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86 F150 with EFI, bad mileage and a few other symptoms

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Old 01-20-2018, 03:18 PM
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86 F150 with EFI, bad mileage and a few other symptoms

Hello,
I posted about this the other day, but hadn't pulled codes yet so I'm posting again now that I've done so.

I'm new around here, and I've only had my truck for a couple of months. It's an 86 F150 Lariat auto 4x4 with a 302 V8. I've got a few symptoms, and I'm thinking they're all related, so I hope someone can point me in the right direction.

First, I'm getting really terrible mileage. Under 10mpg, definitely running rich. Also, the engine does a little bit of "chugging" at certain rpms. Usually lower rpms in first gear. Once I give it gas or it hits into 2nd it usually stops. Last, it sometimes dies when going from drive to reverse.

I thought it might be something with too much gas being pushed in, so I checked the fuel pressure. Key in and engine off, its at 40psi which I believe is good, but when I turn the engine one and idle it drop to 30 which I think is low. And then it barely changed when stepping on the gas. Not sure if I'm leaking somewhere but I'm not certain what common problems that this could indicate.

A couple of other notes: I recently changed the ignition module. And I know that the tank selector valve isn't functioning correctly, I found that out when I ran out of gas because it was still pulling from the front tank after I switched to the rear. Also I didn't notice the "chugging" symptom until after I had run out of gas the one time, but that could be coincidence.

Pulled codes today
KOEO
31 - EVAP control system below minimum voltage
87 - Primary fuel pump circuit failure

KOER and dynamic
44 - Thermactor air system fault
31 again
34 - EVAP control system fault / Voltage higher than closed limit
- Also listed as Defective EGR pressure transducer sensor

I'm planning on changing the O2 sensor, EGR valve, and main fuel pump for starters. Thank you for any direction ahead of time!
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Old 01-21-2018, 10:26 AM
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To me that sounds like a good start but I don't know the EFI systems like others do.
I would say code 31 & 34 would not cause too much issues unless you have a vacuum leak but it sounds like the solenoid(s) could be bad as this seams to be a common issue.


Let us know how you make out and update this thread as starting a new one would lost all the information that may have been given to help you.
Dave ----
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Old 01-21-2018, 02:14 PM
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Originally Posted by jdd32 View Post
​​​I'm planning on changing the O2 sensor, EGR valve, and main fuel pump for starters. Thank you for any direction ahead of time!
That sounds like a reasonable plan, but with one caveat. Make these changes one item at a time and then go for a test drive. That way, if a new part is defective or something else was disturbed in the process, you'd know what to undo in case the symptoms get worse.

Also, have you tried the basic tune-up items yet? Before getting too deep, I'd suggest new plugs, distributor cap, rotor, and a fuel filter. If that doesn't help, I won't feel bad because those are inexpensive wear and tear parts that need to be routinely changed anyway. I've fixed many a driveability problem with just those parts, despite convincing myself the problem was going to be far worse.

After that, I'd suggest the oxygen sensor next. Before anybody chimes in otherwise, the oxygen sensor is not just "pollution crap". The computer adjusts the air/fuel ratio based on input from this sensor (among other things), so it is very important. The oxygen sensor has a limited life span, too, living in such a harsh environment. Once they drift out of calibration, they can cause all sorts of problems, so I think you're on the right track. Just stay away from bargain brands, especially universal ones that require splicing the wires. Get a good name brand with the correct connector.
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Old 01-21-2018, 02:55 PM
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Code 34 on this truck is a EVP code, (EGR Valve Position sensor). This code can be the sensor on the EGR is bad, or the EGR is not closing all the way because of a piece of dirt in it. If the EGR is leaking by because of a piece of dirt, then you are getting some EGR at idle, and that can cause all sorts of bad things to happen.

You said you were going to buy a new EGR valve. That should elminate that code. If it doesn't, then the position sensor on top of the valve may be bad.
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Old 01-21-2018, 08:16 PM
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Thanks for the replies! Went and got the fuel pump and O2 sensor today. They'll have the EGR valve tomorrow.

FYI I've already done a tune up, except I didn't replace the plugs because when I pulled one off it looked almost new.

Replacing the pump was fairly easy. But how in the heck am I supposed to get the O2 sensor off? On this model it's located on the passenger side on the back of the exhaust manifold. I was working from underneath by the wheel well. I have an offset o2 sensor socket but there's no room to get a socket wrench onto it once the I have the socket on the sensor. Not enough room for a crescent wrench on it. I snipped the cable (I needed to in order to splice on the new sensor to the connector anyway, and I couldn't reach the connector to detach it behind the motor) so that I could just put a long socket over it. But again I found I didn't have room for the socket wrench in this position.

Couldn't find my 7/8" wrench, so I'm going to pick one up tomorrow and see if I can use that to break it loose and work it out little by little. Man this thing is in such a difficult spot. I couldn't find any videos on removing one like this, so if there's a "right way" to do it, please let me know.

In retrospect, I should've went for a test drive after putting on the pump and before snipping the wire on the O2 sensor. But I didn't think it would be such a pain to get out
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Old 01-21-2018, 10:16 PM
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Originally Posted by jdd32 View Post
But how in the heck am I supposed to get the O2 sensor off? On this model it's located on the passenger side on the back of the exhaust manifold.
Do you have an air hammer? If so, try a pneumatic oxygen sensor remover. I have one and it works great:
​​​​​​

I got mine on eBay. Lisle used to carry one (#43900) but I think they stopped. If you search for "pneumatic oxygen sensor removal tool" or something like that, you should be able to find other sources.

No guarantee this will reach your application, but I've used mine in other tight spots and it's amazing.
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