Transmission? Motor? Need some direction.

[one4fun]

1986 K10, 350 w/700r4 transmission.

Took my K10 out on the sand yesterday for the first time. After 30-40 minutes of driving,, it had no power. The way I would describe it is that it was "chugging". I was in 4H and had the transmission in D2. With the gas pedal to the floor, the motor would not rev and the tires would not spin. It would just bog WAY down.

Back to the asphalt, back to 2WD, hubs unlocked. In neutral, the motor sounded normal, would rev up without any issues. Put the truck in D and it would have what I call "normal" from a stop. After it shifted up into 3rd gear, it would not kick down into 2nd when pressing the gas pedal to the floor. On the drive home, it did one time for a few seconds and then shifted back up to 3rd. If I put it in OD, it would have a noticeable vibration but would kick down into 3rd when accelerating. and back to OD when letting off the gas. Truck did not have much power at all on the pavement after driving it for a few minutes. It has never been a power house since I have owned it, but what I was experiencing yesterday was not normal. Transmission fluid was red and not burnt smelling. No leaks, nothing was visibly burning (transmission not smoking, motor not smoking, etc)

Motor is stock, has Thorley headers, stock carb, stock intake, 33/1250/15 BF Goodrich AT.

Got home late last night so I have not done anything.

Recommendations on where to start looking for the culprit? My "logic" says I over did it with a stock 700r4 and 33" tires on sand, but I would rather get some input from experienced minds that can point me in the right direction for a fix.

Thanks.
Chris

 

[tomtom1954]

Don't know about that trans,mines a manual, but it could be a modulator which back in the day was an easy fix. Hope so!

 

[recian]

Does it have the original big waffle looking catalytic converter hooked to those headers? Your symptoms sound like a clogged converter. They'll build up exhaust pressure after driving for awhile and will allow you to rev in Neutral but no power in gear.
Transmission seems to be working right. It can't shift correctly if the engine isn't running right causing good vacuum to the modulator and good RPMs to spin the pump and make pressure. If the throttle demand is too high for the input pressure (based off engine RPM) then the transmission will do what it can but can't operate properly. Usually if fluid is fine the trans is fine unless it has an obvious missing gear or something like that. Also if you're running a 700r4 you won't have a modulator you'll have a governor but that only controls shifts not power in each gear. I think the engine has some form of restriction causing it.

 

[dhamp]

Does it have the original big waffle looking catalytic converter hooked to those headers? Your symptoms sound like a clogged converter. They'll build up exhaust pressure after driving for awhile and will allow you to rev in Neutral but no power in gear.
Transmission seems to be working right. It can't shift correctly if the engine isn't running right causing good vacuum to the modulator and good RPMs to spin the pump and make pressure. If the throttle demand is too high for the input pressure (based off engine RPM) then the transmission will do what it can but can't operate properly. Usually if fluid is fine the trans is fine unless it has an obvious missing gear or something like that. Also if you're running a 700r4 you won't have a modulator you'll have a governor but that only controls shifts not power in each gear. I think the engine has some form of restriction causing it.

Yeah, that's what I was thinking. Some kind of exhaust blockage such as bad cat or crushed pipe.

 

[MrMarty51]

Does it have the original big waffle looking catalytic converter hooked to those headers? Your symptoms sound like a clogged converter. They'll build up exhaust pressure after driving for awhile and will allow you to rev in Neutral but no power in gear.
Transmission seems to be working right. It can't shift correctly if the engine isn't running right causing good vacuum to the modulator and good RPMs to spin the pump and make pressure. If the throttle demand is too high for the input pressure (based off engine RPM) then the transmission will do what it can but can't operate properly. Usually if fluid is fine the trans is fine unless it has an obvious missing gear or something like that. Also if you're running a 700r4 you won't have a modulator you'll have a governor but that only controls shifts not power in each gear. I think the engine has some form of restriction causing it.

Thats a real good hunch and, correction on the modulator valve was good too.

 

[one4fun]

I have a mechanic who I have used a few times and spoke to him about it. He also thinks a clogged cat is very possible. I will unbolt the headers from the exhaust and see if the power is restored. That should help determine whether there is a restriction in the exhaust system.

