Bad gas milage after 14B swap, need expert advice...

[perley03]

Now I know this has been talked about severly and , but I can't find any reasonable answers. Ever since I swapped my 14B turbo in my gas milage has dropped below 20mpg. There is one very small boost leak around my BISS screw, but nothing to drastically drop my pressure. Boost is set at 15psi, stock fuel system. Just changed my front O2 sensor, and my fuel trims are right around 1% for LTFT. Now, I don't really beat on the car, I mean every now and then I get into boost, but not every time I change gears or anything. Car mostly sees interstate driving, 18 miles a day, right around 70-75mph at 2800rpms, sometimes more than that if I have to make multiple trips to the bank and shit. I had my girlfriend follow me someplace and meet up with some people, and she said every time I let off the throttle there was a big poof of black smoke and it stunk like gas. I can verify this as the tip on the muffler and part of the rear bumper has black soot on it.
What can I do to increase my milage? This is really killing the wallet, at $3+ for 93 oct. at the pump and I only get like 215-220 miles/tank. I even hooked up my logger and keep it on while driving and been keeping an eye on boost and TPS and trying to baby the car the best I can.
The only thing I can think of would be to back my boost off to stock, and probally get a chip from Jeff for a 10.5:1 afr since my car has an EPROM. Help me out guys, as this car probally is going to be parked, and I'm left resorting to my Neon .

 

[93clips]

when your car let out black smoke did u hear a "pop" noise? ### that could mean your car is backfiring, its normal for backfiring with cars with exhaust systems without cats. backfiring on a stock exhaust though is usually (to my knowledge) from running too rich

 

[No_Skillz]

Have you done a proper boost leak test to make sure you can hold whatever boost you're running for at least 10 seconds? Do so if you haven't. You will be surprised.

Check your plugs to make sure you are running NGK BPR6ES gapped at 0.028. None of that iridium, platinum, or super special uber unobtainium hokey pokey.

Check the areas around your manifold and turbo to make sure you don't have any exhaust leaks.

Make sure you didn't damage your MAF at all during the turbo install process.

If your BOV isn't recirculated, that could make you run rich when you let off the boost, hence the big puff of smoke.

Other than that, since you have a logger, post up a log, especially O2 readings.

I believe your drop in gas mileage is most likely due to running rich, especially with the puffs of black smoke you describe. Since this is after a new turbo install, boost leak is the most likely culprit. Pulling your plugs and checking your o2 with a logger is child's play, so you might as well while you're at it. Your spark plugs will most likely be black since you've been running so rich, so a new set will probably be necessry, but no point in swapping in and ruining a new set without finding out why you are running rich.

 

[kenamond]

No_Skillz hit every point I would've suggested. Make sure you're recirculating your BOV. Do a boost leak test to 20psi and fix leaks until the pressure drop from 20psi is no more than 1psi every couple of seconds. Double-check your plugs and gap; higher boost makes it harder for the spark to jump the gap, so if your gap was a bit big, you could misfire when the boost is raised a few psi. You'd probably notice the motor missing under boost, though, and it might backfire as well, as the unburned air/fuel can ignite in the exhaust.

I get around 21mpg running 14-15psi boost with a short commute (100% stop/go) and not boosting very often but not pampering it either.

I suggest that you start measuring mpg more accurately:
Next time you fill up, top it off and reset your trip odometer.
Next time you fill up, top it off again, and record the gallons reading on the pump and the reading on the trip odometer.
Divide trip odometer by gallons and remember it or write it down. That's one sample reading of mpg.
Reset your trip odometer.

Do this for a month or so keeping track of the mileage. It will vary, so don't just do it once. Do it several times to get a feel for your mileage.

Keep in mind that you'll get much better mpg on the highway (I get 28mpg cruising at 85mph), so if you do something abnormal like go on a road trip, those numbers will not represent city driving mileage.

EDIT: Have you checked tire pressure? Abnormal tire wear? Those will decrease mileage, too.

