Thrashing Poor Gas Mileage

imp · Jul 28, 2017

'94 GT 5.0L HO 5-speed, bought recently. New O2 Sensors, brand new (off Motorsports 5.0 in my shop) T.B. with TPS and IAC. Deleted puny K&N filter inter fender and added a big K&N. Previous owner deleted smog pump, belt bypasses it, removed canister and it's valving, plugged vacuum lines. Have not yet explored vapor line from tank, it's not present underhood.

AFAIK, the above cannot account for the dismal 13-15 mpg in town, can it? My '93 Cobra, stock, easily did 20 in town, 25 highway. Both with 3.08s. I'm driving it pretty conservatively. Wondering if the PCM might have been reflashed. Is there any easy way to tell, short of installing factory program, or new PCM?

Suggestions, ideas appreciated. imp

Dan02gt · Jul 28, 2017

If you have a fender mounted CAI that has a 90* bend before the MAF sensor, that can throw its metering off and give you crappy gas mileage. If you have a engine bay mounted air filter that is not shrouded, fan wash can cause the MAF to read incorrectly and cause issues.

If you want to check the PMC tune most of those were done via chip. You can pull the computer out and look in the chip port that's normally covered with a metallic tape.

jrichker · Jul 28, 2017

My standard answer...

Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/

Until you know if there is anything that needs fixing you, have no solid foundation to start with.

imp · Jul 28, 2017

jrichker said:
My standard answer...

Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/

Until you know if there is anything that needs fixing you, have no solid foundation to start with.

Am ahead of that. There were 2 DTCs, which were completely 180 out with one another, have to go back to see what they were but unrelated to anything here. Deleted them. imp

Noobz347 · Jul 28, 2017

imp said:
There were 2 DTCs, which were completely 180 out with one another

Excellent. 4 cycle motors don't function very well if there aren't.

General karthief · Jul 28, 2017

No charcoal canister? You need that. I think the 94-5 is inside the fender in front of the passenger wheel behind the plastic inner fender shield.
I think
Maybe
Probably
Or under the passenger front seat.

imp · Jul 28, 2017

karthief said:
No charcoal canister? You need that. I think the 94-5 is inside the fender in front of the passenger wheel behind the plastic inner fender shield.
I think
Maybe
Probably
Or under the passenger front seat.

Does burning the vapor now and then increase gas mileage? I dunno. 5 mpg down is 25% lower than expected. Not dragging brakes, low tires. Retarded initial timing? Have not yet checked that, but it DOES seem to run hotter than I would expect, but no numbers to back that up. Retarded = hotter, in general. imp

General karthief · Jul 29, 2017

Can advancing the timing too far cause overheating also? The vapor canister is for venting the fuel tank, don't know about changing fuel mileage, keeps the vapors from escaping when parked in enclosed area among other things.
I pay little attention to fuel mileage, I drive mine like I stole it!
And what is this 'peanutbutterjellytime'? too broke for baloney samiches?

Real time recon · Jul 29, 2017

How about the PCV valve ? And more importantly the Metal screen under it. Are they both clean ? When shaking the PCV valve does it make noise ?

General karthief · Jul 29, 2017

imp said:
Does burning the vapor now and then increase gas mileage? I dunno. 5 mpg down is 25% lower than expected. Not dragging brakes, low tires. Retarded initial timing? Have not yet checked that, but it DOES seem to run hotter than I would expect, but no numbers to back that up. Retarded = hotter, in general. peanutbutterjellytime

Find a right shoe that is 25% lighter, or go bare foot, just say'n.

imp · Jul 29, 2017

Real time recon said:
How about the PCV valve ? And more importantly the Metal screen under it. Are they both clean ? When shaking the PCV valve does it make noise ?

Will check into this, thanks for suggestion. Wiring prints show the PCV is "Heated", a new one on me! imp

Noobz347 · Jul 29, 2017

I'll ask a basic question:

How are you measuring your gas mileage?

imp · Jul 29, 2017

Noobz347 said:
I'll ask a basic question:

How are you measuring your gas mileage?

Basic not "trick", right? I filled the tank full as I can get it, 3 or 4 times now, drive about till more fuel is needed, record miles driven per tankful. Why do you ask? imp

Noobz347 · Jul 29, 2017

imp said:
Basic not "trick", right? I filled the tank full as I can get it, 3 or 4 times now, drive about till more fuel is needed, record miles driven per tankful. Why do you ask? imp

I've seen folks try and use the fuel consumed instead of the refill amount while others have used data-logs of various types.

Generally, I like to stick to the same pump at the same station and refuel until the cut-off.

Anything based upon the fuel gauge is probably the least accurate.

imp · Jul 29, 2017

Noobz347 said:
I've seen folks try and use the fuel consumed instead of the refill amount while others have used data-logs of various types.

Generally, I like to stick to the same pump at the same station and refuel until the cut-off.

Anything based upon the fuel gauge is probably the least accurate.

Very true, that! I believe the automatic cut-off is pretty questionable, based on my recent experience with several dispenser nozzles at my usual water hole that cut off many times during fill attempts. One really pisses me off, which in turn, of course, pisses my wife off (at me!). imp

Noobz347 · Jul 29, 2017

imp said:
Very true, that! I believe the automatic cut-off is pretty questionable, based on my recent experience with several dispenser nozzles at my usual water hole that cut off many times during fill attempts. One really ****es me off, which in turn, of course, ****es my wife off (at me!). imp

My wife's car was similar. S-197s for famous for tripping the pump.

Real time recon · Aug 1, 2017

Change that PVC valve and wire screen that's under it.Cheap/easy maintenance,for better gas mileage.Old one on right.New replacement on left.

.

imp · Aug 1, 2017

@Real time recon
I will try that! Thanks! imp

Thrashing Poor Gas Mileage

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