Fuel economy issues!?

[ryanc5413]

I hate to be the voice of reason all the time, however a descreened MAF sensor is just about one of the worst things you can do to your vehicle.

The screens are inside the MAF for a reason, to provide laminar airflow across the sensor wires over a large range of velocities.

Without laminar airflow over the sensor wires, the measured airflow as reported by the sensor will be inaccurate.

Removing them can help FLOW more air at high rpm, but the intake tract is capable of feeding a much larger engine at high rpm as equipped stock.

At certain velocities the air no longer follows a nice path through the intake tract, and starts to tumble.

Unless you have hard data on the descreened MAF, I would remove it.

Gives same mileage with a stock maf. I have compared maf freq with another one of my gmt400s and close is close enough. I have run descreened mafs on 57 gmt400s no problems so far. Something is just off with this truck.

 

[ryanc5413]

This is true, but it won't show where the leak is. If you jump the FP regulator, you can check the system under pressure, and any leak will be easy to find.

What do you mean jump the fpr?? This is a internal unit.

 

[ryanc5413]

First, get rid of big tires, that's easily 2-3 mpg, especially in town with lots of stop and go, and turning. Low pressure and alignment issues will also cause low mileage.

Second, the oiled K&N isn't doing you any favors, especially if over-oiled. It will coat the MAF sensor wires, leading to inaccurate readings.

Replace the bored out MAF with a STOCK MAF. The fuel maps are likely calculated on the stock MAF. Same with throttle body.

Replace the thermostat with a factory replacement.

Check engine grounds, especially the one at the rear of the cylinder head. Not a visual check, a check with a multimeter to determine resistance.

You won't have a check engine light for converter efficiency, since they would have been tuned out in the computer, however data from the post converter O2's are also used in fuel trim.

Check for dragging brakes, especially the return springs in the rear drum brakes. A non contact digital temp gun will help out here.

If rear o2s control fuel mixture that could be the problem. Mine are missing. But the tuner turned rear o2 sensors off. There is no activity with a set plugged in. Do you have any data showing rear o2 sensors control fuel mix? Never in my life have I heard that. There is so many people out there running simulators, and anti foulers and no one.has issues. Are you sure the black box pcm uses data from rears? How in the world would it. The computer doesn't know how efficient the converter is and in my mind it would have to... To have some.sort of base line. Has anyone else ever heard that? Mike this is no offense intended but are you a mechanic or a engineer or did you just read that somewhere?

 

[kennythewelder]

What do you mean jump the fpr?? This is a internal unit.

Watch the video I posted. You remove the FPR and jump the connectors to make the FP stay on. This will keep pressure on the whole system so you can look for leaks. Again, watch the video. You don't want to jump the wrong connectors. This will short out the ECM. This works, I have done this to my truck, following this video. With the throttle body removed, and using a mirror that I could get into hole in the intake where the TB was, you can shine a flash light on the mirror. This will light up the inside of the intake and you can see all the popet hoses in the mirror. I Did this to my truck a few years ago when I was fighting FP issues.

 

[kennythewelder]

FP regulator,,,, Sorry,,, auto correct must have got me..... That is Fuel Pump Relay,,,,, Not fuel pump regulator....

 

[michael hurd]

Short and long term fuel trims explained in this article.


http://m.autoserviceprofessional.co...-how-it-works-and-how-to-make-it-work-for-you

 

[ryanc5413]

Short and long term fuel trims explained in this article.


http://m.autoserviceprofessional.co...-how-it-works-and-how-to-make-it-work-for-you

I doubt my truck even processes rear o2s for trim. I know everything needed about fuel trim. Figured it was rear some where.

 

[ryanc5413]

FP regulator,,,, Sorry,,, auto correct must have got me..... That is Fuel Pump Relay,,,,, Not fuel pump regulator....

Perfect! Thanks bud!

 

[beardeddummy]

All the rear 02s do is check for a cat and if it's working.

 

[ryanc5413]

If they were checked a year ago, that does not rule out the possibility of them giving you issues right now.

I had a friend who's 1998 had stalling, flooding and general running like poop symptoms. Everything pointed to the spider, however, the grounds were bad. Cleaned the grounds and voila~ it does not need a spider.

What backpressure do you have at 3000 RPM in front of the muffers?

Who knows. There are no converters so I doubt it has any. A year ago it was giving wrong economy and it still is except worse. Its not a ground. Please get out of my thread. You are not offering any one any help except bad info