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Diagnostic Help #4458786
07/13/17 09:09 PM
07/13/17 09:09 PM
Joined: Apr 2013
Posts: 123
-
VetteElite Offline OP
VetteElite  Offline OP
Joined: Apr 2013
Posts: 123
-
2008 Saturn Aura
130,000 miles

GM 3.5L High Value V6 - Pushrod w/ VVT
GM 4T45E transmission

I really like this car; looks good, underrated performance, and drives well. At least, it used to... Lately I've been having some issues which I would like to fix the right way without just throwing parts at it. Car doesn't have any codes stored and no CEL. Still drives, but definitely has some problems. If it's a minor fix, I'm definitely willing to keep the car going, but something major and I'll just defer the decision to repair until something actually breaks for real or starts throwing codes.

Symptoms:

1) Hard shifting. 2-3 is the worst, 1-2 and 3-4 can be bad too. This seems to point me to typical GM 4T45e transmission woes. I'm not opposed to eventually putting a reman transmission in the car, but I'm not sure that's actually the problem with the car because of the other symptoms.

2) Occasional hesitation and poor acceleration. Pretty straightforward here, car sometimes doesn't like to get up and go. Other times, press the pedal and it feels like when it was a brand new quick V6 with nothing wrong. I'm thinking this could be MAF or MAP sensor. MAF was cleaned 6 months ago with MAF cleaner.

3) RPM fluctuations. This makes the car really annoying to drive. RPMs like to move around and make the car feel like its lugging and jerking. Even on the highway sometimes the RPMs will move around like the torque converter isn't locked, but then it will "lock up" and RPMs will stay still. Torque converter/transmission problem?

What I know:

Throttle body was cleaned a year ago which fixed a rough idle.

MAF sensor was cleaned 6 months ago with MAF cleaner. It was a long shot attempt to fix some of the symptoms I described without throwing parts at the car.

Engine Vacuum doesn't seem right. Using Torque app I see that my vacuum is around 18 "Hg at idle but drops to around 5 "Hg when driving...and rarely comes back up unless I fully take my foot off the throttle. Normally, I thought the vacuum was supposed to come back up after the initial drop upon acceleration as everything "evens out." This might be a slightly clogged exhaust?

-----

Any thoughts on what may be causing these problems? I don't have a ton of time right now to be troubleshooting and fixing things, but I would like to know what is going on so I can get around to fixing it if possible. Like I mentioned, car still drives and doesn't have a CEL, so I'm not panicked about any of these symptoms yet. I'm moderately handy, can do routine repairs and even some moderately complex ones if you give me a good set of detailed instructions. If it's transmission, I'll be taking it to a transmission shop though.

Re: Diagnostic Help [Re: VetteElite] #4458800
07/13/17 09:22 PM
07/13/17 09:22 PM
Joined: Jan 2007
Posts: 17,501
Clovis, CA
Merkava_4 Offline
Merkava_4  Offline
Joined: Jan 2007
Posts: 17,501
Clovis, CA
If no CEL, then each of the different sensors need to be hooked to a scope to examine wave forms; especially the MAP and MAF sensors.

Re: Diagnostic Help [Re: VetteElite] #4458802
07/13/17 09:27 PM
07/13/17 09:27 PM
Joined: Apr 2013
Posts: 123
-
VetteElite Offline OP
VetteElite  Offline OP
Joined: Apr 2013
Posts: 123
-
That's what is frustrating. Car definitely does not run like it should, yet it isn't throwing any codes.

Re: Diagnostic Help [Re: VetteElite] #4458821
07/13/17 09:40 PM
07/13/17 09:40 PM
Joined: Jan 2007
Posts: 17,501
Clovis, CA
Merkava_4 Offline
Merkava_4  Offline
Joined: Jan 2007
Posts: 17,501
Clovis, CA
The offending sensor(s) are working fine most of the time to keep the computer satisfied, but then act up enough to cause drivability problems. Happens all the time to different cars. You either hook them up to a scope or wait for them to get bad enough to throw a code.

