Erratic tach / electrolysis

[lodaddo55]

1992 C1500. 446K original miles.
1. Unsolvable (so far) problem. On cold start in the morning the tach, with related engine performance irregularities, is jumpy until the feedback system goes into closed loop mode. Wondering if this thing has an electric interference rectifier somewhere or any other thoughts. Have replaced most feedback parts and diligently isolated plug wires from any metal and themselves.
2. Had the intake removed and reset at 417K after it was leaking coolant at the heads. Since that time I have had to replace two heater returns lines as they are being eaten alive inside the fitting to the point the coolant gets past the o-rings. Just pulled the third one out which was OEM and installed in October and the same condition was occurring. Wish I had a photo of the second one as it was unbelievable. This is not corrosion but some electrical action that is literally burning holes in the end of the tube. It looks as though someone used a plasma cutter on it. Block ground is clean and good as is the intake ground at its connection point.

 

[RichLo]

Up until you said there were plasma cutter holes at the wiring connections, I was going to say it was just the Idle Air Control Solenoid and an unrelated issue with your coolant system.

Pictures of the electrical plasma cutting corrosion would help enormously

 

[tpass]

My 1993 quick connect on the intake looked the same way, like someone ground on the end of it. Electrolysis is pretty powerful stuff, thats why they put those huge sacrificial anodes in home hot water heaters and zincs on boats.

basically your quick connect fitting is the sacrificial anode. anti-freeze is supposed to slow it down but loses effectiveness over time.

 

[lodaddo55]

Up until you said there were plasma cutter holes at the wiring connections, I was going to say it was just the Idle Air Control Solenoid and an unrelated issue with your coolant system.

Pictures of the electrical plasma cutting corrosion would help enormously

Thanks, the IAC was replaced. Wish I had saved heater return line too for photos. It is actually the end of the heater return line where the aluminum tube inserts into steel manifold fitting. I know it's electrolysis but can't figure out why it has become such a problem with short term implications after I ran the OEM equipment for 417K miles.

 

[lodaddo55]

My 1993 quick connect on the intake looked the same way, like someone ground on the end of it. Electrolysis is pretty powerful stuff, thats why they put those huge sacrificial anodes in home hot water heaters and zincs on boats.

basically your quick connect fitting is the sacrificial anode. anti-freeze is supposed to slow it down but loses effectiveness over time.

Thanks, that makes sense. Being a drag boat guy I know how much fun mixing electricity and water can be. At this stage I am considering replacing the steel fitting at the intake with a brass hose barb fitting and eliminating the aluminum return with rubber hose since the quick connect is simply an assembly line convenience. Me and the truck on on a race to see who gets to the end first and I hope I win.

 

[PlayingWithTBI]

It is actually the end of the heater return line where the aluminum tube inserts into steel manifold fitting.

I'm confused, are you talking about the fitting that screws into the intake manifold? FYI the intake manifold is aluminum. I don't remember any steel fitting there.