Back side grounds

[Funracer]

Been chasing a low rpm stumble for years. Just after putting the plenum back on last year (replaced the injectors, no stumble help) I read somewhere on the
forum here about a pair of grounds located on the back side of the engine block. The posting said they were easy to get to with the tranny removed or somewhat accessible with the plenum removed. Since I had just put mine back on I decided to wait until the next time I had it off to clean them up.

My plenum and other parts are out for porting/powder coat so last weekend
I went searching for these elusive ground posts. They can be seen generally
on the aft side engine "sketches" or whatever you call them at the beginning of the "Engine" chapter in the Service Manual. The passenger side ground shows 4 wires grounded and the drivers side shows 5 in one pic and 6 in another.

I began by looking for the passenger side ground. It is visible by pulling the plug wires forward and looking straight down between the firewall and the block. Notice 4 wires but only 3 connectors on the post:



I had a tough time removing this bolt because the wire connectors were bent back over the bolt head and prevent a socket or wrench (13mm or
14mm if I remember) from gaining purchase. Finally staightened them upright with a crowbar and then was able to get a socket onboard and
pull the bolt:



Once the bolt is out the wires are long enough to bring up top. I cleaned
all the connectors shiny and bolt and reinstalled with a light coat of dielectric grease.

It took me an hour or so to get the passenger side done (I know I am
slow. I just plan for it). The drivers side was more difficult. You can just
see it here at the tip of this long screwdriver. The pic is taken from the
passenger side looking over to the drivers side:



I always said that if I could see something I could get to it. Access to this ground bolt is blocked by no less than three things. The large wire bundle
above, the windshield wiper motor behind and a wire bundle clip that is attached to a large bolt directly below the ground bolt. The clip can be seen popped open in the pic above.

There is NO WAY to get this ground bolt out without removing the wiper motor first. Fairly straight forward. A tip: follow the manual procedure.
Do NOT try to remove the large wiper motor bolt that holds the drive arm to the motor. Pull the plastic screen below the DS wiper arm and loosen the 4 nuts (10mm) that hold the wiper motor arm to the wiper transmission arms (pic below). Then back the motor out of the firewall



Then after all that unbolt this:



Now, if you have lots of extensions and knuckles and angled socket
handles you can prob get to the ground bolt around the outside of the
large wire bundle overhead. When you finally get it out:



Mine had 5 wires. One diagram in the manual shows 5 wires but one shows
6 so not sure why the difference. Cleaned and replaced as the other.

Hope this gets rid of my stumble but I might never know as I am doing
many other things during this trip "down under". It was kind of a PITA but
maybe worth it if you are waiting for you beautiful newly ported intake
parts to come back.

[Schrade]

Great info there + snappics

Unless I'm mistaken, one of those ground connectors is for the dash LCD / CCM circuit, and causes the flicker that almost every C4 seems to have, post 17 years,

I don't 'mind' if a problem gets solved by accident (NOT Plug n Pray / Fully Automatic Assault Wallet), but I MUCH prefer seeing what was wrong - even if only a high impedance reading on the MM.

[Dynomite]

Originally Posted by Funracer

Been chasing a low rpm stumble for years. Just after putting the plenum back on last year (replaced the injectors, no stumble help) I read somewhere on the
forum here about a pair of grounds located on the back side of the engine block. The posting said they were easy to get to with the tranny removed or somewhat accessible with the plenum removed. Since I had just put mine back on I decided to wait until the next time I had it off to clean them up.

It was kind of a PITA but maybe worth it if you are waiting for you beautiful newly ported intake parts to come back.

Great thread
One of those ground wires on the passenger side is the direct ground for HVAC fans......I know because I forgot to connect that ground recently when installing the engine. Rather than connect that ground on that ground bolt of Engine case I connected it on the rear bolt of the Plenum

For the reasons you describe perfectly

[george1945]

Great pictures and information. I hope someone is keeping all the information that gets posted here and publishes it in a trouble shooting guide for those of us crazy enough to buy one of these cars.

[5ABI VT]

here is a photo from when I did my clutch and trans tunnel.. visible on the sides of the starter at the top of the photo

[Starman]

For a stumble, have you ohmed your injectors? With the plenum off, now is the time. They should be 14 ohms. Less indicates they are going bad - Don't know what you put on, but I would check anyway. I replaced the whole set with the RC units - no more stumble.

[RodB]

Originally Posted by Funracer

Been chasing a low rpm stumble for years. Just after putting the plenum back on last year (replaced the injectors, no stumble help) I read somewhere on the
forum here about a pair of grounds located on the back side of the engine block. The posting said they were easy to get to with the tranny removed or somewhat accessible with the plenum removed. Since I had just put mine back on I decided to wait until the next time I had it off to clean them up.

My plenum and other parts are out for porting/powder coat so last weekend
I went searching for these elusive ground posts. They can be seen generally
on the aft side engine "sketches" or whatever you call them at the beginning of the "Engine" chapter in the Service Manual. The passenger side ground shows 4 wires grounded and the drivers side shows 5 in one pic and 6 in another.

I began by looking for the passenger side ground. It is visible by pulling the plug wires forward and looking straight down between the firewall and the block. Notice 4 wires but only 3 connectors on the post:



I had a tough time removing this bolt because the wire connectors were bent back over the bolt head and prevent a socket or wrench (13mm or
14mm if I remember) from gaining purchase. Finally staightened them upright with a crowbar and then was able to get a socket onboard and
pull the bolt:



Once the bolt is out the wires are long enough to bring up top. I cleaned
all the connectors shiny and bolt and reinstalled with a light coat of dielectric grease.

It took me an hour or so to get the passenger side done (I know I am
slow. I just plan for it). The drivers side was more difficult. You can just
see it here at the tip of this long screwdriver. The pic is taken from the
passenger side looking over to the drivers side:



I always said that if I could see something I could get to it. Access to this ground bolt is blocked by no less than three things. The large wire bundle
above, the windshield wiper motor behind and a wire bundle clip that is attached to a large bolt directly below the ground bolt. The clip can be seen popped open in the pic above.

There is NO WAY to get this ground bolt out without removing the wiper motor first. Fairly straight forward. A tip: follow the manual procedure.
Do NOT try to remove the large wiper motor bolt that holds the drive arm to the motor. Pull the plastic screen below the DS wiper arm and loosen the 4 nuts (10mm) that hold the wiper motor arm to the wiper transmission arms (pic below). Then back the motor out of the firewall



Then after all that unbolt this:



Now, if you have lots of extensions and knuckles and angled socket
handles you can prob get to the ground bolt around the outside of the
large wire bundle overhead. When you finally get it out:



Mine had 5 wires. One diagram in the manual shows 5 wires but one shows
6 so not sure why the difference. Cleaned and replaced as the other.

Hope this gets rid of my stumble but I might never know as I am doing
many other things during this trip "down under". It was kind of a PITA but
maybe worth it if you are waiting for you beautiful newly ported intake
parts to come back.

Sent from my iPhone using ZR-1 Net Registry

[gbrtng]

a low RPM stumble from 3-1/2 years ago - did it ever get fixed?