Whats going on with my 80!!?? Wits end... (1 Viewer)

[PZLCruiser]

I searched and searched the forum to no avail so hoping you guys could help before i have to go the dealership.

So when driving on the highway or in 4th gear im noticing the RMPs bounce up and down, only when coming up to an incline or when the truck asks for power. Its sort of like when the truck goes from a jog to a run to get through an incline while applying the same foot peddle pressure throughout. The RPMs dont fluctuate much just like 200-500 rpms only for a second or two at a time. Annoying when you have a hill or incline that takes a min to get over, the RPMs go up down up down up down. I can hear the engine working so its not just my tach. All other gears its not noticeable but she likes to settle into 4th when putting along and thats when i notice it.

I have taken off the throttle body a few times for past repairs and wondering if maybe something to do with the cables. Ive played with the throttle cable position and the transmission cable position and nothing made a noticeable difference. Praying its not the transmission. Transmission fluid level is good. TPS?

Im stumped and getting frustrated. My neighbors probably think im crazy because I adjust the throttle body cables and go for a drive and do it again and again like 12 times last night. Didnt help so i put the cables back how they were as best as I could. What should i try next!?

 

[icorradoi]

I would start by checking the intake tube for any rips or tears allowing unmetered air into the throttle body as well as making sure that the throttle body gasket is good and is creating a good seal. You can spray carb cleaner/starting fluid or use propane near the suspected areas and look for RPM fluctuations.

 

[danthman114]

try turning the OD off. what are the rps at when it downshifts out of overdrive?

 

[PZLCruiser]

I would start by checking the intake tube for any rips or tears allowing unmetered air into the throttle body as well as making sure that the throttle body gasket is good and is creating a good seal. You can spray carb cleaner/starting fluid or use propane near the suspected areas and look for RPM fluctuations.

I did a full PO401 fix, replaced the intake tube and TB gasket along with all the vacuum hoses and more. I could check that bolts and screws are tight. That was last year and everything has been good up until a few weeks ago.

 

[PZLCruiser]

try turning the OD off. what are the rps at when it downshifts out of overdrive?

I dont think OD is on. The OD dash light works and all, sometimes i hit the OD button with my knee but id see the dash light and notice the gears riding out more. I am curious to see if it does it in OD. Ill try tonight.

 

[inkpot]

try turning the OD off. what are the rps at when it downshifts out of overdrive?

Try just pushing down on the gas pedal a bit more. Most likely it is your torque converter going in and out of lockup

 

[flintknapper]

Try just pushing down on the gas pedal a bit more. Most likely it is your torque converter going in and out of lockup

^^^^^ Yep. Normal

 

[80t0ylc]

Try just pushing down on the gas pedal a bit more. Most likely it is your torque converter going in and out of lockup

I also will hit the OD off button, to keep it from shifting on it's own. I've noticed that with OD off, it will settle in 3rd with torque converter locked, so when I hit the button, there's a slight rpm rise and then it'll drop slightly when TC locks and hold the rpm better on the hill. It's better on the tranny with TC locked - it runs cooler.

 

[NLXTACY]

I make no claims

 

[PZLCruiser]

^^^^^ Yep. Normal

yah it goes away when I do push on the peddle more but why? Something getting warn out with the torque converter?

 

[PZLCruiser]

I make no claims

didnt say im at my absolute wits end yet haha

 

[80t0ylc]

yah it goes away when I do push on the peddle more but why? Something getting warn out with the torque converter?

I doubt it. Ya gotta remember, you're pushing 3+ tons down the road with a 6 cylinder engine.

 

[Tools R Us]

Under some conditions, highway speed, IIRC ~40ish % throttle opening, it is on the programing threshold of torque converter lock, so will hunt, on-off. Ways to "fix" the "problem", slightly add throttle to keep it unlocked, slightly reduce throttle so it stays locked or down shift to 3rd. It's part of living with an old school relic! To permanently fix the "problem", trade it in on a new big tree or something that has more sophisticated programing!

 

[PZLCruiser]

Under some conditions, highway speed, IIRC ~40ish % throttle opening, it is on the programing threshold of torque converter lock, so will hunt, on-off. Ways to "fix" the "problem", slightly add throttle to keep it unlocked, slightly reduce throttle so it stays locked or down shift to 3rd. It's part of living with an old school relic! To permanently fix the "problem", trade it in on a new big tree or something that has more sophisticated programing!

So what about the throttle body cables and the throttle position sensor? Whats with that cable going to the transmission? Could a combo of it all be giving me the hunting TC issue?

 

[jfz80]

So what about the throttle body cables and the throttle position sensor? Whats with that cable going to the transmission? Could a combo of it all be giving me the hunting TC issue?

Sounds like the transmission kick down cable. Wouldnt hurt tightening it up to spec or new mud suggested spec but dont think it will fix your described issue here.

 

[morganism]

Does it idle up when AC turned on? Are the dash lights doing anything diff?

Think the EGR will do this when it starts sticking. As it gets worse, it will start affecting idle.

Ground the coil/ignitor case w a separate wire, and see if it helps. They added one in the 100 series.

 

[Tools R Us]

So what about the throttle body cables and the throttle position sensor? Whats with that cable going to the transmission? Could a combo of it all be giving me the hunting TC issue?

The TPS is one of the inputs used to determine shift timing, it can be adjusted a few degrees, but would just slightly move the hunting. The cable going to the transmission simply adjusts system pressure, affects shift firmness, has nothing to do with shift timing.

Haven't driven yours, so don't know what the deal is. But if it's clutch lock hunt, under some conditions, it's normal, so "fixing" it would involve a new ECU, like aftermarket, with different programing. In this case, the easiest way to accomplish that, would be to trade it in on a newer car.

 

[PZLCruiser]

Does it idle up when AC turned on? Are the dash lights doing anything diff?

Think the EGR will do this when it starts sticking. As it gets worse, it will start affecting idle.

Ground the coil/ignitor case w a separate wire, and see if it helps. They added one in the 100 series.

No dash lights or check engine light. My AC belt is off so not sure if that would load the engine if I turn it on. The EGR is new like 10k miles ago so should be the culprit. Ill check out my grounds and see what they look like.

 

[PZLCruiser]

Sounds like the transmission kick down cable. Wouldnt hurt tightening it up to spec or new mud suggested spec but dont think it will fix your described issue here.

yah ill play with it some more and see if it helps.

 

[PZLCruiser]

The TPS is one of the inputs used to determine shift timing, it can be adjusted a few degrees, but would just slightly move the hunting. The cable going to the transmission simply adjusts system pressure, affects shift firmness, has nothing to do with shift timing.

Haven't driven yours, so don't know what the deal is. But if it's clutch lock hunt, under some conditions, it's normal, so "fixing" it would involve a new ECU, like aftermarket, with different programing. In this case, the easiest way to accomplish that, would be to trade it in on a newer car.

yah maybe id better just throw in the towel and sell for super cheep.