I tried to post this but it disappeared? Why? I have a 1994 ford 460 V8 in my motorhome F 53 chassis. The Ford truck dealer says it wouldn't tell them what was wrong to cause poor idle and dying. They made it worse. Can anyone tell me what part I need to get (and where to get it) to make it show error codes so they can try to fix it? Are there any suggestions as to what I should try before I take it back to a shop?

 

Not sure if they put the diagnostic modules on motorhomes etc.

Going by memory(on several cars I have owned) since my 94 F250 is at home and I can't look...

I forget the exact designations now, but there was an older style pre 95(?) OBD I and EEC II test port. Then there is ODB II and I think it is EEC IV, not sure what happened to III or if there is a V now. So I might be goofed up on II vs IIvs IV etc. The plug type and testing is very different and you will know what to look for once you see a few. Ditto when you shop testers.

The diagnotic plug is usually under the dash on the driver side, usually visible just under the lip of the dash often above the dirvers right shin. I think with OBD II and EEC IV it is required to be under the dash in that location. With OBD I or EEC II it might be in the engine compartment usually up high along the firewall right in front of the cowling on the drivers side. It is usually in a pig tail off a main cable run. The connector is typically rectangular and if I recall about as big as the first knuckle of your thumb for the older OBD I or I think EEC II(?) types. The newer OBD and I think EEC IV type is about 2 inches wide by about 3/4 high.

I am pretty sure my 94 Truck is the older OBD I or EEC II(?) type. I think in 95 or 96 they went to OBD II or EEC IV. I have not needed to test my 94 so this is why I am foggy.

There are a lot of testers out there some really just cheap flashers and some which will read out codes in almost english.

I have an older EEC II and OBD I tester, forget brand, but it works OK on my older Ford(89SHO).

I have a newer OBD II type that I know works on Chebbies and I think the EEC IV. I believe it is an OMNI Nova. I like it, it works fine and has a decent manual and decode info.

The key to diagnostics is to have a good code manual. It is surprising how many codes aren't in the cheap do it yourself pamphlets. This happened to me when I went for a free code read at Autozone a few years back. It came up with codes they didn't have a clue about. Lucky I had a shop manual. Also a Chiltons/Haynes will usually have some decent code info. And of course a shop manual is pretty good.

One quirk with a few Fords... Not sure why or if it is common but my Wifes Mercury Villager doesn't require a code reader. You just watch the blinkin lights on the dash. It is a Nissan engine but I think it uses a variation of the Ford EEC system. It is in the Chiton/Haynes manual, but essentially you short out some connections in the test port, and watch the check engine light flash and write down the code, kind of like Morse code. Works pretty well actually and all it costs is a paperclip and a manual. I have read that you can do this to many OBD I EEC II systems.

Even though what I saw above is muddled, if you get a decent code reader and manual, you will find it much easier to debug a car. Strangely, I have gotten better diagnosis using my tester than the dealer told me what it would take to fix. Of course the dealer wasn't trying to save me money and could have been ignoring the code I told them my reader was squawking about. If the reader squawks, it is probably right and at least will get you in the ballpark or where to start looking.

Good Luck,

Jim Henderson

 

Poor idle and dying could be the idle air motor or tps potentiometer...


Dick