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What could cause my car to lean out while crusin

Wilford Brimley

Is posting from the grave
Joined
Jun 26, 2008
Location
Marysville, wa
So it's idles at 14.2 to 14.8, once I start going it starts leaning out 15.5, 16, and the video here shows what it does while crusing, at some points it almost goes down to 20....this just starting happening kind of out of nowhere



 
Maybe a bad o2 sensor?
Do you know how to test an O2 sensor? I think the cheap oscilloscope thread might be a step in the right direction. Any of the sensors that are inputs for the fuel map could be at fault. O2 sensor is a likely culprit, but you’d have to do some diagnostics to find out. Fuel pressure could be an issue. Have you checked fuel pressure? What type of engine management do you have? Stock LH? Or aftermarket?

It could be anything, your going to have to give us more info and do more leg work.
 
Do you know how to test an O2 sensor? I think the cheap oscilloscope thread might be a step in the right direction. Any of the sensors that are inputs for the fuel map could be at fault. O2 sensor is a likely culprit, but you’d have to do some diagnostics to find out. Fuel pressure could be an issue. Have you checked fuel pressure? What type of engine management do you have? Stock LH? Or aftermarket?

It could be anything, your going to have to give us more info and do more leg work.
I don't my man, it's lh, I don't know how to test fuel pressure, I'll do some searching
 
I don't my man, it's lh, I don't know how to test fuel pressure, I'll do some searching
Which LH? Any mods? Fuel pressure is pretty easy to test if you have a fuel rail with a schrader valve on it. If not, then you have to connect some adapter inline with the fuel hose to test it. Basically, just hook up a fuel pressure gauge (can be rented from autozone etc) downstream of the fuel pressure regulator and drive it until it acts up and if the pressure is dropping below 40 psi at the same time you are leaning out, check fuel pump, filter and fpr. Fuel pressure sounds like the culprit to me. O2 sensors usually just stay fucked up would cause problems at lower rpm and idle and don’t do intermittent stuff like what your video showed.
 
Which LH? Any mods? Fuel pressure is pretty easy to test if you have a fuel rail with a schrader valve on it. If not, then you have to connect some adapter inline with the fuel hose to test it. Basically, just hook up a fuel pressure gauge (can be rented from autozone etc) downstream of the fuel pressure regulator and drive it until it acts up and if the pressure is dropping below 40 psi at the same time you are leaning out, check fuel pump, filter and fpr. Fuel pressure sounds like the culprit to me. O2 sensors usually just stay fucked up would cause problems at lower rpm and idle and don’t do intermittent stuff like what your video showed.
Thanks bro will do
 
i had a similar set of symptoms before when the in tank pump went flakey. when the gas got warm it'd start to lean out and was worse under load.

Is the main pump making any noise/cavitation when this happens?
 
i had a similar set of symptoms before when the in tank pump went flakey. when the gas got warm it'd start to lean out and was worse under load.

Is the main pump making any noise/cavitation when this happens?
It's OK for the first like 3 minutes... once it starts warming up it gets shitty
 
Does it have an oiled aftermarket air filter? I've seen comments that those can gum up the MAF hotwire and cause lean conditions.
 
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