Can having a bad egr valve affect your mpg? Can having a plugged cat affect mpg? The reasons I'm asking these questions is that I'm getting about 20 mpg which I think is pathetic. My goal is like 23 mpg. I know my egr valve is bad, so if I replace that, get a new high-flow cat and a high flow cat-back, do you think I could gain 3-4 mpg?

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yellow 86 Camaro
LG4 700R4
ROH RH 17x9
Bridgestone Potenza RE730 255/45ZR17 all around
Pioneer head unit
Kenwood speakers
Infinity Beta Digital 300 amp
2 Infinity Perfect 12s

Now KYB equipped!!

 

Matthew,

A failing EGR can reduce you MPG by not providing detonation control, and forcing the ECM to retard the spark at cruising attitudes.

A plugged cat will restrict the exhaust and cause the engine to work harder to produce power. Some of the power of the engine is wasted in trying to pump the exhaust gasses through the restricted system.

Anything you can do to make the EGR functional will probably be worth the expense and trouble if you use your car for more than just stop-and-go city driving. The fuel you save will quickly offset the cost of repairs, and you stand to make more power as well.

The same goes for the exhaust system. No engine (well, except a Wankel or two-stroke) is designed to operate best with exhaust backpressure. Any automotive engine will provide the greatest power on the least fuel with a free flowing exhaust.

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Later,
Vader
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Justice and Freedom will Prevail

 

um wankels it is even more more of an issue with back pressure

if you see how the exhuast port on these cars work they create a very strong exhaust pule that if it gets blocked can cause a lot of chaos for the rest of the system

the only wankel I know of that needs backpressure is the 86-88 N/A and that is not due to the motor but the design of the second set of intake tacks, but in 89 they changed it from backpressure in the exhaust to having it work of the air pump so again less back pressure is better

 

20MPG with a LG4!???????????!!!! i got 13 MPG when i had my LG4...you are doing something right!!!! maybe my EGR is bad, but wouldnt that set off the check engine light??

 

20 mpg is pretty good for an LG4. My EGR hasn't worked as long as I've had the car and the computer has never thrown a code to let me know, I just found out a few weeks ago.

 

how do i check my EGR to see if its working?? shoot anything to gett better MPG!! i did pass emissions though

 

First of all, do you ever hear a clicking noise when your car is over 200 degrees, in 3rd gear, over 1400 rpm, and part throttle?

 

nope

 

Hmmmm... I got 24 mpg on the highway with my L69 when it was still a L69; more recently, with a Comp XM264HR cam, TES, some double-hump heads, and some 1.6 rockers, and otherwise utterly bone stock (EGR, AIR, EFE, etc. etc. etc., california emissions compliant) it went 544 miles (Cinci to South Bend RT) on 25.8 gallons... it drove from California to Ohio with about the same mpg... this is all of course with 3.73 gears and a 5-speed... seems like a LG4 shouldn't have too much trouble getting 20 mpg

 

damn my LG4 must be messed up then!! it was clean as a whitstle thugh,, no sludge in that thing at all. and now my 350 gets 13-15mpg with the stock ignition and EGR...the ignitoin is going by by this weekend though.

 

Then it's probably ok. If you really wanna find out, just plug the vacuum port on the carb and drive it around to see if it makes a difference. Or, you could run a test on it by putting it in park, holding it at 2500-3000 rpm, running a vacuum line from the carb straight to the valve, then connecting and disconnecting the line from the valve to see if the engine speed changes. If you're getting 13 mpg, you should probably check your oxygen sensor.

My current engine gets 21 mpg with my stock LG4 setup, I haven't run it only on the highway though. I think you could gain about 3-4 mpg from egr and exhaust.

 

the O2 is only around 3000 miles old

 

Then I dunno. Just check to make sure everything's working right.