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#4115252 - 07/15/21 02:35 AM 07 P71 - terrible MPG, possible FPR issues?
STR Offline
Stranger

Registered: 07/09/21
Posts: 6
Loc: TX
Sorry guys, I looked through the first few pages and didn't see anything that really applied.

First off, hi, new member, 2007 P71 detective car (supposedly - the idle hour meter confirms it didn't idle much, at least, and no center console or signs of a cage).

My mileage is absolutely terrible - 10-13 mpg for the most part. Most of it is city driving, but highway is only getting 13-15, and it just doesn't seem like it has the power that it should. My SO has told me it blows black smoke when they're behind me and I stomp it as well.

I'm using FORScan Lite for Android to get my FPR readings for now. When cold, it's seeing 38-40 PSI (which seems normal). When warm, it's showing 70-80 PSI. That seems... excessive. If I hammer it, I'll get a strong smell of raw gas inside the car for a minute or so afterwards, and it'll hesitate/buck a little if I lay into it without easing in. 2 injectors are damp where they meet the fuel rail, but not obviously leaking at idle.

The only powertrain related code it's thrown has been EVAP, but that was fixed with a new gas cap.

I suspect the injectors being damp are a symptom - 70 PSI seems pretty high to me, though I haven't found a schrader to check pressure the proper way, I've only been able to check it via what the PCM is seeing.

There's no fuel inside the vacuum line from the FPR, no gas smell from that line either.

This is my first EFI Ford - I'm pretty shocked at how much info I can pull from the PCM, but it's almost like information overload. Should I be looking at the FPR, or is there something that could be commanding higher fuel pressure?

I have not yet logged fuel trims, but I plan to next time I drive it.

Thanks guys.


Edited by STR (07/15/21 02:39 AM)

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#4115290 - 07/15/21 04:12 PM Re: 07 P71 - terrible MPG, possible FPR issues? [Re: STR]
RF_Overlord Offline

Poobah

Registered: 12/14/02
Posts: 7673
Loc: MA
Black smoke is a good indication of the engine running pig rich, which will also account for the poor fuel economy. Check inside the tailpipes for lots of black soot. By all means check the fuel trims...you'll likely find them way out of whack. 70-80 fuel pressure is very high.
_________________________
'03 Mercury Marauder (The Blackbird)
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Too many mods to list / Driveway Queen

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'00 Grand Marquis GS (Silver)
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#4115298 - 07/15/21 05:26 PM Re: 07 P71 - terrible MPG, possible FPR issues? [Re: STR]
2008interceptor Offline
Over the Hill

Registered: 09/02/02
Posts: 3280
Loc: Pennsylvania
I'm not sure if this is possible. However were this a flex fuel car could a bad sensor cause it think it's using flex/e-85 and it's dumping the extra fuel in for it? Another thing to check would be the maf could be fouled.
_________________________
2008 Ford Crown Victoria Police Interceptor P71 with street appearance package.

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#4115300 - 07/15/21 05:31 PM Re: 07 P71 - terrible MPG, possible FPR issues? [Re: STR]
SocalSam Offline
Over the Hill

Registered: 03/30/13
Posts: 2839
Loc: SFV, Calif.
Thinking dirty O2 sensors. They are cleanable. My city mpg is not much better than yours. My highway mpg is better.
_________________________
2004 CV LX Sport #1, 57,000 miles -- Never was
2004 CV LX Sport #2, 121,000 miles -- Current
2008 CVPI Arizona Beige, 121,000 miles, 677 idle hours -- Current
2005 CVPI Ex-San Diego P.D. -- 2 month loaner


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#4115316 - 07/15/21 07:30 PM Re: 07 P71 - terrible MPG, possible FPR issues? [Re: STR]
Chaplian Offline
Insert witty title here
Poobah

Registered: 08/26/12
Posts: 5479
Loc: Chicago, IL
Originally Posted By STR
Sorry guys, I looked through the first few pages and didn't see anything that really applied.

First off, hi, new member, 2007 P71 detective car (supposedly - the idle hour meter confirms it didn't idle much, at least, and no center console or signs of a cage).

