My 1991, F-150, 5.0L has the check engine light on. There is black smoke coming from the tail pipes. Fuel economy is very poor, the engine will not run past 3k rpms and she is very down on power. Previously the light would come on and the engine would stutter then the light would go off and the engine would stutter. At times the idle would race up to 2500 rpms. Now the light just stays on, and the motor is down on power with black smoke coming from the tail pipes. What should I check first?

 

You need to pull the codes, click here to find out how. <!--StartFragment --> How To Run a Self-Test

Then report back and tell us what codes so we can help you.

 

I agree with subford - go to Walmart or Autozone and buy a code scanner ($25, and worth every penny to have one in your garage!) and let the truck's computer point you in the right direction. The book that comes with the reader gives good instructions and has a basic description for each code. Some of the more experienced users on here will be able to help if the code it gives is not obvious.

-Chris

 

Sub and Torque are right. My $30 code reader is the best tool I have ever bought! One visit to a shop to read your codes will cost you $55, unless you have an Autozone nearby.

 

OK. I attempted to check the codes with the instructions that subford linked me to. When I turn the key with the STI plug grounded, the fuel pump keeps running. It sounds like fuel is being recirculated, and the check engine light will not blink. It just stays on. I repeatedly turned the key on and off until the fuel pump stopped running and I was able to read 2 KOEO codes b/f the light stayed lit and the fuel pump came back on

The codes are 21 and 24. 21 is ECT out of self test range 0.3-3.7 volts and 24 is ACT sensor out of self test range 0.3-3.7 volts.

The truck will not start now it just cranks and doesn't even burp, like it wasn't getting fuel or wasn't getting spark. I am going to borrow the g/f's car and head into town to buy a code reader to see if that will give the full codes. <o></o>

 

If you can't get codes with the jumper wire method, you won't be able to get any codes with a reader (unless it can read the "fast codes" before the blink out codes are displayed).

 

I bought a code reader, and it is reading quite a few codes and it reads different codes from one check to anouther. I decided to take the truck to a local independant repair shop that has done right by me in the past. They say that "for starters" the MAP sensor and the computer are bad. I am waiting for them to get me a price on how much this will cost.

 

Marty, I wish you would have waited a day, I think we could have saved you some $$$$$$$. During your test with your scanner, the codes will display themselves TWICE, so you may have thought you had a bigger problem than you really have.

First off, what you should have done was get your codes, write them down and post them here. You have the same symptoms when my MAP sensor went out, $53, 2 screws, 1 connector, and 1 vacuum hose, 10 minutes tops. My truck WOULD NOT RUN because of this piece of plastic. I think yours is about $65-$100, depending where you go.

I hope your mechanic doesn't take you to the cleaners. If possible, get your truck back, do the MAP sensor first and go from there. If it runs, clear your codes with the scanner or disconnect the negative battery cable for a minute, run your truck for an hour and check for new codes.

 

lv2race, I priced the MAP sensor at 2 Ford dealers and one was more then the shop wants and the other dealer was about the same as the shop is charging me for that part ($137). Both Dealers said that the computer is no longer made by Ford and that it would have to come from an auto parts store, which I found odd. The computer is going to cost me $235 at the most according to the shop.

Anyway...I am sure that you are right that if I had been more patient you guys could have helped me figure it out and it would have been cheaper. The shop says that they are sure that the MAP sensor and computer are bad. The total parts and labor price is about $500. That is a lot more then I had hoped it would cost to get her fixed, but I don't think that the shop is robbing me.

I want to thank all of you who posted here to help me. I will be sure to post again to let you guys know how it turn out.

 

It's your money. But just so you know, it's very rare for a PCM to go bad. It does happen, but most experienced mechanics would not reach that conclusion until they had tried about 10 other things.

 

The replacement of the ECM and MAP sensor appear to have fixed my truck..

andym, how do you know that they didn't check 10 other things first? Obviously at least one of the 2 parts that were replaced, if not both, were the cause of the problems. If all that the truck needed was an MAP sensor, then why was the ecm giving me many codes? Can a bad MAP sensor fool a good ecm into thinking that there is a problem with: the air charge sensor, the engine coolant sensor and the power steering switch? All of those codes along with the MAP sensor code are now cleared out.

 

Sounds like your shop did you right again.

 

I had the same problem one time with my 302 and it turned out that the fuel pressure regulator was bad. When you pulled off the little vacuum hose on the top of the fuel pressure regulator with the engine running it would shoot gasoline out the hood in front of the truck (guess the diaphram was bad). It was dumping so much fuel that the fuel in the cylinders was getting past the rings into the oil. The fuel mixed in the oil eventually swelled the silicone pan gasket and it also had to be replaced.

-Jammyster