1984 Buick Riviera 5.0L V-8 has jerked/shook/bucked a few times

[adamant0720]

So this has happened only twice so far:

- both times I'd say around 40-50mph.

- was driving w/ trans in OD

- all was smooth until bam! a good buck/shake/jerk happened, lasting around 1-2 seconds, and it was fairly loud sounding as well

- both times I immediately let go of the gas pedal and it seemed to go back to normal.

- it actually scared my wife 2nd time it happened lol.

- since the 2nd incident, I've switched to driving in D only (not OD), guessing perhaps OD might be related somehow

- I've had the car for 2 years, and it's got about 38k miles on it

 

Any thoughts on what it might be, and how to diagnose?

 

Thanks!

Scott

[avgwarhawk]

What is the condition of the transmission fluid?  The transmission control solenoid my be going bad. 

 

Edited March 9, 2022 by avgwarhawk (see edit history)

[RivNut]

I had problems on two similar Rivieras from that 79-85 generation.  The solenoid for the lock up converter fails and the converter stays locked. I found that before coming to a stop shifting into neutral unlocks the converter.  It is a simple inexpensive fix to replace the solenoid, but not something I would do in my driveway. Take it to your local mechanic.  

[adamant0720]

2 hours ago, avgwarhawk said:

What is the condition of the transmission fluid?  The transmission control solenoid my be going bad. 

 

When I checked the dip stick it seemed fairly clean and full. 

 

1 hour ago, RivNut said:

I had problems on two similar Rivieras from that 79-85 generation.  The solenoid for the lock up converter fails and the converter stays locked. I found that before coming to a stop shifting into neutral unlocks the converter.  It is a simple inexpensive fix to replace the solenoid, but not something I would do in my driveway. Take it to your local mechanic.  

Any way to test if solenoid might be going bad? If its simple, why not try and do in my driveway (other than getting crushed by car when under it, assuming you need to get under the car to replace it...)

 

Thanks!

[RivNut]

When mine went bad I’d step on the brake to come to a stop and the car acted as if it had a manual transmission in it and I wasn’t using the clutch to disengage the engine from the transmission.  No real way to test it that I know of.  Hope you have all the correct tools if you’re thinking it’s a DIY job.

[SpecialEducation]

My ‘82 bucked a little from time to time. It was the coil failing. 
 

New coil, smooth as silk. 

[SpecialEducation]

17 hours ago, RivNut said:

Just unplug the 4-pin electrical connector on the transmission. That will disable the TCC. 
 

But that doesn’t sound like what the OP is describing. 

Edited March 10, 2022 by SpecialEducation (see edit history)

[adamant0720]

18 hours ago, RivNut said:

When mine went bad I’d step on the brake to come to a stop and the car acted as if it had a manual transmission in it and I wasn’t using the clutch to disengage the engine from the transmission.  No real way to test it that I know of.  Hope you have all the correct tools if you’re thinking it’s a DIY job.

Well not thinking of attempting it so much right now, if the symptom doesn't come back by leaving it in D instead of OD I'll probably just go with that as my fix lol... just was kind of curious the scope of the job.

[adamant0720]

1 hour ago, SpecialEducation said:

My ‘82 bucked a little from time to time. It was the coil failing. 
 

New coil, smooth as silk. 

hmm. the ignition coil? the shudder i had felt seemed like something bigger than say a misfire but honestly i'm not sure I've been in a car when it misfired so I can't really say I know the difference.  

 

it did stall on me once - but it had been a few weeks since last taking it for a drive and I kind of chalked it up just to that. 

[SpecialEducation]

2 hours ago, adamant0720 said:

hmm. the ignition coil? the shudder i had felt seemed like something bigger than say a misfire but honestly i'm not sure I've been in a car when it misfired so I can't really say I know the difference.  

 

it did stall on me once - but it had been a few weeks since last taking it for a drive and I kind of chalked it up just to that. 

Not as much like a miss and more like someone turning the key off and on rapidly. 

[EmTee]

I may be wrong, but I recall reading somewhere some time ago that the torque converter doesn't lock in "D" (i.e., 3rd gear), only in "OD".  Maybe it is a TCC solenoid issue.

[RivNut]

3 hours ago, adamant0720 said:

Well not thinking of attempting it so much right now, if the symptom doesn't come back by leaving it in D instead of OD I'll probably just go with that as my fix lol... just was kind of curious the scope of the job.

