bad gas mileage

T77911S · 09-20-2016, 03:54 AM

i am getting very bad gas mileage in my bmw 88 325is. down in the teens.

do you think injectors could cause bad gas mileage?

checked engine temp sensor, O2 sensor, cap rotor, plugs.

ckelly78z · 09-20-2016, 04:05 AM

Take it to an autoparts store and have it scanned for codes. Most likely a vacumn/air leak. Some free (no cost) things to do is to check your plug gap, and clean your cap/rotor on the end of the rotor, and inside the cap at the end of each wire (sometimes a crusty buildup is present that can be scraped off). If it's been awhile for a tuneup, it wouldn't hurt to mount a new fuel filter, and run a fuel injector cleaner through the tank. Replace the air filter, and check your PCV valve while at it.....of course change the oil if due.

I replaced the plugs on my 2004 Mustang GT a few weeks back, and the gap had widened out to .080" when stock is .054". It runs a whole lot better now, especially after the fuel system cleaner and fuel filter. I question myself whether this stuff had ever been changed by the P.O. in 150,000 miles !

T77911S · 09-20-2016, 04:34 AM

new cap and rotor.
ne wplugs
valve adjustment
timing belt

its always been hard to start since I have had it and I have suspected injectors or fuel pressure reg.

I did run injector cleaner thru it yrs ago when I got it and it made it run better. I suspected leaky injectors so I pulled them several yrs ago and checked them but none were leaking then.

sometimes when I start it I smell fuel like it is dumping too much, part of why I suspected injectors/fuel pressure.

speeder · 09-20-2016, 06:02 AM

It sounds more like you have a fuel leak, if you are smelling gas. I'd say that there is zero chance that you have 6 dirty injectors, though one bad injector that is dumping fuel could cause bad mileage but not without other running symptoms.

I'd start with making sure that all temp sensors are working and that your car is not running on its cold circuit all the time.

asphaltgambler · 09-20-2016, 06:33 AM

Uh.........sorry you're not taking an '88 BMW to somebody to scan for OBDII information.........
...

T77911S · 09-20-2016, 10:50 AM

it only smells when I start it.

it probably has 250k+ miles on it

Robert Adams · Robert Adams's Garage

All the above could be the issue, but I found that the plug gap was critical to the 944S2 getting good mpgs. Although they are "supposed' to be set at the factory, I no longer count on it. By the time the gorillas in shipping get done, its wonder they work at all. Out of spec one way or the other and my mileage dropped like 20% to 30%. Might be worth a shot; won't cost anything but your time check.

1990C4S · 09-20-2016, 01:14 PM

I would have the exhaust analyzed. If your mileage is bad it is likely running way too rich.

I doubt the injectors are the issue. Does it have a MAF?

fastfredracing · 09-20-2016, 02:05 PM

cold start injector sticking open/leaking fuel ?

Joe Bob · Joe Bob's Garage

Try a bottle of Techron. If MPG still sucks consider having the injectors pro cleaned.

masraum · 09-20-2016, 04:05 PM

Quote:

Originally Posted by Robert Adams

All the above could be the issue, but I found that the plug gap was critical to the 944S2 getting good mpgs. Although they are "supposed' to be set at the factory, I no longer count on it. By the time the gorillas in shipping get done, its wonder they work at all. Out of spec one way or the other and my mileage dropped like 20% to 30%. Might be worth a shot; won't cost anything but your time check.

Not to mention, not every car that takes a particular car is going to need the same plug gap.

masraum · 09-20-2016, 04:06 PM

Quote:

Originally Posted by ckelly78z

Take it to an autoparts store and have it scanned for codes. Most likely a vacumn/air leak. Some free (no cost) things to do is to check your plug gap, and clean your cap/rotor on the end of the rotor, and inside the cap at the end of each wire (sometimes a crusty buildup is present that can be scraped off). If it's been awhile for a tuneup, it wouldn't hurt to mount a new fuel filter, and run a fuel injector cleaner through the tank. Replace the air filter, and check your PCV valve while at it.....of course change the oil if due.

As someone else stated, it's an '88, so no OBDII. Besides, if it had codes, then there would be a check engine light. That wasn't mentioned.

masraum · 09-20-2016, 04:07 PM

Quote:

Originally Posted by T77911S

i am getting very bad gas mileage in my bmw 88 325is. down in the teens.

do you think injectors could cause bad gas mileage?

checked engine temp sensor, O2 sensor, cap rotor, plugs.

Always best to start with a very thorough tune up on the fuel and ignition side.

speeder · 09-20-2016, 04:51 PM

Quote:

Originally Posted by speeder

I'd start with making sure that all temp sensors are working and that your car is not running on its cold circuit all the time.

Quote:

Originally Posted by fastfredracing

cold start injector sticking open/leaking fuel ?

Start here.

Por_sha911 · Por_sha911's Garage

A bottle of Techron is not going to do squat if you have a problem that is killing MPG that badly.

Is the car down on power?
Have you checked the air filter?
Do you have a dragging brake caliper in the rear?
If automatic is the trans shifting properly?

John Rogers · 09-20-2016, 06:12 PM

See if there is a dyno shop near by and if so have them do a run on it. They will measure plug voltage, each exhaust outlet temp, how the injectors are firing or ALL those things you can not do by poking and prodding!

As Wayne Baker ( famous racer) sez.......an hour on the dyno is worth 4 at the track!

fanaudical · fanaudical's Garage

Verify no vacuum leaks (check everything - brake booster too).
Verify ignition operating well and timing correct.
Cold start injector stuck open or other fuel leak is a good possibility.
Still have the catalytic converter? Is it flowing freely?

john70t · 09:18 AM

https://en.wikipedia.org/wiki/BMW_3_Series_%28E30%29 identifies it as a https://en.wikipedia.org/wiki/Motronic fuel system.

So it uses a MassAirFlow/MAF wire (instead of the ManifoldAbsolutePressure/MAP in the L-Jet)
These can get dirty. I've heard they need special cleaning spray instead of carb cleaner.

Looks like it might have a knock sensor (affects timing) and probably a O2/lambda (long term fuel trim).

I'd start with external fuel leaks and check timing first.
Is there strong gas smell at the tailpipe or at the engine with startup?

An infrared thermometer will show if the cat is clogged after a drive.There should be strong pulses from the tailpipe.
-Or dragging brakes.
-Or cylinders still cold.

1990C4S · 09-21-2016, 09:11 AM

Also, check the O2 sensor signal. If the wiring is bad the car can run super-rich....

Por_sha911 · Por_sha911's Garage

"it probably has 250k+ miles on it"
Have you done a leakdown? What gas mileage were you getting before the problem?
Clogged catalytic Converter would usually also have overheating. The converter and other problems would also have it being down on power.