Hello:

I am having the darnest time trying to figure out what has happened to my Ford truck in the past 24 hours. I am at wit's end, and I am thinking about taking it to a mechanic.

Here's the brief history. I have a 1995 Ford F-150, 4.9 liter truck that has been reliable for the past 11 years. Very happy so far. It has 110,000 miles. For the past few weeks, the "Service Engine" light has been intermittently going on and off, but the truck was still running super. I never had any problems at all with the way the truck was running, even when the light would decide to turn on.

Yesterday, I took the car to AutoZone and the young man working there hooked it up to an orange computer device (I forget who makes that particular code reader, but it's portable). Anyway, he hooked it up and told me that he wasn't getting any readings. He then told me to crank up the truck. It was at that point that the truck began to run like crap. He wondered why it was doing that. Well, he still wasn't able to get the computer to read anything, so he told me that was all he could do. Upon pulling out of Autozone, the truck was running terribly, the truck was like hick-upping sort of, and now, the Engine light was staying on permanently. Could this device have reset something?

I took the truck across the street to Murray's, and the guy there did a dianostics test with the same computer that the guy at AutoZone used. This time, he ascertained that it was the MAP sensor. He told me to first check the hoses. When I left Murray's, the truck was running horribly! The truck was idling high, and when the automatic transmission would change gears, it bucked really hard! (the last thing I need now is a screwed up transmission). Anyway, I rode back to Murray's and the manager confirmed to me that if the MAP sensor was bad, this would be the problem, but still recommended me checking the hoses to the sensor first. Well, I went home, and the ride was terrible. Anyway, picked up a MAP sensor at at another place and installed it on my truck that night. The problem still existed, and the truck actually runs super rich. There is black soot coming out of the tail pipe. I decided to call it a night.

This morning, it's the same problem, and I have even checked the hose going to the new MAP sensor. I am really upset. The car didn't buck as much, but it's still riding terribly, and the Engine light is still on all the time. Soot is still coming out of the tailpipe.

I took it back to Murray's today and had it checked one more time. This newer guy didn't know at first how to operate everything on the Actron tester, but he got it running and something interesting happened. While the unit was hooked up to the truck's testing terminals (located in the engine compartment) the Engine light went off, and the car was running super. Then, he unhooked the electrical terminal from the 12-volt battery (the device uses alligator clips on the battery for power), the truck completely stalled. Then, it was back to the same bad performance. The truck light is on again, the truck is running rich, and now I am contemplating just calling a qualified mechanic ($$$$$$) and hoping that it doesn't cost an arm and a leg.

Can anyone give me any advice. I do have a mechanical background in HVAC, and I do know how to fix things. I have a Chilton's and Hanes manual for this truck, but I don't know where I should look next. Your help would greatly be appreciated. Steve

 

Did you disconnect the negative battery cable prior to changing out the MAP sensor? Do that first for a minute to reset your codes, then start your truck and let it run for a while, if it will stay running. A bad MAP sensor will make your truck run like crap.

 

This is a response from roller_steve to the first person that responded to my post: Yes, I did actually unplug the red terminal from the battery and then I discharged it to the ground to make sure there was no capacitance left. This should have reset it after 15 minutes, but the problem still exists. I hope Autozone sold me the right part, but I have every reason to believe they did. Anyway, is there anything else besides a bad MAP sensor that would cause the truck to run erratic like it has (bucking, changing gears real hard, and running rich)? What is the most common problem on this truck related to these symptoms. Also, why would the computer that was used at AutoZone cause the truck to run like crap after the fact? A couple of people have told me that this should not have happened. Could the computer have affected the internals of my system to make it run this way. As stated in the post, my truck (despite the light coming on intermittently) was running fine. After pulling out of Autozone, it was like the difference between night and day. Steve

 

Did you check the Fuel pressure regulator? There was a guy that had a problem with the fuel pressure regulator failing. It caused the engine to run rich and foul the spark plugs and eventually foul the Oxygen sensor in the exhaust.

 

I have just made an appointment for my truck to be serviced, but it will take a week. Anyway, from what you're saying, the rich burning fuel mixture could be the result of a bad fuel regulator, which fouls up the plugs and oxygen sensor? What would cause this first, and would you recommend I remove the plugs and check to see if they are all sooted up? I have already spend 50 + on a MAP sensor, and I would like to know if it's worth replacing these parts regardless. Steve

 

pull off the air hose that connects to the throat body

block open the throttle, take a can of spray throttle body cleaner, spray it well inside of the throat, reach inside with an old tooth brush and brush the crap outta the throat, continue to spray and brush

there are air holes inside there that plug from the rotten gas we have to use, also the air carries some stuff with it thru the air cleaner..the light should go out

then take another can and run it while spraying into the opening,

try this, it worked for me

 

Hello: Thanks for the advice on cleaning the ports, but what hose am I to remove? Basically the soot buildup and problems I was having after the kid at Autozone hooked up the computer could just be a coincidence. But I don't know. If it's not the MAP sensor (which I am sure now it isn't), then I can imagine there are a few things that are making this thing run so crappy, and so fuel-rich -- oxygen-starved. Please follow up on what hose to remove and where it's located. I have a 95 F-150 4.9 liter with and inline-6 engine. Steve

 

i also have the same truck[ not your truck, but my own]

the plastic air hose that goes from the snorkel to the air cleaner assembly

if the guy has freckles, dont trust him, [too young]

 

Test the fuel pressure regulator by pulling the vacuum hose while the engine is running. If there is any gas in that vacuum hose, the regulator is bad and should be replaced.

 

Hello: Which vacuum hose are you referring to? Are you talking about the hose that is hooked up to the pressure regulator? There are lots of vacuum hoses on the engine block/engine manifold. Steve

 

Yes disconnect the one vacuum line from the top of the fuel pressure regulator.