More engine trouble

[Conti2K]

Well, a little while ago (about 3 months) I took the car (2000 Continental) to the dealer because I was getting CEL codes that both bank 1 and bank 2 were running lean... the gas mileage had slowly but steadily been dropping (reached somewhere around 17.5mpg in town at that point, which was a little less than I liked) and it idled rough on occasion... so they ran their diagnostics and determined my IAC valve and MAF sensor were busted, which they both replaced. So since then my mileage hasn't gotten any better. It's actually steadily decreased. I'm currently getting closer to 15mpg in town... (I even replaced the spark plugs with some iridium (sp?) autolites and replaced the filter with a K&N filter)... a few days ago the CEL came on again... I checked it and lo and behold - it was P0174 again (for bank #2 running lean)... took it back to the dealer, and again, the MAF sensor is busted... Now of course I appreciate they ran the diagnostic free of charge (because they didn't fix it before)... and I also appreciate it that they replace the MAF sensor for free (since it's under a 12K mile warranty)... but it's not really gotten me any closer to figuring out what the issue is that's *causing* the MAF to die twice in 3 months... not to mention the mileage that just plain sucks...
Anyone have any suggestions as to what to have them check out? Things I've heard so far were MAP sensor and EGR valve... anything else?
Thanks folks!

 

[torquemonkey]

Very similar to the issues I have. Check engine lights and low MPG. I had changed my IAC and the idle still was a little rough. Cleaned the MAF wires, no improvement. Plugs looked good and were changed less than 5K miles ago. Eventually the car began to spit and sputter and I checked the fuel pressure. It was @30#. Swapped in a new fuel filter and the pressure had dropped,(pump on its last leg?).
Hopefully improvements are on the horizon as the pump change out will be done in the next few days.

 

[MichiganTeddyBear]

hmm maf failing so soon.. poor quality replacement part by dealer???

some people have problems with K&N filters causing maf failures/dirty mafs... its the oil they use. too much of it and it causes maf problems. I might even bet the 2nd maf wasn't bad, but maybe dirty from the airfilter oil??

also, O2 sensors can cause problems.. usually running rich, causing poor milage... now if the o2's are saying its too lean, the computer will try to richen the mix... bad gas milage results. that might be a path to go down. O2's don't always cause codes if they fail. they can get 'stuck' in a condition where they are always outputting the same value, regardless of what they are seeing. and many times this value is withing the 'non failure' parameters for the sensor.

 

[Conti2K]

Very similar to the issues I have. [snip] Hopefully improvements are on the horizon as the pump change out will be done in the next few days.

I'd be interested to hear if it made a difference. My car's going back to the dealer to have the new MAF installed... not sure it'll make a difference, since it seems like they're just dealing with the effects, not the cause)

 

[Conti2K]

hmm maf failing so soon.. poor quality replacement part by dealer???

Well, I'm going to keep my fingers crossed and hope this second replacement will be a solution to the problem, but we'll see. Not getting my hopes up just yet.

some people have problems with K&N filters causing maf failures/dirty mafs... its the oil they use. too much of it and it causes maf problems. I might even bet the 2nd maf wasn't bad, but maybe dirty from the airfilter oil??

Hrmm... are you sure about that? I read through the instructions and it said not to use any oil on it, so I was assuming it didn't have any oil on it. I still have the old filter though so I could try that.

also, O2 sensors can cause problems.. usually running rich, causing poor milage... now if the o2's are saying its too lean, the computer will try to richen the mix... bad gas milage results. that might be a path to go down. O2's don't always cause codes if they fail. they can get 'stuck' in a condition where they are always outputting the same value, regardless of what they are seeing. and many times this value is withing the 'non failure' parameters for the sensor.

If this persists I'll definitely have them look at that... I do have the software and hardware to read all kinds of stuff from the OBD port... I wonder if it's something that could be figured out from that.

 

[MichiganTeddyBear]

A lot of K&N's used oil to help filter the air (soaked the cloth). If yours says no oil, then yours don't need it, and oil on the MAF shouldn't be a problem.

if the new MAF don't fix the problem, definatly get the codes and see if they say anything. Also, if the setup you have allows monitering the O2's in real time, you can see if they change output as your driving the car.. they should change under various loads..

Another thing that can be checked in real time if you can, is what the ECT is telling the computer what temp its running at. if its telling the computer its cold, that will adversly effect the milage. example: my 94 jimmy with a bad thermostat (stuck open) never warmed up during winter... changing that alone gave me almost 5 mpg increase in cold weather.

 

[torquemonkey]

If this persists I'll definitely have them look at that... I do have the software and hardware to read all kinds of stuff from the OBD port... I wonder if it's something that could be figured out from that.

What brand or type of software are you using? I'm in the market and could use some guidance.

Thanks.