Poor MPG after mods

90coug

Registered User
So I've worked on my bird quite a bit and it puts a grin on my face every time I drive it. Thing is, it's just really bad on gas now and I'm not sure if it's normal. I have 3.55 in the back and my car is a manual (I know, just haven't gotten around to switching them out), is this a big culprit for the poor mpg? I'm averaging 9.8MPG :eek:

I also believe that my tune is a bit on the rich side. I had to travel to the dyno and mail the chip back and forth to have it tuned so it was never perfect. I've been meaning to get a QH but don't have cash for it at the moment. I had the fuel pressure at 50 PSI when tuned (I had a junky meter and it said it was at 40 but now have a better one), could the tune with high FP cause the poor MPG? I have my mods listed in my garage if anyone is curious.

Is it possible that I'm actually seeing the right MPG? What do you guys think?


Thanks,

-B
 
well first off...not many people want to go searching for your mods list...so I always put all info needed in the thread.

Second, we have very similar mods and I have never tested my MPG, but I would say I get probably around 15mpg highway

So 9.8 average might be about right
 
No way in hell. You are washing down your cylinder walls and causing cumulative damage to the motor at 10mpg. The car should get 15mpg at an absolute worst (unless you are racing it all the time), and can get as much as 20-22mpg with 3.55's.

There is nothing in the chip that would cause 10mpg so you need to start checking things. Start by setting the fuel pressure right or ditching the AFPR altogether as you simply don't need it. I'm going to get my pedestal out now and state that *if you have an AFPR you MUST have an in cabin fuel pressure gauge*. If you don't want to spend the money on the gauge, then put a stock regulator on.
 
My sc is my only car and if i got 9-8 MPG when i get my heads and cam with some OD that won't he good form me
 
Dave, you told me to keep it at that since that's what we tuned it at. I'll change it right away. I don't smell fuel at all so it's not leaking. I did do an oil change not long ago and it did kinda reak of gas. It performs really well though :)

Oh and I do have a IN-Cabin gauge, it's static at 50psi all the time <--- will fix tonight and put to 40

I do race it all the time, in fact it's just the weekend car and it get's abused
 
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Dave, you told me to keep it at that since that's what we tuned it at. I'll change it right away. I don't smell fuel at all so it's not leaking. I did do an oil change not long ago and it did kinda reak of gas. It performs really well though :)

Ugh. Well I hate AFPR's for applications that don't require them. I don't know what mods you are currently doing or what you currently have so if you have changed something I can't imagine that the tune is right anymore. I'm not giving you a hard time, it's just that I seriously don't remember what you have and something tells me you've been making some changes to the car. Maybe I'm off base. :confused: Would be par for the course lately.

What you need to understand is that the EEC goes closed loop for 95% of all conditions during which an AFR of 14.7 is demanded. This AFR will generate decent mileage. If the EEC cannot go closed loop or can't generate 14.7 AFR on it's own, it will generally throw a CEL or run very poorly or inconsistently. In other words, there should be an indication. If it isn't going closed loop then things are completely FUBAR for some reason and really need to be fixed. Being that I can't be there with you hands on, you are going to have to be "my eyes and ears" to let me know if something is wrong.

To conclude, a tune is never "slightly rich" except perhaps at full throttle. A car should never be "slightly rich" driving around. If it is then there is a serious issue. This applies to all SC's, including those with solid roller cams and 30psi boost. ;):p
 
The only thing changed is a 5% jackshaft pulley and some high flow cats and new down pipes, that's it.

Mods done at time of tune

60# injectors
90mm lightning MAF
85MM TB
MPX w\ 10% pulley, raised top and coated rotors
CAM 550 lift, 224 intake and 230 exhaust duration
ported Big valve heads
ported stock exhaust
255lph pump
3.55 gears

I'll fix the FP and drive it under boost for a while. Easier said than done :p
 
Oil smells like gas

If your oil smells like gas then, then it sounds like a leaky injector!

Tom
 
Dave, tell me what you think.
Does this look like it's climbing with the boost correctly.
I have my doubts so I thought I would record it the best I could.
The video's are so so, fast forward to the end of the second one for another glimpse of the boost and FP.
I would put the stock FPR back on but's I'm not up for that much work at the moment.
I've forgotten, do you set the pressure with the vac hose on or off?

Here is an attempt at the boost while I'm driving

Here is a better shot for the fuel pressure and where it's going.

Here is a quick shot of both while reving it
 
Ok, so it's not so bad. You have a fuel pressure gauge. Now you just need to know how to set your AFPR.

Go to your diagnostic connector and jumper the fuel pump feed. Then turn the key on but don't start the car. Observe pressure with pump running but engine off. Set pressure to 40psi.

Then you'll have to get a wide band on the car and see what AFR you are getting at WOT. I'll reburn the chip for you accordingly.

Because you have a lot of cam and live at high altitude, we may have to make some further adjustments to get satisfactory performance. You may be suffering from excessive boost syndrome. :p
 
Ok, so it's not so bad. You have a fuel pressure gauge. Now you just need to know how to set your AFPR.

Go to your diagnostic connector and jumper the fuel pump feed. Then turn the key on but don't start the car. Observe pressure with pump running but engine off. Set pressure to 40psi.

Then you'll have to get a wide band on the car and see what AFR you are getting at WOT. I'll reburn the chip for you accordingly.

Because you have a lot of cam and live at high altitude, we may have to make some further adjustments to get satisfactory performance. You may be suffering from excessive boost syndrome. :p

I think I am experiencing excessive boost syndrome, lol might be why my gas mileage is so poor :)
I set it just as you suggested. When I start the car it idles around 34 or so, is that right? Or should it idle around 40?
 
Seems about right... remember that fuel pressure is being controlled by manifold pressure, go into vacuum, pressure is lowered below reference which is 40psi as Dave mentioned, go into boost, then it goes above reference.

Reference fuel pressure is based off of atmospheric pressure. What you are trying to do is keep the "environment" that the injector is pushing fuel into a constant so the EEC doesn't need to worry about that and it thinks the injector is running at atmoshperic pressure all the time. It commands a pulse width of 5ms and expects that x amount of fuel is being injected no matter what is going on inside the manifold.

Something like that anyway.

Fraser
 
Seems about right... remember that fuel pressure is being controlled by manifold pressure, go into vacuum, pressure is lowered below reference which is 40psi as Dave mentioned, go into boost, then it goes above reference.

Reference fuel pressure is based off of atmospheric pressure. What you are trying to do is keep the "environment" that the injector is pushing fuel into a constant so the EEC doesn't need to worry about that and it thinks the injector is running at atmoshperic pressure all the time. It commands a pulse width of 5ms and expects that x amount of fuel is being injected no matter what is going on inside the manifold.

Something like that anyway.

Fraser

Fraser, good to know. I'm glad to see it's where it should be now. It runs like crap however, maybe I'll bump it back up before I take it to the dyno?

bryce
 
Did you disconnect the battery for awhile to clear adaptive?

Fraser

I tinkered with it a bit more and it runs fine now with the correct FP PSI. I will also clear the battery.

Dave, Fraser and everyone else, thanks a million! Don't know where I would be without the members on this board. Dave, I know your busy with the shootout so I'll send you the chip sometime after the first week of October.

bryce
 
I tinkered with it a bit more and it runs fine now with the correct FP PSI. I will also clear the battery.

Dave, Fraser and everyone else, thanks a million! Don't know where I would be without the members on this board. Dave, I know your busy with the shootout so I'll send you the chip sometime after the first week of October.

bryce

Better yet, bring the chip to the shootout. Do all the driving yourself though.:p
 
Ha, that trip will never be forgotten, I still give Chris crap about it to this day.

The shootout would be a blast and it's been on the list but the 1200mi 20hr drive is holding me back :D One of these days I'll fit it in, maybe make a trip out of it and visit the northern east coast area.

Could you imagine the gas bill with my 9.8 MPG issue? :eek:
lol, not to mention the fear of being stuck in Wakeeny KS again!
 
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