92 Riv stalling, vacuum leak

Max Blast

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1992 Riv
Hi

I just cleaned my 92's engine bay and replaced all visible rotten vacuum lines - and didn't do it right obviously because now I have stalling on the overrun, no kickdown and no cruise control. IIRC that is powered by the vacuum line that tees off as shown here.

1597619699623.png
The line that goes down goes to the kickdown solenoid, and holds a vacuum.
The line that goes up I think goes to hvac and cruise control - can anyone confirm? It seems to hold a vacuum.
Also, I broke that check valve when I replaced the lines and can't find anything like it. Anyone know the p/n?
Right now I just have a tee in there.

Hoping that some old codger here has a vac line diagram and experience with this.
 

Max Blast

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1992 Riv
The manual is on its way from ebay.

In the mean time, I have eliminated the stalling problem. That was attributable to a loose vac line to the fuel pressure regulator. I also relined the connection to the cruise control diaphragm and cruise is now steady vice surging.

The only driveability problem I am left with is that it won't kick down. I'm stuck in 3rd or OD and its as sluggish as a pig. It'll shift manually just fine.
I've checked the connection to the transmission vacuum clock and it holds vacuum. No leaks from the vacuum supply on the manifold or in the hard lines going to the vacuum clock.

On the 92, what triggers a kickdown/downshift? I think I understand that it could be the Throttle Position Sensor via the ECM, as I can't find a TV cable going from the throttle body to the trans.
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LARRY70GS

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98 Riviera, 70 GS455 Stg1
The manual is on its way from ebay.

That's good, it will help you now and in the future.

On the 92, what triggers a kickdown/downshift? I think I understand that it could be the Throttle Position Sensor via the ECM, as I can't find a TV cable going from the throttle body to the trans.

Should be the 4T60E. Quite possible that the PCM looks at the TPS. You can check the TPS with a voltmeter. There should be 3 wires going to it. One should be a 5 volt reference signal, one should be ground, and the third will be the signal wire back to the PCM. If you can check the signal wire back to the PCM, you should see around .40-.60 volts at closed throttle, and 4.5 volts at full throttle. The voltage should increase uniformly and not jump around as you smoothly operate the throttle with the engine off.
 

Regal LTD Coupe

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1993 Buick Regal Limited coupe 3800 (& 1990 Lincoln LSC SE)
I don't know what they were doing with the '92 Riviera specifically but my '93 Regal I believe was the last year they used the 4T60 before switching to the electronically controlled 4T60E in the next year or two (on my Cadillac they switched to electric in '92 I believe). How good is your transmission fluid and filter? Once I switched to Amsoil and a new old stock Wix filter and got rid of the old 60k mile fluid, the transmission now shifts far more often in a very smooth fashion.
 

Max Blast

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1992 Riv
How good is your transmission fluid and filter? Once I switched to Amsoil and a new old stock Wix filter and got rid of the old 60k mile fluid, the transmission now shifts far more often in a very smooth fashion.

It's not good and that can be it, but I think the root cause is me disconnecting vacuum lines and washing the engine bay. So I need to put it together the way it was.
 

Regal LTD Coupe

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1993 Buick Regal Limited coupe 3800 (& 1990 Lincoln LSC SE)
It's not good and that can be it, but I think the root cause is me disconnecting vacuum lines and washing the engine bay. So I need to put it together the way it was.
Possibly, but I edited my post above. Yours may only be the 4T60 and not the 4T60E but confirm yourself. Given how much electronics were used in the Riviera I wouldn't be surprised if they had used the 4T60E, if it even makes any difference to your issue.
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Max Blast

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1992 Riv
Here are some actual shots of the engine bay. It’ll be much easier when I have the factory manual, but if you see something wrong, holler.
 

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Regal LTD Coupe

Active member
807
172
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1993 Buick Regal Limited coupe 3800 (& 1990 Lincoln LSC SE)
I believe '92 was the last year for the cast iron upper intake on the the Series I.. am a bit jealous.
 

Max Blast

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1992 Riv
That's good, it will help you now and in the future.



Should be the 4T60E. Quite possible that the PCM looks at the TPS. You can check the TPS with a voltmeter. There should be 3 wires going to it. One should be a 5 volt reference signal, one should be ground, and the third will be the signal wire back to the PCM. If you can check the signal wire back to the PCM, you should see around .40-.60 volts at closed throttle, and 4.5 volts at full throttle. The voltage should increase uniformly and not jump around as you smoothly operate the throttle with the engine off.

something amiss here...voltage never rose over .6 volts with throttle opened. SES light is not on but works. I’ll swap in a known good tps and see.

vacuum at thetransmission vacuum governor is a steady 15inhg so that is fine.

Got the manual today. It’s a brick.
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Max Blast

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1992 Riv
Vacuum modulator. 15" is a bit low. My 3800 fully warm in Park makes a full 20" of vacuum.

15 in hg is on the low side at the vacuum source - the manual states 13-17 inhg at the vacuum modulator in Drive as the spec.

It pulls 20 in hg at the source when the idle is about 50 rpm higher, so I think I have no leaks anymore.

All clues point to TPS - voltage never moved off of 0.4 and it ran just as crappy with it unplugged so that's why the idle is off and the vacuum is low. it didn't trigger a SES light because the voltages are still in band - for an idle condition.

New one is in the mail.
 

LARRY70GS

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Oakland Gardens, N.Y.
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98 Riviera, 70 GS455 Stg1
Very good. There might be a certain amount of adjustment on the TPS mounting. I believe .40 volts, 4.5 volts wide open is what you are looking for. The Chassis manual should tell you.
 

Max Blast

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1992 Riv
TPS was the culprit.

so let me close this one out.
I probably shorted the TPS when washing the enginebay. As a result the engine went to open loop operation, causing low vacuum, poor idle, no kickdown, and just poor performance in general. The cruise control issues were a different cause, vacuum hose supplied by Napa was too big.

Swapped it out with a NOS AC Delco unit and all is well. Vacuum steady in the 17s.
Onward to the headliner!
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