I currently own a 1989 F-150 standard cab with a 4.9 ltr engine. The story; Well I needed a truck so I found this one for $250.00 dollars. It ran good, but just needed the transmission rebuilt. So we buy it get the transmission rebuilt, send it on a 5 hour trip up to my house and walla its here.

1 week later after arriving the Ignition inside the steering column goes out. So I spent the next 2 months starting it by rolling down a hill. I got the push button start hooked up so thats no problem. Ok, everythings fine...

I run out of gas and I try to get the truck started again. Well the trucks battery goes. I get another one and then I find that there is no spark after trying to turn it over for 30 minutes. Now what could it be.... we test the ignition module and it's a bright light but no flash. So we change the ignition module and it gets started.

Before it ran out of gas and the spark stopped it did something suspicious. It started loping at idle. Now that we have it started back up, it lopes at idle again. When you try to hit the accelerator past 35% the engine almost dies, but just enough for it to backfire constantly. I took off the sparkplugs and they are all black coated from running rich.

Now my computer is throwing on a check engine light. This is the weird part. I try to hotwire the computer but there is no flash. I know im doing it right, I guess the wires broken somewhere.


My suspicion on the whole incident is the TPS. I remember working on a truck in the past, same year. Where the engine would lope and backfire really bad.

I checked the TPS and the voltage is 5.0 at idle and it actually decreases when you apply throttle.

5.0 idle and -4.0 at full throttle. I checked my manual and the manual sais the tps should read 0.5 at idle and 4.0 at full throttle.

I checked the resistance of the tps and its at .500 and it does not move if I touch the throttle. The book said it should move.




Heres my question.

I don't have alot of money, and my time is very limited. Do you think it is the TPS? I need somone elses history on this and expierence. I can't get anyone to read the codes because no one has the computer and I can't hotwire it. So that is out of the question.


What do you think?



:added

Also when I make a vacuum leak for some reason it makes it able to drive and not lope. It raises the idle abit. I have videos let me add them here.

 

Well I checked the TPS with a voltmeter again, and it's correct.


Now what!

im stumped and nobodys helping me

 

Well, for $250 I guess you expected one thing after another. When you say it's loping at idle do you mean it feels like it's missing? Does it continue on through the RPM range or is it just at idle?

You can take it to Autozone and they'll run the codes for you. Checking the code can't be out of the question; it's a crucial step in the diagnosis of any fuel-injected vehicle.

Just my advice, roll-starting a truck for 2 months to avoid fixing the ignition switch sounds a little counter-intuitive!

 

Checking the codes is out of the question.

I tried hotwiring the computer to spit out the check engine light code.

Nothing....


Then my brother brought over his $1000.00 dollar snap-on computer reader for the truck.

The computer read "Error".

The dash's check engine light is on.





I havent had time really to deal with this truck. In the last two weeks we have finnaly gotton it legal and started driving it. Thats when all of the problems started happening.

 

try cleaning the idle air control valve and check the throttle body gasket. they like to get sucked into the intake.

 

While it is completely plausible you have fried the computer, pulling codes on these OBD I trucks is not difficult and does not take a $1000 scanner. The OBD I code puller is about $25 at the parts store, autozone and advance auto will do it for free. Or you can do it yourself with a paperclip or short piece of wire and count the check engine light blinks to get the codes.

It could be a number of things...step one is to pull the codes.

 

Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical

and if it dont yet work try this:
Ford Fuel Injection » No Codes?

 

Hey thanks man, thats exactly the type of stuff I Was looking for.

I've tried reading the flashing lights, hints hot wiring the computer... but it didnt work.


Thanks again, ill update you on how the situation goes. My stepdad whos a mechanic in south Louisiana said old Fords like these have a bad habit of not flashing codes because of wiring problems.