CEL and crappy gas mileage

[firerescue251]

About two weeks after i installed an MAC intake in my truck the CEL came on the codes were pulled and they showed P0171 and PO174. I have replaced the PCV Valve and cleaned, as best as i could, the MAF. Also my gas mileage has dropped drastically from like 65 miles per 1/4 tank to about 18 miles per 1/4 tank. ANY SUGGESTIONS ARE APPRECIATED!

 

[performancenut]

Try replacing the stock intake and see if your issues go away.

 

[firerescue251]

I still think it may have something to do with the MAF. I'm in the process right now of cleaning it thoroughly and recharging the filter. Not really going to know what to do if this doesn't work.

 

[performancenut]

I still think it may have something to do with the MAF. I'm in the process right now of cleaning it thoroughly and recharging the filter. Not really going to know what to do if this doesn't work.

There is a lot of info. on oil from the filter contaminating the MAF wires. Iit is recommended to oil very sparingly.

 

[firerescue251]

Would a contaminated MAF decrease gas nileage any and if so how much. Oh and how long does it take for the drive cycle to end after resetting the computer?

 

[steves97z28]

go to autozone and get some electrical spray cleaner, DQ or something like that, and spray down the MAF i had to do the same thing in my camaro

 

[firerescue251]

ok. went to autozone. cleaned the MAF. Cleaned and oiled the filter. Now idling weird when coasting at 45 -55 mph. RPM's at 1000-1500-1000-1500-1000 until foot is put back on the gas. So far no CEL. Oh and seafoamed it.

 

[firerescue251]

OK CEL back on again, after 30 or so miles. F**K this! Old intake system is going back on.

 

[Paraphoe]

What happened with this? Update?

 

[firerescue251]

ok. check engine light came back on, even with replacement of the stock intake and stock filter. had a mechanic out of my FD look at it. he unplugged my MAF while it was running warm and nothing, no high idle, no low idle, the rpms just stayed the same. I think the MAF sensor was bad for so long that the computer learned how to keep the engine running without the MAF sensor. THINK A NEW MAF SENSOR IS IN ORDER.

 

[BlusploderAWD97]

is that the last?? mine is doing the same with the gas but the truck runs horrid with the maf disconected. I got ram air that i fabed myself and a KN i think the oil might be my probrlem.

 

[firerescue251]

anyone have any input on whether they think the MAF sensor is the cause of the problem.

 

[firerescue251]

Anyone Have Any Suggestions?

 

[performancenut]

I feel that the signs and symptoms described are MAF related- especially if a trial replacement of the stock air box didn't resolve your problems. So, it could likely be the MAF itself. The next step would be a MAF meter swap or replacement.

 

[firerescue251]

already have one on order. Advance Auto Parts said it should be in tomorrow by 9 AM its gonna cost about 140 bucks for an aftermarket. Will have it in as soon as i pick it up. HOPEFULLY IT WILL RESOLVE THE PROBLEM!

 

[firerescue251]

Also have a used MAC Intake for a 1996 - 2001 4.0 OHV (About 700-800 miles on it) will sell for 110 dollars shipped and a New MAC Intake for same years and engine for 150 dollars shipped.

 

[firerescue251]

Family mechanic told me today that the INTAKE GASKET is usually and commonly known as the problem with the good old pushrod. Got the gaskets will be tearing into it ASAP. I also tried spraying carb cleaner around the intake plenum, but didn't hear any change in the rpms. Does that mean that the intake gaskets are good?

 

[kponhlo]

I replaced my intake gaskets for rough idle. When warm it ran fine; intake seasled tight from engine heat. When cold though, especially in winter, it ran like garbage. I was never able to get carb cleaner to make any change in engine rpms either, but when I got it apart I found that the gaskets were indeed not sealing right, and it warms up now without surging and dying.

If your cold startup is smooth though, your gaskets might not be bad or as bad as mine were. Its kindof a pain to change them, so if it ain't broke...

Just my $0.02.

 

[firerescue251]

yeah, i tore it apart, and the first thing was i could untighten the bolts to the intake plenum with my hand, second the gaskets were shot, hard as a rock and definitely worn down, probably not holding a good seal. any more experiences with this problem and the p0171 and p0174 codes posted would definitely be appreciated.

 

[firerescue251]

the gaskets solved the problem. NO MORE CEL, gas mileage is back up, and runnin strong.