1.8 4g37 excssive fuel consumption 12.5 mpg

[91-talon-tsi]

94 eclipse 5 speed with rebuilt 1.8 4g37 sohc. 37,000 miles on rebuild. Runs good, but have to keep the idle adjusted high at about 1500 rpm because if adjusted properly at 800 rpm = or - 100 rpm. It drops way down to 400 or 500 rpm when I turn on the a/c and headlights.

Ignition timing is set at 5* BTDC with all electrical components off and timing terminal grounded. Checked spark plugs and the tip are light grey/white.

The Idle air control doesn't seem to be working at all and the car is getting 12.5 mpg in the city with the a/c on. No cel or codes thrown. After driving for awhile, there's a smell of unburned or partially burned fuel (almost smells like old or rotten fuel for some reason)

The tail pipe has some black soot at the tip and it seems that the engine is running rich for some reason. Can a bad Idle air control valve cause the engine to run rich ? What else on this car besides a bad o2 sensor can cause the engine to run rich ? I have not checked the o2 sensor yet, but I just want to know if that's the only thing that can cause the engine to run rich or if it could be something else.

 

[1990AWD]

First things I would try are MAF or O2.

 

[91-talon-tsi]

Are there any simple tests to check the MAF and o2 sensors ? The thing that doesn't make sense is that the CEL isn't on. It comes on for a few seconds when you start the engine and then goes out like it's supposed to.

 

[DSM1G90]

AC on a 4G37 will kill MPG alone.
Motor is just too small for the size and weight of the chassis.
They should have taken the SOHC 4G63 to use for the NT vehicles and just did a DOHC turbo for the premier vehicles.

the 4G37, on a good day with AC off, will just barely get over 30mpg with a decent tailwind on the freeway. Otherwise, it's a 23 to 27mpg vehicle during the summer and plan on 21 to 25 during the winter.

Doing a lot of town driving?

Also, when AC is on, the idle HAS to ramp up to handle the drag from the compressor-which in fact, I bet it's ready to go out with being that old and they will produce major drag on the motor.

What's the MPG with AC off?

Bet, the o2 sensor is getting super tired and this will not throw a CEL...causing your A/F mixtures to be off. Did you do the timing with the ECU connector grounded? For I've seen timing with the dist cranked all the way advanced and it was pointing to the required marks.

For more 3G37 chatter, head to this link dedicated to the motor: www.dsm1eights.org
Good luck - DSM

 

[91-talon-tsi]

I haven't tested it with the a/c off because my windows don't work (previous owner attempted power conversion, long story...) and it's been extremely hot outside. The ecu connector was properly grounded when I adjusted the timing. When I bought the car about a month ago, I filled up the tank with 100% 87 octane fuel and drove 120 miles on the highway doing about 75 mph with the a/c on.

When I arrived at my destination, I topped off the tank and it took 3.9 gallons. So, it was getting about 30 mpg highway, but why would there be such a vast difference between highway and city driving ? 12.5 mpg city and 30 mpg highway.

EPA ratings online say the car should get 21 city, 24 combined and 29 highway. It's getting about 9 mpg less than what it should be getting in the city and as far as I know it may still be getting the 30 mpg highway that it did when I bought it. I haven't done much highway driving lately, so I'm not sure if it's still doing that good.

 

[DSM1G90]

EPA estimates are just that: estimates taken at a certain shift point, road speed, tire pressure .. and AC .. OFF .. and when the car rolled out of the factory all toasty and new .. It's all 'gray area' - nothing factual.

Never follow those estimates. My 1991 1.8l has lesser figures due to an automatic. I just barely get 21 in town and that's not even getting the tach above 2500 RPMs.

If you drive like "Grandma Moses", maybe, just maybe you can hit those numbers. Town driving slugs the MPG right where it hurts.


Get the o2 sensor replaced .. maybe that'll pick up the MPG's.

 

[Mischif]

My stock 1.8 gets well over 30 mpg combined. Even my turbo one can squeeze out 30mpg most the time. All standards tho.

 

[Arthris]

Oh come on ppl. Excessive, HIGHLY excessive fuel consumption is a dead give away. Maf will cause drivability issues and o2 will cause issues once warmed up. You have a bad engine coolant sensor. Its a two wire sensor on the thermostat housing below the thermostat. IDK if its setup like the 4g63 where there are three sensors. Once for the A/C once for the Instrument cluster and the one for the ECU. MAF will cause a CEL, o2 will not and CLT sensor will not aswell. Only way to see that is to get a logger and see what the ecu is seeing. But I willing to guarantee that it is the clt sensor.

 

[DSM1G90]

The AC compressor hogs about 15hp off the front end of the crank when engaged and a little 1.8L with stock 92hp, along with it can't breathe too well - that's a bit of work.