 

[perley03]

No_Skillz hit every point I would've suggested. Make sure you're recirculating your BOV. Do a boost leak test to 20psi and fix leaks until the pressure drop from 20psi is no more than 1psi every couple of seconds. Double-check your plugs and gap; higher boost makes it harder for the spark to jump the gap, so if your gap was a bit big, you could misfire when the boost is raised a few psi. You'd probably notice the motor missing under boost, though, and it might backfire as well, as the unburned air/fuel can ignite in the exhaust.

I get around 21mpg running 14-15psi boost with a short commute (100% stop/go) and not boosting very often but not pampering it either.

I suggest that you start measuring mpg more accurately:
Next time you fill up, top it off and reset your trip odometer.
Next time you fill up, top it off again, and record the gallons reading on the pump and the reading on the trip odometer.
Divide trip odometer by gallons and remember it or write it down. That's one sample reading of mpg.
Reset your trip odometer.

Do this for a month or so keeping track of the mileage. It will vary, so don't just do it once. Do it several times to get a feel for your mileage.

Keep in mind that you'll get much better mpg on the highway (I get 28mpg cruising at 85mph), so if you do something abnormal like go on a road trip, those numbers will not represent city driving mileage.

EDIT: Have you checked tire pressure? Abnormal tire wear? Those will decrease mileage, too.

To no_skills also:
The bov is recirculated. Brand new NGK BR6ES plugs, gapped with a wire gapper at .028". I did a boost leak test, held 20psi for 6 seconds and fell to 6 after 10. I even took a bottle of soapy water and soaked each coupling and the intercooler and came up with one small leak around the BISS screw. I ordered a new kit form Mach V along with a new dipstick and PCV valve, but the BISS screw still leaked. Not much, but enough to make some bubbles. So I think I'm alset with the boost leak issue.
I track my MPG the way you described it to me. Pull up to the pump, fill it. Once it clicks, I usually round up to the nearest $0.50. Take the milage on the odometer and divide by number of gallons. Like last time, I went 218 miles, filled it with 12.23 gallons. That makes it 17.8mpg.
As I mentioned above, I installed new plugs with a new front O2 sensor from sparkplugs.com. Also bought new OEM wires from local dealer. There is no hesitation/studdering while accelerating, so that leads me to zero misfires. I've included an attached log from last night, hence the low air intake temp (68*). The car seems to go really good, pulls strong all the way to 6500rpms.
Thanks for the advice guys, but I basically already did those checks. My first check was a boost leak, but then I checked everything else. Still coming up stumped as to why I'm getting such crappy milage.

 

[kenamond]

To no_skills also:
The bov is recirculated. Brand new NGK BR6ES plugs, gapped with a wire gapper at .028". I did a boost leak test, held 20psi for 6 seconds and fell to 6 after 10. I even took a bottle of soapy water and soaked each coupling and the intercooler and came up with one small leak around the BISS screw. I ordered a new kit form Mach V along with a new dipstick and PCV valve, but the BISS screw still leaked. Not much, but enough to make some bubbles. So I think I'm alset with the boost leak issue.
I track my MPG the way you described it to me. Pull up to the pump, fill it. Once it clicks, I usually round up to the nearest $0.50. Take the milage on the odometer and divide by number of gallons. Like last time, I went 218 miles, filled it with 12.23 gallons. That makes it 17.8mpg.
As I mentioned above, I installed new plugs with a new front O2 sensor from sparkplugs.com. Also bought new OEM wires from local dealer. There is no hesitation/studdering while accelerating, so that leads me to zero misfires. I've included an attached log from last night, hence the low air intake temp (68*). The car seems to go really good, pulls strong all the way to 6500rpms.
Thanks for the advice guys, but I basically already did those checks. My first check was a boost leak, but then I checked everything else. Still coming up stumped as to why I'm getting such crappy milage.

If you're leaking down that fast in a boost leak test, you still have some leaks. Did you do the test on a warmed-up motor? Was the air leaking out the oil cap (if you removed it) or the VC breather (if you didn't remove the cap)? I'd double-check the PCV valve during the test, as some OEM valves will leak brand new, and all Autozone/Carquest/etc. ones will leak brand new. Also, did you block off the MBC so the small bleeder doesn't leak boost?

