97 Explorer XLT V8 Runs Rough poor power/mileage!

[l2sail]

Hello we have a 97 XLT with a V8, 4WD with the following symptoms:

-Idles rough (extremely)
-Gets poor fuel mileage ( normally 18-20 highway, now 12-15!)
-Can pull spark plug wire from 3 different cylinders (I think its 3,5 and 8) and still runs the same (no drop in engine sound/rpm)
-Pulling the plugs from these cylinders shows they are wet and thus getting fuel.

Whats been done, its been brought to two garages (1 a ford dealer) and the diagnostic test at both said to replace the #8 fuel injector or the injector wiring harness or the PCM. (Gave a PCM selftest fail code)

Garage one:
Replaced spark plugs and spark plug wires
cleaned the fuel rails (found some rust residue)
Replaced the #8 injector
Tested the injector cablling
Tested compression (all good and level)
Replaced the ignition packs (both)
Tested fuel pressure (Good)

Garage two (Ford Dealership)
Ran diag and it said to replace the PCM which they did and it didnt correct issue.
They they recommend to replace the injector on #8 or the wiring (same as 1st garage)

I know some of the codes the diag gave and I can add them if helpful, I just dont have them with me now.

So at this point we are at a loss, we dont want to keep soaking money into the vehicle, if I dont get any other suggestions we will try replacing the injector in # 8 again and then the wiring harness but I doubt that will fix it, the number 1 garage is not a dealer but specializes in fords. Also the injector replaced was from Ford directly, not an aftermarket unit.

The 1st garage suggests the problem is a HARD engine problem that the computer doesnt have sensors see/diagnose and with the inputs it is getting is adjusting things it can contol, IE timing, fuel delivery and so on to try and correct the issue. IE possibly internal timing chain issue, sticky valves (not closing quick enough when engine running)

Any and all suggestions will be greatly appreciated.

THank You

~ Phil Morneault

[exploded99]

A little backyard mechanicing may help:

pull the wire off of each of the bad cylinders, check the spark. Compare it to the spark on a good cylinder. My guess is with all the new ignition parts, spark on the bad cylinders will be fine - the same as on the good cylinders.

You have tested compression, its ok. If valves were not closing properly, you would get a back fire into the intake manifold (intake valve) or out the exhaust ( exhaust valve) - but you don't have that. A good compression test and no backfiring tells us that the engine internals are probably ok.

Ok, if engine internals seem ok and ignition checks out ok, then why are the plugs wet? They should be firing just fine. That almost certainly means those cylinders are getting too much gas and flooding, plugs are fouled.

Injectors could be bad, but I doubt it. You simply don't have three injectors fail all at exactly the same time. Also, you replaced # 8 injector, and you have the same problem - fouled plug. This tells us the injectors are probably ok, and replacing them most likely will not help.

So, for some reason, the injectors must be open too long, and must be flooding those cylinders. Bad PCM, bad injectors or bad wiring could cause that. But as I said I don't think it's bad injectors, and you have a new PCM. So, we are pretty much left with wiring.

My guess is the garage checked the injector cabling to the #8 injector, and got a 0 ohm reading, which normally means the connection is good. (Obviously they must be getting a code which indicates a problem on this injector - both garages suspect it.)

But I bet they did not check for a short between injectors 3, 5 and 8 - that is more difficult. If you have a short, injectors 3, 5, and 8 would all fire every time ONE of them was fired by the PCM, so you would get 3 times the amount of fuel to each of those cylinders, flooding them.

So, my money is on the engine wiring harness being shorted. You can have the shop test for a short, or just go ahead and replace it, but I think it's about 275.00 plus labor. Check the junk yards, you may find a used one if you are ok with that.

Post the answer when you solve the problem, I am curious if the harness tiurns out to ne the problem!

[l2sail]

Well we have brought it to another FORD garage and soposedly they have found the problem but either I dont understand what they said or Im thick. They said it was the Exhaust spring?? Never heard of that. After the cost for diag, labor and parts it will be $475. Ill update more when I find out what that is from them and if it really fixed it.

~ Phil

[exploded99]

No exhaust springs on my V8, unless they mean exhaust valve springs ... don't know. Post your codes if you have time - I am curious. Also, was it cylinders 3, 5 and 8?

[l2sail]

Yes you are right its the exhaust spring/s I havent gotten to talk to the mechanic but when I do Ill update this. THanks for the interest.

[exploded99]

Originally Posted by l2sail

Yes you are right its the exhaust spring/s I havent gotten to talk to the mechanic but when I do Ill update this. THanks for the interest.

Just curious what it turned out to be - you spent quite a bit of cash on this one- were they right the last time?

[l2sail]

Hi All, it was the number 8 cyl exhaust valve spring. $500 later to change a $15 part.

Thanks for your comments.

~ Phil