BMW Check engine light problem- Fuel Trim out of whack..

Hoping someone around here has seen/heard of this or a similar problem.

I've got a '96 BMW 318ti daily driver (1.9l M44 4 cyl). I went to get it inspected (NC State inspection- OBD) and figured out that the check engine light was not working- bulb was blown and I just never noticed it. I replaced the bulb and it lit up, generic OBD scan tool gave me a code P1140, which is something with the MAF or TPS. I have since replaced the TPS with a known good one, same with MAF (at least the seller told me it was good...), replaced the rubber intake bellows between the MAF and the throttle body, checked for air/vacuum leaks, etc.

Car stil throws the P1140 code.

I did get some Freeze Data from the scantool- here's what it says (2 different occurences of the same code):

P1140 RPM 1536 1093 Load Value 7.0% 6.6% Coolant Temp 199F 82F Short term fuel trim1 0.0% 0.0% Long term fuel trim1 0.7% 0.0% Short term fuel trim3 -100.6% -100.6% Long term fuel trim3 -100.6% -100.6% Vehicle Speed 3 mph 1mph Fuel system1 open open Fuel system2 n/a n/a

Based on my interwebz education about fuel trim, seems like the DME/ECU is trying to compensate for a "perceived rich condition" by cutting back on the fuel by 100.6% (which I think is the max it can display)- thus the "-100.6%" reading. I have occasionally smelled raw fuel when I first start the car, so now I"m thinking I've got an injector or 4 leaking down when the car is parked, and/or a leaky injector(s) while the car is running.

Car has ~210k on it, and the PO was not exactly a stickler when it comes to preventative maintenance.....

Any ideas from the brainiacs out there???

Thx, Rig.

Pre-Cat O2 sensor(s). Replace them.

I had this problem on my M. Your O2 sensor is dying but not dead. It's sending weird mixture signals to the computer that our outside of what the normal map range should be. But the O2 sensor isn't dead enough for the computer to register it as dead.

Ahh, yes- that was one thing that a tech friend of mine mentioned as a possibility- along with a bunch of other stuff- so a first hand opinion like yours is good info.

Thanks for the quick reply- I'm off to check prices on the pre-cat O2 sensor........

;)

Salanis wrote: Pre-Cat O2 sensor(s). Replace them. I had this problem on my M. Your O2 sensor is dying but not dead. It's sending weird mixture signals to the computer that our outside of what the normal map range should be. But the O2 sensor isn't dead enough for the computer to register it as dead.

Also, learn from my mistake when I did this job: there is a good chance that a "universal" O2 sensor (the one where you splice the wires) will not work. On the M cars, at least, the unit is a different style than the universal ones. I had to buy a new OEM style unit.

It looked like this was just a trait on the M tuned engines though.

I think on bimmerforums some one has found a cheap replacement.

Autozone has Bosch 13559 in stock nearby for $62. Cheapest so far for sure, and it's supposed to be the OEM sensor- no cutting/splicing.

I'm planning to pick one up today after work, and see if it cures what ails my car.

I'd be willing to bet that the o2 sensors in this car are original, ~12 years old with ~210k miles on them, couldn't hurt to replace the pre-cat sensor.

I'll update when I know something.

Keep the ideas coming!!! ;)

They've probably been replaced at least once. My experience is that O2 sensors last 75k-125k miles.

Does the 318 have 1 or 2 pre-cat sensors? If you only have one, that's cheaper and easier.

one.. it's a 4 cylinder

Well, so far so good. I replaced the O2 sensor with the Bosch 13559 from Autozone for $61.99 + tax- cheaper than anywhere else including any of the el-cheapo online places (for a direct fit OEM replacement sensor).

I've driven approx 80 miles since changing the sensor + resetting the CEL, and all is good. I checked the status of the OBD monitors tonight using my scantool and they all came up OK, so I'm going to the inspection place tomorrow AM to get this beeeyotch inspected.

Thanks Salanis for the tip- I owe you a beer or 12.... ;)

Bret.

well, crap on a stick.

I did not have time to get to the inspection place, and then Sunday afternoon I had to fly out of town- so I drove this car to the airport and the !^(&#%*!& check engine light is back on!!

I didn't have my code reader with me, so I'll have to check it when I get back next weekend- but I'll bet it's the same code- just have to figger out what the cause is.....

Any further ideas?

Dump a bottle of Techron concentrate in a fresh tank. Flog it hard.

Well, it's throwing the same code, but the freeze frame data is different. No longer has the short term fuel trim out of whack, but the long term fuel trim is 100.6%. I'm thinking (and hoping) that the past problem is still in the DME memory and it's causing it to throw the code. I reset it again today, threw in 4 bottles of FI cleaner and I'll drive it and see what happens this week.

Time is running short- DMV gave me an Aug 01 deadline to get it inspected, I'll be running the LeMons race in SC next weekend and working all this week and next. Not much time to troubleshoot this beater.......

If I don't get it fixed I might just have to part it out- silly, isn't it????