94 4.0 running rough and eating spark plugs

[Brant Kieffer]

Ive got a 1994 4.0 with the a4ld and ive been having issues with the engine struggling to stay running and destroying the spark plugs. I originally thought that i had a bad head gasket so i replaced the gaskets and had the heads checked by a local machine shop and they said they were fine. after doing the head gaskets i replaced all sensors, maf, throttle body, injectors, plugs, plug wires, coil pack, water pump, and ac compressor. once i had all that done i started it up and it threw a few codes that i will have to find where i wrote them down. Everything that ive checked should have fixed it, i know that all the codes were saying that my new sensors were shot, a new part being bad i could understand but not all of them. im starting to think that the pcm has gone to shit. Anyone had this issue before?

 

[Angie]

any chance your 02 sensor is bunged up and plugged? what exactly you mean when you state plugs are getting eaten? ignor the codes for now as the money bomb you dropped on the engine needs to be "broken in" sorta speak .... and you are jumping to non factual conclusions saying PCM ....

when you say struggles, you mean in idle? or being on the road?

cheers

 

[Brant Kieffer]

i should have said that the o2 sensors were replaced as well, as for the plugs getting eaten i could put a brand new set in and 2 of the 6 have the ceramic inside the plug disappear. ive checked the compression too and all cylinders are in nominal range with no big jumps. and as for the struggles its acting like half the cylinders arent firing. the reason im thinking pcm is that i read a thread a while back about the 5 volt regulator inside the pcm going bad and presenting the issues that im having. ill try to find the thread and link it to you

 

[RonD]

Welcome to the forum

There are 3 capacitors in the PCM that should be replaced after 20+ years, easy to do if you solder, under $5 for parts
No, never read about THE 5v power supply failing on these or newer ones, all sensors run off this power supply in 1994 and 2011, I am sure it could happen but certainly not common, I would say very very..........very rare

What can happen is that one the the 5v wires to a sensor can short to ground, cutting off the 5v to all sensors, doesn't blow the power supply, its protected, but will cause ALL the sensor to show codes

The 3 blue capacitors seen here: http://www.auto-diagnostics.info/ford_eec_iv
Replace with black of same value, they last longer

Check coil pack, often gets miswired
3 4
2 6
1 5
front

The 5 6 4 side is where mistakes are made, on the coil pack or at the spark plug end, easy to mix up 4 and 5 or 5 and 6 wires at the cylinders
I still do after after 25+ years of having distributorless coil pack V6 engines
And did it 30+ years earlier on distributor engines, lol
One thing is sure, "if you KNOW firing order is 100% correct" then you are wrong, if you are not sure then its most likely correct

Motorcraft, Autolite or NGK are the only spark plugs that will last in a 4.0l OHV
0.054" gap

Broken electrode ceramic was a bad spark plug or something was bouncing around in the cylinder

Is exhaust clear?
Plugged exhaust will cause poor running
Pull O2s if you are not sure, start engine, it will be LOUD, but if it REVs better then you have clogged exhaust

 

[rumblecloud]

Ha! I was just about to post a link to that string -- you beat me to it. (I have it bookmarked and reference it often.

Here it is anyway

 

[Brant Kieffer]

Ok today i double checked the wires and they are correct, put brand new ngks in and pulled o2 sensors i also took a bore scope and checked each cylinder which were free of debris except for some carbon on top of pistons 4 and 6 fired it up and same issue. im starting to think my trucks money hungry lol

 

[Eddo Rogue]

My truck hated the NGK's. Nothing specific just ran like crap. I switched over to the Autolite and she ran much better.

 

[Brant Kieffer]

Well i Finally got the time to get the computer fully out and opened it up and these are the spots that ive found. How would i go about fixing this?

 

[RonD]

If you solder or have a friend that does its pretty easy to replace these
An electronics repair shop can also do it for you, they will usually have the correct capacitors "in stock"

Take lots of pictures so you can see location of each capacitor and its Value, i.e. 16uF 50v(volts)
Also each capacitor will have a stripe on the side denoting negative side, its important

These are called radial capacitors

Get the 3 replacements, under $5, but some times you have to buy 5 at a time because they are so cheap its not worth selling them one at a time, lol

You have to match uF exactly
But you can use a higher voltage, i.e. if it shows 16v then you can use 25v, 50v or 100v as long as uF matches
Do not use lower voltage

The circuit board has a spray on coating to protect it, on both sides, just FYI

A "solder sucker" is a good tool to use to remove the old solder so you have an open hole to install the new capacitors
After old ones are removed clean the area as best you can
90% or higher Isopropyl alcohol is great for cleaning electronics
Lower percentage has water in it so leaves a residue

Install the new ones making sure to match the Negative stripe orientaion and uF/voltage values to each location

I did this a few years back and my 1994 runs much much better

 

[Shran]

FYI that capacitor goo is corrosive. So even if you replace them, there is a chance that the traces on the circuit board are damaged as well. You want to do a continuity test on ANY trace that has been touched by that... your second picture looks terrible. It is possible to fix traces by soldering on bypass wires but if you've got several it's probably easier to buy a reman ECM than spend hours fixing yours.

 

[RobbieD]

PCB (printed circuit board) repair kits used to be available, which consists of strips of heat-setting trace material, and the foil collars for the pass-throughs (holes). There also used be the green conform coating, in applicator pens, to reseal the PB after a repair.

Changing those caps, and repairing the PB if needed, ain't that bad if you've got the tools, and patience. A reman ECM, or a shop or somebody with the tools and know-how, may be a better option for most people.

 

[Brant Kieffer]

Well after some consideration I took it to a computer guy I know that can solder and he looked it over and said that the board was too far gone near the capacitors for him to repair it, he also noticed on the back side of the board had some significant water damage and was surprised that the truck even started let alone run. Looks like I'm back to buying a new pcm sadly. I'm not giving up on this dam truck though lol

 

[RonD]

Good place to look for local used parts: https://www.car-part.com/

1994
Ford Ranger
Computer box - engine
skip area
YOUR Zip code
Search

New window will open and you can select which Ranger engine and transmission type
search

30 year old computer may need new capacitors

 

[Brant Kieffer]

Well as of today I got another computer with the same program code and the capacitors replaced, when I put it in the truck and started it the truck rev-bombed to about 4 k rpm then died, restarted again with same issue and that’s where I called it. Is there something I’m missing? I thought these computers were pre programmed and would be a plug and play situation.