, 325k, 285 BFG ATKO2s, sliders, fridge, no second or third row.

Thanks

 

[Rivman1243]

How long are your trips and does the truck get up to operating temp? On the later trucks they run very rich until they get up to 160 degrees or so, then they lean out. I don't know about the 93's but if you're making a lot of shorter trips even if you get on the hwy I would imagine Toyota still ran them rich when cold.

Interesting

 

[retrofive]

I agree with the EGR delete AND throwing the code it could be running in "limp" mode which will kill your MPG. Ive seen mine in both states and gone from 8-9mpg back to 13-14mpg. With that said right now Im aruond 10-11 More work to be done.... but not expecting much.

 

[cc93cruiser]

If you deleted the smog crap on engine, Yank those Cats out, it will wake up the 1fz..

 

[bloc]

There was a recall for 93/94 o2 sensors so you should check with the dealer - you might be able to get new o2 sensors installed for nothing. And that's a good thing because they are a royal pain in the ass to remove. And unusually expensive because the 93/94 sensors are different and the only trusted parts are denso and toyota - which are denso.

The EGR delete may actually be a factor. The code may be causing the ecu to retard dynamic timing.

I thought OE supplier for the early trucks was NTK/NGK? Could be wrong. That's what I'm running on mine and they seem perfect.

Also, my EGR has the resistor installed.. if anything it runs a bit lean.. based on very slight rattle at throttle tip-in if the engine is hot, hot ambient temps, and anything but premium fuel. Probably have a LOT of carbon in the CC though in my case.

 

[Dragos80]

On a different car I have a EGR delete. I monitor the engine parameters with torque. When the engine is cold, it dumps a lot of fuel to make the engine run hot until it reaches the optimal operating temperature, then the EGT goes down and the EGR starts to "work". It stays closed (at 0%) until the engine warms up to about 165F.
If you run short trips the EGR will do this, even if the engine is relatively warm, for a minute or two. So driving in the city for short intervals will kill your MPG fast.

I am not saying this is your problem, just telling you how the EGR may affect performance. It could be part of your problem.

 

[Timpanogos Slim]

On a different car I have a EGR delete. I monitor the engine parameters with torque. When the engine is cold, it dumps a lot of fuel to make the engine run hot until it reaches the optimal operating temperature, then the EGT goes down and the EGR starts to "work". It stays closed (at 0%) until the engine warms up to about 165F.
If you run short trips the EGR will do this, even if the engine is relatively warm, for a minute or two. So driving in the city for short intervals will kill your MPG fast.

I am not saying this is your problem, just telling you how the EGR may affect performance. It could be part of your problem.

Well it's normal for a gas engine to run rich when the engine is cold.

The engine coolant temperature sensor is a heavily influential signal in electronic fuel injection. And in early EFI systems, the computer can behave in thoroughly stupid ways when the temperature signal is bad. Up to and including 90's saturn/opel engines that try to empty the gas tank into the cylinder as fast as possible when your sensor is bad. Like it's trying to hydrolock your cylinders with gasoline. Requiring an immediate oil change once you fix it. Not exaggerating.

Putting a jumper in the egr temperature sensor connector didn't do diddly on my '94 and i decided i'd rather just have a working EGR system since i live in a county where i have to pass emissions inspection + sniffer test.

 

[LS1FJ40]

It was sluggish prior to the EGR Delete. Haven't noticed any discernible difference after the delete.

When I deleted the EGR on my 92 3FE I immediately noticed a difference in the seat of the pants.

I am assuming he O2 sensors are original. Exhaust is all original. I will call the dealer tomorrow to find out about the O2 sensors. And run it by my muffler shop to have them back flow test (or whatever it is they do) the cats. They did this on my 92 when I replaced the O2 sensors. I picked up my O2 sensors from a company that @jonheld recommended. Not sure if they carry the sensors for the 93-94 model. Jon what was the name of that company?

 

[Timpanogos Slim]

I thought OE supplier for the early trucks was NTK/NGK? Could be wrong. That's what I'm running on mine and they seem perfect.

Also, my EGR has the resistor installed.. if anything it runs a bit lean.. based on very slight rattle at throttle tip-in if the engine is hot, hot ambient temps, and anything but premium fuel. Probably have a LOT of carbon in the CC though in my case.

It was Denso. NGK/NTK might be ok but there are limited reports, and the 93/94 sensors are different from the 3fe sensors or the obd2 sensors. And different from 'universal' replacement parts. The denso kit is more than $200 which is madness considering they are narrow-band.