7.3 mpg

[AlaskaTy]

With 1/4 of my driving being on the highway using 92 and only seeing 5lbs of boost maybe 3 times during the week that I drove I only managed 7.3 mpg. This truck use to get about 16 mpg if I drove like that. My 50# injectors were flow tested before I put them in, I have a new afpr, fresh tune up with UR5's, conrad cap/rotor, and MSD 8.5 wires. I'm at a loss here, I have no idea why it's getting such horrible gas mileage. I even dropped my fp down to 40#s and it seems to be getting worse. Does it sound like my rings are washed out or something else to do with my internals? I've had this engine built twice, can't really afford round 3 at the moment. Thanks.

 

[blk00z28]

Re: 7.3 mpg

WOW, thats really low. Are you sure your injectors are stuck wide open? lol

Not to many of you will believe this, but I can run 5 times at the track, cruse at 95mph on the highway there and back and get 22-24mph. I've done this 2-3 times in a row too. (On these same trips, I go thru like.. 3 gal's of Meth though, heh)

 

[SY756]

Re: 7.3 mpg

With 1/4 of my driving being on the highway using 92 and only seeing 5lbs of boost maybe 3 times during the week that I drove I only managed 7.3 mpg. This truck use to get about 16 mpg if I drove like that. My 50# injectors were flow tested before I put them in, I have a new afpr, fresh tune up with UR5's, conrad cap/rotor, and MSD 8.5 wires. I'm at a loss here, I have no idea why it's getting such horrible gas mileage. I even dropped my fp down to 40#s and it seems to be getting worse. Does it sound like my rings are washed out or something else to do with my internals? I've had this engine built twice, can't really afford round 3 at the moment. Thanks.

How's the truck running? You might check to make sure the diaphram in the AFPR doesn't have a pinhole leak or tear in it, letting gas into the plentum via the vac hose. I know you said it's new but that happened to me. Have you checked your oil for a gas smell? Just a couple of ideas.

 

[Syclone#1992]

Re: 7.3 mpg

I would definately check the AFPR, cause something is definately not right.....what is a FULL list of your mods, cause you seem to be having a lot of problems....something is definately not right.....did another sytyer come out and look at it? If you continue driving the truck you are only making problems worse!

 

[bezerk]

Re: 7.3 mpg

you have a chip in there, are you running in open or closed loo? and what are your o2 volts?

 

[AlaskaTy]

Re: 7.3 mpg

I would definately check the AFPR, cause something is definately not right.....what is a FULL list of your mods, cause you seem to be having a lot of problems....something is definately not right.....did another sytyer come out and look at it? If you continue driving the truck you are only making problems worse!

Mods:
RPM built short block with 412 cam, L35s (lightly ported), JE pistons, Eagle Rods, upper and lower intake port matched etc.
RPM built tranny w/ 9/11 2800 stall convertor
50# injectors
Custom chip (Jim and I burned a chip to keep my truck from stalling)
3-bar MAP
MSD 6a
MSD coil
MSD 8.5 wires
NGK UR5 plugs
Conrad cap and rotor
New stock distributor and ignition module
New AFPR (that are of my engine really smells like gas)
ATR cold air intake w/out the isolater box (conical K&N on the end of the tube)
Optima yellow top battery
CVR protorque mini starter
New rear end w/eaton posi
ATR aux IC
Jabsco IC pump
3/4" heater hose IC lines
Aluminum IC scoop

My oil smells like fuel, so I change it every few hundred miles or so.
Overall the truck runs pretty well (at least below 9#s of boost - detonates above 9#s)
The chip is open loop and my o2 mV at idle (875rpm) are 900mV

 

[gkrcr882]

Re: 7.3 mpg

You are definately getting too much fuel if the oil smells like it. Might be because of a stuck injector (or a few) or the AFPR like previously mentioned. Don't drive the truck if possible, since you can do some serious damage if the cylinders are being washed:2cents:

 

[live1053rulz]

Re: 7.3 mpg

Yikes, so would it be best to check the AFPR vac lines for leaks or is it more likely to be a stuck injector? Should I worry getting like 10 or 11 mpg in kind of the same situation?

 

[QUICK STORM]

Re: 7.3 mpg

pull your injectors out, get a jig or something made to hold injectors in a row allowing you to pressurize them with air. once you do this fill up a pan with water, deep enough to have all the injector pintles sit underneath the water, pressurize the injectors with air and watch for bubbles. you should have the air regulated to low psi, if you have an air bubble every 10-20 secs they should be ok.

remember a leaky injector will flow, just not when you want it too. after you do this, pull your spark plugs and squirt oil into the combustion chamber, so you can try get all the fuel off of the cylinder walls. and check you AFPR could be leaky like everyone else is saying. hope this helps.

 

[SY756]

Re: 7.3 mpg

Yikes, so would it be best to check the AFPR vac lines for leaks or is it more likely to be a stuck injector? Should I worry getting like 10 or 11 mpg in kind of the same situation?

As far as the AFPR, it isn't really the vac lines that would cause the problem, it's the diaphram in the AFPR that could cause the trouble. It could have a tear or a pinhole in it. To check, all you have to do is pull the vac line off the AFPR and kick on the pump. If fuel shoots out, then, "Houston, we have a problem"

 

[dgoodhue]

Re: 7.3 mpg

The chip is open loop and my o2 mV at idle (875rpm) are 900mV

That is rich for idle, what is your fuel pressure. I haven'tused an open loop chip, but I would guess you want the O2 sensor to be around 450-500mV and it would probably oscillate some.

 

[George Blake]

Re: 7.3 mpg

You burned a chip to keep your truck from stalling.
If a bunch of fuel was added to keep it from stalling, my bet would be you have a huge vac leak somewhere. Do the tire tube deal and find your leaks and then set your chip up for that.
I just noticed that your truck idles at 875 rpm? Vac leak. You need to find it.

 

[live1053rulz]

Re: 7.3 mpg

As far as the AFPR, it isn't really the vac lines that would cause the problem, it's the diaphram in the AFPR that could cause the trouble. It could have a tear or a pinhole in it. To check, all you have to do is pull the vac line off the AFPR and kick on the pump. If fuel shoots out, then, "Houston, we have a problem"

Got it, thanks for the info. I think I'm alright there, but I'll double check.

 

[bezerk]

Re: 7.3 mpg

are you sure you have a right chip?
and idling above 550mv or so it must give you a code 42 (o2 to rich)
and i doubt it's a bad injector

 

[AlaskaTy]

Re: 7.3 mpg

You burned a chip to keep your truck from stalling.
If a bunch of fuel was added to keep it from stalling, my bet would be you have a huge vac leak somewhere. Do the tire tube deal and find your leaks and then set your chip up for that.
I just noticed that your truck idles at 875 rpm? Vac leak. You need to find it.

Where should I idle? I thought 875 was pretty good.

are you sure you have a right chip?
and idling above 550mv or so it must give you a code 42 (o2 to rich)
and i doubt it's a bad injector

There may be a problem with my o2 sensor, I used an o2 sensor wrench to get it out on the hopes that it was bad, but I ended up just stripping the sensor. The side got dented, but it's still sealed. The chip was burned according to what that sensor was telling me, so if it was giving bad information, then the chip is wrong. Vacuum at idle is 17.6, and datamaster didn't throw any DTC codes. The "flag" in the upper right box had me at a 1 on the o2 lean/rich box indicating rich, but nothing else. I'll bike tube it, but last time I did that no vac leaks were found.

 

[AlaskaTy]

Re: 7.3 mpg

That is rich for idle, what is your fuel pressure. I haven'tused an open loop chip, but I would guess you want the O2 sensor to be around 450-500mV and it would probably oscillate some.

fuel pressure has been dropped to 40#s from 45#s.

 

[dgoodhue]

Re: 7.3 mpg

The chip was burned according to what that sensor was telling me, so if it was giving bad information, then the chip is wrong.

I didn't notice that you have a custom chip, you intended to burned the chip for 900mV at idle? That is more like what you want for WOT but not at idle or part throttle.

 

[AlaskaTy]

Re: 7.3 mpg

I didn't notice that you have a custom chip, you intended to burned the chip for 900mV at idle? That is more like what you want for WOT but not at idle or part throttle.

so do you think it's the chip that's causing my truck to run so rich? Like I said, I don't know how reliable the o2 sensor info is, so I'm going to get it torched off and a new one put in as soon as i get the time. I thought WOT was supposed to be around 1000+ ?? Thanks

 

[dgoodhue]

Re: 7.3 mpg

1000+ mV just means its pinned, it like running 15.3 psi on the 2 bar map. A narrow band o2 isn't suposed to be accurate for WOT but most will find with a WBo2 that high 11 AFR is 910-930mV range.

 

[QUICK STORM]

Re: 7.3 mpg

did you check the AFPR? 975mv is way to high, thats basically Full rich all the time, listen to the guys here, its great info.