Re: Diagnostic Help [Re: VetteElite] #4458831
07/13/17 09:53 PM
07/13/17 09:53 PM
Joined: Nov 2004
Posts: 1,859
SD
zrxkawboy Offline
zrxkawboy  Offline
Joined: Nov 2004
Posts: 1,859
SD
I would take a look at the TPS.


"Think of all the Ford owners who will someday want an automobile." John Dodge

Re: Diagnostic Help [Re: VetteElite] #4458843
07/13/17 10:04 PM
07/13/17 10:04 PM
Joined: Nov 2010
Posts: 808
VA
Thax Offline
Thax  Offline
Joined: Nov 2010
Posts: 808
VA
From what you are describing , possible cause could be the throttle body assembly. The throttle position sensor is integrated in this unit. I would perform a capacitor discharge on the battery. Then perform a throttle body relearn procedure. Unfortunately I think this is going to require a fully bi-directional scanner with scope function to properly diag.


2000 Ford Explorer Limited 5.0L AWD
2018 KIA Soul EX 2.0L
ASE P2 Parts Specialist
AIA Import Part Specialist
KIA certified Senior Technician, Hybrid certified.
Re: Diagnostic Help [Re: VetteElite] #4458884
07/13/17 11:44 PM
07/13/17 11:44 PM
Joined: Dec 2016
Posts: 7,171
Waco, TX
Linctex Offline
Linctex  Offline
Joined: Dec 2016
Posts: 7,171
Waco, TX
Originally Posted By: VetteElite


Symptoms:
1) Hard shifting. 2-3 is the worst, 1-2 and 3-4 can be bad too.
2) Other times, press the pedal and it feels like when it was a brand new quick V6 with nothing wrong.
3) RPM fluctuations.


1) Pressure control solenoid? That's what it sounds like

2) & 3) - you've got a bad ground somewhere. Add some bonding straps and see if the problem goes away. These new computerized cars love having good grounds.


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
Re: Diagnostic Help [Re: VetteElite] #4458949
07/14/17 04:18 AM
07/14/17 04:18 AM
Joined: Nov 2006
Posts: 20,586
MA, Mittelfranken.de
Trav Offline
Trav  Offline
Joined: Nov 2006
Posts: 20,586
MA, Mittelfranken.de
Originally Posted By: VetteElite

Engine Vacuum doesn't seem right. Using Torque app I see that my vacuum is around 18 "Hg at idle but drops to around 5 "Hg when driving...and rarely comes back up unless I fully take my foot off the throttle. Normally, I thought the vacuum was supposed to come back up after the initial drop upon acceleration as everything "evens out." This might be a slightly clogged exhaust?
Any thoughts on what may be causing these problems?


Transmission shifting issues are routinely misdiagnosed due to engine performance issues, engine doesnt run right the transmission doesn't run/shift right either its really that simple. It looks you might be dealing with a partially clogged cat, that will cause all you describe without throwing a code until it gets so bad it causes a misfire and flashing CEL.
Hook up a mechanical vacuum gauge to the engine, to insure proper readings, if its indicating a bad cat its time to go a bit further down that road.

http://www.aa1car.com/library/converter.htm


ASE L1, Master. Deutsch Meisterbrief.
Re: Diagnostic Help [Re: VetteElite] #4458953
07/14/17 04:30 AM
07/14/17 04:30 AM
Joined: Mar 2004
Posts: 21,121
Upstate NY
Donald Online content
Donald  Online Content
Joined: Mar 2004
Posts: 21,121
Upstate NY
Easy to diagnose the problem. It's a Saturn.


2015 Subaru Forester 2.5 engine/CVT
2015 Ford F250 w/Powerstroke
2016 Subaru Crosstrek CVT (wife's)
Re: Diagnostic Help [Re: VetteElite] #4458992
07/14/17 05:45 AM
07/14/17 05:45 AM
Joined: Aug 2005
Posts: 919
dayton oh
kc8adu Offline
kc8adu  Offline
Joined: Aug 2005
Posts: 919
dayton oh
sounds more like a clogged cat to me.
disconnect the pipe in front of it and look at the vacuum again.with a real vacuum gauge.
do a before and after.
if the map is lying to the pcm same result.transmission is being programmed to shift with the data the pcm sees.
if engine is down on power and the shift is being performed for the power it is supposed to have under said condition it will seem harsh.

