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Old 10-27-2012, 01:25 AM   #1
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Exclamation 1988 f150 inline 6 getting less than 5 mpg and running horribly

Hello everyone I have a 1988 f150 300 straight six. I bought it a few months ago for $300 not running but the problem was it was hooked up to the rear tank only and the pump in the rear tank was out so I switched it over to the front tank and it started right up. Ever since I had it running it has been getting HORRIBLE gas milage for example one morning I put $10 in the tank and drove about 10 miles and it died on the side of the road and my gas guage doesn't work so I never know how much gas I have. Since then I have hooked the rear tank up and still gets terrible gas milage. Also since I've had it it has been running incredibly slowly, my Pontiac grand am 4 cyl runs a lot quicker than it does. I thought maybey it was the oxygen sensor because there is an exhaust leak where the sensor is so I clipped the wires and still no change. There are no visible leaks and I have driven it then looked around the tanks and engine for any spots wet with fuel and I can't find any. I do notice that there is a smell of gas when the truck is idling but that's it. I'm just clueless and hoping someone can help me solve this problem. Thanks
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Old 10-27-2012, 11:29 AM   #2
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firstly, FIX your O2 sensor, just cutting it will not help anything.

next, go through both your fuel system, and clean it entirely, and also check your intake as well as exhaust for air leaks

I would NOT be surprised if your injectors are sticking open and making the motor run like garbage.

getting injectors cleaned and flow tested is no big project to do either.
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Old 10-27-2012, 01:35 PM   #3
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Yeah I already spliced the wires back together and there are a few leaks in the exhaust but nothing major. The kid I bought it from already got it all cleaned out. He pulled both of the tanks off and cleaned them out and it's got new pumps. Is there a way to Check if the injectors are sticking open?
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Old 10-27-2012, 09:32 PM   #4
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beyond taking them to a shop, I personally dont know. I'm not an EFI person, carburetors are what I deal with, being a classic motorcycles mechanic.

Also, go over your wiring, and see if maybe theres a short somewhere that could cause the ECU to think it NEEDS to provide more fuel.

obviously something has failed, or isnt right. if ALL else fails, rip the EFI junk out and slap a dual carb intake on that bad boy. PROBLEM SOLVED.

seriously though, I just remembered a POSSIBLE cause. check fuel pressure, and see what the manual says it should be at. when I was at a mechanic shop, we had a 240SX in that wouldnt run because the fuel pump was shoving WAY too much pressure downstream to the injectors and FORCING it past them.
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Old 10-28-2012, 04:19 PM   #5
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I was looking over the exhaust and found that the pipe between the catalytic converter is disconnected and you can move it and see inside the catalytic converter and it looks clogged. I'm not sure how any exhaust gases can eat through it. I checked the fuel pressure and it looks fine. No shorts or defects in the wiring that I can see. But actually since I have messed with the O2 sensor it seems to be doing a lot better on gas. I have been driving it quite a bit and I can still hear a bunch of gas in the tanks.
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Old 10-28-2012, 10:21 PM   #6
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well, a disconnected/bad O2 sensor can have a substantial affect. my uncle once owned an old van, with a little 4 cylinder that SHOULD, key word being SHOULD get 25-30mpg, it got 10. why? bad O2 sensor, and it was a dodge....
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Old 10-29-2012, 08:20 PM   #7
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Default Plug wires and catalytic converter

I would check the plug wires and see if you get arcing when the engine is idling. Do this at night in the dark start it and look for blue sparks.

If everything is ok with plugs and wires, pull the pre cat )2 sensor and start it to see if that makes a difference. If the cat is plugged, the truck will run considerably better with the o2 sensor removed.
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Old 10-29-2012, 09:27 PM   #8
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Yeah it's defiantly getting way more milage but it's still running bad. I'm guessing its because of the cat but I'm not sure.
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Old 10-29-2012, 09:29 PM   #9
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And I checked it and its arcing. I'll probably go ahead and replace the cap, rotor and wires. And should I pull the 02 sensor completey out?
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Old 10-30-2012, 12:21 AM   #10
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I'd start by simply doing the tuneup stuff. that often makes a PHENOMINAL difference in how it runs/drives.
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Old 10-30-2012, 12:21 AM
 
 
 
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