kevinb70

1998 3.1L, 182K


171/300 codes along with major loss of power


Anyone check to see if I'm missing anything in sequencing my diag?


before the 171/300 codes were being set off frequently:
-------------------------------------------------------
*in the month prior - once or twice code set off (300 misfire) which I thought was the plug wires at the coil packs were a little loose, pulled off, stuck back on, twisted a little bit. Problem went away.
*changed oil a week ago (pretty sure I didnt knock anything loose, don't think there is a vac hose near the oil filter)
*I do have a K&N oiled cotton filter which I have used for about 8-10K miles (over a year old, not many miles on this car lately) which might could contribute to a dirty MAF sensor.
*Have done lots of short-trip low speed (1.5mile to work) runs and very few long-trip high speed runs in the past year


this weekend on a trip I kept getting a code 171 (lean) and 300 (misfire) along with dramatic loss of power.
------------------------------------------------------------------
SES light would occasionally blink briefly, and occasionally the SES light would go out. Light would come on normally when trying to accelerate

Symptoms are:
* on very light pedal, car will accerate nicely - usually
* on heavy/moderate pedal, car will lose so much power as to decelerate, tranny will even drop to lower gear, engine will rev and still decelerate.
* WOT on slight uphill will cause deceleration, compared to light pedal can often hold my speed constant.
* on slight downgrade can get my speed back up to 70-80 quickly - think that eliminates blocked cat (also the erratic behavior at the start doesn't seem cat related)
* while level can accelerate and maintain 70, with some loss of power
* esp on a light hill, can't accelerate past 20-30 til I get on level ground
* gas mileage was horrible
* bad performance even when cold (problems in closed and open loop - rules out many sensors, like O2 which arent used in open loop) seems like performance is a bit better while cold, but I can still notice something wrong.

my main concern was getting my car home, my next concern was my cat being ok after the drive back

* spent a little time looking for vacuum leaks, the pipe going to the valve cover gasket on the firewall side of the engine seems a little loose, but I've noticed that long ago. Not finished with this inspection.
* will disconnect MAF and drive briefly
* will throw a fuel pressure gauge on tonight while I take a short drive to autozone for new plugs (AC Delco) and wires (seem a tad loose) and regular fram air filter- bout time to replace wires/plugs. and electrical contact cleaner or MAF cleaner. Will also get a fuel filter tho I have never successfully fixed a problem by replacing the FF (note to self: check to see if I need a quick disconnect tool for that)
* when I get home I'm going to replace plugs, wires, air filter, fuel filter, clean MAF sensor. check vacuum lines.
*check FPR vacuum line to see if any fuel is in there

My ECT sensor is accurate - I have a temp gauge indash and it was showing typical temps.

Have new laptop hard drive on order so I can't do a diagnostic and check sensor readings (& short and long term trim) on it til this weekend when I reload my laptop.

maxwedge

Great info, but what year is this? Low fuel pressure or dirty maf or air entering the engine behind the maf most common here.

__________________

kevinb70

woops... its a 1998 (edited original post)

drove home (1.5m) for lunch with the MAF disconnected. Ran a bit better, didn't lose power like it does sometimes and I could accelerate better over 30mph over a slight incline. Only threw code 102 which was b/c MAF was disconnected (102 MAF sensor low).

Checked fuel pressure. With gauge connected, turned key to on, 40psi. Drove around with gauge on windshield, highest rpm pressure went to 46-48psi (due to higher voltage from alternator?) but driving it was a steady 40psi, no noticable dip when pushing the pedal down. This corresponds to a pressure check I did a couple of years ago.

Pressure kept 40psi after turning car off. By the time I had finished working on the car, pressure was around 20psi (~20 minutes of work).

Opened up the MAF, delicately cleaned the dust off the forward side (it was pretty dusty) of the 3 sensors inside.


Drove back with engine still lacking power. Didnt throw any codes.

Ruled out:
Fuel pump
Dirty MAF (Could still be bad)
O2 Sensor (because I have the problem in open loop too)


Possibilities:
FPR
Faulty MAF
Vacuum leaks <<--- IMO most likely culprit. First thing is sealing that loose vacuum line fitting to the firewall side valve cover. It is "floppy" loose.
Fouled plugs <-replacing
Bad Plug Wires <-replacing



Oh probably unrelated but bringing up because it could possibly have something to do with vacuum lines:
occasionally the air stops blowing thru the vents when the fan is running, im thinking when I last replaced my car stereo, I may have jarred a vacuum line off the A/C controls. After a little while the air will blow thru vents again. Wiggling temp control sometimes helps to get the air going. However I have had this problem long before my engine started running bad.

maxwedge

Vacuum leak like that is too small, maybe the throttle body, check vacuum at idle, scan it and look at maf inputs.