Re: Diagnostic Help [Re: Donald] #4458999
07/14/17 05:50 AM
07/14/17 05:50 AM
Joined: Aug 2005
Posts: 919
dayton oh
kc8adu Offline
kc8adu  Offline
Joined: Aug 2005
Posts: 919
dayton oh
not even close.if that was sarcasm you are wrong.
its a saturn in name only.
Originally Posted By: Donald
Easy to diagnose the problem. It's a Saturn.

Re: Diagnostic Help [Re: Trav] #4459019
07/14/17 06:13 AM
07/14/17 06:13 AM
Joined: Mar 2010
Posts: 5,368
Iowa
The_Eric Offline
The_Eric  Offline
Joined: Mar 2010
Posts: 5,368
Iowa
Originally Posted By: Trav
Originally Posted By: VetteElite

Engine Vacuum doesn't seem right. Using Torque app I see that my vacuum is around 18 "Hg at idle but drops to around 5 "Hg when driving...and rarely comes back up unless I fully take my foot off the throttle. Normally, I thought the vacuum was supposed to come back up after the initial drop upon acceleration as everything "evens out." This might be a slightly clogged exhaust?
Any thoughts on what may be causing these problems?


Transmission shifting issues are routinely misdiagnosed due to engine performance issues, engine doesnt run right the transmission doesn't run/shift right either its really that simple. It looks you might be dealing with a partially clogged cat, that will cause all you describe without throwing a code until it gets so bad it causes a misfire and flashing CEL.
Hook up a mechanical vacuum gauge to the engine, to insure proper readings, if its indicating a bad cat its time to go a bit further down that road.

http://www.aa1car.com/library/converter.htm


Agree on possible bad converter. A good sign is your MAP readings at part throttle that aren't coming back up.


2005 Lincoln Aviator 4.6 DOHC
2000 Honda Accord 2.3
2001 Hyundai Elantra 2.0
1979 Ford F-150 351M
Re: Diagnostic Help [Re: VetteElite] #4459068
07/14/17 07:27 AM
07/14/17 07:27 AM
Joined: Apr 2013
Posts: 123
-
VetteElite Offline OP
VetteElite  Offline OP
Joined: Apr 2013
Posts: 123
-
I appreciate everyone's responses, except Donald; why would you even post in my thread? This car was widely praised and respected - even winning north american car of the year - precisely because it wasn't the typical [censored] GM had been spewing out.

Sounds like most everyone agrees with my gut that it's an engine problem, not a transmission problem. I actually don't have a mechanical vacuum gauge, so this sounds like a good excuse to go get one. That could at least help us figure out if its the cat vs a sensor.

I'll keep bad ground in the back of my head too. Car is driven on salted roads all winter and, while it's not badly rusted, there is some corrosion in the engine bay area.

Re: Diagnostic Help [Re: VetteElite] #4459096
07/14/17 08:09 AM
07/14/17 08:09 AM
Joined: Apr 2017
Posts: 1,481
Ontario, Canada
mightymousetech Offline
mightymousetech  Offline
Joined: Apr 2017
Posts: 1,481
Ontario, Canada
Could also be VVT related. Stuck solenoids?


Mighty Mouse Tech
BMW Tech, Former Acura Tech
2010 Civic Si Castrol 0W40, Redline MTL
2013 BMW 135i M Sport Edition Castrol 0W40, Redline MTL
Re: Diagnostic Help [Re: VetteElite] #4459107
07/14/17 08:24 AM
07/14/17 08:24 AM
Joined: Jun 2003
Posts: 5,951
Illinois
SHOZ Offline
SHOZ  Offline
Joined: Jun 2003
Posts: 5,951
Illinois
Or the vapor emission valves stuck open?

Does it have an Idle Air Control valve?


2008 Hyundai Accent 1.6L 5 sp manual hatchback
2010 Hyundai Genesis Coupe Track 2L Turbo 6sp manual
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