'97 Deville, runs rough with A/C on

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'97 Deville, runs rough with A/C on

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Cadillac >> Cadillac Models >> Cadillac Deville >> '97 Deville, runs rough with A/C on

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'97 Deville, runs rough with A/C on - 7/17/2007 5:40:35 PM

DeFormula

Posts: 13
Joined: 2/19/2007
Status: offline

My '97 Deville runs great except when I have the A/C on. It idles smooth but while driving it runs rough and feels like it has a bad miss and occasionally backfires. As I said, with A/C off it runs great and the A/C itself works good and doesn't make any noise. Does anyone have a clue what this could be? Thanks.

Dave

Post #: 1

RE: '97 Deville, runs rough with A/C on - 7/17/2007 9:04:01 PM

Katzmans Caddy

Posts: 1268
Joined: 12/3/2006
Status: offline

Hard to figure these things out from a distance but what is happening is that the AC is putting a load on the engine when the compressor cycles on. This load is uncovering a problem. If it feels like a miss and backfires that's what you have imo, a miss. . Do you have a code? I'd go through the standard items for a miss. Being a 1997 do you know if your spark plug wires have ever been changed? If not they probably need to be by now. Spark plugs, when changed last? Then there is the coils if problem still persists. I always suggest fuel and air filters too.

(in reply to DeFormula)

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RE: '97 Deville, runs rough with A/C on - 7/18/2007 3:28:01 PM

DeFormula

Posts: 13
Joined: 2/19/2007
Status: offline

quote:

ORIGINAL: Katzmans Caddy

Hard to figure these things out from a distance but what is happening is that the AC is putting a load on the engine when the compressor cycles on. This load is uncovering a problem. If it feels like a miss and backfires that's what you have imo, a miss. . Do you have a code? I'd go through the standard items for a miss. Being a 1997 do you know if your spark plug wires have ever been changed? If not they probably need to be by now. Spark plugs, when changed last? Then there is the coils if problem still persists. I always suggest fuel and air filters too.

Thanks for the reply, good stuff. Everything you mention (except coils) is fairly new (less than 20K miles). The other thoughts I have are...dirty injectors, sticky throttle body, crud in the gas tank. I do not have a scanner to pull codes, although I do know it needs an O2 sensor because the SES light is on and the scanner I borrowed a year ago said that. Could the O2 sensor be causing this problem? Seems unlikely to me and it wasn't having this problem until recently.

(in reply to Katzmans Caddy)

Post #: 3

RE: '97 Deville, runs rough with A/C on - 7/18/2007 5:34:24 PM

FLCaddytech

Posts: 507
Joined: 6/22/2006
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if you have been driving for a year with the SES light on, then you have no idea how many other codes may have set since the last time you had it scanned.

Step 1.
Scan for codes
Step 2.
Repair the obvious problem first then move on to the next issue.

(in reply to DeFormula)

Post #: 4

RE: '97 Deville, runs rough with A/C on - 7/18/2007 5:40:45 PM

DeFormula

Posts: 13
Joined: 2/19/2007
Status: offline

Thanks. The SES light comes and goes. Sometimes it is off for a month at a time (I know about the gas cap so that isn't it) but your point is well taken. I'll get ahold of a scanner and go from there.

(in reply to FLCaddytech)

Post #: 5

RE: '97 Deville, runs rough with A/C on - 7/20/2007 2:06:02 PM

DeFormula

Posts: 13
Joined: 2/19/2007
Status: offline

Additional info, it seems to occur once the engine is warmed up, not when I first start it up. Any additional ideas? Thanks.

Dave

(in reply to DeFormula)

Post #: 6

RE: '97 Deville, runs rough with A/C on - 7/20/2007 3:07:06 PM

stomper

Posts: 1447
Joined: 6/18/2007
Status: offline

something there does not like heat.
that points to electrical or electronic.

quote:

ORIGINAL: DeFormula

Additional info, it seems to occur once the engine is warmed up, not when I first start it up. Any additional ideas? Thanks.

Dave

(in reply to DeFormula)

Post #: 7

RE: '97 Deville, runs rough with A/C on - 7/20/2007 6:39:57 PM

FLCaddytech

Posts: 507
Joined: 6/22/2006
Status: offline

The engine computer runs in open loop until it warms up. Uses a base program from the TPS CTS and MAF.
When it reaches operating temp it uses feedback from the o2 sensors for fuel control.

< Message edited by FLCaddytech -- 7/20/2007 6:41:20 PM >

(in reply to stomper)

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RE: '97 Deville, runs rough with A/C on - 7/20/2007 7:34:37 PM

DeFormula

Posts: 13
Joined: 2/19/2007
Status: offline

So if one of the o2 sensors is bad it could be giving faulty info to the computer and causing it to run like crap when warm(?)

(in reply to FLCaddytech)

Post #: 9

RE: '97 Deville, runs rough with A/C on - 7/20/2007 10:25:07 PM

Stealth

Posts: 2999
Joined: 2/18/2007
Status: offline

going by FLCaddytech either that is it or the O2 sensors are off-line?

quote:

ORIGINAL: FLCaddytech

The engine computer runs in open loop until it warms up. Uses a base program from the TPS CTS and MAF.
When it reaches operating temp it uses feedback from the o2 sensors for fuel control.

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(in reply to FLCaddytech)

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