My mileage is absolutely terrible - 10-13 mpg for the most part. Most of it is city driving, but highway is only getting 13-15, and it just doesn't seem like it has the power that it should. My SO has told me it blows black smoke when they're behind me and I stomp it as well.

I'm using FORScan Lite for Android to get my FPR readings for now. When cold, it's seeing 38-40 PSI (which seems normal). When warm, it's showing 70-80 PSI. That seems... excessive. If I hammer it, I'll get a strong smell of raw gas inside the car for a minute or so afterwards, and it'll hesitate/buck a little if I lay into it without easing in. 2 injectors are damp where they meet the fuel rail, but not obviously leaking at idle.

The only powertrain related code it's thrown has been EVAP, but that was fixed with a new gas cap.

I suspect the injectors being damp are a symptom - 70 PSI seems pretty high to me, though I haven't found a schrader to check pressure the proper way, I've only been able to check it via what the PCM is seeing.

There's no fuel inside the vacuum line from the FPR, no gas smell from that line either.

This is my first EFI Ford - I'm pretty shocked at how much info I can pull from the PCM, but it's almost like information overload. Should I be looking at the FPR, or is there something that could be commanding higher fuel pressure?

I have not yet logged fuel trims, but I plan to next time I drive it.

Thanks guys.


How many miles on the car? What have you done to it so far?
_________________________

2003 Crown Vic HPP- 226,xxx miles. Projector Retrofit. 3.27s. Dual exhaust. 11.25" torque converter. Arnott Limo Duty HPP-rate rear air springs. (Stolen by the old man)
1995 Impala SS- 28,293 miles. The Lovely Lady
2003 BMW 325i Sedan- 138,xxx miles. Eibach Springs, Bilstein shocks, polyurethane bushings, Projector Retrofitted lights, 330i brakes, 330i rear-end, 235/45/r17 Sport Comp 2s. Autocross machine.
2003 BMW 325i Wagon- 118,xxx miles. Eibach Springs, Koni Yellow shocks, M3 differential (LSD), M3 rear suspension/brakes, 330i front brakes, M3 6 Speed manual, Alcantara headliner.
2017 Mazda3 GT Hatchback- 57,xxxx miles. 2.5L, fully loaded. The Daily Grind.

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#4115336 - 07/15/21 09:07 PM Re: 07 P71 - terrible MPG, possible FPR issues? [Re: STR]
MurkyMerc Offline
Rookie

Registered: 01/06/15
Posts: 51
Loc: NH
My stock '05 MGM averages 19-21 mpg combined for reference.

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#4115728 - 07/20/21 07:13 AM Re: 07 P71 - terrible MPG, possible FPR issues? [Re: STR]
STR Offline
Stranger

Registered: 07/09/21
Posts: 6
Loc: TX
Sorry for leaving you guys hanging.

I replaced the fuel filter a few days ago, which was..... yuck. This pan had only been used once, to catch coolant on another car - all of that grit came out of the filter (the dry splash marks are dried coolant, though). Probably the original - it had a Motorcraft stamp on it, and was as dirty as the rest of the underbody:


The car has 124k, and the only work I've done since purchase has been new headlights, a gas cap, one tire, and now the fuel filter. Plugs are on the list - OE Motorcraft only, I've heard too many stories about plugs parting ways with the head on the modular motors. I know it has the revised Dorman intake manifold (likely done while in police service), a new serpentine belt, and a new tensioner. Things I know it needs are the ABS module, plugs (just due to unknown age on them), an idler pulley (squeaking), and 3 tires at some point (possibly a wheel or two as well, but I replaced the one tire that was separating just to get it safe to drive).

The fuel pressure has settled down to normal now that the filter is replaced. I have a hunch that maybe it was leaning out a bit under heavy throttle, and the PCM + FPDM were cranking the pressure up to compensate? No longer smoking at all, fuel trims are back to where they should be, though I haven't driven it enough to run through a tank since the filter replacement.

I did find gas inside the electrical connector on two injectors, I suspect that was caused by the pressure being so high for so long. So it'll be getting a set of used injectors soon (and probably some pigtails, one plug had the tab break off when removed). I'm still giving the FPDM the side eye as well; there's no reason for it to be running this rich without throwing codes.

The gas smell after hammering it is gone too.


Edited by STR (07/20/21 07:18 AM)

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