If all of the boost leak air seems to be making it to the motor, it could be worn rings or intake valve stem seals.

And how about your tire pressure and alignment?

 

[ekanddsm]

Your not going to get any great gas mileage under boost. I would look at how hard the car is working to cruise.

Flat road, freeway speed, how much vacuum do you get to maintain 70mph with the cruise set. 10-15in should be good. If your puffing black smoke you are rich, but I would look at
o2 signal to see if you are fully sweeping while cruising.
Do you have a maft-safc, or something else that isnt tuned?

 

[ekanddsm]

I didnt see the o2, Check that O2 to see if its working properly

 

[perley03]

If you're leaking down that fast in a boost leak test, you still have some leaks. Did you do the test on a warmed-up motor? Was the air leaking out the oil cap (if you removed it) or the VC breather (if you didn't remove the cap)? I'd double-check the PCV valve during the test, as some OEM valves will leak brand new, and all Autozone/Carquest/etc. ones will leak brand new. Also, did you block off the MBC so the small bleeder doesn't leak boost?

If all of the boost leak air seems to be making it to the motor, it could be worn rings or intake valve stem seals.

And how about your tire pressure and alignment?

Test was done on warm motor, MBC unhooked and tester was clamped on the outlet hard pipe. There was air leaking out the oil cap before, and causing too much crankcase pressure to blow out the dipstick. That's why I bought a new PCV valve and dipstick. I did a boost leak test afterwards and posted the results in the above reply.

Tire pressure on all four 225/45/R17 are 43psi. Alignment, well we won't go there. The guy I bought it off of put on cheap-o lowering springs, which rides rougher than a 3-ton truck. I had it aligned at the college on their Hunter machine and the camber was -1.9* to -2.1*. I got the toe to within 0.07" on the front, and 0.03" on the rears, but I couldn't do anything about the camber. I ordered a full Tokico Illumina spring and strut package, but have not been able to install them yet due to work (working 50-60hrs a week now, and Saturdays ).

Your not going to get any great gas mileage under boost. I would look at how hard the car is working to cruise.

Flat road, freeway speed, how much vacuum do you get to maintain 70mph with the cruise set. 10-15in should be good. If your puffing black smoke you are rich, but I would look at
o2 signal to see if you are fully sweeping while cruising.
Do you have a maft-safc, or something else that isnt tuned?

I didnt see the o2, Check that O2 to see if its working properly

Yes I realize that you will not get the greatest gas mileage under boost. I did this log just for this purpose, for you guys to look at. Cruising at 70-75 I'm seeing right around 12in/hg of vacuum, this is just at about where I am about 95% of the daily drive. I live 1/2 mile from I-95 and travel north 9 miles, and my work is 1/3 mile from the off ramp. Speed limit around the house and work are both 25mph, and most of the time its in 3rd just cruising. Like I said, I'm still stumped on why its running so rich.
By the way, O2 reading the furthest to the right on the log.

I've been thinking about buying a used SAFC and leave it at factory settings except between 2-3krpms and adjusting it leaner little by little, as this is where my cruise rpm's are. I don't see full boost until about 3200rpms anyway, so I don't think this will interfere with my a/f ratio while in boost.

 

[kenamond]

That's still leaking down a lot of boost test air. So even after replacing the PCV valve, checking that it is actually holding boost (boost test with the PCV valve unscrewed from the VC and not getting any air leaking out of it), you still leak down that fast?

If you're leaking all of that boost leak test air in the head/combustion chamber, then I'd suggest a compression test. Or you have other boost leaks. Did you spray the injector/head interface with soapy water (injector seals/insulators)? Head/IM gasket?

 

[ekanddsm]

Ok, the 4g63 is a stout powerplant, thats why we all tend to abuse them, that aside,
Your not seeing full boost until 3200 rpms out of you 14b?
theres a issue there, and your boost leak test should take at least 30-60 seconds to bleed off from 20 psi down to zero

I had my 14b slow to build boost(4000 rpms for 10psi) ended up being a cracked hot side.
Then she decided to blow oil under boost, did a boost leak test and had bubbling noise from oil cap, prepared for the worst, did the boost leak test and unbolted the oil feed line to the turbo, and i got bubbly oil.

