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Discussion Starter #1
I'm doing a fuel pressure test trying to find my poor fuel mileage problem (12 MPG down from 16 with same driving habbits). New explorer motor with lonnie tune, 02 MAF, 22c's and wires, 180* t-stat, etc. I have already contacted lonnie and we are sure it's not the tune as he has done this exact set-up many times and I'm the only one with a MPG drop.

KOEO - Can't figure out how to make the pump run other than cycle key. Haynes says to ground a pin at the data link connector, but shows the one under the hood for the older models and I can't find mine in the Ford CD I have. It says to use equipment to turn on the pump that I don't have.
Anyway, cycle key 2 times = 40 PSI and holds = middle of range. OK

Engine running with Vacuum hose on = 30 psi = minimum of range. So-so

Engine running with Vacuum hose off = 40 psi = minimum of range. So-so

Now here's the weird part. The book says to shut it off and see if it hold a minimum of 30 psi. Well, mine will sometimes and sometimes won't. Pulling the vaccum hose to the FPR makes it hold more often than with it on. But most times it drops to 5 psi as fast as the engine dies.

When I squeeze close the return line, I get 60 psi. I believe this tells me the pump is good.

I think it is the FPR letting it bleed off since it happens so quick, but it may be the pump bleeding off according to the CD.

Up-date: just went out to verify one of the reading for this post. Now that it has been running for a few minutes off and on.

KOEO = 38 psi on the first key cycle. Yeah!
Still at min for vaccum hose on and off FPR = 30 and 40 psi respectively. Huh?
WOT = 40 psi. tech article says if it doesn't go below 39 psi, it's ok.
Bleed-down test after 5 minutes of engine being shut off, it actually went up to 40 psi after engine running at 30 psi.

What do you experts think? No problem, FPR bad, Pump bad, or is this normal between cold and hot running temp. I'm stumped.

Car has 165K and don't know if the FPR or pump has ever been changed. I have no cats and don't smell fuel and can't find any external leaks.

thanks,
Rob
 

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Your bleed down is too fast... they all bleed down, but it should take some time...The FPR bleeding down gives you less constant press, and should be addrerssed .. Get A good adjustable like a Kirban or something, but not BBK as they are Po-Po.... I dont think thats your problem tho'.You might try switching back to stock tune for a while, just in case, as no tune is infaillable, and also the stock MAF should be usedwith stock tune... if thats ruled out then what you may have to address is the injectors themselves.... there really isnt much else, and your pressure isnt that high, so its not fuel pressure (lower makes better mileage) Also theres the possibility of o2 sensors going... they will usually last 100k or so, but you should be throwing a code then.... I thought my 14-16mpg was a tad low, but....
in any case good luck
 

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My 4.6l runs great and I just had the shop verify the fuel PSI today because I'm going to stick an adjustable regulator on tomorrow. I want to know where it was now so I could set the new regulator at it's base. Key on engine off 39.5 PSI. Car running at idle with vac on 34 PSI. With vac off 41 PSI. At 150,000 miles on the Odometer. I will say several things about gas milage: 1) You can't judge milage by one tank. 2) In town with lots of start ups will suck it down 3) Highway takes 1000 MI. to see. 3) Switching from stock gears to a higher set up will absolutley require more gas, but you will enjoy the HP at higher RPM's. 4) 0pening the intake or exhaust one step at a time, allows the engine to breath more air, which requires more fuel. 5) The mods we do end up producing 25% more horsepower tops with a stock bottom end, and result in about a 25% reduction in gas efficiency. So at $2.15 a gallon for premium, you have to make a choice. Are you willing to go the extra mile for performance, or do you want to do other things.
 

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Discussion Starter #4
Leland Jacobson said:
Your bleed down is too fast... they all bleed down, but it should take some time...The FPR bleeding down gives you less constant press, and should be addrerssed .. Get A good adjustable like a Kirban or something, but not BBK as they are Po-Po.... I dont think thats your problem tho'.You might try switching back to stock tune for a while, just in case, as no tune is infaillable, and also the stock MAF should be usedwith stock tune... if thats ruled out then what you may have to address is the injectors themselves.... there really isnt much else, and your pressure isnt that high, so its not fuel pressure (lower makes better mileage) Also theres the possibility of o2 sensors going... they will usually last 100k or so, but you should be throwing a code then.... I thought my 14-16mpg was a tad low, but....
in any case good luck
02s are new from Dan. Reused injectors with unknown mileage. If any were replaced, I'm sure it was only the one causing a problem at that time. I wanted to get new ones, but the swap drained the $s too fast. I'm sure you know what I mean. I'm gonna keep checking other things first. I haven't torn the fender wells apart yet to re-check the vacuum lines. Unlikely, since I changed them with the new 96/7 fuel lines. But It's worth a try.

So, you say the bleed-down being bad is not the fuel mileage problem. But you say it should be addressed. Could you please elaborate. I know it's supposed to work that way, but don't understand why it needs to work that way or the consequences of it not.

Thanks for the advice on which FPR to get.

