Input from Automotive Service Techs Please

[MiCarl]

We're having an issue with the 2002 Intrepid (2.7L V6) my daughter drives.

 

Sometimes (and becoming more frequent) when accelerating from slow speed or stop there is a massive hesitation. The RPMs might rise a little bit but then acceleration stops and the tach stays steady. I can hear the intake noise from the open throttle plate but there is no power. No perceptible stumble, just no power. If the pedal is released the engine idles fine. After 15 seconds or so everything straightens out and it runs great.

 

The service engine light seems to be non functional. The OBDII is showing five codes, four for the four oxygen sensor heater circuits and one for a multi cylinder misfire. I'm assuming the multi cylinder misfire is being set when we see the hesitation. My understanding is that the O2 heater circuits should not create a driveability issue.

 

For those of you that have been around outboard boat motors: The engine sounds just like when you open the throttle butterflies on an outboard without pushing the linkage that works the spark advance. There is the BWAAAA of intake noise but little RPM increase and no power.

 

I had similar behaviour with a Virago where the TCI was not advancing the timing.

 

So I suspect the hesitation is being caused by a failing PCM not advancing the ignition timing. Of course the problem is intermittent enough there is little chance of verifying that with a timing light.

 

Appreciate any feedback on my reasoning or alternative thoughts.

 

Thanks.

[Flyinfool]

I have had grate luck with this device for finding intermittent issues.

http://www.davisnet.com/drive/products/carchip_products.asp

It plugs into the OBDII port and monitors the engine while you drive, When a code is generated it takes a snapshot of the engine parameters to help see just what was happening at that moment in time, it will also tell you exactly where in the drive cycle (Time and distance since start) you were.

Another feature is its ability to monitor driving habits like hard acceleration and hard breaking. great for kids. It will also tell you if they unplugged it to hide what they are doing.

 

Being an '02, how many miles are on the plugs, wires, etc....

 

Good luck, I hate intermittent issues.

[tim44]

I had a similar problem with my 3.3 engine. I replaced the O2 sensor and the problem went away. I thought for sure it was a cam or crank sensor as I had problems with the cam sensor before that. But after asking around I was told the O2 sensor would cause that kind of problem. Hope this helps.

[eusa1]

next time it happens, stop and check the amount of exhaust pressure comming from the tail pipe, it's possible your having a cat. converter failure, and is also a common concern for that model.

that would also explain the o2 codes. and the tach behavior.

 

 

mike.

[93 venture]

I have seen mass air flow sensors do this kind of stuff, also anouther thing is fuel pressure.I would hook a gage up to the fuel rail and put it under the wiper arm and keep a eye on the pressure.

[GigaWhiskey]

Had two '04 Intrepids until recently. Glad they are gone! One had an issue similar to yours but it got traded in with that issue. The other was prolly the worst car I ever owned.

 

If you get it right, get rid of it fast. Get ready for that $1k water pump change.

[BuddyRich]

Kinda of doubt if its a cat failure unless they have installed some kind of bypass in recent years. I had one fail on me the the 80's. Car would not go over 35 no matter how much peddle I used. Its like having a tailpipe crimped to 1/8 its original size so the engine can't breath and it near goes away till its replaced.

[MiCarl]

 

If you get it right, get rid of it fast. Get ready for that $1k water pump change.

 

She goes to school out of town. End of Dec. she called and said she skidded on the ice, hit a sign, and damaged a strut. $400 to fix. In March she was home and when I saw the car I realized she'd spun through more than one sign. Thing looks like it's been through a garbage disposal. No getting rid of it unless I pay someone to haul it away.

 

Besides, it has an almost brand new water pump.

[Guest seuadr]

I have seen mass air flow sensors do this kind of stuff, also anouther thing is fuel pressure.I would hook a gage up to the fuel rail and put it under the wiper arm and keep a eye on the pressure.

this is where i would put my money as well. Mass Air Flow.

[eusa1]

i ate fish once, but that doesn't make me a fisherman...

 

i'm glad to offer my $.02 :confused24:however it always seems that someone will offer a negative remark to another member offering assistance or information from years of experience.

 

the cat. converter "bypass" has not yet been approved:rotf:

good luck with your repairs. mike

[Snaggletooth]

I vote for mass air flow sensor to. Had a problem with my Lincoln doing that same thing, took it to a friends shop to leave it and he had it fixed in 10 minutes. A loose connection on the intake and the sensor got dirty. Cleaned.....tightened and no problems since.

 

The connection on the intake got knocked loose during an accident and the got worse over time.......sound familiar?

 

Worth checking.

[bongobobny]

I can direct you to a fairly good site that I used to frequent,

www.dodgeintrepid.net

 

There are some pretty knowledgeable people there...

 

The 2.7 was a poor engine to begin with. Suposedly on 2001 they made some changes to helpimprove the longevity of them but there were still issues. We still have our 2002 R/T with the 3.5 which was a much better one. We have had it for 90K so far.

 

You may want to consider putting in a 3.2 engine if you can find one in a boneyard cheap. They were a lot more durable..

[ctraylor]

next time it happens, stop and check the amount of exhaust pressure comming from the tail pipe, it's possible your having a cat. converter failure, and is also a common concern for that model.

that would also explain the o2 codes. and the tach behavior.

 

 

mike.

that would be my guess since you have the O2 codes. I would look at the CAT being stopped up. Sounds just like a plugged up exhaust.