Needless to say it was time for a 20g.

I'd say get your boost leaks under control, dont use a aftermarket 02 sensor, and check for any exhaust leaks before the o2. I am leaning towards the o2 you put in, as all your problems showed up after it

 

[No_Skillz]

When you are driving normally, make sure your O2 is cycling normally. What brand is it?

 

[perley03]

Ok, the 4g63 is a stout powerplant, thats why we all tend to abuse them, that aside,
Your not seeing full boost until 3200 rpms out of you 14b?
theres a issue there, and your boost leak test should take at least 30-60 seconds to bleed off from 20 psi down to zero

I had my 14b slow to build boost(4000 rpms for 10psi) ended up being a cracked hot side.
Then she decided to blow oil under boost, did a boost leak test and had bubbling noise from oil cap, prepared for the worst, did the boost leak test and unbolted the oil feed line to the turbo, and i got bubbly oil.

Needless to say it was time for a 20g.

I'd say get your boost leaks under control, dont use a aftermarket 02 sensor, and check for any exhaust leaks before the o2. I am leaning towards the o2 you put in, as all your problems showed up after it

There is a crack on the wastgate flapper, but I'm not too worried about the spool since I'm fwd, and when the boost hits, the front tires break loose. Basically first gear is useless. I changed the O2 sensor when I did the 14B swap, along with all new gaskets (mani->turbo, turbo->O2 housing, O2 housing->downpipe).

When you are driving normally, make sure your O2 is cycling normally. What brand is it?

O2 sensor is a Denso direct replacement, not the universal.

Maybe later today I will dig out the boost leak tester and air compressor, and test again.

 

[S_Ranger]

I have a boost leak tester made, but I don't have access to a air compressor. I have an air tank that lets out air at a steady pressure but the psi I don't know.

If I go to a gas station and use theirs it seems stronger but I can't measure how much psi I'm pushing through, anyone know a solution?

 

[tkelly27]

Grab a pressure gauge from home depot or a super cheap ebay boost gauge.

If you are getting 15mpg and black smoke on shifts, I would look into your BOV recirculation hose. However, I'm getting 20-25mpg on my (stupid) vented setup, so there is most likely something else wrong too. It could also be that the metered air blasts through a gap in one of the charge hoses when the pressure spike of the throttle closing hits.

Try not hitting boost and see what happens to your mileage.

 

[S_Ranger]

Grab a pressure gauge from home depot or a super cheap ebay boost gauge.

Where am I going to mount it? It looks like it'll thread into something.


Sorry, not trying to jack your thread.

 

[tkelly27]

Drill a hole and epoxy a plastic fitting onto the end of the PVC cap. That has held over 20psi for me.

 

[kenamond]

S_Ranger:

Buy a 10-gallon portable air tank ($40 at Lowe's), fill it up past 80psi (if it's not in the red range on the air tank's pressure gauge), and use it to charge the intake tract.

If you don't already have an aftermarket boost gauge, buy one ($50 for an Autometer gauge at Autozone). Most mechanical boost gauges come with hardware and vaccuum line. The line will connect to the gauge with a brass fitting and compression ring. Then you just splice the line into an existing vaccuum line under the hood with a T-fitting. If you aren't ready to or don't want to mount it in the cockpit, just mount it temporarily under the hood where you can see it by following the vfaq instructions. You can remove it and cap the hose when you're done, but set it up so that you can reconnect the gauge and repeat future boost leak tests (you should do them regularly, as rubber/plastic parts degrade over time and begin to leak, and your PCV valve won't last too long).

Then you can boost leak test and watch the boost gauge as you add air. Bring it up to 20psi (or 5psi higher than the boost level you're running), stop adding air, then see how quickly it leaks back down. Should take several seconds to leak down 1psi.

Big leaks can usually be heard. Smaller leaks can be identified by spraying key areas with soapy water in a spray bottle and looking for bubbles. Couplers, gaskets, o-rings, seals, PCV valve, cracked vaccuum lines, and perforated/corroded IC pipes and/or IC are the common sources of boost leaks.