Extremely Low Mpg...why???

rideapony · May 22, 2017

I think I understand the operation, but for some reason the valve is opening to the wrong direction.

I re-plumbed the valve and the fuel vapors smell disappeared.

I haven't run a KOER test yet. But by default I can predict I won't see error code 85 because the venting valve is operating electrically correct. It opens and closes but the flow is wrong.

My issue most likely will be that she is running extremely rich, either injectors related or O2. Just a few days ago I started feeling explosions inside the exhaust pipes
from time to time. I felt one of those today. It seems like excessive fuel is coming in and igniting inside the pipes.

General karthief · May 23, 2017

You would be able to smell gas at the tips
Pull the coil wire and crank it over a couple revolutions and smell the tail pipes.

Mustang5L5 · May 23, 2017

rideapony said:
I haven't run a KOER test yet.

My issue most likely will be that she is running extremely rich, either injectors related or O2.

If that's the case, you'd get codes for the o2 sensors when running KOER codes, and if any injectors are dead, they would show themselves when running the cylinder balance test which disables one cylinder at a time to test output.

Not doing these two tests is just creating unnecessary guesswork.

rideapony · May 23, 2017

Thank you guys for staying helping me thru this troubleshooting.

I'll do that quick fuel smell test and then run a KOER test to see if I get any clues about this issue

Thank you all!

rideapony · May 23, 2017

Here is an update:

I just ran three tests using my code reader.

Timing advance operation by the computer: the computer is performing the time advance correctly, 30 degree total advance

KOER: Error codes #'s 12, 94, 44

Cylinder Balance Test: Code 90 (System is OK, all cylinders are contributing equally)

I kinda wanted to see at least one error code that had a direct correlation with my absurd fuel consumption.

So how to solve the three error code from the KOER test?

And even more important... Now where to go from here????

Thank you all

Mustang5L5 · May 23, 2017

Code 12 is referencing the idle speed controller being out of range. Remove the IAC, and clean it. Reinstall it, but do not plug it back in. With it unplugged, open the throttle stop screw a few turns, and start the engine. The idle should be high. Then, back the idle screw down until you get a nice, stable, but low idle. At this point, shut the engine off, unplug the battery for 30 mins, plug the IAC back in, and then start the engine and allow it to relearn idle. This WILL wipe all the codes, so do this towards the end.

Code 94/44 are common codes, referring to the air injection system from the smog pump. Either allyour smog stuff is removed, or the crossover tube is clogged up. They typically do not affect how the car runs though.

But you are right, I don't see any codes that pertain to your fuel consumption. Have you pulled a spark plug and inspected the plugs to see if they look like you are burning rich? Do you happen to have a fuel pressure gauge you can hook up to the rail? The FPR vac line doesn't smell like gas, does it?

rideapony · May 23, 2017

Yeah I will reset the base idle.

The entire smog system has been removed the right way (I guess) and as you said and as far as I know it is not a factor for high fuel consumption.

I don't have any fuel smell out of the regulator vacuum fitting, and yes I do have a fuel pressure gauge. I will check how much pressure I'm running at.

I just pulled plug No 1 and this is how it looks, I see black carbon dust like running rich...

Mustang5L5 · May 23, 2017

That plug doesn't look too bad to me. Usually rich Plug would be darker on the ceramic portion.

What is the full list of mods on your car? I know you said you had an SN95 MAF, but with 19# injectors? it a 306, but what else is on the motor?

rideapony · May 23, 2017

Update:
I just went to replace the FPR, I missed checking my fuel pressure before I replaced it but I just measured the fuel pressure with the new FPR: Vacuum off is about 41 psi, vacuum on 39 psi. Will see how it behaves.

Motor mods are: 306 stock block, TWF street heads clamped with ARP studs and 7/16 1.6 Pro magnum RR's, TWF stage-1 cam, TWF Heat U/L intakes, Speed pro flats with molly rings, 65mm TB, Stock MAF sensor and tube, 210 lph Fuel Pump, 1 5/8" Ceramic BBK shorties,

I was using the MAF tube and electronics out a SN95. This set up is calibrated to 19 pounders.
I went back to the stock 55mm MAF sensor and tube thinking that was the problem but still the same.

Thank you all!

Mustang5L5 · May 23, 2017

Well, none of your codes indicate rich. I'm not sure the plugs do either. While your mpg is low, it is city driving with a v8.