This when you take it to a professional shop for advice. No need to make compensations for something not working correctly.

[71GS]

We had a 92 Riv once that started bucking so bad I was sure the trans was junk. A mechanic buddy found a bad plug wire. I couldn’t believe it.

 It was perfect again after a new set of wires. Just a thought. 

Brian

[pfloro]

17 hours ago, EmTee said:

may be wrong, but I recall reading somewhere some time ago that the torque converter doesn't lock in "D" (i.e., 3rd gear), only in "OD".  Maybe it is a TCC solenoid issue.

The torque converter clutch in my THM325-4L ('84 Toronado) did lock in "D".  Ratio is "D" is 1:1 (crankshaft to transmission O/P). Ratio in "OD" is .69:1...  You should still feel the "buck" in "D" if due to the TCC but it may be less pronounced (less load on the engine).

 

Disconecting the connector at the transmission will disable the TCC.  This a good way to isolate the problem.  However, it's not a good idea to drive for too long with the trans in "OD" and the TCC disabled. This will raise the trans fluid temperature because the crankshaft speed is lower and the torque converter is multiplying torque... 

 

Please keep us posted.

 

Paul 

[pfloro]

After giving more thought to this problem, I've come up with a potential cause.  The exact same thing happened with my 1984 Toronado when it was maybe 6 years old (~40,000 miles).  The "bucking" was perhaps not as strong as you described,  but it was very noticeable.

 

The "TPS" (Throttle Position Sensor) may be failing. This sensor is a variable resistor which tells the ECM (Electronic Control Module) how far the throttle has been opened.  All GM "CCC" (Computer Command Control) cars have this sensor.  On carbureted engines, it's located under the top section (Air Horn) of the carb. The analog voltage signal from this sensor (~.41V - idle / ~4.5V - WOT) provides the ECM with important information about engine operation. 

 

The TPS signal is used (among other purposes) to lock & unlock the Torque Converter Clutch.  Once vehicle speed reaches ~40 mph and the ECM issues a TCC "lock" command (aka: apply), the TPS signal is monitored by the ECM (to control the TCC).  If you press a bit on the accelerator to speed up, the TCC unlocks (aka: release). This is because the ECM "sees" a higher TPS voltage (above the unlock threshold). When you then ease off the throttle, the TCC again locks because the ECM sees a lower TPS voltage. If you take your foot off the accelerator and coast, the TCC is unlocked because the TPS signal drops back to the idle value (~.41V).  We're not talking about a downshift from OD(4th) to D(3rd), but a TCC unlock commanded by the ECM.  Applying more throttle would not only cause a TCC unlock, but also cause a 4->3 or a 4->3->2 downshift.

 

When the TPS's resistive material begins to wear out, the signal can become erattic. While cruising above the TCC lockup speed, the TPS can falsely tell the ECM that you have lifted you foot from the accelerator. The ECM will then unlock the TCC. Almost immediately (when the ECM sees the correct signal), it will command a lock.  If these erratic signals occur back-to-back, the bucking, etc. will be pronounced.

 

Because the erratic TPS signal is intermittent and because the CCC system is "primitive", a DTC (Diagnostic Trouble Code) won't be set and the Check Engine light won't illuminate.

 

The TPS sensor is not a sophisticated device. There are tiny fingers which slide over the resistive material.  Since it's purely mechanical action, it wears out.  In my experience, the TPS sensor is the weak link in the CCC system.

 

I experienced this situation on a level state highway while cruising at ~50 mph.  Initially, I suspected transmission trouble. After troubleshooting, I realized the TPS was the cause.

 

There is an easy way to monitor the ECM's lock signal to the TCC...

If there is interest, I'll be happy to share my knowledge and experience.

 

Paul

Edited March 12, 2022 by pfloro (see edit history)

[adamant0720]

On 3/12/2022 at 7:08 AM, pfloro said:

There is an easy way to monitor the ECM's lock signal to the TCC...

If there is interest, I'll be happy to share my knowledge and experience.

Hmmm some interesting ideas here. Sounds like it would be a fairly simple fix to replace it, if it's faulty. I've only had the car for 2 years, so no idea how old the current TPS is, possible it is indeed wearing out.

 

So what's the easy way to monitor ECM's lock signal to the TCC?

