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Ted G.
Ted G., ASE Certified Technician
Category: Car
Satisfied Customers: 6107
Experience:  20 years auto repair experience, ASE Master Tech, Mechanical Failure consultant, Expert Witness
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2004 Ford F-150 4.6 Truck normally gets gh teens in mpg. All

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2004 Ford F-150 4.6 Truck normally gets high teens in mpg. All of the sudden it is getting 14. Has new plugs, coils, and fresh oil change. It also doesn't have a check engine light

Does it feel like it's running well, or does it feel like it's missing?

Customer: replied 1 year ago.
No, it seems to run like a top
Customer: replied 1 year ago.
It runs well

What we have seen a lot of is injectors leaking because of ethanol deposits causing them to stick slightly open. This runs the fuel mix a little richer and drops fuel mileage (but the truck will run pretty good.) A quick way to check it is measure fuel pressure as the truck is shut off. If it loses pressure at the rail quickly then it usually means the injectors are not fully sealing. It is also possible to see evidence of it on a scanner that would show fuel trims to be very low (the computer trying to compensate for the extra fuel).

Customer: replied 1 year ago.
I have an Otc genesis and a snap on prolink will that work to see trim codes?

I think the Genesys might, I don't know about the Snap On. Look in parameters for fuel trims, long and short term.

Customer: replied 1 year ago.
Ok, what should the fuel trim codes read? like percentages. also my o2 sensors are not cycling consistently or they are inconsistent in their voltages. Should I replace them?
please look over these pictures and let me know.

It looks like your B1S1 sensor is kinda weak. that 12% fuel trim may be due to that. You really want to be consistently under 10, but 12 is still probably not going to set an O2 sensor code. There really is no smoking gun there, but if the trim didn't comedown with a new O2 I would start to think an injector may be clogged a little.

Customer: replied 1 year ago.
well, none of the o2 sensors had a steady pattern of switching. Should I go ahead and replace all of them? the truck does have almost 200k miles.
Customer: replied 1 year ago.
also, at least B1S2 and B2S2 are not even cycling. They are staying staying up around .70v all the time.

Well, remember that you are looking at computer generated data read by a scanner and not the actual voltage from the sensors, so it will not show a true switching pattern. The downstream sensors have no effect on performance so you don't really need to change them, and they normally run much lower and slower switching than the fronts. That being said, the computer uses the difference between back and front to monitor the cats, so when you change the fronts you may start to get a P0420 code because of the weak rears, then you'll need to change the rears also. In order to really see the voltages on O2 sensors you have to put them on a scope, but your numbers are somewhat suspect and O2's don't cost a lot.

Customer: replied 1 year ago.
Ok so when should I suspect the cats?

To analyse the cats properly with the O2's you have to use a scope, most scanners will not give you a good pattern. You could do a vacuum test to see if you have any backpressure in the exhaust , but unless they are really clogged I don't think you'll see anything, and it runs well. If this is a customer's car replace the O2's and warn that they may show up a cat problem. If it's yours do it in phases, fronts, rears, and finally cats if a 420 shows up and won't go away. I have seen a lot of older trucks do that after new O2's so always warn about it if it's a cust car.

Customer: replied 1 year ago.
Ok so now the truck started running really rough and throws codes p0301 and p0316. Also the exhaust smells really bad. The smell comes and goes but when it's on it smells really really bad. I'm guessing it's just super rich?

Yup, sounds like it may be that #1 injector sticking. ST fuel trim should probably be negative too, correct?

Customer: replied 1 year ago.
I didn't check that. But when I disconnected the connector to #1 injector it didn't affect the engine idle at all. And the connector was REALLY hard to get off and now it won't go on but very hard. I have heard of the connectors going bad. Possible?

If the connector was bad it would run lean, sounds like you are rich.

Customer: replied 1 year ago.
Ok, one problem is the brand new accel coils we put on cyl 1 failed. I just swapped them with #2 and the misfire followed. Put the factory ford with 200k miles back on and the misfire is gone. But we still don't know about the fuel wxonomy
Customer: replied 1 year ago.
Also it has been idling and we haven't spotted that bad exhausted smell either. Could a bad coil cause a bask exhaust smell?
Customer: replied 1 year ago.
These are the before and after pics of the fuel trim. Before I changed the coil and after.
As a frame of reference, the 28% fuel trim was the before.

Looks like the coil could be the issue. See if your scanner will read Mode 6 and look for the 50 series counters. These are misfires. 51 will be high because of that code but you may also see some others. Those coils ate suspect too.

Customer: replied 1 year ago.
could that bad cool cause the fuel economy problem?
Customer: replied 1 year ago.
the rich running smell

Absolutely. But early on you daid you replaced the coils.

Customer: replied 1 year ago.
I did replace all of the coils but apparently the coils are used are not very good

Yeah, there is a lot of Chinese junk out there. At one point you couldn't even find those coils so everybody started making them, and some are pretty bad. If you can get that Mode 6 data, it might show other coils that are weak too.

Customer: replied 1 year ago.
We put accel coils on them. They weren't cheap either!

May not have been real, lots of clone stuff out there, it's kinda crazy.

Customer: replied 1 year ago.
The truck had another episode of rough running this morning. I tried to check the mode 06 misfires on my genesis evo but mode 6 test 53 is not in there. I can't find the misfires anywhwre

Ford only shows misfires in Mode 6 until the counts get very high. Does your Snap on tool show Mode 6 info?

Customer: replied 1 year ago.
I think it does. I'll have to check it later.

Cool, let me know.

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