nayrb64

I have been battling same issues on my truck for a few months (it's not a daily driver so not too stressed). Today, after wits end on testing and re-testing things, pulled the PCM out JUST to either fix it or eliminate it. Bad caps. 47uf @ 16vdc - all three corroded with one broken. Replaced all of them tonight and will install in the morrow. I suggest you do likewise. It will drive you nuckin futs to keep chasing and testing every little thing when nothing makes a difference. Eliminate the PCM/ECM in your truck before throwing parts.

In my humble opinion that is.....

vjsimone

nayrb64, What Year & Engine do you have?

Yeah nayrb64, and a valid opinion, those of us that have been working on vehicles for years are familiar with the Cap issue. There are a few threads on another Forum dedicated to the Cap issue. I have a bag of those 2 caps (3.3uf & 47uf) sitting on my workbench. Some computers have 3 of them.

The Cap issue is one of many components that have to be explained away as one stumbles thru the troubleshooting process.

If the green.machine can attempt to retrieve codes, if he can, that will tell us; 1. That the Code function in the computer is/not corrupt. 2. Maybe what components are related to the problem.

Those Capacitors are part of the +5vdc power supply in the computer that provide the +5v Reference voltage to a few of the Sensors (STI, EVP etc..) If the Caps are defective then the Reference voltage at those sensor may be something other than +5v and will throw off the signals these sensors are sending to the computer and then the computer makes incorrect output signals to devices like the Air Controller, EGR System, Injectors, etc. See attached schematic.

So, this same +5v Reference is used by the OBD-I circuit to initiate the KOEO & KOER test. If his Computer is not putting this +5v out on the STI connector, via computer Pin # 48, then we will have him check the wiring and possibly replace these Caps.

(Credit to "Subford for these schematics);

vjsimone

The "single wire" is the STI, and should have +5vdc when key is On. I will have to check mine to see with key off what the resistance measurement might be. I would think it would be a very high in circuit resistance, .1 ohm may indicate a short to ground, I will check.

As far as the "2 center bottom pins", mine has no wire in the right center pin, and the left center pin is the Code Output (STO) from the Computer, I will check that one again for values..

nayrb64

Replaced the caps - didn't check for the 5vdc at pin 48, but the truck has had no change. Runs like crap Also, I cannot get the KOEO Check Engine lights to give me code faults. This is becoming more and more frustrating

vjsimone

You should start your own thread, load of people will help you through this...
List you configuration, year, model, engine, etc.
List the history you know.
List what you have done to date.

Updated;
Oh, I see you have started one....... EGR issue..