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1019 Views 51 Replies 10 Participants Last post by  JordanS
Hello all. I had (have) an issue with my 04 SE that I have posted about in here before, but so far none of what has been suggested and what I have tried has resolved my issue. So, I want to come at it from a different direction. I want anyone who is familiar with my issue to forget they ever heard about it, and let's start over from a different set of premises.

So here's my issue: In the cooler temperatures of the morning (40-45 degrees F) my car will "buck" out of cruise control and trigger a MIL- occasionally throwing a P0121 code. After driving it for 20 miles or so, it will drive just fine, giving me practically no problems for the next 30 miles of my commute. It seems the warmer the weather, the better it performs. However, on a rainy or misty day it is hardly drivable. It constantly "bucks", gives MIL, and throws codes. The "bucking" makes it hard to accelerate moderately back up to cruising speed because each time it bucks, I lose acceleration.

It's not PERFECT on dry, warm days. Usually shortly after startup it will still "buck" once or twice when accelerating from a stop. But it is definitely worse in the cool mornings and wet days.

Any thoughts?

Thanks!

Chris
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intake ambient air temp sensor maybe?
should be on the intake before the throttle body.
if that's been replaced, i never said anything. 馃槀
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intake ambient air temp sensor maybe?
should be on the intake before the throttle body.
if that's been replaced, i never said anything. 馃槀
馃槀 I have come back to that conclusion half a dozen times too. But I replaced that sensor last year trying to solve this same issue. 馃し鈥嶁檪锔
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Hello! Nice to meet you. 馃ぃ
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Hello! Nice to meet you. 馃ぃ
馃槀 You don't know me!
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Hello all. I had (have) an issue with my 04 SE that I have posted about in here before, but so far none of what has been suggested and what I have tried has resolved my issue. So, I want to come at it from a different direction. I want anyone who is familiar with my issue to forget they ever heard about it, and let's start over from a different set of premises.

So here's my issue: In the cooler temperatures of the morning (40-45 degrees F) my car will "buck" out of cruise control and trigger a MIL- occasionally throwing a P0121 code. After driving it for 20 miles or so, it will drive just fine, giving me practically no problems for the next 30 miles of my commute. It seems the warmer the weather, the better it performs. However, on a rainy or misty day it is hardly drivable. It constantly "bucks", gives MIL, and throws codes. The "bucking" makes it hard to accelerate moderately back up to cruising speed because each time it bucks, I lose acceleration.

It's not PERFECT on dry, warm days. Usually shortly after startup it will still "buck" once or twice when accelerating from a stop. But it is definitely worse in the cool mornings and wet days.

Any thoughts?

Thanks!

Chris
What parts have you ruled out/replace trying to chase this issue? I just want to make sure I鈥檓 up to speed on where you鈥檙e at.
Do you have a cover page on for TPS reports?

Err, have you changed the TPS?

Sent from my SM-G996U using Tapatalk
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What parts have you ruled out/replace trying to chase this issue? I just want to make sure I鈥檓 up to speed on where you鈥檙e at.
Ugh... I replaced the TPS, MAP, Crank Position, Cam Position, and Intake Air sensors. Then did it again using Mopar or NTK sensors to make sure they weren't the problem. Then I replaced the wiring harness to make sure there wasn't a short there.
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Do you have a cover page on for TPS reports?

Err, have you changed the TPS?

Sent from my SM-G996U using Tapatalk
Yes, that was one of the first things I did. Then the MAP, Crank Position, Cam Position, and Intake Air Temp sensors. Then the wiring harness.
We may be coming into the wrong season here to do this, but could you warm up individual components with a heat gun, to see if you can warm up just the component that is failing when cold?

Sent from my SM-G996U using Tapatalk
Ugh... I replaced the TPS, MAP, Crank Position, Cam Position, and Intake Air sensors. Then did it again using Mopar or NTK sensors to make sure they weren't the problem. Then I replaced the wiring harness to make sure there wasn't a short there.
. I鈥檓 not a super experienced mechanic, but if there is a relay for the cruise control module then maybe that鈥檚 some thing that I would check to make sure it鈥檚 OK. I don鈥檛 know. It鈥檚 honestly just a shot in the dark and definitely not a professional opinion but that鈥檚 my two cents.
Spark plugs? Coils? The interface where the springs (that electrically connect the coil output to the spark plug) make electrical contact with the coils sometimes gets corroded. You can get the coil boots, which include the springs - Rock Auto and the regular parts stores have them - a lot cheaper than replacing the coils. Wipe the output contact of the coils free of any dirt or corrosion.

Put a light to medium coat of ignition-grade silicone grease (the foil paks at the parts stores are perfect for that, or buy a small tube) on both tips of the springs (spring pressure will press thru the grease for good electrical contact while protecting against moisture/corrosion), around the ends of the boots where they seal against the coil, where they seal against the valve covers, and the other end where they seal around the spark plug ceramic.

How many miles on the plugs? Proper gap? Be aware that plugs with large gaps (from wear) cause over-voltage stress on the coils' internal and external insulation, causing them to arc internally or to nearby external grounds (easiest path if spark plug gap is too wide). Once an arc happens, a conductive carbon trace path forms, making the next arc easier so that even if the old plugs are replaced, the arcing will still occur, and coils then have to be replaced to correct that.

Moisture and temperature of course affect voltage threshold for arcing.

