Major MPG Difference - Looking for some thoughts on this...

I recently retired a '01 SC2 - It had the SOHC and a 5 speed manual. I purchased it years ago with about 85K miles. I would consistently get 40 MPG out of this car. I did run non-ethanol premium in it. I did have two fill ups in a row that I got 44.1 MPG.

Well, I recently gave this car to a friend in need and it just turned over 338K miles. I was still getting 36-37 MPG running plain ol' 10% ethanol 87 octane (I live in Oregon and travel between two cities over a mountain pass. I live at 2600', the mountain passes are 5100' and 4200' and the city on the other end is about 500'.) The 44.1 MPG was going over the 5200' pass.

So I replaced my old '01 SC2 with an '01 SC2 that has 170K on the vehicle and about 30K on a rebuilt DOHC. It also has the 5 speed manual. The thing is, I am only getting 25-27 MPG going over the same two passes.

The car seems to run fine, it does crank a little longer than I feel it should before starting, like for 4-6 seconds. No missing, no sputtering when going up hills. It does lose a little speed going up the hills, but that's understandable. I have not really started looking at the engine, like fuel and air filters, plugs and wires, etc... I have an ICON T7 tablet I plan to plug in and see if shows anything, as well. I'm Just looking for some thoughts on this and what other things besides the obvious maintenance items listed above.

Also, there may be a bit of a loss of power. My old SOHC model I would cruise along at 80 MPH no problem. The new to me car, it seems like it struggles to maintain 80 MPH in the same places.

Thanks in advance.
Ken

 

For comparison, i has a 97 and still have a 95 SC2, 277K and 244K that get 35 on flat highway since i drove both off the lot.

The SC2 is geared differently (different tranny) and feels different in the seat. Hills are not its forte. Go take a drive in WV and you'll see. It is because of where the shift points and rpms are, hence the power bands.

Run a wet and dry compression test to see what you're working with. 30K on a property rebuilt dohc should be 205+ each cylinder.

Assuming no issues there

If you just obtained the vehicle:
OEM plugs NGK 5643 (check part #)
New air filter
New wires if over the resistance limit
Clean throttle body
New fuel filter
Techron in the tank
New fluids all around.
For the low cost, I'd do pads and rotors all around, paying attention to the as found condition of the caliper slide pins. You may have a caliper not retracting all the way.
Check for bearing play
Replace the rear sway bar end links (moogs have grease fittings)

As for seemingly lower than expected mileage

1) Make sure the ects sead something reasonable versus ambient temperature and when running. If not, replace ECTS with brass unit, not AutoZone not advanced auto not O'Reilly's. Get a Delphi and replace the pigtail. The temperature reading that is inferred from this sensor has a huge effect on fuel to air mixture. In fact, it may be part of the reason for the extended crank at startup if it is significantly different reading at ambient temperature.

2) Replace the front oxygen sensor with the denso equivalent of the OEM which is a denso labeled ACDelco. No Bosch. This is the other main contributor to the determination of the air fuel mix. They get poisoned about every 125K and then kill your mileage.

3) Check fuel pressure. If too high, you may be going through fuel too quickly and running too rich a mixture, which again might be affecting startup. Also watch for bleed off of the fuel pressure with key on but engine off. It should stay constant.

4) catalytic converter/resonator/muffler maybe partially clogged.

Where does the temperature gauge read when driving 65 on a flat road? Or just in general what it warms up?

Usually a clogged cat presents with no power going uphill and a higher operating temperature. You can pull off the front O2 sensor and hook up a back pressure gauge to see if there is significant back pressure. Even the resonator and muffler can clog with material from the cat as it breaks up and gets pushed backward in the exhaust flow.

So that is a reasonable summary of what I would look at, what I would do, and how. The front O2 The ECTS and connector, and the stock spark plugs gaps at 040 should have the biggest bang for the buck in terms of performance improvement / recoupment.

 

Derf, thanks for the info. I saw a couple other posts on the ECT and pigtail -- I was going to explore that tomorrow on the next day. I still need to plug in my Icon T7 and see what it shows me. I've been forced to start wrenching on my vehicles again. My mechanic retired and I wouldn't trust the other mechanics in this small town with servicing a Matchbox car.

The temperature hangs out just below the half mark on the dash gauge. It doesn't seem like it's running hot. I still have plenty of power going up hills, the little 1.9l just doesn't like it. My previous '01 was the same way with hills.

I will order a few of these parts and be ready.

Thanks again, and will update as I go though this process.