Diagnostic help

[new guy]

I've got a 1985 GMC Jimmy that I pull my pop-up camper with and we were headed back from a Tn state park when I noticed something felt wrong. It felt almost like I had a tire going flat. Luckily I was at my exit when I pulled off. I stopped along the side of the road check them all nothing low, lose, or scrubbing so I think to myself maybe it was the road got a little bumpy and it got into an awkward bounce I take off and 1st-4th was smooth but once it got into overdrive it started surging. I was afraid that the transmission was slipping ar first and stopped at a gas station to check the fluid level was good didn't have an awkward smell so I push to get home. Once I got home I was turning it around and noticed that when in drive or reverse it has a wicked ruff idle but in park or natural it idles fine so it makes me think it's the torque converter. Is there any way to check before I buy a $200+ dollar part and take the tranny out? Thanks,

 

[dyeager535]

Do a good visual inspection of the engine bay. Plugs, wires, cap, rotor, all electrical and vacuum connections, hoses, and lines.

In gear brings RPM down, which can show a problem you won't see in neutral/idle when RPM is higher.

A vehicle won't move with a bad torque converter. Locked TCC will cause the engine to completely stall at a stop, a slipping TCC would be felt while cruising, similar to an intermittent slipping clutch.

If the torque converter fails, the vehicle doesn't move. If any prior warning that it's going to fail, MAYBE you'd hear some noise as parts wear on each other, but I've never had one fail. Either way, it's how the vehicle is propelled, if it fails, there is no movement. As with any tranny failure, theoretically if something fails, you need to rebuild the trans.

On a side note, I'd be curious to hear those who HAVE had a converter fail, what their experiences were. I can't think of any posts I've seen about converter failure that weren't TCC problems.

 

[ScottyREwing]

I myself just made a post in which I am suspicious of the torque converter. My truck is choking and coughing and sputtering under load but only once it drops to 2nd gear and above. Its as though the carb is getting too much or too little fuel. I have a new fuel pump on the truck and all vacuums look fine but still not sure. My issue began after the truck overheated and stalled out. Later once cooled and under way... maybe 20 minutes on the road it began and hasnt stopped since.

Mine isnt a sensation of rubbing, or gears or anything though... its just coughing and sputtering and rpm's instantly drop.

I'm curious if this torque converter can cause this issue or I should look elsewhere.

Good luck to you with your issue.

 

[wasted wages]

Both of you need to post up the COMPLETE spec's on your rigs......

Helps us guys help you......

Things like what type engine,,, ,mileage on the engine/ truck...
Carb or FI ?
Transmission type....T 350 / T 400 / 700r4 ?
Transfer case type ??
Axles type ?
Tire size ?

all of these things can come into play when trying to help diagnose your problem...


My guess on the truck that overheated is a possible jumped timing chain that gave up when it ran hot... (nylon cam gears can do this with high mileage engines)

post up a little more info please !!

 

[new guy]

Both of you need to post up the COMPLETE spec's on your rigs......

Helps us guys help you......

Things like what type engine,,, ,mileage on the engine/ truck...
Carb or FI ?
Transmission type....T 350 / T 400 / 700r4 ?
Transfer case type ??
Axles type ?
Tire size ?

all of these things can come into play when trying to help diagnose your problem...


My guess on the truck that overheated is a possible jumped timing chain that gave up when it ran hot... (nylon cam gears can do this with high mileage engines)

post up a little more info please !!

Mine is a crate 350 with a 700R4, tranny was rebuilt 5,000 miles ago engine has 30,000 on it. Its carbonated with stock axlesand ttransfer case, has 31's, nothing fancy or special.

 

[rampage]

Mine is a crate 350 with a 700R4, tranny was rebuilt 5,000 miles ago engine has 30,000 on it. Its carbonated with stock axlesand ttransfer case, has 31's, nothing fancy or special.

Well there's your problem right there!

 

[new guy]

Well there's your problem right there!

I don't think this is a Carb issue, would be nice to have EFI buy oh well other stuff needs that money.

 

[ScottyREwing]

I dont want to post further on my issue and hijack this thread. My issue is here
http://coloradok5.com/forums/showthread.php?t=311057

Thanks gang

 

[Fordum]

I don't think this is a Carb issue, would be nice to have EFI buy oh well other stuff needs that money.

He was just mentioning that you had carbonated your engine..........

They tend to run all fizzy when you do that.......

But, of course, we knew that you meant Carbureted, as in having a carburetor.

As for a question about a torque converter failure, I have only run into one that I know of.
Guy had a Ford Mustang, about a 69 model. 302 engine, probably a C4 tranny, maybe a C6.
I don't know what started everything, but when he called me he had put in new points and plugs and it would not idle when he put it in gear.

He wanted me to show him how to set the dwell with a meter. I checked the point gap first, because I knew this guy's abilities and wanted to be sure he had actually put them in right.
They looked OK, so I told him crank it up.

Car idled just fine. Good throttle response. Then he dropped it in gear, and it tried to lurch backward and died.
He could hold the brake and give it gas and it would run, but you could tell it was in a load.
I told him it was his transmission, but he assured me it was the points. I checked everything again, and told him to take it to a transmission shop.

He told me I did not know what I was talking about, and left. I watched, and he had to hold the brake and stay on the gas at the stop sign.

We were all going to college and staying at the same apartment complex in Orlando.
Next day, he said it had stopped stalling and was working fine. Two days later, he left on a trip to his home in New York.