Not saying that's the problem. Something to consider/try.
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Spark plugs? Coils? The interface where the springs (that electrically connect the coil output to the spark plug) make electrical contact with the coils sometimes gets corroded. You can get the coil boots, which include the springs - Rock Auto and the regular parts stores have them - a lot cheaper than replacing the coils. Wipe the output contact of the coils free of any dirt or corrosion.

Put a light to medium coat of ignition-grade silicone grease (the foil paks at the parts stores are perfect for that, or buy a small tube) on both tips of the springs (spring pressure will press thru the grease for good electrical contact while protecting against moisture/corrosion), around the ends of the boots where they seal against the coil, where they seal against the valve covers, and the other end where they seal around the spark plug ceramic.

How many miles on the plugs? Proper gap? Be aware that plugs with large gaps (from wear) cause over-voltage stress on the coils' internal and external insulation, causing them to arc internally or to nearby external grounds (easiest path if spark plug gap is too wide). Once an arc happens, a conductive carbon trace path forms, making the next arc easier so that even if the old plugs are replaced, the arcing will still occur, and coils then have to be replaced to correct that.

Moisture and temperature of course affect voltage threshold for arcing.

Not saying that's the problem. Something to consider/try.
Spark plugs are brand new. I replaced them 3,000 miles ago when I replaced my water pump/timing chain. I can inspect the coil assembly for corrosion. Would any of these conditions cause a P0121 code in your opinion?
Spark plugs are brand new. I replaced them 3,000 miles ago when I replaced my water pump/timing chain. I can inspect the coil assembly for corrosion. Would any of these conditions cause a P0121 code in your opinion?
馃憤

Rectangle Font Parallel Pattern Number


I wouldn't think the things I described would cause that.
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馃憤

View attachment 43315

I wouldn't think the things I described would cause that.
Yeah, I'm inclined to agree. But the P0121 code is consistent. Every time it "bucks" it lights up my MIL for a brief second. Sometimes it stays lit and then clears when the car bucks again. Occasionally, the MIL will stay lit long enough for me to pull over and check the code, and when I do it's the P0121 code. I replaced all the sensors and the wiring harness to eliminate the chance it was a short somewhere. The only thing I haven't replaced that seems to use the same 5v signal is the AC compressor. I have unplugged the AC compressor to see if it still has the same issue because someone said that if that were the problem then unplugging it should eliminate the issue. But I'm not 100% sure that is accurate, and when unplugged, it still does have the same issue.
not the a/c compressor.
but the pressure sensors in the lines can short causing problems.
but it should draw down the whole signal, not just to 1 sensor.
strange
do our cars have 1 temp sensor?
or like many cars do they have one for the guage and 1 for the pcm?
if 2, maybe the pcm one is n't registering right.
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not the a/c compressor.
but the pressure sensors in the lines can short causing problems.
but it should draw down the whole signal, not just to 1 sensor.
strange
do our cars have 1 temp sensor?
or like many cars do they have one for the guage and 1 for the pcm?
if 2, maybe the pcm one is n't registering right.
The a.c. system has 1 pressure transducer. It's the thing sticking out of the high pressure hose (the hose that goes from the compressor to the condenser coils in front of the radiator, AKA discharge hose) with an electrical connector (3 wires) on it. It's on the metal part of the high pressure hose between the compressor and the rubber part of that hose.

There is only 1 engine coolant temperature sensor on these cars. Its output wire goes to the PCM. The PCM uses that 1 input to (1) enrichen the fuel mixture and raise idle speed until engine reaches normal operating temperature, (2) control the radiator cooling fans, and (3) control the temperature gauge reading.

(There are other temperature sensors: Ambient temperature sensor (only used to determine battery charging setpoint voltage); intake air temperature sensor; transmission oil temperature sensor; if ATC equipped, cabin air temperature sensor (built into ATC head unit); and evaporator temperature sensor (causes PCM to turn compressor off to prevent evaporator condensation from freezing on fins if evaporator gets too cold).)
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The a.c. system has 1 pressure transducer. It's the thing sticking out of the high pressure hose (the hose that goes from the compressor to the condenser coils in front of the radiator) with an electrical connector (3 wires) on it. It's on the metal part of that hose between the compressor and the rubber part of that hose.

There is only 1 engine temperature sensor on these cars. Its output wire goes to the PCM. The PCM uses that 1 input as a coolant temperature signal to (1) enrichen the fuel mixture and raise idle speed until engine reaches normal operating temperature, (2) control the radiator cooling fans, and (3) control the temperature gauge reading.
Because the wiring harness has plugs that connect to the AC Compressor, the AC Transducer, and the Coolant Temp Sensor and the wiring harness has been replaced, should I be looking at one of these sensors as a possible culprit? The fact that the presence of water/vapor/moisture makes the problem worse seems to indicate to me that there may yet be some exposed wiring on a sensor somewhere that is getting wet and causing a short. Does that make sense? Any other thoughts?
"...should I be looking at one of these sensors as a possible culprit?"

Everything is fair game.

Was the possibility of a bad PCM considered/discussed/investigated in your previous thread that we're supposed to ignore?

Possibility of connector not fully mated, or a corroded/loose connector terminal. Don't know what connectors were involved in your harness replacement. PCM connectors would be first to consider. Also, connector terminals have been known to unlatch snd partially push out the back of connectors before fully mating with mating half.
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cdmccul suggested using heat to see if you could make problem temporarily disappear when problem was present.

Other side of that coin: When problem not present, spray a mist of water at different areas to see if you can induce temporary failure (and, subsequently, heat to see if you can clear it).

Intermittent problems are the worst!!
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