87 m20 with poor fuel mileage - 19mpg

[E30-Ellerman]

Sorry for posting another poor fuel mileage thread, I'm aware there are multiple threads about this topic but I haven't found one specific to my concerns.

So I have an 87 and I had the factory fuel cooler system with the lines going from the driver side, across the firewall and down to the a/c lines... I removed the a/c unit and all lines, then removed the fuel cooler lines and swapped the fuel line to go straight from the fuel tank to the FPR (I believe that's where it goes, it's connected right at the thermostat housing area). Wondering if this is causing me to have poor fuel mileage due tooooo? Maybe my system had increased fuel pressure to pump the fuel between the lines back to the fuel rail? I'm not sure. It never changed how the vehicle drove or idle'd so I assumed it didn't have any negative effects.

I don't have anything to go off as I hadn't driven the car prior to removing the lines. I have no cat, just a straight pipe to resonator and muffler so it smells very rich.

Wondering if the fuel cooler setup and me not doing anything else except for switching the fuel lines could be messing up my fuel mileage. Right now I get about 200 miles to 10 gallons of fuel.

Thanks!

[Kershaw]

How old is your o2 sensor? Spark plugs? AFM?

[E30-Ellerman]

o2 sensor I'm not sure of, will replace that. Spark plugs are brand new, haven't checked the AFM yet. I've only gone through a couple tanks of gas so just starting out with going through it.

Mainly concerned I messed something up or needed to do something else when removing the fuel cooler lines - was only done on the e30's for like 6-8 months I believe so I'd imagine there isn't many people with knowledge of the system.

[goldenbb]

If I believe my car's computer, which I don't, mine says 19.2mpg but it's pretty much all in-town driving. I have new plugs, new wires, brand new O2 sensor, and much more. I have not dicked around with the AFM, though. I don't think the baby six is particularly good on gas in today's sense.

https://www.fueleconomy.gov/feg/bymake/BMW1990.shtml

[Cephas]

Mixed city/highway mine shows about 21 to 22. The couple times I tracked this car I would reset the mpg setting. I think I got 7 or 8 mpg.

[E30-Ellerman]

Hmm ok. I've read people getting mid to high 20's... First couple tanks were more city than I normally drive and I was driving it fairly hard and highway trips was also fairly hard. Know I need to clean my air filter so I'll do that, replace the o2 sensor and throw some seafoam in the tank and see if that helps... Already seafoamed the engine through the intake.

Thanks for the feedback and responses!

[turbo55]

How is the coolant temp sensor? If the ECU thinks the engine is cold, it will run a richer air/fuel mixture. Also, if you have an exhaust leak, the o2 sensor will be sensing a leaner than actual a/f mixture and also causing the ECU to run rich.

[Kershaw]

Around town 18-19mpg is accurate, with highway driving a 325i should get 25mpg.

A 325e or 318i will get high 20s, I got 29-30mpg all the time in my 325es. In my 325ix, I would get 21-22mpg with 95% highway driving.

And lol @ tracking. 7-8mpg is pretty good on the track.

[packratbimmer]

Yes - if doing a lot of hard and/or city driving, 19 mpg is about right. I have gotten as high as 29 mpg on a coast to coast seven week trip. Have never broken the 30 mpg mark with a 325i.

[dnguyen1963]

For me...winter time 20 - 22 mpg city. Summer time @ 24 mpg city and 29 - 30 mpg highway with the top down.

[E30-Ellerman]

Going to replace the coolant temp sensor as well... Temperature gauge stays just left of the middle mark more towards the 1/4 mark normally... Fluctuates a bit, never gets to the middle though.

I have a 325es (2.93lsd) with the m20b25 swapped in.

[BMWManiac]

For me...winter time 20 - 22 mpg city. Summer time @ 24 mpg city and 29 - 30 mpg highway with the top down.

You get 29-30 mpg with the m20 in an e30? Sorry, but I don't believe you. That is 430 miles on a single tank of gas.

[dnguyen1963]

You get 29-30 mpg with the m20 in an e30? Sorry, but I don't believe you. That is 430 miles on a single tank of gas.

Yep. It's okay if you don't believe. There are other members that can achieve that kind of gas mileage here. You can hyper-mile in almost any engine. We are not talking about revving to the limiter on the highway here. I did not believe other members achieving that kind of number until I tried it myself. Go out on the highway and set the cruise control at 70 mph and see what you can get.

[itsonlygeorge]

I've done 33 mpg from Ohio to SC in my 325e... through the mountains...

[estoguy]

You get 29-30 mpg with the m20 in an e30? Sorry, but I don't believe you. That is 430 miles on a single tank of gas.

True Story, bro. My 3.5 year average for fuel economy in my Eta is 7.8L/100 km (that's 30.15 MPG US, 36.21 UK). 430 miles out of a tank is entirely possible.