92 Suburban possible transmission issues?

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AyWoSch Motors

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Hi all, my first and biggest question...

My daily driver 92 Suburban K1500 recently developed some pretty bad issues. I would assume its transmission related, but not sure.
Here are the symptoms:

It started loosing power about a week ago, started having a harder and harder time getting going and getting up to speed. Then I started having a really hard time getting up hills at any speed.
It seemed like it was bogging really bad, like the way a carburetorated truck would be like if it was running super rich or if a float got stuck wide open. And when I let off the gas it would speed up a little before slowing down.
It eventually got worse and worse, so bad that it wouldnt go much over 30mph. But in park it runs great. Real snappy throttle, sounds healthy, about 60lbs of oil pressure, but in gear is where all the trouble starts.
So I checked the ECM codes, threw a code for the EGR system failure, a Electronic spark control module fault, and the Vehicle speed sensor. I replaced the ESC module and the EGR valve and it didn't change a thing. And the speed sensor has been throwing a code ever since I got it.
Then I thought I'd check the timing, because I'd never messed with it since I got it. I checked the timing, and it was really far off from the mark. Then I unplugged the plug on the firewall and it almost stopped running, was really rough. It was so far retarded that I couldn't even see the mark, so I adjusted the base timing without the electronic advance. I advanced it until I could see the mark, and it seemed to run better. Then I tried to advance it until it was near 0°, but it would start running really bad, so I retarded it again until it was running smoother. Plugged the plug back in. After I did that, i took it for a ride, and it seemed to have more power, but still not back the way it was. So I don't know if its engine or not now.
But then I figured I'd drive it home and test it a bit, and it started making horrible noises. Sounds like a diesel when it's running now. When it's in park or neutral, it doesnt make any noise, but when it's in drive or reverse it makes the noise. If you hold the brake and press the gas a little when in drive, its really bad. Sounds like a gravely metal rattling sound like a powerstork diesel at idle. And driving home going up a small incline that I usually do 65mph up, it wouldn't do over 30mph up.

Also, now when I start it up, sometimes it runs no problem but other times it dies 2 seconds later. But then even when it's running fine in park, you put it in gear, and it instantly dies. Only way to get it ti move right now, is to start it, rev it instantly to keep it running, slip it in the neutral quick, then keep the RPMs up and drop it in gear real fast, and sometimes itll stay running.
But the trans is making horible noises.

What would you think it is?
Is there a part I could change or something I could fix, or am I in for a new trans?

I'm really stumped. My first guess would be the transmission. Maybe the pump have up, maybe the torque converter is full of sludge, or something finally wore out enough to break.
When I first got the truck, I changed the trans fluid, trans filter, and gasket. The fluid is still bright red and full, doesnt smell burnt.
TBI 350ci small block, with 4L60E, both original to the truck, 302k miles.

Please help, I need my Burb back soon.
 

AyWoSch Motors

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I found a 4L60 in a 92 GMC truck yesterday for $120.
Engine is full milkshake, so chances are it was parked with the trans still working fine. Guy said it's good.

Guess I'll just swap trans and install a new torque converter, and see where we're at from there.
 

Schurkey

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It started loosing power about a week ago, started having a harder and harder time getting going and getting up to speed. Then I started having a really hard time getting up hills at any speed.
It seemed like it was bogging really bad, like the way a carburetorated truck would be like if it was running super rich or if a float got stuck wide open. And when I let off the gas it would speed up a little before slowing down.
1. Test fuel pressure, fuel volume.

2. Catalytic converter plugging

3. How old are the O2 sensor(s)? How old are the distributor cap, rotor, plug wires, and spark plugs? Air filter?

So I checked the ECM codes, threw a code for the EGR system failure, a Electronic spark control module fault, and the Vehicle speed sensor. I replaced the ESC module and the EGR valve and it didn't change a thing. And the speed sensor has been throwing a code ever since I got it.
Connect scan tool, look at the data stream. Codes "can" be useful, but the real clues are in the data. Verify every sensor, verify the computer outputs.

Look at the short- and long-term fuel trims.

Clear the codes, see what comes back.

Does the EGR solenoid work? Vacuum hoses disconnected or cracked? Intake manifold exhaust passages plugged with carbon?

Then I thought I'd check the timing, because I'd never messed with it since I got it. I checked the timing, and it was really far off from the mark. Then I unplugged the plug on the firewall and it almost stopped running, was really rough. It was so far retarded that I couldn't even see the mark, so I adjusted the base timing without the electronic advance. I advanced it until I could see the mark, and it seemed to run better. Then I tried to advance it until it was near 0°, but it would start running really bad, so I retarded it again until it was running smoother. Plugged the plug back in. After I did that, i took it for a ride, and it seemed to have more power, but still not back the way it was. So I don't know if its engine or not now.
Find TRUE TDC for #1. Verify the timing mark on the damper aligns with "0" on the timing pointer.

Is your timing light accurate on other vehicles?

But then I figured I'd drive it home and test it a bit, and it started making horrible noises. Sounds like a diesel when it's running now. When it's in park or neutral, it doesnt make any noise, but when it's in drive or reverse it makes the noise. If you hold the brake and press the gas a little when in drive, its really bad. Sounds like a gravely metal rattling sound like a powerstork diesel at idle. And driving home going up a small incline that I usually do 65mph up, it wouldn't do over 30mph up.