I might be tempted to swap out the o2 sensors to a new fresh set, as they could be drifting a tad, but short of that, I'd almost want to get a wide band and actually measure what your air/fuel ratio actuallly is

rideapony · May 23, 2017

I know what you mean, I'm getting frustrated as this don't make much sense.
There is one posiblibity, that some of the sensors failures don't get registered in the computer memory until the sensor is completely broken. For instance here are some statistics of a MAF performance I found

Could there be similar list of failures on O2 sensors???

And yes A/F ratio wide band would be the best, but don't have one

Thank you all

Mustang5L5 · May 24, 2017

Those are mostly OBD2 codes. Uncertain to if the primitive OBD1 system we have has the capability of registering that beyond voltage ranges being out of spec. A bad MAF would in fact cause the car to run rich, but you've tried two now correct?

It is frustrating, because here's an example of the car not giving you any codes that point to a partocular problem, but a suspected problem nonetheless. I really hate blindly throwing parts at an issue and guessing.

I guess routine maintenance would be my next step. Have you cleaned the MAF sensor? I'm assuming since you've tried two MAF's this isn't the case. You've pulled spark plugs and inspected though. What about fuel filter? Relatively new?

If there was a sensor I'd blindly swap out, it would be the o2 sensors. Rockauto.com has Motorcraft O2 sensors for $29 each. I'd probably replace these, clean the MAF, perform the idle reset procedure, reset the computer, and then put a few miles on the car and repull the codes and see what you get then

rideapony · May 24, 2017

I feel the same, certain sensors will start downgrading their performance over time and not sure if the computer has the capability of measuring and to save possible out of spec condition. I know in some instances the computer triggers a warning of out of range condition but maybe this is not the case on all the sensors and actuators.

I did try two different MAF sensors and give constant cleaning with MAF cleaner. I'm reluctant too to replace parts arbitrarily first because probably unnecessary cost and second you loose track of what really solved the problem.

Although I try to be on top of maintenance, this problem has been there for a while and I've neglected it but it is time to solve this once and for all. I will remove and inspect all the plugs and replace them along with the fuel filter and clean the air filter. I have a K&N filter and I heard that this filter could cause MAF contamination, I don't see any residues on the resistors but I spray them and let them air dry very often just to be sure.

I will consider replacing the O2 sensors but like I said if I make so many changes at a time I will loose track of what was the root of the problem.

Very good suggestions, I appreciate it and thank you for your time and help!!!

rideapony · May 24, 2017

Update:
I just removed all the plugs but I don't see a hard indication of over fueling.

Now, a restricted fuel filter it's said will affect fuel economy (MPG) so would I see more carbon on the plugs or less?

General karthief · May 24, 2017

A couple questions
Didn't see what trans you where running, maybe you did but missed it
Rear gear
Rear tire size

rideapony · May 24, 2017

You're right, didn't include that as that is not a motor mode, but here 'ya go:

T5 z specs
3:55
245/45/17

I friend of mine told me that that high fuel consumption is because the low vacuum readings due to a Trick Flow stage 1 cam. Does anyone has the same etup I have and can you tell me what are your vacuum readings? Here I have about 9 In... is that too low due to possible vacuum leak???

General karthief · May 24, 2017

The reason I wanted the gear, trans and tire size was questioning your speedo reading, you did change your speedo gear, right?
I would say 9" at idle is low for a stock engine but yours is built, cam overlap can effect vacuum too, so not sure what the vacuum is telling us, it should be steady and not bounce,

rideapony · May 24, 2017

Yeah I changed the speedo gear.

Vacuum is at 9 steady at idle. I hope to hear from somebody using the same street twisted wedge heads, TFS stage 1 cam, and intakes on a 306 block, post vacuum readings. maybe I have a vacuum leak somewere.

My friend told me that if the vacuum is low the MAF is out of control because there is not much suction thru the TB and it gives erratic measuring to the MAF. He said that whoever sales these cams must sell you the appropriate MAF..... By God I've never heard that before!!! as far as I know you get a new MAF caibrated when upgrading injectors but that's it. So he said that with that low Vacuum reading

General karthief · May 24, 2017

Never heard of that but I'm not an expert,

Noobz347 · May 24, 2017

rideapony said:
MAF is out of control because there is not much suction thru the TB and it gives erratic measuring to the MAF. He said that whoever sales these cams must sell you the appropriate MAF..

No

Extremely Low Mpg...why???

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