Hi everyone. Forum newbie here with my first post and a request for help!

Lately, the engine in my car seems to be working harder to maintain speed than it used to. For example, it used to be I could cruise down the highway @ 55 MPH and the tach would be at ~1500 RPM. Now, the engine seems to be running ~1700 RPM to maintain the same speed. There has been a corresponding 10%-15% drop in fuel economy.

Car specs:
Convertible '90 RS+
Engine: 305 TBI L03
Transmission: TH700R4
Mileage: ~162K miles
Engine is completely stock.

I used one of the online calculators, plugged in the information about my car, and it verified the engine should only be turning 1450 RPM to maintain 55 MPH.

My first thought was that the torque converter wasn't locking up. However, I tapped the brakes while cruising, and the RPMs jumped up, indicating the torque converter is working.

Does anyone have any ideas what else I should check or have checked?

TIA
Kevin

 

well first things first, you have to make sure the engine is running good

tune up
o2 sensor
cat (may be clogging up)
compression check (162k)

thats about all I can tell ya, but I'm still a 19 year old, that works on cars on the side

 

Do the above mentioned.
A long shot could be an exhaust restriction, like the cat.
Also, these gauges in our cars suck, so maybe your tach is becoming less accurate, though I doubt it.

Either way, good luck and welcome aboard.

 

tune up time

 

maybe u should check ur tires.. tire pressure maybe too low

 

Thanks for responses guys!

I have checked the tires and had regular maintenance done, including 30K and 60K service schedules.

I don't think the cats or O2 sensor has ever been replaced and are original. As I understand it, O2 sensors should be replaced periodically anyway;
Chilton's says every 30K miles. I checked the service records and didn't see any mention of an oxygen sensor in the itemized parts lists of the records.

I'm going to take the car in to have the cats and compression checked and replace the O2 sensor.

 

Hey knp, I noticed you're from MD. On July 27th we're having a 3rd Gen get together at a car show. Check out the Mid-Atlantic board for my post https://www.thirdgen.org/techbb2/sho...662#post729662 and also the post Let's Set a Date for more info.

 

Hey, if it has a 700r4 with a lockup torque converter, how can the rpm change at the same speed in the same gear? It seems to me it doesn't matter how bad the engine runs, the same rpm at the crank is the same rpm at the trans. tailshaft unless there are problems in the transmission/torque converter (slippage???).
The only time I've seen rpm changes the tach was bad. I've seen 2 bad tachs so far. I was suspecting the lock up torque converter, the transmission (I have little faith in 700r4s) or that maybe it really wasn't a 373 rear after all. But it was the tach both times.

 

Yes make sure the converter is locking up. If it isnt, you will see an increase in RPMS and heat, and a Decrease in gas mileage and tranny life.

 

(I am not a mechanically inclined person. For example, until a few months ago, I didn't even know what a cam was or that there are different rear-end gear ratios. I have a coworker that has been very patiently explaining automobile fundamentals to me).

I checked the torque converter by driving the car down the highway at a steady speed and pressing the brakes gently. When I did that, the RPMs increased. I was told by the Chevy dealer this would indicate the torque converter was locking up.

Kevin


P.S. Mark- Sorry I couldn't make it on Saturday.

 

It's not until JULY 27th. Think you can make it?

 

DOH!! I just kind of skimmed the thread, and saw "Saturday", but didn't look at the date!!! July 27th is OK. Only thing that sucks is that it's about a 90-minute trip each way from Howard County.