hey guys,

I was just wondering if I can replace the computer in my truck? It has a few funny problems like dying in reverse and being sluggish, and I was wondering if the brain can be changed. If so, what does it cost, how hard is it to replace, and do you even think it will help?

I have Speed Density I am almost certain as well. It is a 351 in a 93

 

A new computer is easy to replace, I believe they're about 150-200 bucks. The computer is actually just above the gas/brake pedals but is a little to the edge of the truck. You have to unscrew some of the plastic inner fenderwell to pull it completely out. Just a bolt on the harness releases the plug. Your truck is definitely a SD truck unless someone did the conversion for it (but I doubt it). SD has no sensor between the air box and the thottle body.

 

What makes you think it's the computer? How many miles are on the engine and trans? When was the last time the trans was serviced? When was the fuel filter last changed? What's the fuel pressue, compression? How much blow by does it have? Sound to me like a tired motor and a tranny in need of a flush, filter and fluid change.

 

Okay, here's the deal.

This was my dad's truck when he got it brand new. It has been taken impeccable care of (look at my gallery - the truck still looks like that now). We recently changed the timing chain, cleaned the throttle body, changed the water pump, and it runs great. The engine idles smooth, responds well, burns no oil, and gets decent mileage.

When the pickup had 75k on it and was still dad's, dad noticed a very sudden change in it - the truck lost alot of power and mileage dropped from about 14.5 to 13. Since then the truck had run fine, but the power has never returned (it is now pushing 153k). He always suspected it was a loose timing chain, but changed that did not significantly increase the power. Also, around that time it developed a problem of the rpms dropping to 300-500 when in reverse (the engine also had to be warm) and sometimes dying violently when put into reverse. In addition, the transmission would often shift very hard from 1st to 2nd and on. However, a couple of months ago that last problem got so annoying that we replaced the tranny computer and now it shifts smooth and solid all the time! Oh, and when it was diagnosed the tech guy said that the tranny was in near perfect condition - it was only the computer causing trouble.

So here's the theory - at the 75k mark something happened that goofed up the computers (who knows what) and caused these stupid problems. I am just wondering if it is worth the gamble of swapping out the computer to see if it till fix the power/mileage/reverse problem. Thanks for your input!

 

i liked the picture. you should do a new one same pose with that chevy blaster in your hand!

 

There's only one computer - it controls both the engine and transmission. I don't think that this is a computer related problem either. Try pulling the codes and see what comes up. If you don't know how to get the codes, go to http://fordfuelinjection.com and click on "Getting Codes."

 

Some sort of fuel delivery problem?

I do think though that is has to be an electrical thing. Some sensor or something.

And quicklook, you're right. I think I'll take another shot of me next to my truck, maybe holding a rifle or something!

 

Sorry, I mispoke myself.

The tranny computer was NOT changed - the valve pack was. So could it still be the comp? Is there a diagnosis i can do?

 

Have you pulled any codes from the computer? Look up to my other post and click that link. That will show you how to do the computer self diagnostic test. If there is a problem you will get one or more codes that can point you in the right direction. The computer is not something that commonly goes bad.

 

It's more likely it wouldn't run at all if the computer was the problem.

If the timing chain was stretched it would idle rough and run better or worse depending on what tension was on the chain.

I had an old Caddy w/429 that would haul a$$ down the freeway but as soon as you stopped and idled it would sputter & backfire and the lifters made all sorts of noise.

Rebuilt it and replaced the old crumbling teflon coated chain with a double roll timing chain and gears and the problem was gone.

I'd experienced hard shifts in my old 66 f-100 from the vacuum modulator hose coming off. Caused it to shift at a higher rpm. Don't know if it would even have a vacuum modulator if it's computer controlled though.

 

How old is the fuel filter? It is possible that at around 75k he got a tank of bad gas, this will do a few things, clogs injectors, can mess up the pump(s), and causes nasty deposits on the valves. I would do a seafoam treatment, and see what happens. Change the fuel filter, and then cut the old one open to see if there is any foriegn material in it. It may be a weak fuel pump. Get a high pressure fuel pressure tester and check the fuel pressure. It sounds to me like it could maybe be a bad oxygen sensor.

 

I agree with everyone, I would highly, highly, doubt that it is your comptuer. It's probably something simple to fix like a fuel filter or oxygen sensor like suggested above.

 

okay, thanks for the replies. My fuel filter was changed not more than 10k ago, and as I had said the timing chain I replaced 1k ago. The engine burns no oil, idles smooth, etc.

I have not pulled the codes. I tried the procedure on that one website but could never get the check engine light to blink.

The o2 sensor is a suspect. I believe it has its originals. Since it is a 93, it would have two of them, correct? I think I priced them once and they were about $50 each, so I don't want to replace them unless I know they're the problem. How can I test them?

 

There's only one O2 sensor on a '93. There's not much in the way of testing them. Does your check engine light come on when you first turn the key to 'run' (not when you are trying to get codes)? I would really try to make sure the light works, and make sure that everything is in proper working condition in terms of the code readout. If everything is fine with the check engine light and wiring and you still can't get any codes, then I would start to suspect the computer, although I wouldn't automatically condemn it.

 

Okay, when it says " length of wire that can connect the STI to the negative battery terminal" and then "ground the self test input" it is talking about the same thing?