Electrical gremlins

[bnc04]

Aw man, this is driving me nuts.

88 Chevy 90k on it. Original 350 TBI. A/T

Purrss along just fine and starts up fine most of the time.
Periodically, when the brakes are pressed or turn signal is used or blower motor/air or heater is on of windows are used or radio is used or headlights are used or any above the combination is used, the voltage will drop and the truck will start to idle rough. By drop, it could be anywhere from the original 13 down to 10 or 8 or to the red line. Most of the time, it will recover and purr along like nothing happened.

It also has this symptom, When attempting to start, buzzer, lights etc are all fine and it will not turn over at all. Sometimes, holding the key in the start position (5-20 seconds)will allow it to fire. Sometimes not.

It stranded the wife yesterday and I need to get this addressed now.

Yesterday I fixed it by tapping the starter and solenoid, it fired up and ran great all the way home. When home it did not start the first time I tried then fired on the 2nd try. After that it fired fine. It was dark and late so I didn’t do any trouble shooting.

I did an conversion to a quicksilver megashifter a year or so ago and I can’t remember if the scenario started around that time or not but I think it did.

I also installed backup lights at about the same time.

Other than that pretty much stock.

I have replaced the alternator about 6 months ago. I cleaned out and made sure I had good grounds at the taillights and wiring back there. Replaced the brake plunger actuation switch. The automatic shift coller is fully rotated to the left. I added grounds to the engine compartment, ( firewall to battery) The engine grounds look good and I have continuity from the engine to batt ground and frame to batt ground.

I’m going to pull the starter this morning and have it tested but it being so intermittent makes me think testing will be of no help.

Can you guys list what steps I should take to see if I can narrow this down a little?
I’m nowhere near as savy as you all so you may have to explain things a little more clearly at times.

Can I start pulling fuses when this happens to see if I can isolate a short somewhere?

Sorry for the long post, But I have a few hours t lay with it this morning and this weekend would like to get a game plan together to fix this thing.

Thanks for any help and suggestions. I’ll write them all down and start looking at each one.
Brett in Colorado

 

[bnc04]

Another update if this helps.
Volts across batt sitting not started. 12.23
Volts across batt when running 14.5
Volts acorrdding to voltmeter in truck about 10 when truck is running.. Sometimes will go to 14 and sometimes to 8 depending on turning stuff on or off.. see above post.
Volts according to voltmeter in truck when ing key is turned to on but not started 8.

 

[camokrawler]

i would check the internal voltage regulator even though that should have nothing to do with ur starting problem but most likely it will be something with the starter solenoid or it the wiring to it. hope this helps.
camokrawler.

 

[73k5blazer]

it almost sounds as thought your have extremely high resistance somewhere and the thing can only run thing at a time.
Voltage regualtor (inside alternator, so alternator) would be a good start.
Save that, check your connections at the starter, then check them at ignition switch as well. perhaps your ignition switch is bad?
What happens when you sitting there without the truck running, and operater the windows and brake lights? does the voltage drop then.
Check all your connections everywhere. battery, alternator, starter, ignition switch. Doesn't hurt to clean them up a bit, smear some electro grease on them while your at it. See if that helps.

 

[bnc04]

Sorry for the long delay, I finally was able to get back in town and do some work on the blazer.

I replaced the alt and starter solenoid with no change in the symptoms. I'll be getting and trying the ignition switch today or tonight hopefully.

I ran another ground from the Neg batt post to the body and also ran a separate ground from the block to the body since I could not see to verify the condition of the rear ground strap condition.

All the wires I have looked at seem to be n good condition and I've cleaned up what I have looked at or had to remove during the above changes.

Does anybody have any other additional thoughts on what to look for? Right now my eggs are all in the ignition switch basket.


Oh.. And yes, when I run windows or accessories ( air compressor etc) with the jey off, it draws the gauge right down to 8 when it is acting up. Other times, it works fine.)

Damn intermittent electrical is a killer.
Thanks again,
Brett

 

[bnc04]

Allright, I just replaced the ignition switch and the spymtom is the same. Right now, It will not start at all. I hooked up another battery and the symptom is the same.

Does anybody have the pin out and voltages I should be seeing in an 88 blazer at the ignition box? I have no idea where to go at this point. Any help would be really appreciated.

Brett

 

[AZ79K5Project]

Did you check the wire(s) from the alternator? You could have a bad or a short in the charging wire or if it is the three wire (don't remember the name) the exciter(?) wire causing the alt to shut down. Were those wires spliced anywhere? Corrosion = resistance

(don't kill me - I don't remember what each wire is called)

One more - have you load tested your battery to see if your battery is going bad? Dropping to 8 to 10 volts, that's a big drop. I would expect some heat from something if there is a short dropping 6 volts off the system.

 

[bnc04]

There is no splices in any of those wires, there still in the looms. I did inspect that and the looked good. I may start replacing all the wiring in the charging system if I can't nail this, I'll start with the main batt and starter cables tomorrow and go from there. I think's it something to do with High resistance, as stated earlier, or a short to ground or a flaky connection. If you could see the truck, you would know why it's hard to trace, All the wiring is factory routed and still in looms.Which makes for great hiding spots

While i was in the no start failure mode, I did hook up via jumper cables, a fully charged deep cycle batt to see if I could even turn the starter. The symptom was exactly the same, So I'm guessing the Batt is ok.

Thanks again,, keep trying
Brett

 

[fatbob]

I vote for bad battery cables. There is probably corrosion under the plastic. And while you can get the volts through, you may be having trouble getting enough amps through to power everything. Next time it happens, wiggle the battery cables while someone is cranking it and see if there is any change.

 

[bnc04]

After replacing the ignition switch with the same symptom I went though and replaced the both battery cables with brand new ones and new connectors on each end. I ran the + to the starter and the alt. I also rechecked the connects at the new solenoid. Ran the - cable and added star washers and verified every ground had good contact. It started right up, when I operated things there was minimal draw and it looked like I had it whipped so I cleaned up the tools and took a shower, Came out for a test drive. No start again, after several tries it started and is acting the same way, Intermittently loads will cause it to drop voltage rather significantly ( 14-9) or so. An example, If I turn the blower motor on, it may drop,, or it may not,, If it drops, I tap the brake pedal a few times, and sometimes I can get it back up to 13-14 volts on the voltmeter.

WTF is going on?

Sorry for all the posts, I’m not too good of a mechanic but I try and think about things in a logical manner, Which, not understanding how the electrical system works and not being very fluent in Multi meters makes it tough.

Is there a possibility that a short or corroded wire that runs from the starter back to the connector at the alt and then to the hot post of the alt be causing this? It sure seems like it is a regulator issue in that it happens when I drive, when I am stationary, and at odd times which is caused by adding a load to the system. Once I get it running, anything from a blinker, to using the brakes, to turning on the radio or activation the heater/air blower motor can cause the volts to drop ( according to the gauge in the dash.. When this happens,, sometimes I can activate another item to create a load and it will bounce back…

I guess maybe it is time to start cutting up the wire looms and tracing all these wires back to the firewall and look for anything that is apparent..

One other thing,, I do have a b/m auto shifter on the console. I have the collar on the steering column wire tied to the left. Should I short the neutral safety switch to something and make sure that is out of the loop also? I can’t see how this would cause the scenario with the loads but I’m at my limited wits end..

About ready to invite whomever over and provide all the beer they want to diagnose this thing!

Thanks again for listening
Brett

 

[3 on the tree]

I don't know much about the later models. Does it have the large bulkhead connector. If so, I would unplug it and check for corrosion at that connection. Ain't electrical fun??????