[GigaWhiskey]

I can direct you to a fairly good site that I used to frequent,

www.dodgeintrepid.net

 

There are some pretty knowledgeable people there...

 

The 2.7 was a poor engine to begin with. Suposedly on 2001 they made some changes to helpimprove the longevity of them but there were still issues. We still have our 2002 R/T with the 3.5 which was a much better one. We have had it for 90K so far.

 

You may want to consider putting in a 3.2 engine if you can find one in a boneyard cheap. They were a lot more durable..

 

Spent some time on that site for sure. Both my engines were 2.7's.

[bongobobny]

Yah! Same screen name there as well! Haven't been on that site since I got the '84 VR and joined this site. Many tales to tell! I was one of the charter members of dodgeintrepidchat.net as well! Remember "Long Thread" well. Sure was a bunch of charactors there, and made a few friends as well. Problem being I enjoy motorcycles a lot more, and being a little older I fit in better with this crowd of geezers on our rolling barcoloungers!

 

Hmm, seems as there was a friendly rivalry between 1st and 2nd Gens there as well..

Edited April 25, 2010 by bongobobny

[Karl C.]

My first thought would be an o2 sensor. but the easiest thing to check is this, the gas cap. The car is made to run with a certain amount of preesure in the tank and if that pressure is not met it will act different. Also you can take the car to advance or autozone and they can check to see if there are any codes. Just make sure you know what these codes can really be for. For example quite a few times a code can say you have a clogged up cat but in reality it is an o2 senor. Seen this quite a few times. I cannot remember what code is thrown when it isusually a gas cap tho.

But anyway just a thought and not ment to be a know it all or etc...

 

Good luck.

[big mike]

A complete system on a car is designed to work together. If you have a lean or rich condition your o2 sensors will read back to the computer and cause the fuel injection system to force more or less fuel to the intake. If you have a lean condition (more air than fuel) then your car will not fire properly causing the sensors to read back to the computer that you have faulty spark. If my calculations are correct I would say your fuel filter is plugged and causing the whole mess. When you have a fuel filter that is plugged it will allow a small ammount of fuel to go through, however as you apply pressure to the accelerator it forces more fuel through the filter pushing sedement in its path and choking off the line. As you release this pressure it will again settle and allow the fuel to pass. I would start by replacing the fuel filter. Then go from there.

 

Hope it helps,

Big Mike

[93 venture]

A complete system on a car is designed to work together. If you have a lean or rich condition your o2 sensors will read back to the computer and cause the fuel injection system to force more or less fuel to the intake. If you have a lean condition (more air than fuel) then your car will not fire properly causing the sensors to read back to the computer that you have faulty spark. If my calculations are correct I would say your fuel filter is plugged and causing the whole mess. When you have a fuel filter that is plugged it will allow a small ammount of fuel to go through, however as you apply pressure to the accelerator it forces more fuel through the filter pushing sedement in its path and choking off the line. As you release this pressure it will again settle and allow the fuel to pass. I would start by replacing the fuel filter. Then go from there.

 

Hope it helps,

Big Mike

 

I think all it has for a filter is a strainer in the tank, but it could be pluged.Or the pump is taking a dump.

[MiCarl]

With the use of a recording scan tool I think I solved this.

 

The codes are not a heater circuit issue. They are "O2 sensor circuit high voltage" (P0132 and it's sisters). I misunderstood the descriptions because they all contained the phrase "This code indicates that the heated oxygen sensor reading is too high", and mistakenly thought it was referring to the heater voltage.

 

The PCM is putting a 1.725 bias voltage on the O2 sensors instead of the 0.450 volts it should.

 

Under Symptoms the description states: "You will likely not notice any drivability problems.", which sent me down the wrong path. Here's why I think that was incorrect:

 

As the bias voltage was creeping up it caused the PCM to determine a rich condition. It compensated by turning the mixture leaner and updating the fuel trim tables. The long term fuel trims were at -35%. So on start up (open loop) it was running lean until the oxygen sensors started to function and put it in closed loop. The O2 voltage was still indicating rich so the PCM took another 25% of in the short term fuel trims.

 

Now it's lean enough to detonate under acceleration. The knock sensor indicates this so the PCM dials the spark advance back to about 0, causing a complete loss of power.

 

Tramping the pedal puts it back in open loop, the extra -25% fuel trim goes away, the knock stops, the PCM puts back the spark advance and the car accelerates briskly.

 

I sorted all this out after I pulled the connectors from the PCM to clean them. That caused the trim tables to zero out. Now that it's not aggressively lean it never leaves open loop (O2 voltages stay above 1.25) and drives just fine with the default fuel delivery.

 

Ordering replacement PCM first thing Monday morning.

[Wolf]

Would you like the actual test from alldata before you order it?

[buddy]

Replaced another PCM on one of our Dodge 3/4 ton Pickups at the city. Was running like crap then it would not idle at all kept dieing. This makes the third PCM on three trucks in two years.. Once the PCM was replaced all three ran just fine with no problems..

[Wolf]

Chrysler has a lot of reflashes for their computers. Cheaper than buying another one, Thought they do break quite often.

[MiCarl]

Refurbished, current updates, lifetime guarantee - $150.

 

Of course the way my daughter drives that lifetime guarantee is probably less than 90 days:big-grin-emoticon: