map sencor trouble
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Senior User
Joined: Jan 2014
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From: Cornerbrook Newfoundland
map sencor trouble
Hey guys i'm in need of your expertease again. i have a friend who owns a 95 ford f150 with a 4.9 engine, and him and i have been trying to solve a problem with his truck. when he fires the engine up, it runs fine, but after putting it in drive and driving just a few feet, it stalls. we,ve checked several possible problems, but all seem to have checked out except one. maybe i'm doing this wrong, but i know you guys will set me straight. i pulled my truck along side of his, '' now this is before i stripped the engine '' and started testing a few things. one thing i noticed about his truck, is that when i pull the vachum line to the map sencor, it continues to stay running. but when i perform the same test on mine, my truck died instantly. this would indicate to me that my sencor is working properly. right? so if his truck continues to stay running without the line in place, would this indicate a bad map sencor? or would there be some other problem that would cause the same result?
any advice you can provide to help me help him solve this problem would be most welcome. thanks. T.C.M.
any advice you can provide to help me help him solve this problem would be most welcome. thanks. T.C.M.
Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
At cold idle the the computer does not look at the MAP sensor.
See sensor chart at this link:
Fuel Injection Technical Library » EEC Computers
However I do remember pulling the vacuum line off a 1988 302 once and black smoke came out of the tail pipe and it ran ruff but do not remember how warm the engine was. I do not think the engine quit running when I did that.
See sensor chart at this link:
Fuel Injection Technical Library » EEC Computers
However I do remember pulling the vacuum line off a 1988 302 once and black smoke came out of the tail pipe and it ran ruff but do not remember how warm the engine was. I do not think the engine quit running when I did that.
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Senior User
Joined: Jan 2014
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From: Cornerbrook Newfoundland
warm or cold the engine acts the same way. sometimes it'll work fine, then other times like when he's coming up to a stop light, as soon as he lets his foot off the gas pedal it stalls. i always thought that the engine would not run without the map sencor connected. every vechicle i've done this to with a working map sencor, always instantly stalled when the vacuum line was disconnected. this was one way i could tell if the sencor was working. but on my buddy's ford the engine continues to run without any rough idle or anything when the vacuum line is disconnected from the sencor while running. but as soon as there's load on the engine, it stalls. i don't know if there's a broken vacuum line somewhere or if it's electrical. i just need some idea of where to begin to look for the problem. thanks. T.C.M.
Last edited by truck crazy man; Feb 23, 2014 at 01:20 PM. Reason: misspelled word
Logistics Pro
Joined: Mar 2005
Posts: 4,698
Likes: 47
From: Mexico, Missouri
It should be easy enough to check for vacuum. Is there any vacuum when you remove the vacuum line? Should be quite noticeable.
Also, what codes does your friends truck have?
Need KOEO DTC's
Need KOER DTC's
If you can post these, it may greatly improve how to diagnose his problem.
Also, what codes does your friends truck have?
Need KOEO DTC's
Need KOER DTC's
If you can post these, it may greatly improve how to diagnose his problem.
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