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96 Cavalier, loses power, no MIL codes, ???
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bonsaicult
Novice
Dec 17, 2007, 6:41 PM
Post #1 of 11
(3691 views)
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96 Cavalier, loses power, no MIL codes, ???
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I've got a 1996 cavalier, 163k miles, still runs great, but it has developed a loss of power at times,
step on the gas and it chokes, sputters and threatens to stall, eventually it will clear itself, but
it will happen again 5 minutes later. It hasn't set any codes, has a new fuel filter, air filter, pcv valve.
I'm stumped.... if the fuel pressure was low i'd get a lean code, ignition problem, misfire code, I don't
have a obdII scanner, a mechanic suggested hooking one up and watching when it happens, to see
any thing out of spec.
Just wondering if anyone else has encountered anything like this, Thanks
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Dec 18, 2007, 2:44 AM
Post #2 of 11
(3681 views)
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Re: 96 Cavalier, loses power, no MIL codes, ???
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Get a code reading anyway. More parts stores are doing this just for the asking,
T
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DanD
Veteran
/ Moderator
Dec 18, 2007, 5:37 AM
Post #3 of 11
(3679 views)
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Re: 96 Cavalier, loses power, no MIL codes, ???
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Tom’s right have the system scanned but maybe not just for codes. Most code readers will only tell you set codes not pending codes. A pending code is where the PCM has a set of perimeters it must see before it’ll turn on the MIL and set a fault code to memory. For example a misfire must be seen a number of times in concession before the PCM will act. I other words the PCM is seeing something wrong and is waiting to see it on a regular basis before it’ll prompt you with a MIL.
Also with a proper scanner, you’ll be able to pull up data like the misfire counter. The misfire counter tracks all cylinders and places a number beside it on screen.
The number 0 (zero) beside a designated cylinder, means no misfire detected. A number of 20 to 50 will be a misfire that you can begin to feel but will not set a code or flash the MIL.
Anything above 50 to 100 is hit & miss whether a code will set but you’ll defiantly feel one and likely see a flashing MIL. A count of 75 and up will set a code and it’ll feel like you’re in a rocking chair with the way the car is running.
My point being is that a scan tool is more then just a code reader, when it’s used by an experienced tech.
If on a road test I see a count of 20 or so on one cylinder I’m not going to ignore it and wait for a code to set, I’m going to that cylinder to investigate.
One last thing, not all misfires are caused by an ignition problem. Anything that may hinder complete combustion can and will cause a misfire. Dirty or failing injectors, vacuum leaks, EGR valve leaking, opening at the wrong time or to much, engine mechanical and the list goes on & on. So even if this car does set a misfire code, don’t automatically think spark plugs and wires are going to fix it.
Hopefully I wasn’t to long winded here but so many people think scanning a computer is just code reading, it’s a lot more then that. I’m just try to explain why we at a garage charge for a scan; we don’t put the scanner away back in the toolbox when there isn’t a code.
Dan.
Canadian "EH"
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bonsaicult
Novice
Dec 18, 2007, 3:20 PM
Post #4 of 11
(3675 views)
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Re: 96 Cavalier, loses power, no MIL codes, ???
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Hmmmmm.... I guess i'll have to spend some of my holiday bonus on the scanner, but I know that
AZ has a loan a tool where you purchase the scanner and when you are through,
you return it for a full refund, any suggestions for an inexpensive scantool with the features i will need?
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DanD
Veteran
/ Moderator
Dec 20, 2007, 5:33 AM
Post #5 of 11
(3665 views)
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Re: 96 Cavalier, loses power, no MIL codes, ???
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Inexpensive is a relative term don’t you think? I bought my scanner that we use here at the garage on sale for the low price of about $8000.00. That was a few years ago, since then I’ve had to add new software a number of times at about $2000.00 a hit.
For what I have, it’s been relatively inexpensive; now for you to spend this kind of money to repair your own vehicle would be nuts.
Take the vehicle in and have it diagnosed; if you don’t like or understand the diagnosis post back and we’ll see.
Dan.
Canadian "EH"
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way2old
Veteran
/ Moderator
Dec 20, 2007, 5:39 AM
Post #6 of 11
(3662 views)
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Re: 96 Cavalier, loses power, no MIL codes, ???
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If you are going to Auto Zone anyway, have them read the codes for you and post the code numbers back here. They do it for free hoping you will buy a part.
Being way2old is why I need help from younger minds
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bonsaicult
Novice
Dec 20, 2007, 4:02 PM
Post #7 of 11
(3659 views)
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Re: 96 Cavalier, loses power, no MIL codes, ???
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Just as a re-cap, the car does not set any codes, the last code was due to a perforation in the
fuel filler neck that was easily repaired.
I'm looking at getting a ELM327 adapter to attach to my laptop, the price is decent and the features are
incredible depending on whether you use free software, or purchase software.
Everything I've read on this setup seems like it will do the job for this car, and all my other vehicles also.
Here is a link to the adapter...
http://cgi.ebay.com/ebaymotors/ELM327-OBD-2-CAN-BUS-USB-Interface-Scanner-OBD-II-Tool_W0QQitemZ230194429821QQcmdZViewItem
Thanks to everyone for your help, Colin
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bonsaicult
Novice
Dec 26, 2007, 7:03 PM
Post #8 of 11
(3648 views)
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Re: 96 Cavalier, loses power, no MIL codes, ???
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UPDATE: I've ordered the ELM327 OBDII scanner for my laptop,
I mentioned what was occurring and someone suggested looking at the catalytic converter, that the ceramic
monolith might have broken away and at times it gets lodged in the end of the case in a way that
prevents the exhaust flow, this would explain why there were no codes, and no performance!
Sounds good to me, gonna check it out...... Ciao
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bonsaicult
Novice
Jan 27, 2008, 4:11 PM
Post #9 of 11
(3617 views)
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Re: 96 Cavalier, loses power, no MIL codes, ???
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UPDATE***
I got the ELM327 scanner, very impressive unit, I highly recommend this scanner, I got the serial port unit
because i've heard about problems converting the serial data to USB. I've picked up a Palm Vx, for $20.00,
serial cable for the palm for $12.00, and a null modem serial adapter M/M, to connect it up.
All totaled, still under $120.00 for a full functioning scanner, with real time sensor data recording
capability, as well as the DTC reader, and ability to reset the MIL.
On to the saga of the Cavalier, When the car "acts up", ie starts to stall, I noticed that the
O2 sensor outputs for both sensors dives down below 100mv, when the car is running well
the 1st bank O2 is running around 800-900mv, and the 2nd bank 600-700mv.
Any clues as to why?
For now i've disconnected the front O2 sensor to keep the ECU in failsafe mode because the fault seems
to be in the ECU or a bad sensor.
Thanks
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Guest
Anonymous Poster
Jan 28, 2008, 3:30 PM
Post #10 of 11
(3606 views)
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Re: 96 Cavalier, loses power, no MIL codes, ???
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any update? --> Fuel Pressure Regulator<---
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bonsaicult
Novice
Feb 7, 2008, 5:35 PM
Post #11 of 11
(3584 views)
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Re: 96 Cavalier, loses power, no MIL codes, ???
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### UPDATE ###
So far so good, as I anticipated, the car runs flawlessly in failsafe.
The car is being replaced in a few months so that is the way it will stay until I get rid of it.
I'd still like to know what or which sensors are affecting the car, but perhaps the ECU is at fault.
I'm not willing to spend any more $$$, but I would really like to know what was up.
Neverless, It's running great with the upstream O2 sensor unplugged so........
Thanks .....
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