Thanks!

[pfloro]

You will be able to safely monitor when the TCC solenoid is being energized by the ECM while driving...!

 

1) "Make up" a simple 12V test light. Use a small "glass wedge" bulb (#194 or equivalent) and solder ~2' leads onto each bulb terminal. These bulbs were used in the side markers and instrument clusters on millions of cars of the era. Any auto parts store will carry them.  A bright white 12V LED can also be used.

 

2) Under the steering column (or slightly to the left or right) is the ALDL connector (Assembly Line Diagnostic Link). These terminals allow you to access rudimentary information from the ECM and "Flash Out" (via the Check Engine light) any stored Diagnostic Trouble Codes. 

 

3) Connect one lead from the test light to terminal "A" (top row / far right connector).  Connect the other lead to terminal "F" ( top row / far left connector).

 

4) Terminal "F" is connected to the 12V source which feeds the TCC solenoid and is grounded when the TCC is energized by the ECM. Terminal "A" is an ECM/chassis ground.

 

5) Make a little white paper sleeve, slide the test light in from behind, and keep it a bit recessed in the sleeve. Tape it to the top of the dash so it's easily visible while driving.  The goal is to prevent sunlight from washing out the test light.

 

6) The light will glow whenever the ignition switch is in the "Run" position.  It will turn off when the ECM energizes the TCC solenoid. 

 

7) When functioning correctly, the light will go out when the TCC locks. With your Riviera, this should occur at about 40mph under light throttle.  Try slowly applying a little more throttle and watch the light come back on when the TCC unlocks.  Back off the throttle and the light will go back out when the TCC again locks.  Coast without any throttle and the TCC will be unlocked (test light on). You will quickly see & feel how the ECM controls the TCC. It's pretty neat...!

 

Now..., if the TPS is worn out and causes the ECM to unlock the TCC when it shouldn't, the test light will momentarily turn back on during that malfunction.  However, it's going to be very brief and you may not notice it.  With my Toronado, the worn out TPS quickly developed a "dead area" so the TCC was unlocking/relocking often and my test light was flashing in lockstep. 

 

Because computing power, memory, etc. was quite limited in GM's first engine managment system, the On-Board Diagnostics (OBD I) are primitive.  This requires more creative thinking when troubleshooting...!

 

***

 

Before rigging up this test light, I still think it's a good idea to disable the TCC electrically, cruise for short periods in OD, and see if the bucking occurs. If it does, the TCC is ruled out. It's possible that you're having an engine ignition problem which is momentarily interrupting the spark... 

 

There is a way to electrically disconnect the TCC without getting under the car (just under the dash).  I'll leave that discussion for later...!

 

Paul

 

 

 

 

Edited March 15, 2022 by pfloro (see edit history)

[adamant0720]

20 hours ago, pfloro said:

Because computing power, memory, etc. was quite limited in GM's first engine managment system, the On-Board Diagnostics (OBD I) are primitive.  This requires more creative thinking when troubleshooting...!

thanks, that's a pretty cool approach for monitoring the TCC! I will definitely try this idea out. Maybe take it out at dusk/night, so the light is more obvious

 

I think I will just experiment with the light bulb approach for now, as it's only happened twice for me and I don't want to drive too long w/ the TCC disabled and risk overheating the transmission fluid etc.

 

but feel free to go ahead and tell me how to disable it under the dash

 

Scott

[pfloro]

 

On 3/15/2022 at 5:50 PM, adamant0720 said:

but feel free to go ahead and tell me how to disable it under the dash

Scott,

 

On your '84 Riviera, there are two "plunger" switches mounted on a bracket in front of the brake pedal arm. When you step on the brake pedal, the plungers extend and "things happen". 

 

1) Remove the wide black plastic cover which surrounds the brake pedal arm.  There are several screws at the leading edge of this "sound absorber panel".  Around the bottom, there is a large "U" clip which surrounds the steering column.  Pull the panel down to remove it.

 

2) Push the brake pedal arm and you'll see the switch plungers extend. One of the switches (see picture) has one electrical connector and a vacuum hose attached. Ignore this switch as it's the cruise control "brake pedal cancel".   The other switch should have two connectors on it. The picture may or may not be accurate.  