Bout a week later, his roommate mentioned that his transmission had gone out on him about the time he got home and was being rebuilt so he was going to miss some classes.

When he made it back, I asked what was wrong with the transmission. He said it just quit pulling and would not go in any gear.
He took it to Aamco if I remember right. I know he was charged somewhere in the neighborhood of $1500!

That was when you could buy a complete tricked out transmission from some of the aftermarket boys like B&M for about $600.
Never said he had a lot of sense..........

Plus it started slipping on him a couple of weeks later, and spent about the next month in and out of the local Aamco.

 

[new guy]

He was just mentioning that you had carbonated your engine..........

They tend to run all fizzy when you do that.......

But, of course, we knew that you meant Carbureted, as in having a carburetor.

As for a question about a torque converter failure, I have only run into one that I know of.
Guy had a Ford Mustang, about a 69 model. 302 engine, probably a C4 tranny, maybe a C6.
I don't know what started everything, but when he called me he had put in new points and plugs and it would not idle when he put it in gear.

He wanted me to show him how to set the dwell with a meter. I checked the point gap first, because I knew this guy's abilities and wanted to be sure he had actually put them in right.
They looked OK, so I told him crank it up.

Car idled just fine. Good throttle response. Then he dropped it in gear, and it tried to lurch backward and died.
He could hold the brake and give it gas and it would run, but you could tell it was in a load.
I told him it was his transmission, but he assured me it was the points. I checked everything again, and told him to take it to a transmission shop.

He told me I did not know what I was talking about, and left. I watched, and he had to hold the brake and stay on the gas at the stop sign.

We were all going to college and staying at the same apartment complex in Orlando.
Next day, he said it had stopped stalling and was working fine. Two days later, he left on a trip to his home in New York.

Bout a week later, his roommate mentioned that his transmission had gone out on him about the time he got home and was being rebuilt so he was going to miss some classes.

When he made it back, I asked what was wrong with the transmission. He said it just quit pulling and would not go in any gear.
He took it to Aamco if I remember right. I know he was charged somewhere in the neighborhood of $1500!

That was when you could buy a complete tricked out transmission from some of the aftermarket boys like B&M for about $600.
Never said he had a lot of sense..........

Plus it started slipping on him a couple of weeks later, and spent about the next month in and out of the local Aamco.

Haha I had completely over looked that stupid spell check and dumb phone operator..... I hope it isn't the tranny, it has very little miles on it from the previous rebuilt. Must say if it is I will not be going back with the 700-r4.

 

[wasted wages]

I would look at all of the vacuum hoses first.... especially any that could have been knocked loose during the trans work,,, IE: the modulator hose...

next I would check to make sure your dizzy hasn't moved and retarded the timing...

Being as you have a fairly new drivetrain ( crate engine ) I wouldn't suspect jumped timing or anything like that....

maybe jack up the front and rear axles, put the transfer case in neutral and rotate everything by hand... a stuck brake caliper or bad brake hose has tricked a person or two before.....

 

[paratrooper307]

Wouldn't hurt to take a look at the flexplate/converter and make sure all the bolts are tight, not cracked or warped, etc. When my flexplate was cracked, it make a very light ticking in park, but as soon as it was in gear, the load put on it make the ticking louder. Could be you have an issue that is exacerbated when you put a load on it.

Other easy things to check, TV cable, TCC lockup wiring/vacuum sensor. Problems with either can cause driveability issues while moving.

A vacuum problem is a distinct possibility. A minor leak that might not be apparent at higher rpm can manifest at a lower rpm (in gear) or when under load and low rpm (in OD). A vacuum gauge can help isolate if it's an engine problem. You can also disconnect the torque converter from the flexplate, and push it back to take the transmission out of the equation for engine troubleshooting.

 

[new guy]

I've got a 1985 GMC Jimmy that I pull my pop-up camper with and we were headed back from a Tn state park when I noticed something felt wrong. It felt almost like I had a tire going flat. Luckily I was at my exit when I pulled off. I stopped along the side of the road check them all nothing low, lose, or scrubbing so I think to myself maybe it was the road got a little bumpy and it got into an awkward bounce I take off and 1st-4th was smooth but once it got into overdrive it started surging. I was afraid that the transmission was slipping ar first and stopped at a gas station to check the fluid level was good didn't have an awkward smell so I push to get home. Once I got home I was turning it around and noticed that when in drive or reverse it has a wicked ruff idle but in park or natural it idles fine so it makes me think it's the torque converter. Is there any way to check before I buy a $200+ dollar part and take the tranny out? Thanks,

Figured I'd do an update, Itook it to a llocal shop where he said the #6 cylinderis dead pprobablya broke/week valve spring or a burnt valve. So he was going to check it at the first of this week and let me which one it was. He did a pressure test on that cylinder and it came to 35 psi and the neighboring #4 cylinder was at 110 psi.

 

[new guy]

Figured I'd do an update, Itook it to a llocal shop where he said the #6 cylinderis dead pprobablya broke/week valve spring or a burnt valve. So he was going to check it at the first of this week and let me which one it was. He did a pressure test on that cylinder and it came to 35 psi and the neighboring #4 cylinder was at 110 psi.

Since I'm going to have to pull the heads off to fix the problemdoes anyone have a head cam intake rrecommendation? Figure I'll swap the stock stuff out for a little bit more aggressive stuff. Keep in mind it is primarily a tow and mild 4X4 vehicle .