I have a 95 Blazer vin "W" with 237,000 miles on it. Over the past year I've replaced, fpr, fuel filter, pump. I have had a problem with stumbling under acceleration but was unable to read codes (damn obd 1.5) Finally found a scanner at O'reillys that would read my truck. Came back with MAT low, TPS low, and o2 lean. I replaced the air charge temp sensor and the tps. Hoping it would resolve the o2 code...no dice. Go back and get the o2 sensor, install, reset computer, NO CEL YAY!!! But I still have the acceleration problem. So I was researching and I came across a thread describing my problem. This guy said his voltage regulator was bad and putting out too much AC voltage and screwing with his pcm. I check voltage on alternator on 200v AC setting of multimeter. Comes back 31.2 v. My headlights pulsate and I have some noise in the stereo. My question is Can my pcm be fried and not throw a code? and will any 100 amp 12v regulator be able to go inline, and how. I saw reference to a thread explaining how to do this, but was unable to find the thread. If anyone can send me a link to it, I'd appreciate it. Thanks :P

Also have replaced, plugs, wires, cap and rotor, battery, starter, seafoamed intake and some in gas fairly regularly...I try to take good care of my stuff, but outside wisdom is always appreciated!

 

Okay.. that was a lot of info to digest but I have some questions of my own.

31 volts of noise is a helluva lot. And it could play havoc with the PCM alright, but what makes you think the PCM is fried?

You fixed a couple things {though I dont get how O2 swap fixed the O2 code which you convenintly dont supply}

But the fact the PCM does seem to respond and the fact it doesnt throw a self-test error code tells me it's working okay. You know it IS a computer and runs on core code that's tested every time it starts, right?

And I dont get the question about a '12v 100a regulator in line'.
What for?

If you have a bad noise coming out of the alternator, it is a bad diode block.. or a poor connection to battery or both then why not just get a new alternator.. or replace the rectifier assy?

You say you read where a guy had the same problem and that caused it.. where did you read it? What if the guy was fulla crap and that had nothing to do with it?
And what did he do.. or was that the reference?
If your battery is good and all the connections:
Neg battery term to chassis, engine block to chassis, and neg to engine

Pos batt term to alt are good and tight..then you still read 30 volts ac, you arent going to fix the basic problem adding on a regulator.

PS: I DO have formal training in both power handling electronics and microcontroller systems.

 

I thought I may be able to run an external regulator inline pre-pcm to avoid the cost of a new/rebuilt alternator. Don't think pcm is damaged, just know that that much noise could damage it. After furthere reading on the other thread, I found that an underlying prob he had was a loose ground on the frame rail, shared by EGR, TPS, and I think air charge temp sensor. Gonna go check it out. So adding an external regulator won't help? Gonna go check the connections while the weather's nice. Thanks for input!

P.S. the other thread was posted by Rifleman... https://blazerforum.com/forum/2nd-ge...problem-42968/

 

Today I took the truck to a reputable starter and alt shop in town, when I mentioned the ac voltage to the owner, he was dismissive, like I had no idea what I was talking about. He hooked up a box to my battery and checked my volts, had me crank then checked again, then about 1500 rpm he checked too. He said," You don't have an alternator problem, if something's wrong with the regulator, it's not showing up now." ...Also I redid the ground on my amp, noise in stereo greatly reduced, if not gone. Can't tell if my lights are still pulsating, it's very subtle sometimes. Still have erratic bogging down, but I can carefully push through it and after about 2200 rpm it climbs on up the range normally. (if you're thinking "cat", I don't have one... removed it, no after cat o2 sensor)

Some things on my list to check:
pickup coil, ground at sp23 (described in linked thread above), fuel leakdown