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 Question on 1999 Riviera Engine issue

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Mike9874
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Question on 1999 Riviera Engine issue  Empty
PostSubject: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyMon Mar 23, 2020 10:56 am

Well I have recently bought a 1999 Riviera. I also have a 1997 Riv too.
I've had this 99 for about 6 weeks now, and gone thru it quite a bit.
Replaced spark plugs
Replaced the wires
Replaced the fuel filter twice
Replaced the Fuel Injection Pressure Regulator
Engine Camshaft Position Sensor
Crankshaft Position Sensor
Replaced the fuel pump twice, on 2nd new pump.

Now for the issue I am having....
Runs fine, starts right up.
Mileage is 83,858
I am the 2nd owner of this car.
The problem I am having is everytime I floor the gas pedal , or even only floor it 3/4 of the way down, just enough to engage it into passing gear.
It takes right off like a jet....BUT soon as I take my foot off the gas pedal, the engine shuts down and I coast to a stop. It starts right back up fine.
The engine only shuts down if floored and put into passing mode. If I don't floor it, the engine does not shut down. My mechanic has been trying to figure out this problem for the last 4 weeks now. No engine code errors show up at all. No errors can be found anywhere. He has no idea what it is right now.

Thought I would ask you folks if you've ever seen a issue like this before in your Riviera's ????  
Thanks guys, Mike.....
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albertj
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PostSubject: Re: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyMon Mar 23, 2020 12:08 pm

Mike9874 wrote:
Well I have recently bought a 1999 Riviera. I also have a 1997 Riv too.
I've had this 99 for about 6 weeks now, and gone thru it quite a bit.
Replaced spark plugs
Replaced the wires
Replaced the fuel filter twice
Replaced the Fuel Injection Pressure Regulator
Engine Camshaft Position Sensor
Crankshaft Position Sensor
Replaced the fuel pump twice, on 2nd new pump.

Now for the issue I am having....
Runs fine, starts right up.
Mileage is 83,858
I am the 2nd owner of this car.
The problem I am having is everytime I floor the gas pedal , or even only floor it 3/4 of the way down, just enough to engage it into passing gear.
It takes right off like a jet....BUT soon as I take my foot off the gas pedal, the engine shuts down and I coast to a stop. It starts right back up fine.
The engine only shuts down if floored and put into passing mode. If I don't floor it, the engine does not shut down. My mechanic has been trying to figure out this problem for the last 4 weeks now. No engine code errors show up at all. No errors can be found anywhere. He has no idea what it is right now.

Thought I would ask you folks if you've ever seen a issue like this before in your Riviera's ????  
Thanks guys, Mike.....

Have not seen this one before BUT it sounds like what could happen with wiring problems.  I would check the wiring that would flex if you floored the engine for breaks in the conductor inside the insulation, along with the connectors attached thereto.  My hunch (could be BS) is that as soon as you take your foot off the gas, the engine rocks in its cradle and moves the wiring.  Maybe just a loose connector?  Not sure.   I would think to especially check the wiring at the ignition module and the large connector at the firewall. I would *also* check all the wiring that you/your mechanic disturbed in component replacements (fuel pump, crank/cam sensors, etc.) -- wiggle while running (stay the h-ll away from moving/rotating parts) and see what changes.

...and if it ends up being a broken wire, repair your motor/transmission mounts. The engine should not move all that much; if it does the mounts are wack.

Albertj
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LARRY70GS
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LARRY70GS

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Question on 1999 Riviera Engine issue  Empty
PostSubject: Re: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyMon Mar 23, 2020 5:43 pm

Well, since it stalls ONLY when you take your foot off the gas, I would first check the throttle position sensor. If you have a good scan tool, you can watch the voltage as you go from closed to open throttle. It should increase and decrease uniformly in both directions. Secondly, I would look at the fuel trims to see if it is running rich (large negative numbers ). If so, I'd clean or replace the MAF.

