iggy305

Hi Gents, I recently bought a 94 f150 6cyl 5 speed. It is really nice and I am planning on restoring it to its original glory. My problem is that it has the check engine light on and I can't get it to shut off. It was running lousy when I got it and I replaced the MAP sensor and I saw an immediate improvement. It was like night and day. When I took it for a test drive the check engine was off and I was super happy and then after a few minutes it went back on. A mechanic friend of mine ran a system check and he told me I had to replace the coffee can vacuum can, which I did but that did not help, light is still on. I went through the engine and all lines appear to be ok. I removed and cleaned the egg valve and everythig seems to running ok, just can't get that light to come off. When I start the truck in the morning it is off but then after a quarter of a mile the light comes on. it is really annoying. Has anyone dealt with this? If I go to the dealer will they definitely be able to get that light to shut off? Also, I have read that gas caps might cause the light to come on I was wondering what you guys think about that. Lastly, my truck runs great on tank number one, but on tank number two, it takes a while for the truck to start and when I drive on tank two I can feel that it runs a bit rough. If the fuel pump is going bad could that be setting off the check engine light? Any suggestions would be very helpful, hopefully someone has dealt with this before.

Steve83

The dealership techs probably know less about that truck than you do. Click this & read the caption:


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You may have to read it a few times to absorb & process it all. Then follow the links in it for more info. The gas cap is not monitored on these old trucks. Get a Haynes manual & read it:


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You should also collect all the truck's details as this caption describes, and put everything into your signature:


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iggy305

Thanks for the info. I will have someone plug it up to a computer to see if I could narrow it down. I just hope it will be an easy fix and I hope that dam engine light goes off.

Steve83

There is no computer that will plug up to it. Click that thumbnail, read the caption, and break out a paperclip - that's all it takes.

iggy305

Steve, I got to give you an update and I feel pretty stupid. I looked over the info you sent and it wasn't pretty easy for me to absorb, it will take me a bit before I can try it but I began searching posts and youtube videos so I decided to do what I had already done before like three times and what everyone online always recommends. I manually checked every vacuum line to make sure they are not broken and they are in their correct place. Well as I was going through this I realized that the Coffee can has two plugs and its labeled, one says manifold and the other says solenoid. I followed the lines and realized that I had plugged the two lines the wrong way. I changed them up and plugged them where it belonged and I got in my truck to take a long drive and guess what, NO FREAKEN ENGINE LIGHT!
It is late now so I will drive it again tomorrow and hopefully it is cured. Now I have to deal with an air bag code of 51 which after research I learned that its a burnt fuse in the airbag control module. After I get that airbag light to shut off I will be good to go! light bud, thanks for responding and thanks for the info on the codes that you sent me. I have saved them for future reference.
Goodnight and thanks again.

Steve83

The fuse isn't the problem - it's a symptom. The module intentionally burns that fuse to disable the whole system when a dangerous condition is detected. Do not simply bypass the fuse (replacements are NOT available or recommended) - find the original problem by testing each circuit (there aren't very many).


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DO NOT test through an airbag detonator (circuits 614-615). Even a digital multimeter could cause the airbag to deploy. Once the root cause is identified & repaired, replace the airbag module from a local JY. But look inside before buying so you don't get one with a burned fuse:


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