 

3) One of the connectors on the second switch is for the brake lights. It's "Normally Open" (NO) and closes when the pedal is depressed.  The other connector is the "brake pedal unlock" for the TCC. This switch is "Normally Closed" (NC) and opens when the brakes are applied. This is the connector to disconnect. You'll have to experiment and determine which one of the two to disconnect.  Before disconnecting, you may want to see how it functions.  While cruising with the TCC locked, keep you right foot on the accelerator (TCC stays locked) and lightly press the brake pedal with your left foot. The TCC will unlock. If your test light is connected, it will illuminate.

 

All of my tips & tricks were used over the 28 years that I owned my 1984 Toronado...  I pretty much read the shop manuals cover to cover and became intimate with the CCC system.  

 

Happy Troubleshooting...!

 

Paul

 

 

 

Edited March 18, 2022 by pfloro (see edit history)

[adamant0720]

On 3/18/2022 at 12:22 PM, pfloro said:

While cruising with the TCC locked, keep you right foot on the accelerator (TCC stays locked) and lightly press the brake pedal with your left foot. The TCC will unlock. If your test light is connected, it will illuminate.

Hi, quick update. I got the test light hooked up, and it seemed to work.. light would go off right around 40mph meaning TCC locked. Releasing the gas pedal or applying more gas would make the light turn back on (TCC unlocked) just as you described.

 

One question, it seemed at any speed tapping the brakes would always make the test light turn off and that isn't exactly the behavior you describe above. So wondering what that means, perhaps this is a symptom of the underlying problem (or another problem all together?) I definitely tried several times lighting tapping the brakes when the light was off, but light never came on. 

 

I didn't experience any shudder this weekend as I test drove it. I did stall the car LOL but I think I took it out a bit too quickly on Saturday after starting it up (had been sitting for a week, took maybe 7-10 seconds to turn over) it stalled after 1-2 minutes of  20-30mph driving as I came to a street light. Also tested on Sunday, it started right up and I let it sit for a minute at high idle and it ran fine: no stall, no shudder.

 

So I'll keep the light rigged up and keep an eye on things...

 

[pfloro]

I was mistaken... The action of your test light when you "ride the brake" is correct. The light will always turn off (or stay off) when you press the brake pedal. This is because of where the switch is located in the circuit.  It's been many years since I had the Electrical Troubleshooting Manual in front of me.  I did include the 3 manuals (Chassis, Electrical, Body) in the sale of my Toronado 10 years ago so unfortunately they are gone...

 

******

 

While you are waiting for the bucking problem to reappear, this might be a good time to become familiar with the diagnostic function of the ECM.  It's actually easy and quite interesting.

 

Although the CCC system will only turn on the "Check Engine" light when a hard failure occurs (and store a Trouble Code), it will sometimes set & store a code for intermittent problems. A hard failure can be a disconnected sensor connector, a broken ECM harness wire, a completely failed sensor, or a way out of spec sensor value (e.g.: way lean or rich).  The ECM will clear the trouble code if the problem doesn't reappear after a certain number of engine starts. 

 

The Check Engine light is used to "Flash Out" any stores trouble codes.

 

1) Bend a regular sized paper clip into a "U" shape. Make sure the ends are of equal length and about 1/4" apart. 

2) With the ignition ON and the engine NOT running, insert the paper clip into terminals "A" (upper row - far right) & "B" (upper row - terminal to the left of "A"). 

3) The Check Engine light will go out and the ECM will enter diagnostic mode.  You may hear a ticking sound from the carburetor. This is the MCS (Mixture Control Solenoid) being cycled. FYI: the MCS is always being cycled whenever the engine is running but the engine's noise masks it.

4) The Check Engine light will begin flashing. There will be flashes followed by "long" pauses in between and then flashes followed by "short" pauses in between.  The flash & the long pause represents a "unit of 10" while the flash & the short pause represents a "unit of 1".  Each stored code will flash 3 times and the next stored code will follow. When all codes have been flashed out, there will be a longer pause and the sequence will repeat.  The sequence will continue until you remove the paper clip.

5) When the engine is not running, the ECM will not see the Distributor Reference Pulse. This sets a code of "12" which is technically not an error code.  Look for 1 flash with a long pause followed by 2 flashes with short pauses. After a slightly longer pause, a "12" will flash again. After it flashes "12" a third time, any additional codes will be flashed out. If the group of 12s repeats, there are no more stored trouble codes.