Also, now when I start it up, sometimes it runs no problem but other times it dies 2 seconds later. But then even when it's running fine in park, you put it in gear, and it instantly dies. Only way to get it ti move right now, is to start it, rev it instantly to keep it running, slip it in the neutral quick, then keep the RPMs up and drop it in gear real fast, and sometimes itll stay running.
But the trans is making horible noises.
How do you know it's the transmission making noises? Sure it's not detonation when the engine is under load?

What would you think it is?
Is there a part I could change or something I could fix, or am I in for a new trans?
You need WAY more diagnosis before you start changing parts.

I'm really stumped. My first guess would be the transmission. Maybe the pump have up, maybe the torque converter is full of sludge, or something finally wore out enough to break.
Yeah, that's possible. Not my first guess.

Since I parked my truck, its formed big puddle of ATF under it. What could that be connected to?
Most likely connected to a transmission leak. Pan gaskets get a lot of blame, but with OEM gaskets, it's usually something else, drooling down onto the pan gasket, and then dripping off from there. Torque converter seal, tailshaft seal, manual shaft seal, TV cable seal, dipstick seal, speed-sensor seal, servo seal, electrical-connector seal...

Hopefully, not a cracked case.
 

AyWoSch Motors

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1. Test fuel pressure, fuel volume.

2. Catalytic converter plugging

3. How old are the O2 sensor(s)? How old are the distributor cap, rotor, plug wires, and spark plugs? Air filter?


Connect scan tool, look at the data stream. Codes "can" be useful, but the real clues are in the data. Verify every sensor, verify the computer outputs.

Look at the short- and long-term fuel trims.

Clear the codes, see what comes back.

Does the EGR solenoid work? Vacuum hoses disconnected or cracked? Intake manifold exhaust passages plugged with carbon?


Find TRUE TDC for #1. Verify the timing mark on the damper aligns with "0" on the timing pointer.

Is your timing light accurate on other vehicles?


How do you know it's the transmission making noises? Sure it's not detonation when the engine is under load?


You need WAY more diagnosis before you start changing parts.


Yeah, that's possible. Not my first guess.


Most likely connected to a transmission leak. Pan gaskets get a lot of blame, but with OEM gaskets, it's usually something else, drooling down onto the pan gasket, and then dripping off from there. Torque converter seal, tailshaft seal, manual shaft seal, TV cable seal, dipstick seal, speed-sensor seal, servo seal, electrical-connector seal...

Hopefully, not a cracked case.
Wow, that's a lot of answers and questions. Thank you for the help and suggestions.
Lemme see if I can address them all...

I have no way of checking the fuel pressure, but I did recently change the fuel pump.

Could it be the Cat? It's still there. I've thought about cutting it out, but everybody has told me dont bother.

O2 sensors are original, never been touched.

Distributor cap and rotor have never been charged by me, I'll put it that way. They look orginal.

I changed the spark plugs and wires a few months ago, as well as the air filter.

I dont have a scanner tool for OBD1 port, I was using the technique of jumping the A B termails and counting the flashes.

I have no idea about the EGR seloinid.

I did check the vacuum lines and the manifold, they're both fine.

I plan on attempting the properly set the timing, and see if itll run better.

Timing light works fine on other vehicles, have used it plenty.

My friend crawled under the truck with it in gear and me revving it. (Emergency brake on and wheels chocked). And I can hear it very loudly, very much so sounds like it's coming from the transmission area.

I'm not completely sure about detonation, never heard that in person.

I had replaced the trans pan gasket, and the other day when it started to leak, I crawled under and tightened all the bolts. Still leaky. It appears its coming from above the pan.
 

Erik the Awful

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Could it be the Cat? It's still there. I've thought about cutting it out, but everybody has told me dont bother.
Disconnect the downpipes from the manifold and hang them in place with baling wire or coat hangers. If you want to stay in good graces, warn your neighbors because it's gonna be loud. Drive it up and down the block quick, and then park back in your driveway before the police show up. If it runs great, your cats are clogged. Replacement cats aren't cheap, but they aren't horribly expensive either. Before you replace them check your O2 sensor, because if it's running rich that's likely why your cats are clogged.
 

AyWoSch Motors

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Disconnect the downpipes from the manifold and hang them in place with baling wire or coat hangers. If you want to stay in good graces, warn your neighbors because it's gonna be loud. Drive it up and down the block quick, and then park back in your driveway before the police show up. If it runs great, your cats are clogged. Replacement cats aren't cheap, but they aren't horribly expensive either. Before you replace them check your O2 sensor, because if it's running rich that's likely why your cats are clogged.
I'm out in the country, 2 miles from payment, no worries about cops out here. I got an open headers big block blazer that I run around, so I'm familiar with loud, haha.

At this point I'll probaly just cut it out entirely and weld in a peice of pipe.

How would I "check" and O2 sensor?
I do remove it, or clean it, or what?
 

AyWoSch Motors

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The truck is fixed!!! Back to running like it was, better even.
Turns out it wasnt the transmission, or any part going bad. It was the timing.

Whoever suggested that the sound I thought was the trans was actually the engine pinging... ding ding ding, you got it.
I got out the timing light today to start tinkering with it, and noticed the Advanced degrees knob at the back of it had gotten turned all the way to 65. So the night I was messing with it in my buddies drive way, and I thought I was making it better, I was actually making it way worse.
I set the gun to 0, unplugged the thingy on the firewall, set the engine to 0tdc, and plugged the thingy back in. Running like new again. Snappy throttle, and the sound went away, and it not shutting off anymore.
And after changing those 2 parts aswell, its running a lot better, has more power.


So problem solved! Thanks all for the help. And i hope this helps anyone with a similar issue in the future.
 
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