Ed, I figured at first that there would deffinately be a fuel mileage trade-off with the HP increase. But got concerned when lonnie said that I am the first to say it went down. He said most gained 1 to 2 MPH. So, I'm just trying to see if something is bad that I don't know about. For example, during my search on the car, I found that the vapor purge line from the tank to the charcoal canister, had bad hoses where it junctions into plastic around the fuel filter. Probably doesn't have anything to do with MPG, but needed to be fixed anyway.

Somethings gotta be wrong when others are getting into the 20s on the highway with blowers, steaper gears (I've still got open 3.08s), etc.

Not stressin' about it, just need to track the problem down.

Thanks,
Rob
 

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girdnerg; Bleed down causes a variable in fuel pressure, so part of the time youre running lean due to low pressure, then the computer corrects the fuel injector pulse width to compensate, then a change in load, or throttle position and the whole cycle starts anew.... the computer cant keep up as fast as it is because of the bleed down variable compounding a dynamic situation... untill you get a reg with some stability in it the tune will be off, on either side in a drive cycle and the computer will be working its a55 off... I doubt that any FPR holds its pressure verry long after shut down, but It should hold it for a while... if you dont show 5-10 lbs, say ,about 5 min after shut down I would replace it... however thats just my opinion, there are folks out there that would disagreewith anything I say... Also, did you double check the wireing in the MAF against whats on Lonnies web site? you just may want to eyeball it again... and no matter what be sure and give us a final post when its all figured out...... ;)
 

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Discussion Starter #6
Thank you Leland, that was what I needed to know. The way you described it, it does sound like that may have an effect of MPG since the computer is working it's A55 off and can't get a stable pressure.

I'll check the MAF wiring again. I did catch the pig-tail differences, held the two next to each other and did one wire at a time. But, at this point, I'll try anything.

thanks,
Rob
 

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Discussion Starter #7
MAF wiring is correct.

A - red
B - black/white stripe
C - Tan/blue stripe
D - Blue/red stripe
E and F - lonnie said didn't matter for IAT.

Rob
 

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Check Gas Cap :confused: for a good seal - Leland is 100% correct on bleed down it should hold pressure.


girdnerg said:
Thank you Leland, that was what I needed to know. The way you described it, it does sound like that may have an effect of MPG since the computer is working it's A55 off and can't get a stable pressure.

I'll check the MAF wiring again. I did catch the pig-tail differences, held the two next to each other and did one wire at a time. But, at this point, I'll try anything.

thanks,
Rob
 

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Discussion Starter #9
Well, thanks for the help guys. I have NOT been able to duplicate the failure. I have done the FP test 4 times now and it passes everytime. Either the problem fixed itself, I accidentally fixed it while messing around (the CD did say to tap on it), or most likely, the first 2 tests were operator error (me).

LST MN-12,
The Fuel cap is new from Dan. I even cleaned up where it seals when I put the new one on.

Went crazy with the carb cleaner today trying to find a vacuum leak. I get a little change in idle when I spray the charcoal canister purge valve. I'll search and find out how to troubleshoot that. I'm not familiar with it's operation.

Once again thanks gentlemen. I'm sorry if it was me just hooking it up wrong or something. May have been the crazy highs and lows in the temp lately.

The search continues :)
Rob
 

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Winter fuel will cause your mileage to vary sometimes as much as 4-5 MPG
 

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Hey timb,
Hope you are doing well.
I took that into account. But the change happened from the end of DEC to now.
It's just that it points to something being wrong and I don't mind chasing it down.

See the post above for a small vacuum leak I found. I'm gonna troubleshoot that and see what comes of it.

Thanks,
Rob
 

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Cool. Good luck with it. We are doing just fine down here...in fact my wife is pregnant again so I better get all my projects finished soon :)
 

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Discussion Starter #13
timb said:
Cool. Good luck with it. We are doing just fine down here...in fact my wife is pregnant again so I better get all my projects finished soon :)
Congradulations! You haven't figured out what's causing that yet :D It took us 4 times to figure it out, lol.

I'm very happy with the way the car runs. I just keep reading how others gain MPG with the tune, and how others are getting in the mid to high 20s (with and without a tune). Well, mine never got above 21 MPG (freeway) even with the stock motor. Then after all the new parts; motor, 02s, plugs, wires, MAF, etc. I thought that it would get back up to where it is supposed to be, but it didn't. I/we will get it figured out.

Rob
 

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girdnerg said:
Congradulations! You haven't figured out what's causing that yet :D It took us 4 times to figure it out, lol.


Rob
I'm not sure but I think it was all that time without power after the hurricane with nothing else to do :diablo:
 

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Discussion Starter #15
Well, I finally did a highway MPG test.

165 mi of mostly 65-75 mph, about 10 mi of it was sem-city (still doing 65 on the thru-ways in town, but still some stop and go. One WOT to merge onto freeway.

20 mpg! That's a lot closer to what it should be.

Man, I had no idea that winter gas would drop mileage so much. Still gotta figure out it the EVAP purge valve is working corretly or not. That's the only place carb cleaner will cause an engine change (slight).

Thanks Gents,
Rob
 
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