Hi Guys,
I am noticing a new issue with my 1994 GMC suburban 5.7 L with 160k miles :
The Tach, oil pressure and fuel gages will jump about 2 lines for no apparent reason. The condition is not speed or vibration related ( happens at both idle and running at 60 MPH ) Sometimes they will jump on their own, and sometimes 2 of them will jump together. When this happens I do not notice an " actual " increase in RPMs ( when at idle )
Any Ideas ?
Probably bad grounds.
The first one to look at is a small black wire that is screwed into the same bracket that your obd1 port is screwed into.
Disconnect your battery cables, negative first before you repair any power issue.
Pull that wire and clean that bracket and clean that ring terminal.
The next place to look is your negative battery cable and the small wire that comes off of that cable and screws into the inner fender.
Pull it clean it, and sand some of the paint off of the fender so you get a better connection.
The sheet metal grounds use a ring terminal that has little sharp points sticking out of it and a rather odd underhead ring self tapping screw.
That ring is supposed to drive the points through the paint when it tightens down.
The screw is galvanized and the ring terminal is brass and the whole thing goes into painted steel.
The next things to look at are the ground wires at the intake manifold.
Should be two studs with ground wires attached to them at the front of the intake.
Pull them, clean them and I would also cut open the plastic convoluted tubing of all of the intake wiring harnesses and look for shorts and bad wires.
Top of the intake is a pretty hostile environment for wires.
Next take a good hard look at the engine grounds.
You should have a flat braided ground strap that goes from the back of the passenger side cylinder head and down to a stud sticking out of the firewall and another strap from that same stud down to the frame.
I can almost gaurentee you that they are crudded up green or broken.
The ground from the back of the head to the firewall stud is a real ******* to get at.
My 94 k2500 has a mystery bracket that bolts to the head.
I cleaned the paint off of the bracket and through bolted a ground wire to it.
That stud that comes through the firewall is pretty weak so dont overtighten it.
Again, clean the paint off so you get a good ground.
If you strip the threads off of that stud?
Find a spot in the firewall where you can drill a hole without hitting anything and clean the paint off and through bolt it.
The strap that goes from that stud to the frame is pretty much the same thing.
Clean the frame, clean the bolt.
You do not need to buy gm tinned ground straps.
I used cheap ass 10 buck each battery cables and that was at least 5 years ago.
The only thing left is the stock battery cables themselves.
Which is quite likely what is the cause of the problem.
If you have the original 1994 battery cables in your truck they are bad.
The plastic coating makes them look great from the outside.
They will look like brand new.
But when you cut the plastic off they are rotted green fuzz all of the way into the wire.
The other problem with gm side post connections is that inside of that plastic is a ring terminal with 4 stamped lugs that are supposed to dig into the lead of the battery and prevent that cable from moving under vibration.
But that never worked.
The cables are so heavy and unsecured that those little lugs could never stop that from happening.
And, for that to even have a chance, everytime you disconnected a sidepost you had to make sure that when you reconnected it that every one of those little lugs went back into the same divot that it came from.
If you miss a little bit when you clamp it down?
It digs another hole in the lead right next to the other hole and now you have a bigger hole and you have swinging gm sidepost cables.
If you have an aftermarket battery where the plastic standoff is just a bit too long a brand new gm sidepost cable will not properly connect.
The gm sidepost battery is such a great example of perpetual yet never ending engineering failure that it was part of my project management courses.
It is part of what they called "The GM Way"
Basically a set of rules that engineers and designers had to operate within.
A great example of this is to look at any 60s GM muscle car.
Big huge wheel openings and gigantic fender flares with 14×7 inch rims.
Because back in the 1930s customers in Alaska bitched about hitting ruts on the dirt roads and popping tires.
That became part of the "GM Way" and that is why a 69 gto or a Cutlass or a Chevelle looks goofy as hell on stock rims.
They look like some old lady trying to hitch her skirt up while shes chasing a loose chicken.
Big car, wee little tiny wheels.
With big tall narrow spongey tires
The reason that Chevrolet became the dominate force in racing was driven by the dealorships.
And that hidebound GM mentallity led them to keep devoloping that same 1950s based enigine because they were tooled up and locked into it.
Meanwhile, back at ranch. Ford had the truly awfull Y block and the only slightly less awfull FE blocks.
I could go on for days on this subject.
The big difference to us is that I can go into a parts store with my year and model and get a chevy part.
If I go in to find a ford part I need to know if it was manufactured in Michigan?
Yes.
Was it built on Monday?
Yes?
Before or after lunch?
I dont know.
Did the Detroit Lions play on Sunday?
Yes.
Did they loose?
Probably?..Maybe..?
Okay, so was the guy who installed your clutch from gratiot or maybe someplace out in berkley and how pissed off was he put the truck toghether.
Wait.. You said they built it on a Monday right?
We only show Tuesday parts available after a Lions win so we have to back order you untill the year 2075 but will call you when it comes in.
Go downtown and try the detroit pizza just go back to your hotel before the sun goes down and it will be ****** great.
