Will replacing these sensors help with fuel mileage?

[leviathan4444]

Hi,

I've been reading on this forum for a bit, but this is my 1st posting. I've found it rather helpful, and I just wanted to start by saying thanks to all those who post here.
Here's my question. I have an old 89 SHO, and am on rather limited budget. I'd like to get the best gas mileage I can out of it within a reasonable expenditure. My question is, will replacing the O2 sensors, and the ECT sensor be helpful in getting better mileage? I have to replace the ACT sensor because its throwing a code, and I've cleaned my MAF sensor already just for good measure. I'm also considering replacing the knock sensor if you guys think its a good idea.
Also what sensors are really important for good gas mileage and performance?
Just a side note, I've considered new spark plug wires, and plugs, but the plugs in there now aren't that old, they were changed at the last 60k tune up, and I currently don't have time to pull the intake off to do the wires. I'll do it eventually, but just not immediately.
I'd appreciate any thoughts you all have.
Thanks,
Curt

 

[hawkeye18]

Short answer: Yes!

You should change the ECT every time you're in there... it's so cheap it'd be kinda lame not to. The ACT and ECT are both very important in determining proper fuel strategy (read: fuel economy). Also, you should change the 1-wire sensor that feeds the idiot gage in the dash. Why? I mean, dang dude, it's right there! Make sure you get a 1" deep-well to get at the ECT. Don't forget the teflon tape!

The knock sensor is a PITA to get to, and is a very, very simple sensor and it very rarely fails... so I wouldn't recommend bothering unless it's bad.

Sounds like you got your head on pretty tight for a n00b!

Oh yeah, if you don't know when the last time the 02s were replaced, replace them.

Protip: Don't place heavy loads on the engine below ~1500 rpm. That'll cause the rod bearings to go SCREEEEEEEEEEEE against the crank. Which is Bad.

 

[leviathan4444]

Thanks for the info, and reply

Thanks for the info and replying. I'll plan on replacing both the ACT, and the ECT, as well as the O2s. Since the knock sensor is not throwing a code, I'll just leave the exisiting one there.

As for heavy loads on the rod bearings, thanks for the tip. I'll try and avoid that. In the past I have run the car at low revs in high gear (<1500 RPM), but I don't usually mash the gas in high gear. I will use a little throttle to part throttle in high gear at low speeds. Is a bit of throttle, in 5th at around 30MPH too much for the bearings?

 

[hawkeye18]

uh... you shouldn't really be applying any throttle under 1200 RPMs. Certainly not in 5th. At lower RPMs, the oil pump is incapable of supplying enough oil to the rod bearings, which starves them and makes them spin.

I would say to desperately avoid applying more than 15-20% torque below 1500RPM. It takes a very, very large amount of gas saved to offset the cost of a new engine...

 

[1993MTXSHO]

I dont apply a load under 2k I usually run my car between 2k and 2500, i mean it turns 2500-3k rpm on the highway so I think it should run that at lower speeds too. Also if you're tryign to get better gas mileage, low rpm doesn't = good mileage. You loading the engien more most likely, and down shifting would actually be better as the engien spins more free and easy.

 

[leviathan4444]

Thanks for the pointers. I'll be avoiding that in future driving. I really wasn't aware that low RPM driving was an issue with the rod bearings. Hopefully I haven't damaged them.

 

[itwonder]

Another mileage killer is exhaust restrictions from an old system that is all rusted up on the inside. One simple check is to see if the mufflers sound like there is loose stuff inside when you shake them. The cats deteriorate and go bad too.

 

[SASHO91]

I wouldn't worry about the ACT sensor.... They rarely fail, and really aren't that important(not in the big three).

The top sensors that affect performance(i.e motor's abilty to make power more easily) are: MAF,O2's, ECT, TPS, and BARO/MAP.