__________________

lebky

did you try backpressure test? You can also use vacuum gauge run engine @ 2500 RPM while observing the gauge, if vacuum slowly starts to drop in 30 seconds your CAT can be clogged. You will not have enough power, and your MPG will be bad. hopefully this helps.

kevinb70

adding that to the end of my list... yup will do that this weekend time permitting, been in the back of my mind to do that, wondering if the misfire I had a couple of years ago harmed the cat (no spark = unburned fuel = deposits in cat)

lebky

if you are able to monitor your oxygen sensor, what you can do is monitor the voltage of your cat sensor when engine is in closed loop it should be around 800 mV and it should not change like your #1 O2 sensor from 200mV to 800mv. If your #2 O2 is not close to 800 and all the time this can tell you something about your cat. If it is brwn in collor that is a sign of overheating, also if you hit your CAT with rubber hammer from underneath and if you hear something like a sand inside it is bad.

maxwedge

Actually the cat range is 450-650, 800 is too high for normal cat operation, but yes it should not cycle like the precat sensor, to check cat operation an infrared thermo should be used to check temps before and after the cat. The difference should be at least 100 degrees higher on the outlet for proper cat operation. Of course as stated the back pressure test will really confirm cat blockage.

__________________

kevinb70

Figure I would keep a history while I am resolving my problem over the next few days, in case someone finds this post later and has simliar problems...



Well... havent had time to work on it, other than running a log on a quick drive. This weekend I'm replacing plugs/wires (and doing a compression test [out of curiosity, not diagnosis] since I have the plugs out) and looking for vacuum leak - one known is the valve cover ventilation tube on teh firewall side to the TB - fits loosely in the valve cover hole - which just might be my problem.


Yellow - Vehicle Speed
Blue - TPS angle
Red - Bank 1 Sensor 1
Green - Bank 1 Sensor 2

graph of my O2 sensors in front of the cat. (Bank 1 = front I believe, S1/S2 each side)

For the most part, the red trace seems to look OK, but the green.. you see it hangs up at 800mv. Which means low oxygen, correct?

http://img.photobucket.com/albums/v4.../o2sensor1.gif

Eh, well this weekend I hope to track this down...

lebky

No that plasitc line is not your problem I know what you are talking about it is right above your cylinder #5 right? That line brings clean air into your engine crankcase and pcv on the other side sucks blow-by gases and other emission related staff out of your engine to be burned. Sorry I can not remember the technical term for that hose.

kevinb70

meh havent had time to check out my car much...

yanked the MAF connector and seemed to run a tad better
plugged MAF back in, unplugged EGR elec connectors

was curious and checked compression on 1,3,5 and all within 170-180psi, i suppose pretty good tolerance for 180K (but isn't the #2 the problem child?)

after disconnecting the EGR leads, car runs great. Heavy acceleration I hear pinging (due to no recirculation i assume) but have almost normal power... not quite but pretty darn close..

so the initial lean 171 and 300 misfire could be the egr sticking open, and the fact that I have driven the lumina on very short trips.. 1.5 miles to work with not alot of time on the highway...

again detailing my symptoms:
1) under extremely light pedal, i can usu accelerate lightly with engine sounding fine
2) moderate pedal, or slight incline, engine loses power dramatically... can lose speed on moderate incline and sometimes on slight incline
3) pedal to the floor, engine loses even more power (this is when egr is suppose to be closed)

think that rules out a clogged cat, since i have good accel with egr disconnected, whew

thinking carbon in the egr, so if i can get to it this weekend im going to unbolt the egr, clean it, then feel around in the egr passages in the intake... if i feel any clogging, going to yank the upper intake manifold and clean it and the trottle body and EGR....

and i have done a lower/uppper intake on this car so know this is a pretty easy one

have the two replacement EGR gaskets (one is a tomco Kleen Screen)

-----------------------------------------------
from memory i just need an upper manifold gasket and a throttle body gasket?
anything else I would need here? I dont want to bother a neighbor to take to met the parts place when i should have had it to begin with.
-----------------------------------------------



have a sandblaster for my compressor... any reason to not use it to get the varnish out of the inside? is some varnish ok? (ie: it's smoother than the metal) and just leave it alone, only cleaning out carbon ?

~kev