Can Clogged Cats Cause 171 174?

[crunchie_frog]

Yes, you can use a laptop, just google forscan and download the software. You do need an elm 327 adapter which will connect your laptop to obdii. Forscan software FREE. The adapter should cost you $10 or less (amazon, ebay...) You can see live trends/charts of all your sensors, like in your case the MAF, fuel trim, and O2 sensor readings. Your fuel trims should be maxed at higher rpms but you should see what they look like at idle. At idle, for an air leak, the PCM should be asking for a positive fuel trim (meaning the PCM thinks you need more fuel than what is predicted by the MAF). As you go up in rpms, for an air leak, you should see fuel trim go down because there is more air leaking in at idle since the air leak is directly proportional to manifold vacuum and the leak. As you go up in rpms, vacuum gets less and the air leak goes down relative to the air amount required for the engine and this is why I would think it is a fuel problem. However, I would not rule out cats, bad o2 sensors, bad/dirty MAF, but again, the live data will help you with troubleshooting. Lean codes mean the PCM thinks it needs more fuel than is what the MAF says it needs, the PCM asks for an exact amount of fuel for a measured amount (from the MAF) of air. Like I said, my guess would be fuel to or MAF. Fuel could mean dirty fuel filter, bad fuel pump or bad fuel pressure regulator (in tank for you) or bad injectors on both sides (does not seem likely but possible).

 

[JusTheUsual]

I started looking for forscan and was $5 on iTunes. I guess I need to search more. Plus the one on iTunes was just for Ford. So I wanted to make sure the right one. The elm327 adapters I seen and posted before and they are Bluetooth. I didn't want Bluetooth really, I just wanted the cable. I hate wireless stuff. I will search again in a couple hours for that stuff. Then the thing is, once I get software and connector I'm not sure what this truck should be running at on all the gages that will be on live software watching it compared to what mine. So I need someone else to look at it to see. Maybe I might spot something wrong but not sure right now

 

[crunchie_frog]

Forscan is just for ford and it is free for Windows. Just download for windows on your laptop. Just buy an elm327 adapter that connects you laptop to Obdii. For example just found one on Gearbest for $10.37

 

[jimbalaya]

what's good pressure

Last 171/174 fault I had was a fuel pump. What are you getting for pressure readings? It's worth the $100 to buy the China freight scan tool; this lets you monitor fuel trim, O2 sensor voltage, etc so you may heaad down the right path when repairing the vehicle, rather than blindly throwing parts at it.

Bill

with key on but engine off i get 36psi. with engine running i get 30psi.

my Chilton's book says pressure should be 35-45 psi with key on and engine off. doesn't say what pressure is good when engine running, except that it should not change any more that 5psi when quickly accelerated.

what you guys think?

 

[bill06447]

Seems lower than normal. 40-50 psi is typical Ford pressures. Will it rev any higher in Park/Neutral? Some Fords of this era have rev limiters so you can't blow them up in neutral (my Windstar was about 3500 rpm) if the top limit is the same on the road as parked you may have a ECU issue

Bill

 

[jimbalaya]

vacuum seems ok

Other than a smoke test (might be worth paying someone to do one) it's really hard to find vacuum leaks. On the SOHC motor, intake manifold O-rings/gaskets are always suspect as is the PCV valve elbow.

i bought a vacuum gauge to test the system and got a consistent reading of 18hg. manual [and gauge] says that's good pressure. is that correct?

 

[jimbalaya]

rev ok

Seems lower than normal. 40-50 psi is typical Ford pressures. Will it rev any higher in Park/Neutral? Some Fords of this era have rev limiters so you can't blow them up in neutral (my Windstar was about 3500 rpm) if the top limit is the same on the road as parked you may have a ECU issue

Bill

seems to rev fine in park. fuel pressure stays constant during rev.

 

[koda2000]

i bought a vacuum gauge to test the system and got a consistent reading of 18hg. manual [and gauge] says that's good pressure. is that correct?

Around 20hg is more normal, but that's not really the issue if you're getting the lean codes on both banks (P0171/P0174). when an engine is running it creates vacuum. The reason that the system uses a vacuum ball/reservoir is that under certain conditions (like climbing a hill) engine vacuum drops. The reservoir allows the system to maintain vacuum during occasions when engine vacuum is low, thus allowing vacuum operated servos to continue to work. Your truck requires vacuum for many purposes, a leak ANYWHERE in the system will cause unmonitored air (air not seen by the MAF) to be sucked into the engine. A few common places that can cause leaks;

- bad power brake booster
- evaporation system leaks (emissions)
- bad fuel cap/gasket
- leaking intake manifold O-rings/gaskets
- cracked vacuum reservoir
- broken/cracked vacuum lines
- leaking PCV gourmet and or elbow
- HVAC controls

The best way to identify vacuum leaks is with a smoke test. This forces smoke into the engine and anywhere the smoke gets out is a vacuum leak, Unless your problem's something obvious, it's well worth paying someone to do a smoke test.

 

[jimbalaya]

Around 20hg is more normal, but that's not really the issue if you're getting the lean codes on both banks (P0171/P0174). when an engine is running it creates vacuum. The reason that the system uses a vacuum ball/reservoir is that under certain conditions (like climbing a hill) engine vacuum drops. The reservoir allows the system to maintain vacuum during occasions when engine vacuum is low, thus allowing vacuum operated servos to continue to work. Your truck requires vacuum for many purposes, a leak ANYWHERE in the system will cause unmonitored air (air not seen by the MAF) to be sucked into the engine. A few common places that can cause leaks;

- bad power brake booster
- evaporation system leaks (emissions)
- bad fuel cap/gasket
- leaking intake manifold O-rings/gaskets
- cracked vacuum reservoir
- broken/cracked vacuum lines
- leaking PCV gourmet and or elbow
- HVAC controls

The best way to identify vacuum leaks is with a smoke test. This forces smoke into the engine and anywhere the smoke gets out is a vacuum leak, Unless your problem's something obvious, it's well worth paying someone to do a smoke test.

thanks Koda - I will do that.