_________________
98 Riviera SC3800  All stock except gutted air box.
1970 Buick GS455 Stage1, TSP built 470BBB, 602HP/589TQ
Best MPH, 116.06 MPH, Best ET, 11.54
https://www.youtube.com/watch?v=UHCda-t_Jls
https://www.youtube.com/watch?v=sfT2tEO4XcU
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Jack the R
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PostSubject: Re: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyTue Mar 24, 2020 4:01 am

Possibly relevant if it's a broken wire - Link

Should be looking for problems here either way.
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Mike9874
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Name : Mike
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PostSubject: Re: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyWed Mar 25, 2020 7:13 am

Thanks guys for all your input, I'll be checking for bad wires and connectors soon.
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Mike9874
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Question on 1999 Riviera Engine issue  Empty
PostSubject: Re: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyYesterday at 6:12 am

Well I had a diagnostic tests done at local garage, and the mechanic spent 3 hours testing everything under the sun. Came out with the issue being the Mass Air Flow sensor plus 2 broken motor / transmission mounts.
Got the parts coming Monday, I'll put the MAF sensor in soon as I get it. Then run it for a road test, my mechanic will put in the mounts later this coming week. Had no bad wires or connectors.
Bought a throttle position sensor also. Got that part now. But does not seem to be defective.

Front and rear mounts are broken.
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carguy8888
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PostSubject: Re: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyYesterday at 1:20 pm

Post a picture when you're up and running and glad to see you're on the right track. I just bought all of my transmission mounts on RockAuto and it made a huge difference.
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Mike9874
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PostSubject: Re: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyYesterday at 2:12 pm

carguy8888 wrote:
Post a picture when you're up and running and glad to see you're on the right track. I just bought all of my transmission mounts on RockAuto and it made a huge difference.

I've been buying all my parts from Rockauto for years now. I have Two Riviera's  a 1997 and the 1999. Soon as I get everything done on my 99, I'll put the 97 up for sale.  Got a couple of recent pic's....not the greatest quality  LoL

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Question on 1999 Riviera Engine issue  Img_0411
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carguy8888
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PostSubject: Re: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyYesterday at 2:14 pm

Very nice, I get the picture LOL.
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Mike9874
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PostSubject: Re: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyYesterday at 2:23 pm

I've got a lot more parts to update and install on this 99 Riv. Too long a list right now to brother writing about. But when I'm done should be running really fine. I've had my 97 for about 9 years now. Always wanted a 99 model, but could not find one close enough to my area with low mileage, that I liked.
This 99 needs the proper maintenance done which has not been done for a long time it seems. I've got lots of time to get everything done. No hurry. smile
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albertj
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Question on 1999 Riviera Engine issue  Empty
PostSubject: Re: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyYesterday at 2:56 pm

Mike9874 wrote:
Well I had a diagnostic tests done at local garage, and the mechanic spent 3 hours testing everything under the sun. Came out with the issue being the Mass Air Flow sensor plus 2 broken motor / transmission mounts.
Got the parts coming Monday, I'll put the MAF sensor in soon as I get it. Then run it for a road test, my mechanic will put in the mounts later this coming week. Had no bad wires or connectors.
Bought a throttle position sensor also. Got that part now. But does not seem to be defective.

Front and rear mounts are broken.  

On these 3800 engines, this vintage, I've heard of aftermarket/replacement throttle position sensors dying, but not the OE ones.

My MAF finally quit around 360K miles/22 years of use - it did not fail outright, just gave bad readings. I had to use a scan tool and look at driving logs to figure out what the heck was wrong.

Motor mounts OTOH don't last all that long on this car. They last longer if you don't mash the loud pedal too hard from a dead stop. I've wondered for some time if the 2000 and later mounts for the Lucerne could be fitted.
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Mike9874
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Question on 1999 Riviera Engine issue  Empty
PostSubject: Re: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyYesterday at 3:21 pm

I've got another question, for any of you guys that might know.
I bought a spare gas tank for this 99 Riv. One in it now was pretty rusted out around the top ring.
The Retainer Ring had to be screwed into top of the tank, because the clips that hold down the Retainer Ring were rusted off.

So I bought a used tank off a 2000 Buick Lesabre , 18.5 gallons. Suppose to be an exact fit for this 99 Riv. The only thing that seems to be a little different is the vents on top. The Riv only has 2 top vents.
This tank has 3 top vents. Would this make any difference, I wouldn't think it would, but I see most of the other tanks only have 2 top vents.
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albertj
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Question on 1999 Riviera Engine issue  Empty
PostSubject: Re: Question on 1999 Riviera Engine issue    Question on 1999 Riviera Engine issue  EmptyYesterday at 3:48 pm

I can't imagine why that would make any real difference, but I also would probably ask one or another of the older gearhead mechanics at the dealership about that.

Albertj
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