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 Puzzled by behavior...

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Trevorusn
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Trevorusn

Name : Trevor
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PostSubject: Puzzled by behavior...   Puzzled by behavior... EmptyFri May 29, 2020 11:54 am

So my 96 Riv was driving fine for 15 miles into my 32 mile commute this morning, when some strange behavior began. After going from a stop, I could not accelerate past 2000-2500 RPM, almost as if I hit a wall. Acceleration was pitiful, and after a few minutes of this I had to stop. After letting it sit for a few minutes, low speed driving was ok at part throttle but the moment I floored her she would go to 3k and hit the wall. Tranny is shifting fine, the traction off light came on for a bit but then went off again and has not reappeared. No CELs, dripping fluids, and only once had a whiff of a sulphery smell. Otherwise all seems ok, except at stops I get a low humming that goes for a bit before ceasing. So, anyone have any clue what is up? Is my cat clogged or is something else amiss?
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carguy8888
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Name : Brian Cohen
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PostSubject: Re: Puzzled by behavior...   Puzzled by behavior... EmptyFri May 29, 2020 4:01 pm

I wonder if it went into limp mode? I bet Albert and or Larry will know better.
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albertj
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PostSubject: Re: Puzzled by behavior...   Puzzled by behavior... EmptyFri May 29, 2020 5:00 pm

Trevorusn wrote:
So my 96 Riv was driving fine for 15 miles into my 32 mile commute this morning, when some strange behavior began.  After going from a stop, I could not accelerate past 2000-2500 RPM, almost as if I hit a wall.  Acceleration was pitiful, and after a few minutes of this I had to stop.  After letting it sit for a few minutes, low speed driving was ok at part throttle but the moment I floored her she would go to 3k and hit the wall.  Tranny is shifting fine, the traction off light came on for a bit but then went off again and has not reappeared.  No CELs, dripping fluids, and only once had a whiff of a sulphery smell.  Otherwise all seems ok, except at stops I get a low humming that goes for a bit before ceasing.  So, anyone have any clue what is up?  Is my cat clogged or is something else amiss?

Actually we ought to ask Abaddon. I have no idea what's going on.

First -- is the SES light on?

Second - The low hum might be the air compressor for the rear suspension, which should not run very often. You should look at the rear shocks. If the metal on the shocks is leaking oil, or rusted and perhaps even bulging, you need to replace them. They are nowhere near as pricey as they used to be, there are many choices for less than $100/pair. This won't help your 3000 RPM limit but it will help your braking, ride quality and cornering.

Third -- you need a scanner that will not only pull stored codes but also check sensors; you need to verify that the sensors are neither silent nor lying to the PCM. Taking a log while driving when the car hits limp mode then reading that log will pretty much tell you what's going on.

if you don't have a factory service manual, get one, they are not too much $$ off eBay. It will explain waht you're seeing, which I think is Limp Mode, and have diagnostics that should help you.

So those are my guesses for now. Hopefully others will chime in.

Albertj
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LARRY70GS
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LARRY70GS

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PostSubject: Re: Puzzled by behavior...   Puzzled by behavior... EmptySat May 30, 2020 9:22 am

Sulphur smell could be rich mixtures. I would look at the MAF sensor, and see what it is telling the PCM. You need to scan it. Look at the MAF values and fuel trim numbers.

_________________
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
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Trevorusn
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Trevorusn

Name : Trevor
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PostSubject: Re: Puzzled by behavior...   Puzzled by behavior... EmptySat May 30, 2020 2:14 pm

Another thought that came to mind is fuel pressure.  Not sure how old the pump and filter are but the car seems to have sat for a bit.  The tires that were on it when I got it were old MXM4s with dry rot and barely used treads.  To answer a few questions, no engine lights came on, only the traction off light.  I do indeed have both service manuals, but fuel pressure tests are not possible right now as she won't start but turns over fine. MAF sensor very well could be a possibility, just surprised it would be that dirty.


Last edited by Trevorusn on Sat May 30, 2020 2:18 pm; edited 1 time in total
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Trevorusn
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Trevorusn

Name : Trevor
Joined : 2016-02-22
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PostSubject: Re: Puzzled by behavior...   Puzzled by behavior... EmptySat May 30, 2020 2:16 pm

albertj wrote:
Trevorusn wrote:
So my 96 Riv was driving fine for 15 miles into my 32 mile commute this morning, when some strange behavior began.  After going from a stop, I could not accelerate past 2000-2500 RPM, almost as if I hit a wall.  Acceleration was pitiful, and after a few minutes of this I had to stop.  After letting it sit for a few minutes, low speed driving was ok at part throttle but the moment I floored her she would go to 3k and hit the wall.  Tranny is shifting fine, the traction off light came on for a bit but then went off again and has not reappeared.  No CELs, dripping fluids, and only once had a whiff of a sulphery smell.  Otherwise all seems ok, except at stops I get a low humming that goes for a bit before ceasing.  So, anyone have any clue what is up?  Is my cat clogged or is something else amiss?

Actually we ought to ask Abaddon.  I have no idea what's going on.  

First -- is the SES light on?

Second - The low hum might be the air compressor for the rear suspension, which should not run very often.  You should look at the rear shocks.  If the metal on the shocks is leaking oil, or rusted and perhaps even bulging, you need to replace them.  They are nowhere near as pricey as they used to be, there are many choices for less than $100/pair.  This won't help your 3000 RPM limit but it will help your braking, ride quality and cornering.

Third -- you need a scanner that will not only pull stored codes  but also check sensors; you need to verify that the sensors are neither silent nor lying to the PCM.  Taking a log while driving when the car hits limp mode then reading that log will pretty much tell you what's going on.  

if you don't have a factory service manual, get one, they are not too much $$ off eBay.  It will explain waht you're seeing, which I think is Limp Mode, and have diagnostics that should help you.  

So those are my guesses for now.  Hopefully others will chime in.

Albertj

Thanks for the compressor info, makes sense although she drives great, especially as the rear brakes are all new rotors and pads but when I get the time I'll give the rear shocks a go over.
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carguy8888
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Name : Brian Cohen
Joined : 2019-01-07
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PostSubject: Re: Puzzled by behavior...   Puzzled by behavior... EmptySat May 30, 2020 3:41 pm

I would definitely see if it's throwing any codes soon before you break something expensive, just my opinion. If you don't have a code scanner any chain store will do it for you.
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