Chief_MC

My car is behavin' very strange... I noticed that it is far more powerfull when it is cold than when it's warmed up! And also i have a pretty bad gas mileage...

What could be wrong with it?

Thanks in advance!

Icemark

what do you consider "bad" for gas mileage. The RX-7 has never gotten much better than 15-20 MPG in average driving.

Chief_MC

bad i mean like 18-20 liters per 100 km... i think it is something like 12 MPG...

Icemark

yeah that is actually pretty close to 10 MPG.

Even if you drive with your foot on the gas all the time you should be getting better than that.

Most of the time bad gas mileage can be fixed with a tune up. Replacing all the filters, the spark plugs, spark plug cables, and fluids such as oil, gear/tranny oil, rear end oil and of course coolant.

When was the last time that was done? And is this a North American spec or Euro spec car?

Chief_MC

You know i don't care if my car eats 18 liters per 100 km and rocks, but... if it is crawls i don't think that is pretty normal... Yesrturday i've been beaten by 1.8 Mitsubishi Charisma... I've been really ashamed :-((((

Chief_MC

I've changed all things you've mentioned except coolant and even changed the O2 sensor... Also i did cleaned my injectors, but my gas mileage stayed the same.

It is an American spec car.

Maybe there is an air leak in the air funnel or somewhere in the intake manifold gasket?

Chief_MC

The most strange thing afterall is that when it is cold it rocks! But as soon as it climbs up to it's normal operating temp it starts to be a turtle...

Maybe it has some leak in the intake system which is sucking air from the engine bay and when the engine is cold it sucks cold air, but after warm up it starts to suck a hot air and intake air temp sensor starts to sens it and advances spark to post position, or how do you call it...

The other guess i've been told by a mechanic, he told me that it is possible that engine temp sensor (not coolant temp sensor) is bad and ECU continues to think that engine is cold all the time making it run more rich... It can explain the gas mileage, but hardly it can explain why my car crawling when it's warm...

Icemark

then the next steps I would be looking at (in order)

1. Stuck/ Dirty injectors

2. Something wrong with the emissions system (sensors not reading right or damaged, or stuck open EGR)

3. Poor compression

Its easy to see the air temp sensor on the 88 its on the back side of dynamic chamber. You could try unplugging it and sticking in a 2.7K resister between the two wires and see if that makes a difference

Chief_MC

1. Injectors were checked and cleaned... and are ok.

2. That probably could be the cause but i can't find any good resource on that... I'm thinking about removing emissions complitely... Will it hit my MPG?

3. I didn't checked it yet... But if i have a poor compression how you will explain it's cold behavior?

Icemark

No, the low compression won't make any difference when cold

Chief_MC

I already been thinkin' about replacing intake temp sensor with a resistor, but after you suggested me to do that i will definatly try if it makes any difference...

Chief_MC

I'd like to thank you Icemark, for quick and helpful reply!

Do you have any resource about emissions? How to check everything and maybe remove them?

Icemark

Just the shop manuals cover how to test everything.

Remember putting in that resister in place of the air temp sensor will resultin the RPM jumping up about 500 (which will of course lower your gas mileage even further), so it should only be done as a test.

hitmang11

the colder the air the more dense the air is so more can be packed into the combustion chamber, hense cold air intakes. but if your suckin air from the engine bay that isnt a true cold air system, i notice that my car runs better when its cold too, and it seems to pull harder in the winter then in the hot summer, im sure others notice that too, once again the colder and more dense the air the more can fill the chamber. might wana think about running the intake to sumwhere other than the engine bay, if there is a real real big diffrence in the cold verse the warm there might be sumthing else wrong tho