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1996 F150 P0172 and P0175

  • renegadiel
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16 Mar 2020 23:17 #38408 by renegadiel
1996 F150 P0172 and P0175 was created by renegadiel
Hello first time using a forum because this time im desperate!

Ok here is the thing, I have a 96 F150 v8 5.0 getting P0172 and P0175 which means rich condition both banks.

I have replaced the following:
Fuel pressure regulator
Cleaned MAF
Oil change and sparks
coolant sensor
192 thermostat
Checked TPS and is working properly

Using a scanner at idle I see something weird all STFT bank 1 are oscilating -0.78% to +1.78% STFT bank2 are little off -5.08 to 2.04% BUT LTFT on both banks stay at -25% if I press the pedal they go to -14% or -7% or so. while truck running numbers change a little but as soon as I stop LTFT go back again to -25% on every component change I do a KAM reset to make sure truck relearn values.
I did a vaccum leak test to see if values change and yes all values go to positive.
I also notice engine load at idle is around 42% if pedal press it goes up
what could it be?
MAF??

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17 Mar 2020 00:47 - 17 Mar 2020 06:52 #38409 by John Curtis
Replied by John Curtis on topic 1996 F150 P0172 and P0175
Need more info.

Map, MAF, Baro, Rpm, STFT, LTFT, ECT, TPS, O2s, Calc load

When did the problem begin? Any kind of work done recently?

What I do know is that it’s taking away a lot of fuel. Other PIDS will help aide the diagnosis but first thought is over-reporting MAF.

ECU uses MAF, MAP, Baro, and ECT to determine calc load

Thinking out loud always helps me in the process.
Last edit: 17 Mar 2020 06:52 by John Curtis.

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17 Mar 2020 08:43 - 17 Mar 2020 08:44 #38411 by renegadiel
Replied by renegadiel on topic 1996 F150 P0172 and P0175
please take a look to attached picture
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Last edit: 17 Mar 2020 08:44 by renegadiel.

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17 Mar 2020 10:54 #38412 by Tyler
Replied by Tyler on topic 1996 F150 P0172 and P0175
Time to check fuel pressure, IMO. I see that you've replaced the regulator, but that doesn't mean you have the correct rail pressure.

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17 Mar 2020 11:26 #38413 by renegadiel
Replied by renegadiel on topic 1996 F150 P0172 and P0175
I will do that, I havent yet because as I mention before STFT look good but LTFT is always -25% and engine load around 42% at idle

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17 Mar 2020 17:14 #38414 by Monde
Replied by Monde on topic 1996 F150 P0172 and P0175
The STFTs are within normal range because of LTFTs. The LTFT job is to bring STFT down so the O2s can start switching again for proper air/ fuel mixture. That does not change the fact that the car is running rich, which can be caused also by a high fuel pressure.

Never assume, diagnose!

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17 Mar 2020 20:31 #38418 by ScannerDanner
Replied by ScannerDanner on topic 1996 F150 P0172 and P0175
What are your trims and engine load values with the MAF unplugged

Don't be a parts changer!

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18 Mar 2020 00:47 #38420 by IanMc
Replied by IanMc on topic 1996 F150 P0172 and P0175
Have you checked purge valve ?

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18 Mar 2020 09:31 #38422 by renegadiel
Replied by renegadiel on topic 1996 F150 P0172 and P0175
will do today, actually yesterday night saw one of your videos where you are checking a ford explorer for a MAF problem. will update later, thanks!

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18 Mar 2020 09:32 #38423 by renegadiel
Replied by renegadiel on topic 1996 F150 P0172 and P0175
yes, purge valve is working correctly.

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21 Mar 2020 14:27 #38526 by renegadiel
Replied by renegadiel on topic 1996 F150 P0172 and P0175
Hi ScannerDanner
please see the pictures with my maf disconnected.
engine off disconnect maf then start engine stft values were way negative and after 3 or 4 min tried to go back to 0
Hope this screenshots be good reference for you
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21 Mar 2020 17:59 #38530 by Weycraze
Replied by Weycraze on topic 1996 F150 P0172 and P0175
Among the other requests, let's just make sure you don't have a breathing issue. The scanner you have should provide PIDS for BARO( in in.hg) and ABSolute Intake Manifold pressure(in.hg).

Bring the engine to WOT (under load), you can try snap tests too. The ABS Intake MAN Pressure should rise within 2 in.hg of the constant BARO.

For example if the BARO is 29.2 in.hg, at WOT you want to see no less than 27.2 in.hg. In other words at WOT you want the intake manifold to go to atmospheric pressure. Anything less than 27.2 and you have an air restriction, Hence a possible reason for the higher calc. load.

Paul

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21 Mar 2020 19:36 #38532 by renegadiel
Replied by renegadiel on topic 1996 F150 P0172 and P0175
my truck doesnt use MAP, it is a 96 ford f150 5.0 engine, it only uses MAF.

and yes my scanner reads baro but not in this truck

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21 Mar 2020 20:49 #38533 by guafa
Replied by guafa on topic 1996 F150 P0172 and P0175
Hi renegadiel/guys,

Have you checked O2 sensor activity?

I had one which O2 sensor was always oscillating above 0.7 volts.

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21 Mar 2020 23:30 #38536 by renegadiel
Replied by renegadiel on topic 1996 F150 P0172 and P0175
actually forgot to mention that I replaced them.
today I removed brake booster to make a vacuum and stft and ltft were positive. at the end a failure on system feedback message appear, and as soon as I put the hose back trim values went negative again around -20

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23 Mar 2020 14:06 #38566 by renegadiel
Replied by renegadiel on topic 1996 F150 P0172 and P0175
Hi ScannerDanner
any recomendation after unplugg the MAF? I attached the pictures

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