6) The procedure is not difficult and you will quickly understand how smart the GM engineers were...!

7) To clear all stored codes, remove the paper clip, turn the ignition off, pull the 3 amp fuse from the fuse block, wait 10 seconds, and re-insert. Disconnecting the battery can also be used to clear the codes. 

 

If your TPS is getting flaky, a "21" code (out of range) might have been set. I never saw this with my Toronado but you never know...  If the intermittent situation is very brief, the ECM may not have had time to catch it.  Remember, these computers were very slow (but amazingly fast for their time)...

 

OBD I was used from 1980 until ~1995. More trouble codes were added as fuel injection took over but a given code number always represented the same trouble. 

 

OBD I Diagnostic Trouble Codes

 

Paul

 

PS:  For fun, I've attached a picture of a trashed ECM from my Toronado.  Your ECM looks the same.  The open slot in the lower left corner was for

        the PROM chip.  This chip was specific to a given make, model, and drive train.  It contained "look up" parameters which the algorithms used.

        The ECM wiring harnesses (2) connected to the right side of the circuit board.  The ECM is located behind the passenger side kick panel.

 

 

 

Edited March 21, 2022 by pfloro (see edit history)

[adamant0720]

48 minutes ago, pfloro said:

The Check Engine light is used to "Flash Out" any stores trouble codes.

Good stuff! Yup, I actually did the paper clip check this weekend. I wasn't expecting to see any codes (check engine light has always been off). And I was right, it pulsed 12 3 times, then repeated 12 again. 

 

I've been slowly trying to learn my way around cars and do more of it myself.

 

Replacing the solenoid, if it comes down to that, seems kind of fun actually. Seems like it's drain the AT fluid (I think I saw a drain plug on my pan, but sounds like that might not be standard), drop the pan, replace solenoid, put back pan (guess w/ a new gasket for pan, and new drain plug gasket for sure) and refill w/ AT fluid. Messy, but fun sounding. 

 

[pfloro]

2 hours ago, adamant0720 said:

I've been slowly trying to learn my way around cars and do more of it myself.

The fact that you're getting into the CCC system is great.   You have made good progress already...!

 

I really don't think the TCC solenoid is the problem.  Rivnut and others have had it fail in a particular way.  After it's energized for a period of time while cruising, the solenoid and the moving "pole piece" naturally heat up. It then sticks in the bore.  Although the ECM has de-energized the solenoid when braking to stop, it's still mechanically allowing hydraulic pressure to keep the TCC locked. Of course, you know what happens if you stop when driving a stick shift and fail to put the clutch in...!

 

Your situation is different and I don't think the solenoid is mechanically allowing hydraulic pressure to momentarily drop. I certainly could be wrong. Your thinking is right on by putting a TCC solenoid replacement lower on the priority list for now.

 

It's funny, but my Toronado was driven 200,000 miles over 28 years and the TCC solenoid never failed. I must have gotten a good one...!  

 

I don't think a factory drain plug for the THM325-4L was standard. The GM bean counters wouldn't have stood for that...! If your Riviera has one, it has to be aftermarket. 

 

If you do drop the pan, it's good practice to change the filter too.

A service kit will also include a new rubber-like gasket.

 

****

 

On a related note, if your TPS is going south, replacing it is unfortunately, not a trivial job.  It has to be carefully adjusted which requires a special tool and a digital voltmeter.  Rochester Products (GM division) designed the electronically controlled Quadrajets to be rather tamper resistant. I rebuilt mine several times and obtained the necessary tools. I wish that I still had them.  The good news is that after the carb is properly setup during the rebuild and the CCC system is working properly, the car will run beautifully.  Some folks feel that Quadrajets (of any vintage) are junk. I've heard them called Quadrajunk... IMHO, they are wrong.

 

Paul

 

 

 

 

 

 

 

 

Edited March 22, 2022 by pfloro (see edit history)

[adamant0720]

10 minutes ago, pfloro said:

Your thinking is right on by putting a TCC solenoid replacement lower on the priority list for now.

ya, i'd like more confidence on the actual culprit before doing any fixes.

 

and based on above comments, it sounds like another potential issue could be with the ignition system, maybe i'll read up on ways to diagnose/check in that area...seems anything from the coil to the spark plugs could be a potential cause as well. it could perhaps tie in to the 2 stalls i've experienced.

 

thanks for all the help!