Rough Idle and Bad MPGs

[SethSwitch]

Hey all I am new to the thread an am looking for some help.

I recently put a spectre cai intake on my tahoe and am starting to have some issues. First off I got a check engine light about an hour of driving after the cai. I bought some mass airflow sensor cleanerand cleaned that and the two system lean codes kept coming back. Next I went to the auto zone and they said I needed to really tighten up all the hoses which I did. After about a week I went back in and had the technician check the stft. I took this video of the results at idle and 3000 rpm.

(3000 rpm stft= -6% / idle = 6.5%).

One thing I can think of is that I ran e85 the tank before the problems arose so I'm thinking the fuel filtermy be clogged. Also fuel econ has been awful and engine start is slightly rough.

Any thought or suggestion appreciated.
Thanks, Seth

 

[nharkey85]

MAF data would help. Also check O2 sensor hasnt been damaged or disconnected on that side

 

[SethSwitch]

MAF data would help. Also check O2 sensor hasnt been damaged or disconnected on that side

I don't have a diagnostic scanner so I will try to go back to the auto zone and use theirs again. I am thinking that its probably a bad fuel filter because engine start is rough, acceleration is horrible, and the stft is saying that its not getting enough fuel at high rpms. I am also going to go get my fuel pressure checked tomorrow to see what that tells me. Do you think that this could be a possibility? I have 84,300 miles on it.
Seth

 

[Jason_S]

In the past, a clogged filter usually gave me better mileage before I changed it or it killed the pump. In most of my previous vehicles, the fuel filter was an annual maintenance item. I understand that changing one on one of these trucks is a little more challenging, but I never got around to ordering the parts and finding out.

I can say that I tried running straight E-85 for a few tanks and the truck got progressively harder to start and idled rough. After I switched back to mid-grade, it took about half a tank, maybe longer, for things to go back to seeming more 'normal'.

I don't always buy gas from the best stations, but I periodically run a bottle of injector cleaner through the tanks, and will occasionally stomp on the throttle for a full throttle acceleration in the on ramp to help clear things out.

 

[nharkey85]

Also if you can ahold of a fuel pressure gauge will help diagnose clogged filter.

I know E85 is garbage but i dont see one tank causing so much trouble unless its not a flexfuel system.

Im still thinking this has something to do with the install of the cai or the cai itself

 

[Jason_S]

To call E85 garbage is, I think, unfair. It is less expensive, but you burn more of it to typically get the same net emissions. It's advantage is that it is renewable to a point.

Feed E-85 to a car with a turbo or super charger and you will feel that car really wake up. I also think that when they design engines specifically for E-85 we will also see improvements.

Back on topic:

A quick easy way to rule out or to identify the CAI as the cause is to reinstall your original intake pieces.

 

[SethSwitch]

To call E85 garbage is, I think, unfair. It is less expensive, but you burn more of it to typically get the same net emissions. It's advantage is that it is renewable to a point.

Feed E-85 to a car with a turbo or super charger and you will feel that car really wake up. I also think that when they design engines specifically for E-85 we will also see improvements.

Back on topic:

A quick easy way to rule out or to identify the CAI as the cause is to reinstall your original intake pieces.

I am going to go look at the fuel pressure today so that I can rule that out then my next move would be to reinstall the old air intake. I will keep y'all posted on the findings.
Seth

 

[Jason_S]

Did you check your fuel pressure? Have you cleaned your throttle body?

 

[SethSwitch]

Fuel pressure is good and I had the intake smoke tested and still am having a rough engine start. Will post a video soon.

 

[Jason_S]

Try cleaning your throttle body. They tend to build up carbon and cause the computer to have issues adjusting airflow which gives you a crappy idle.