Need help on 94 ranger either short or bad alternator or something else

[pentode]

I agree the 42V thing is probably a red herring, although I would think it should regulate itself down to 14.4 or whatever even with no load.

What we're left with is that something in the system is failing with a very small voltage increase. I think mechrick's suggestions of looking for shorts/intermittent shorts is the right approach. Given his example with injectors earlier in the thread, I'm back to wondering: has anyone seen a coil pack fail this way? Seems plausible though unlikely. However, we're obviously dealing with something strange here.

 

[pentode]

I should have asked this sooner - do schematics for the computer exist? I feel like I've looked for them before and failed. I'd really like to take a look at the regulation and I/O circuitry.

Edit: can I get someone with good eyes to look at IC13 in the computer photos above? Does it look to anyone else like there's a chunk blown out of it? Should be flat on one side and round on the other. Might be a trick of the light, might just be conformal coating, looks different from picture to picture.

 

[dean94]

All Injectors ohm at 7.4 ohms

 

[dean94]

I don't see an evap canister solenoid or wiring for it i disconnected egr valve still won't run tried unplugging tps sensor still won't run and also tried unplugging Grey metal box on passenger firewall still won't run. Could the coil packs have anything to do with problem i know they are old but don't know how old they are

 

[dean94]

Ohmed both coil packs on connector side of both coil packs i get 0 ohms on wire side of one i get 11.39 ohms and 12.12. on wire side of other coil pack I get 12.96 and 13.02 ohms

 

[pentode]

Where exactly are you measuring 0 ohms? Between which 2 points?

 

[dean94]

Middle pin and either side of middle pin on connector/harness side of coil pack

 

[franklin2]

I agree the 42V thing is probably a red herring, although I would think it should regulate itself down to 14.4 or whatever even with no load.

What we're left with is that something in the system is failing with a very small voltage increase. I think mechrick's suggestions of looking for shorts/intermittent shorts is the right approach. Given his example with injectors earlier in the thread, I'm back to wondering: has anyone seen a coil pack fail this way? Seems plausible though unlikely. However, we're obviously dealing with something strange here.

I can't wrap my head around this theory. The vehicle electronics are made to tolerate fairly wide voltage swings. And it runs fine without a charging voltage hooked to it. So everything is working.

Unless maybe one of the 5v regulators inside the computer has failed? While the 5v supply is designed to tolerate wide varying voltage inputs, the output to the sensors has to stay 5v on the money or the sensors will go wacky. I have never heard of this happening before. I guess anything is possible.

I did a quick scan of the old posts. I see where he replaced the ignition module, but I haven't seen where the ECM has been changed. Not a fan of just changing parts, but I have no other theory. You could hook a voltmeter on DC to the TPS or some other sensor and monitor the 5v supply. With the alternator disconnected and the engine running, it should be darn near 5v. You might get 4.98 or something like that. If it's pretty far off, like 4.5 or something like that, it would be interesting to see what the voltage did when you hooked up the alternator. I wonder if it goes way above 5v?

Just grabbing at anything at this point.

 

[SenorNoob]

I like that theory.^

Yes monitor the 5v. I wonder if the PCM has tolerance all the way up to 12.8 but not 13?

Edit: Not sure what model it's for or how accurate it is: