1994 Chevy C1500 - 4L60e Transmission Repeatedly Bogs and Surges Between 3rd and 4th - Hot Rod Forum : Hotrodders Bulletin Board
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Old 11-21-2016, 11:54 AM
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1994 Chevy C1500 - 4L60e Transmission Repeatedly Bogs and Surges Between 3rd and 4th

Hi All,


I have a 1994 Chevy C1500 with a 5.7 and a 4L60e trans. Odometer has 319k miles.


This truck is rarely on the freeway. The few times I have been on the freeway, I have noticed that it surges and bogs a lot between third and fourth gear., like the transmission can't decide which gear to go with. The problem usually seems to start after 60 mph. But it shifts and cruises nice and smooth on the street.


I did a complete tune up: spark plugs (might be the wrong ones), wires, cap, rotor, ignition coil, O2 sensor, fuel filter, Seafoam in the TBI and the fuel tank. None of this fixed the problem.


I also noticed the temp gauge was also reporting around 150* operating temperature. Never thought much about it.


Then, the radiator started leaking, and I replaced it, along with a brand new hoses, including heater hoses, and a thermostat. Fresh coolant. Again, no change in the temperature reading or the shifting issue. However, a week after I replaced these parts, the temperature gauge was showing close to 100* all the time. I then replaced the Coolant Temperature Sensor, and the gauge showed 150* degrees again. However, since the thermostat was specifically rated at 195*, I decided to find what else was wrong.


I then replaced the heater core (I could hear coolant sloshing inside the cab and the heater core was leaking a tiny bit, apparently), a new thermostat from Stat, and the Temperature Sending Switch (could only find a Duralast version, no cross reference numbers available anywhere, and I had to add a connector to the original wire). On a related note, I noticed the wire going from the harness to the Temperature Switch was quite corroded at one point, so I cut out the bad part and spliced it together. This finally showed the higher temperature reading on the gauge, around 195*. I thought the correct temperature reading would allow the computer to shift the transmission correctly, but it did not.


So, I replaced the Throttle Position Sensor as a possible culprit. Now, either the transmission will still bog and surge repeatedly between third and fourth, or just stay in third, or completely skip third (from what I can tell by ear and feel) go straight into fourth.


I have read that a particular kit called the P1870 Code Buster sold on eBay might fix this problem.


Any thoughts on this?


Thanks in advance!

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Old 11-21-2016, 12:07 PM
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Have you actually checked the voltages on the TPS to verify that it's reading correctly?
P1870 is the code that is set if the computer sense the transmission is slipping.Not sure that is what's going on with yours.
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Old 11-21-2016, 12:16 PM
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Quote:
Originally Posted by jokerZ71 View Post
Have you actually checked the voltages on the TPS to verify that it's reading correctly?
P1870 is the code that is set if the computer sense the transmission is slipping.Not sure that is what's going on with yours.
I have not not checked the voltage on the TPS. I will try to do that tomorrow and report back.
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Old 11-22-2016, 02:24 PM
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I did test the original and aftermarket AutoZone TPS today with a volt meter.


I used this video on Youtube as a guide.


The original TPS shows a reading of 4.8. The AutoZone aftermarket unit shows a reading of 6.9. based on the numbers provided in the video (between 4 and 6), the new unit is no good.


I took the truck for a spin before doing this test, with the AutoZone TPS still installed. The bogging and surging was much more obvious with this unit. After doing the test, I kept the original TPS installed and went for another spin. The truck stayed in third, but had much less bogging and surging.


Someone on another forum suggested it might be a clogged exhaust.








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Old 11-22-2016, 02:45 PM
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I didn't watch the video, but, from my experience, closed throttle should be approx near 0.Maybe .2 at most.
WOT should be approx 4.5 to 5 volts.More importantly tho is that the increase in voltage is steady & linear as throttle is applied.It should steadily increase as the throttle opens with no flat spots, or, spikes.You reference voltage is only 5 volts.
I could see how a plugged exhaust could possibly give you problems, but, I would think you would have other problems as well.Low line psi can also cause these problems, which again could be due to a bad/faulty TPS, MAP sensor, or, even a dirty filter, partially clogged screen to the EPS (electronic psi solenoid).
You could try a short drive with the TPS unplugged, but, be warned, if your trans already has problems, this could finish it off, as doing so will have operating at full line psi.
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Old 11-22-2016, 03:28 PM
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According to this article ("How to Test the Throttle Position Sensor (GM 4.3L, 5.0L, 5.7L)"), the reading should be between 0.5 to 0.9 volts.


I did not test the TPS by moving the throttle, but I will try that tomorrow and see if there are any dead spots.


I agree about the plugged exhaust. I would have expected other issues of some sort while driving on the street. I'll skip the driving with the TPS unplugged for now.


So, on the list of things to test:
- MAP sensor
- Line pressure


Lastly, what happens if the Idle Air Control valve is bad? I unplugged it while the engine was running and nothing happened. Plus, the connector looks like it may be falling apart.


EDIT: For reference, a previous discussion on whether or not to do a fuild and filter change on this transmission: "4L60e - High Mileage Transmission Service". In the end, it was decided to leave everything alone since the history of the transmission's service records was not available.

Last edited by lt1silverhawk; 11-22-2016 at 03:43 PM.
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Old 11-23-2016, 03:47 PM
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I tested the original TPS today by moving the throttle. I made a video of it (posted below) so I could look at the readings on the multimeter afterwards. I moved it back and forth as slowly as possible twice. Everything seems to be ok to my inexperienced eyes.


While I was at it, I also removed and cleaned the idle Air Control Valve. It seemed to be a little dirty. Unfortunately, the gasket was damaged so I'll have to replace that.


I think I will drop the transmission pan next and see what I find, as I have never done anything to it at all. I believe a visual inspection can on help.


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Old 11-25-2016, 08:43 PM
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Today I decided to go ahead and see if there were any trouble codes in the computer. Video below.


I got the codes "15" and "22".


Based on this website (www.repairpal.com), code "15" is "low coolant temp error" due to the engine being cold.


Code "22" is "Throttle Position Sensor error (signal low)"


Based on the testing doe earlier, the TPS seems to be ok. Could it be a wring issue? Or should I try an AC-Delco unit just to see if it makes a difference?


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Old 11-30-2016, 05:46 PM
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Just wanted to post some updates...


I left the battery disconnected overnight to clear the codes. The next day, I reconnected it, and warmed up the truck. I did not drive it. After warming it up, I checked for codes and no codes were flashed.


Today, I warmed up the truck, and checked the transmission fluid. The amount of fluid is much higher than the level indicated for "Hot". Could this be the issue? See picture below.


I then took it for a spin. Still continues to stay in third gear on the highway. Afterwards, I checked for codes, and nothing flashed, except for the "diagnostic mode" code 12. No code "15" (coolant temp low) or "22" (TPS signal low) like before.



Last edited by lt1silverhawk; 11-30-2016 at 05:55 PM.
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Old 11-30-2016, 11:52 PM
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When you check the transmission fluid, was the truck warmed up and still running. You have to check the transmission fluid with the truck running to get a good reading.


Also as far as the codes go - some codes will only display if the same fault is detected over a number of warm-up / cool-down cycles. Most commonly 3 should do it.


There is always the chance that it is a mechanical problem in the transmission - one the computer can not detect. If that is the case it will never throw a code.


Does your transmission have an electronic button for overdrive? If it does try turning that off and see if it still surges or bogs.


With 319k on the transmission I would not be surprised to find it is slipping, has bad or sticking valves or other problems. Doing a fluid change or especially a power flush on a transmission with high miles and low maintenance often will create more problems than it solves.


You may find yourself rebuilding that thing before it is all said and done.


Good luck and keep us posted.
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Old 12-01-2016, 12:04 AM
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Quote:
Originally Posted by Rcav8r View Post
When you check the transmission fluid, was the truck warmed up and still running. You have to check the transmission fluid with the truck running to get a good reading.
Yes, the truck was warming up for a few minutes before I checked the fluid. it was idling in "Park". About 155* on the engine temperature gauge.




Quote:
Originally Posted by Rcav8r View Post
Also as far as the codes go - some codes will only display if the same fault is detected over a number of warm-up / cool-down cycles. Most commonly 3 should do it.
Thank you, that is good to know. I can drive it around tomorrow and see if anything codes pop up after.


Quote:
Originally Posted by Rcav8r View Post
There is always the chance that it is a mechanical problem in the transmission - one the computer can not detect. If that is the case it will never throw a code.
True, there is always a possibility. However, I think it is something external. The reason being that with the original TPS the truck pretty much stays in third gear at higher speeds, with some bogging and surging. With the after market TPS, the bogging and surging is very much amplified. I am also considering looking into the Vehicle Speed Sensor and the distributor as possible trouble spots.




Quote:
Originally Posted by Rcav8r View Post
Does your transmission have an electronic button for overdrive? If it does try turning that off and see if it still surges or bogs.
No, just a regular shift. No buttons for overdrive.




Quote:
Originally Posted by Rcav8r View Post
With 319k on the transmission I would not be surprised to find it is slipping, has bad or sticking valves or other problems. Doing a fluid change or especially a power flush on a transmission with high miles and low maintenance often will create more problems than it solves.
While I was debating doing a simple fluid and filter change, I am now considering trying to siphon out of some of the fluid first to bring it down to a normal level and see if that makes a difference.




Quote:
Originally Posted by Rcav8r View Post
You may find yourself rebuilding that thing before it is all said and done.


Good luck and keep us posted.
Thank you. If it comes down to that, I'll just keep driving it on the street since it runs perfectly on street speeds. Then I'll look into a proper rebuild.
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Old 12-17-2016, 07:27 PM
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Update.


While trying to chase down the issue of not shifting into OD, I ended up attempting to replace the brake light switch on the brake pedal. This was something that came up here and there when searching similar issues online, so I decided to see if it would fix the problem. If it was the problem, then it would be keeping the TCC lock up from engaging.

When I removed the brake light switch (the dreaded metal clip came off without too much trouble), I noticed that the wiring connector had two wires cut off, and three wires were nearby, hanging and exposed. One wire was pink, the other two purple.













I figured the pink wire would go where the pink wire was cut inside the connector, but could not figure out how the two identical purple wires were supposed to be connected. After some searching online, I found an image from this page: Sparky's Answers - 1994 Chevrolet 1500 Pickup, Stoplights Will Not Work With The Ignition On.




The plan is to drop the steering wheel column to get as much access as possible to the wiring connector, replace it properly, and then see if everything works like it should.




Image Credit: sparkys-answers.com





And here is how the original Brake Light Switch looks:


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Last edited by lt1silverhawk; 12-17-2016 at 07:36 PM.
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