Solved No overdrive after intake job... *UPDATE 4.22.2024

[Cheddar_Dan]

Hello,

Just had major intake work done to fix coolant leak. Now the auto trans does not go in to highest gear (overdrive). I suspect a vacuum hose or such, but have you got any ideas to get me started? If not, back to the mechanic we go.

Best!!
.cd

 

[410Fortune]

Yes a 94 has a vacuum modulator on the auto trans that requires a vacuum line. The auto trans vacuum line leads up to the vacuum “tree” on a 94 ohv engine, rear of the intake drivers side. It is a black vacuum hose that goes down the spine of the transmission

Your mechanic should have hooked this up and verified all connections

 

[Cheddar_Dan]

Yes a 94 has a vacuum modulator on the auto trans that requires a vacuum line. The auto trans vacuum line leads up to the vacuum “tree” on a 94 ohv engine, rear of the intake drivers side. It is a black vacuum hose that goes down the spine of the transmission

Your mechanic should have hooked this up and verified all connections

Thank-you, much!!!

 

[Cheddar_Dan]

Yes a 94 has a vacuum modulator on the auto trans that requires a vacuum line. The auto trans vacuum line leads up to the vacuum “tree” on a 94 ohv engine, rear of the intake drivers side. It is a black vacuum hose that goes down the spine of the transmission

Your mechanic should have hooked this up and verified all connections

I see rubber vacuum line from the vacuum tree that moves toward the middle of the firewall and attaches to a metal tube that drops straight down toward the ground. ... Might that lead to the modulator (The modulator that my mechanic says I don't have)?

 

[ChildIdenticant]

I see vacuum line ... middle of the firewall ..metal tube that drops straight down... Might that lead to the modulator

Yes.

 

[410Fortune]

Yes it leads to the passenger side of the transmission, behind the metal heat shield there is a vacuum modulator

The a4ld also has a self adjusting kick down cable that should be reset

 

[Cheddar_Dan]

Yes it leads to the passenger side of the transmission, behind the metal heat shield there is a vacuum modulator

The a4ld also has a self adjusting kick down cable that should be reset

Thank-you, again 410Fortune! If I have any energy left after work today, I will dig deeper into the tube/line mystery!! TY!!

 

[Cheddar_Dan]

I see rubber vacuum line from the vacuum tree that moves toward the middle of the firewall and attaches to a metal tube that drops straight down toward the ground. ... Might that lead to the modulator (The modulator that my mechanic says I don't have)?

 

[Cheddar_Dan]

ANOTHER CLUE: first time night driving since the gasket surgery and I noticed another oddity... Upper speedometer dash lights slowly faded out from about the 35 mph to 55 mph area. I had a bump in the road and the lights returned to normal brightness... Guessing I'm dealing with an electrical harness issue someplace after the massive disruption to fix a intake gasket

 

[410Fortune]

Check the connections at your battery and battery cables

 

[Josh P]

If it shifts fine in gears 1-3, I think it's probably an electrical issue

 

[Cheddar_Dan]

ANOTHER CLUE: first time night driving since the gasket surgery and I noticed another oddity... Upper speedometer dash lights slowly faded out from about the 35 mph to 55 mph area. I had a bump in the road and the lights returned to normal brightness... Guessing I'm dealing with an electrical harness issue someplace after the massive disruption to fix a intake gasket

Hello,

Just had major intake work done to fix coolant leak. Now the auto trans does not go in to highest gear (overdrive). I suspect a vacuum hose or such, but have you got any ideas to get me started? If not, back to the mechanic we go.

Best!!
.cd

More: Truck is shifting normally about half the time now. The shift cable had been positioned incorrectly and was on the firewall side of the EGR valve and had melted slightly. I removed EGR and got the cable back into a normal route and it is no longer flexed up against the EGR valve. Now, after a few days I'm getting CEL with codes 157, 186 and 332. The MAF sensor was replaced 2 weeks ago, so now, I'm ISO more wiring tugs and flubs in hopes of getting to the heart of the oddities. Thanks for listening!! Prayers, please!!

 

[Nedwreck]

The only things I can think of related to intake work, and 1-3 is working normally, is a gross vacuum leak sending a really high load signal to the ECU (thus not allowing or calling for OD). But it seems like 1-3 would be affected somewhat.

410 or somebody chime in please, isn't there a ground strap from the intake to the body? If that was bad, it would cause wonky stuff to happen?

Not mentioned yet is the brake pedal, mine always kicked from OD to D by tapping the brake pedal slightly. Not sure if that signal is in the brake switch or a separate switch. Brake lights work fine? I do the brake tap trick when i start up a sharp hill, since it's gonna downshift anyways (and I'm not heavy in the gas yet).

 

[Cheddar_Dan]

Hello,

Just had major intake work done to fix coolant leak. Now the auto trans does not go in to highest gear (overdrive). I suspect a vacuum hose or such, but have you got any ideas to get me started? If not, back to the mechanic we go.

Best!!
.cd

*A vacuum line smoke test exposed multiple splits and damage in MAF to TB intake tubing. Once the tubing was patched, shifting returned to normal. I'll test drive a few more days before declaring the issue "SOLVED" Thanks again to EVERYONE!!

 

[410Fortune]

Ahhh the old holes in the accordion section of the intake tube! I’m sure you would have gotten some lean codes after a few drive cycles

Well done! Smoke test for the win

Marked this thread solved

A Huge thank you for Coming back and posting the solution