If you can figure it out, you're smarter than I

[wwatsonh]

88, 5.0, AOD

Okay, here's my problem and a not so brief description of what I've done to diagnose/correct it thus far. And yes, I've searched, and I've been to the fordfuelinjection website several times.

I've owned this truck for about 2 years, and the check engine light has always been on (p.o. removed the bulb, I put it back). Code 31 has always been the biggie. I initially changed the EGR valve (it was stuck), then the EVP (the resistance was way jacked up) but that didn't fix it. I then realized that most of my vacuum and/or emission lines were broken, missing, or otherwise inop. So I left it for awhile.

I finally got off my butt, went to the boneyard, and got a new vacuum harness for it (all the hard lines bundled as from the factory). The truck now runs much better. I erased the codes, and started over. Did a KOEO test with my scanner, got a 31 again. (

So....I checked the EGR valve (it moves with vaccum applied from a pump).

I checked the resistance reading on the EVP (4400 ohms closed to 330 ohms with 10in vacuum). According to my books, this is in range.

I next tested the voltage at the EVP harness connector (4.6 volts) again, in range.

Then, I checked the resistance between the harness connector at EVP signal to socket 27 on the connector to the EEC PCM (0 ohms) once again, exactly what it should be.

I then checked the resistance between the harness connector at EVP signal to ground. I got that the circuit was open. Good, no short to ground.

Next, I checked the harness connector for stray voltage at EVP signal (none found). Good, no short to power.

Now I'm stumped.

I want to clear this KOEO code, so that I can proceed with whatever else may turn up when I do the KOER test. I'm trying to be methodical, sytematic, and not throw parts at it until I know what's wrong. ANY ideas/suggestions would be greatly appreciated.

SOMEBODY SAVE ME!!! [-o<

Will

 

[bluesman17]

If it aint broke dont fix it. I no longer have a check engine light and am much happier without it as the trucks running great for the time being.

 

[brian_n_texas]

Will,

I think you are approaching this problem correctly, I wish I had a nickel for every dollar I have spent throwing money at problems by replacing non-faulty parts, I would be a proverbial millionaire.

Do you have a shop manual? Not a Haynes or Chilton, I mean a bona fide mechanics shop manual. If you don't have one, I would suggest that you hunt one down, start with eBay. One of these could definitely help in further diagnostics.

If you do have a shop manual, then - I am guessing here - it could be an intermittent problem in the electronics. First thing I would do is unplug all electrical connections and re-seat them after applying some bulb grease to make sure ALL electrical connections are good (I have a boat, believe me this can often make a difference). After that I would chase down what has to happen to diagnose the electronics, 7 year old chips somewhere could be an issue.

Let us know how it goes, good luck!!

Brian

 

[Tevbuddy]

Is it sluggish at low speeds,like starting out and going slow through ...say a school zone.If so unplug the EGR controls,the vacuum ones.They also have an electrical connection going to them.Then drive it .If it gets better then replace them as a pair.THEY ARE NOT CHEAP......DEALER ONLY ITEM.It is common from late 86-89 or so.

 

[wwatsonh]

For those of you following/helping me out with this....here's the resolution:

http://www.fullsizebronco.com/forum/showthread.php?t=51673

Thanks for all the input/help.

Will