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[recian]

Keep us up to date

 

[dhamp]

 

[one4fun]

The first thing I thought might have caused the problem was I had a spark plug wire that was burned thru in two places where it was resting on the header pipe. Changed all 8 wires a few said ago. Same issue, still no power.

Removed the collector pipe last night from the headers to the exhaust, drove out around the block. No luck. Still no power (and loud as hell!).

I did notice that the truck has a smog pump. Something I have not dealt with before. I have "another" truck from 1975 that does not have any of the smog equipment on it. So, I am not familiar with the issues that it can cause.

I also noticed when the problem started was my fuel gauge started moving erratically. Not bouncing, but instead it would move abruptly. For example, the needle will move from half to 3/4 and sit there, for a second and then it would move down below 1/2, air there for a moment and then move to another spot. It will do this at idle and when driving, but not when the key is at accessory and the motor is not running.

No idea if the two are related.

Any chance that there is an electrical issue causing both issues?

Or, would there be some other blockage in the smog equipment that is causing a build up of back pressure and loss of power? Would this cause erratic movement of the fuel gauge?


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[MrMarty51]

Try hooking a grounding strap from the block to the frame and one to the body, see if that changes the way the gauge is reading.
Check timing too. I think that Your distributor may have that control module under the dash, if so, it could be a problem with that.
I seen a post a while back that had the procedure for disabling that module so that Your distributo will be as a pre module of a HEI.

 

[one4fun]

I will check the timing and install ground wires. Thanks for the info. Wondered about the timing. It starts perfectly and idles great, just when accelerating it chugs. I will pull the plus and check them too.

I did replace the fuel filter, kind of dirty, but no improvement in power.
Checked the coil. Nothing visibly burned or damages that I could tell.
Hoping for good news soon. Any other suggestions, feel free to chime in.


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[GTME94]

Try temporarily removing the gas cap and see if that helps. I've heard of instances where a fuel tank that can't draw in air as the fuel is sucked out can actually create a vacuum inside the tank and then the fuel pump can't pump enough fuel to the engine under load but it is enough for idle.

It's a long shot but is very simple to try out.

 

[Jims86]

The first thing I thought might have caused the problem was I had a spark plug wire that was burned thru in two places where it was resting on the header pipe. Changed all 8 wires a few said ago. Same issue, still no power.

Removed the collector pipe last night from the headers to the exhaust, drove out around the block. No luck. Still no power (and loud as hell!).

I did notice that the truck has a smog pump. Something I have not dealt with before. I have "another" truck from 1975 that does not have any of the smog equipment on it. So, I am not familiar with the issues that it can cause.

I also noticed when the problem started was my fuel gauge started moving erratically. Not bouncing, but instead it would move abruptly. For example, the needle will move from half to 3/4 and sit there, for a second and then it would move down below 1/2, air there for a moment and then move to another spot. It will do this at idle and when driving, but not when the key is at accessory and the motor is not running.

No idea if the two are related.

Any chance that there is an electrical issue causing both issues?

Or, would there be some other blockage in the smog equipment that is causing a build up of back pressure and loss of power? Would this cause erratic movement of the fuel gauge?


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Regardless of what the old gossip crew at the barber shop says, smog pump wont cause issues, unless it is siezed up.
Another thing, you may have the ECM controlled carb. make sure the 4 pin plug is still plugged in on your distributor...old brittle plugs have been known to come apart, and if it has, timing is not advancing.
Those 33s will roast that 700r4 eventually, unless you install bigger gears.

 

[one4fun]

I did check the connector on the dist. Will check again to be sure.

I am seriously hoping it is not something in the transmission or a bad cylinder. I have a compression check on the list of things to check.

I have to ask...why would the check engine light NOT come on? When I turn the key, it lights up. When I start the motor, it turns off right away. Would a scanner help in this case?

Thanks for the info.

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[recian]

The CEL will NOT come on if there are NO codes. The light is supposed to come on at startup as a check function. So you do have a computer controlled carb?