Poor fuel economy help!

dasfps · 12-23-2004, 02:10 PM

I have a 98 318is M44 and suddenly the fuel economy has shot from 400 miles to 250 miles to one full tank of fuel.

I have checked the DME with a peake code reader and their are no faults stored.

I have changed the lambda sensor and camshaft position sensor but still fuel economy is poor.

The inside of the exhaust is coked where as it used to be clean.

I have also changed the fuel pressure regulator.

Any suggestions would be helpful??

blkongry · 12-23-2004, 02:16 PM

Sounds like you lost an Oxygen sensor. If you do, usually they won't trip the computer, but will cause the engine to run rich, making a bunch of soot and causing your gas mileage to plummet. Has the engine lost power?

dasfps · 12-23-2004, 02:20 PM

Quote:

Originally posted by blkongry
Sounds like you lost an Oxygen sensor. If you do, usually they won't trip the computer, but will cause the engine to run rich, making a bunch of soot and causing your gas mileage to plummet. Has the engine lost power?

Yeah I have changed the lambda/oxygen sensor but still no joy.

The engine has lost a little power.

blkongry · 12-23-2004, 02:42 PM

A lambda is an O2 sensor, eh? Hmm... and you say you replaced it. Hmm... well the combination of carbon forming in the exhaust, poor fuel economy, and loss of power is a sign of the engine running rich. That can come from a clogged air intake, bad O2 sensor, or bad DME?? Hmm, I'll have to think on that. Curious to see other's input.

dasfps · 12-23-2004, 02:57 PM

Looking at those options.
How do I know if it is a bad dme. Would the DME not give out a code?

blkongry · 12-23-2004, 04:40 PM

Good question. I would think the dealer would have some sort of diagnostic equipment they can tap into the DME with. If the DME goes 'bad', well, the DME is what looks for out of sync sensor to say if it's bad or not... if the DME is bad, what's to say it has gone bad?

tom busby · 12-23-2004, 07:19 PM

If you have no codes showing, you probably have a bad plug wire or plug wire connection. Check your plug wire to plug connections, and plug wire to coil connections. You might have a bad plug but this is unlikely. You don't get a code for plug wire faults.

blkongry · 09:53 PM

Yeah, but it's an I4... it would just run all choppy and like crap if he lost a plug wire or connection; not to mention that wouldn't cause carbon/soot build up because of running rich. At the most, he may get raw fuel coming down the exhaust and get a backfire.

dasfps · 12-24-2004, 04:50 AM

Thank you guys for your posts but I am still stuck. What should I do next?

tom busby · 12-24-2004, 08:44 AM

Yeah you can have a bad plug wire connection that is not a total dead short with raw fuel. It happened to me about 6 months ago in my LS-1 Camaro. The spring clip on the plug wire went slightly loose and my gas-mileage went from 18 to 15 mpg. I could see that the spark plug at its wire-end was crummy looking from the intermittment/bad connection. So dasfps, did you check your plug wires and connections for a slightly loose end? Did you check the plug wires for continuity?

For troubleshooting, the order of inquiry is: mechanical, fluid, electrical. Start by looking for mechanical flaws, that is, stuff you can touch and see. Compare each plug wire to each other plug wire. Compare each plug to the other plugs. And so on. As a driveway mechanic, I am assuming you don't have any fancy tools that matter here, but that's ok you can still troubleshoot a lot of problems. The toolbox on your trunk lid has a sparkplug wrench and the little plastic clip under the beauty-cover has a sparkplug wire puller. Have at it.

dasfps · 12-24-2004, 09:16 AM

Thank you for your response.

I have changed the wires to 8mm racing magnecors about 4 months ago so that shouldn't be the problem.

I am using NGK platinum plugs which should be good for a 100,000 miles acording to Bmw and i have only done 6,000 miles with them.

As to mechanical faults, what should I check?

What fuel issues could their be? (faulty injectors)

Please help because it is costing me alot on fuel as I do a high mileage.

blkongry · 12-24-2004, 09:23 AM

Hmm, there have been several posts on here regarding platinum plugs and the fact that after a few thousand miles the platinum tip of the electrode can come off. That may be the case with you. A partially buried tip can give partial spark, leading to incomplete combustion, and sooty residue with poor gas mileage. Check those plugs.

Do a search on here regarding the platinum plugs. I think there are a few threads on the topic, and the guys at Pelican have some suggestions of what they know works and works reliably.

tom busby · 12-24-2004, 10:36 AM

Sorry to sound like an obsessed person but the bad connection I wrote about above was also on a set of 8mm Magnecor plug wires. I used pliers to make the spring clip smaller by crimping the end with some leather wrapped around the wire so as to avoid cutting the rubber on the boot.

dasfps · 12-24-2004, 12:59 PM

Thanks I will check both the plugs and wires and report back.

The plugs I am using is what TIS suggests is used on all M44 engines for longer service life up to 100,000 miles.

The plugs are NGK BKR 6EQUP

Do you suugest I should go back to normal?

Why do Bmw suggest this then?

dasfps · 12-25-2004, 03:50 PM

Bump

sellingporsche · sellingporsche's Garage

First off I would check or replace the magnacore wires, I have owned a few sets of them and every set I have owned had at least one wire that went bad extremely prematurely (within a month).

The platinum plugs (in my opinion) are a joke or better yet a marketing ploy to get you to spend more money on a useless plug that the electrode falls off in an 1/8th of the life of a cheap autolite plug.

It may sound sack religious but in my previous 318is I ran NGK plugs, ya ya a jap plug in a german car, sounds kinky but the NGK has a colder firing point which not only gave me better gas mileage, but the motor seemed a little more peppy at cold temps.

Anyways thats my 2 pennies....

Merry X-mas

dasfps · 12-26-2004, 03:40 AM

Thank you for your post.

What do you think i should replace the magnecore with?

The only reason I bought them is because they have a lifetime warranty

How should I test to see if the wires are oK or not?

Many thanks in advance.

sellingporsche · sellingporsche's Garage

dasfps,

I would totally reccomend the ngk plugs and I read above someone already told about using them....

As for plug wires...sheesh use almost anything other than Magnacore...The thing is (as I learned quickly) with a 318 M44 motor it is really nothing more than an advanced (computer controlled) tractor motor....lol Seriously it is built so well that there is very little you can do to it to make it perform better (simple uprgrades), unless you get into turbo or supercharging it....(major upgrades)

8mm wires wont make a noticeable difference in performance or gas mileage (in my opinion) so save your money and buy a normal set of plug wires...save the extra money for a mosselman turbo kit....lol

Good Luck
Steve

Jeron · Jeron's Garage

If you kept the stock wires I would throw them back on, assuming they weren't obviously bad.

I hate Bosch Platinum plugs I had a set go bad within 9 months and spent 3 days self diagnosing before sending it to a shop, just to find out I needed to replace my 100k plugs at 5k miles. Cost me over $100 in all. NGK are my personal favorites.

Pull your plugs and check the coloration to get an idea of what your problem is. They should be dry with tan to black soot. They should not have heavy deposits. There are a ton os websites with sparkplug diagnostic pictures.

tom busby · 12-27-2004, 02:30 PM

The intermittent plug connection problem I was refering to was evident by the lack of a click sound when removing the plug wire, and some grey deposits inside the connector where the spark had been arcing to the plug. Magnecor has some very resilient plug wire boots that force the boot slightly off the plug if the spring clip (inside the boot) is not tight.