emark708

Hello all,

I recently bought and fixed up a 97 Civic DX for my son to use at college. It was quite a roach when I bought it and I've since cleaned it up and had a friend do what was needed to get it to pass inspection. It supposedly has only 98K miles on it but it still seems to have it's share of "quirks". A couple of weeks ago the CEL came on and I had him take it to Autozone to have it read. Was code P0171. Finally brought it home to drive it around a bit myself. Bought a relatively cheap obd2 scanner and cleared the code. Been driving it for a day or so and had the scanner hooked up and it seems fine so I took it out on I95 and noticed that the VSS sensor was not matching the speedometer. While my GPS and the vehicle speedometer seemed to agree that we were going 75 - 80mph the OBE2 VSS reading was an impressive 200+mph. Would this be an issue with the VSS or maybe something else?

Thanks for your time.
Eric

JRCivic1

Either a bad scan tool or a problem with the diagnostic port in the car. Are any other values odd or skewed ???

emark708

Thanks! I stopped by a friends garage on the way home today and he put his Snap-On reader on it and it reads correctly. So as you said, apparently the scan tool is bad. It also told me that it was about to throw a P0170 code which is another lean fuel related code. I drove about 150 miles today and there were two things I noticed, one relating to the scanner. The fuel system kept switching in and out of closed loop mode and at one point it also lost almost all power for about 5 - 10 seconds. It also at one point lost almost all power and it felt like it was starved for fuel. It did not throw any code for that issue and after about 5 or 10 seconds it was fine. My friend suggested trying the O2 sensors first. I suppose this should be a separate thread But thanks I appreciate your help!

JRCivic1

What do your short-term and long-term fuel trim values look like under closed loop operating conditions ???

emark708

I'm not sure which is under OL or CL, I will have to check again. The long term fuel trim stays at 31.3 regardless of OL or CL. Again I'm not sure of which mode, but under one condition the short term varies occasionally between 19.5 and 14.1 and under the other (CL?) it constantly varies between 0 and 46.9. I was keeping an occasional eye on the scanner while I was driving but I noticed that it was usually (but not always) 0 on deceleration, and every one in a while would go to 0 even under acceleration. It also threw the P0170 this morning on the way to work. Thanks for your help!

emark708

@JRCivic1 To add to this. I cleared the P0170 and P0171 codes and it set the LTFT and STFT back to 0. Drove for about 30 minutes this evening and for all but the last 5 minutes both numbers stayed at zero and it appears that the fuel system was OL. In the last 5 minutes the STFT started to change from 0 to 46.9. I let it idle when I got home and it would slowly rise to 46.9 and then go back to 0. Then start to rise and go back to 0. During this drive it again had the issue of almost no power when trying to accelerate for a few seconds and then it was ok. No codes yet. Starting to think it's possessed. Thanks again for your time.

spAdam

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emark708

@spAdam Yep. Checked it early this morning and it is definitely cracked. Ordering a replacement now. Could this be the cause of the loss of power or just the flakey sensor readings? Thanks very much!

spAdam

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emark708

emark708

@spAdam @JRCivic1 Well last night I replaced the manifold and cat, both O2 sensors, and the fuel filter. Thus far it seems to be behaving. The readings from the OBD scanner for LT and ST fuel trim look normal and so far there has been no loss of power. Thank you both very much!

JRCivic1

You are most welcome.

spAdam

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