Where exactly is my tach wire?

[User_name]

And my suspicions about the ecm is correct it SEEMS.
Started it up, tach was going full apesh*t, wiggled it around and suddenly it was running beautifully.
Ran without a single flutter or hiccup to wally world, the hardware store, the gas station, and back home (about 30 mins of driving)
You guys and this forum rock. I can't tell you how much better I feel knowing what exactly the issue SEEMS to be.
Now just need time off work to do a more thorough inspection and figure out a fix. Thinking I either have a loose commotion somewhere or a chaffed wire I overlooked. @PlayingWithTBI @Schurkey THANK YOU! I've been battling this for months!

 

[PlayingWithTBI]

Thinking I either have a loose commotion somewhere or a chaffed wire I overlooked. @PlayingWithTBI @Schurkey THANK YOU! I've been battling this for months!

Glad I/we could help. If that was indeed the cure, you may want to trace your ground wires from the PCM to the water neck bolt where it's grounded. IMO the case shouldn't have to be your ground path.

 

[User_name]

I'll be sure to check it, gonna have to pull the intake for a reseal anyways. The rubber chinawall gaskets have popped out. Will be doing new gaskets and instead of the rubber chinawall seals, I'll use a bead of permatex "the right stuff"
It runs good, intake it's self dosent seem to be leaking. I just HATE seeing the slight oil leak running down the front ofnthe engine.

 

[PlayingWithTBI]

The rubber chinawall gaskets have popped out. Will be doing new gaskets and instead of the rubber chinawall seals, I'll use a bead of permatex "the right stuff"

Yeah, most everyone quit using those rubber gaskets on the china walls years ago. Here's what we've been doing (as well as many others) for years. Look at the 2nd & 3rd pictures. HTH

www.gmt400.com/threads/my-flat-tappet-cam-wiped-out-so-i-decided-to-go-roller.60167/post-1279744

 

[User_name]

One more question. Do these tbi engines use normal sbc intake bolts? I was looking to get some new ones (probably the allen head ones) since I'll be cleaning everything else up

 

[PlayingWithTBI]

Do these tbi engines use normal sbc intake bolts? I was looking to get some new ones (probably the allen head ones) since I'll be cleaning everything else up

Yeah, I used 12pt bolts from O'Reileys IIRC.

You must be registered for see images attach

 

[someotherguy]

@PlayingWithTBI my esc module is located on the intake, passenger side. You might be thinking of the vortecs?

There are some differences in engine management when you have the manual transmission. If you can post a pic of that area of the engine, it would be helpful. For example light duty trucks with automatics got the 3-wire heated O2 sensor in '94, but my '95 3500HD with NV4500 had a 1-wire non-heated O2, original. With the manual trans, your truck may have the old style ECM, instead of the PCM with built-in ESC module. The automatic trucks got away from the external ESC in '93 for the most part.

Anyway I'm Schurkey and Derek; I think you're chasing the symptom, not the cause. I would not rate the tach high on the suspect list at all. Very low, in fact. Inspect the ignition system first.. and also realize the TBI's do have an inherent (very slight) stumble at idle when in closed loop. At least, all the ones I've owned have, regardless of mileage or state of tune.

EDIT - looks like I replied before reading the next page, sorry! Seems you may have found the issue.

Richard

 

[someotherguy]

Glad I/we could help. If that was indeed the cure, you may want to trace your ground wires from the PCM to the water neck bolt where it's grounded. IMO the case shouldn't have to be your ground path.

I don't think it can ground anywhere on the bracket, as it's plastic; I can't see in my mind's eye anywhere the case of the ECM could find a ground through the mounting. Might be a rare case of bad ECM; they do get bad solder joints inside but it doesn't seem to be very common.

Richard

 

[someotherguy]

And my suspicions about the ecm is correct it SEEMS.
Started it up, tach was going full apesh*t, wiggled it around and suddenly it was running beautifully.
Ran without a single flutter or hiccup to wally world, the hardware store, the gas station, and back home (about 30 mins of driving)
You guys and this forum rock. I can't tell you how much better I feel knowing what exactly the issue SEEMS to be.
Now just need time off work to do a more thorough inspection and figure out a fix. Thinking I either have a loose commotion somewhere or a chaffed wire I overlooked. @PlayingWithTBI @Schurkey THANK YOU! I've been battling this for months!

Shoot some DeOxit D5 in the connectors from the harness to the ECM and the socket. The stuff is practically magic, far beyond normal contact cleaner. Then if it continues to give you trouble, you might suspect the ECM itself, though it isn't common for them to go bad on these trucks.

Richard

 

[User_name]

@someotherguy
I'm currently at work. I'll take better pics when I'm home tonight