Chrysler 2.7 V6 Bucking and Surging
My son's girlfriend has a 2000 Intrepid with a 2.7 V6.
It started acting up on her, so I offered to swap cars so that I could take a look at it.
The car starts and idles fine, but starts bucking and surging under light acceleration in the 1500 - 2300 rpm range. Flooring it seems to smarten it up, so that tells me that it's not a fuel delivery problem.
This behaviour is the same in all gears., even at highway speeds.
When I got it back home to my garage, I tried to feather the throttle up into that RPM range with no load on it, but found it virtually impossible to maintain a steady engine speed. No obvious misses, no backfires in either the intake or exhaust.
I "cured" my 2004 Pontiac GP with a can of each throttle body cleaner and MAF sensor cleaner ... so I had a can of each on hand.
I discovered that this car is not equipped with a MAF, so I cleaned the throttle body and the TPS (externally) and blew it dry.
I then took it for another road test, and found no improvement.
There is no "check engine light" on, and no stored codes either (as long as I am using my new Equus 3100 code reader properly)
The code-reader would not return the vehicle information (i.e. VIN) and the "C" is flashing, indicating that it was unable to succesfully run a test on the catalyst.
I'm certainly not a diagnostic expert ... but I have a hunch that it's the TPS that's at fault here.
I'm sure not liking what I have been reading in regards to 2.7's in general. LOTS of customer complaints ... but then again ... does anyone ever use the internet to tell others about their positive expereriences? :D
The 99 used J tech junk for a computer. My MTG 2500 snap on wont communicate with the decrepid at the shop I am at either.( I have the same car with a junk engine). I have had that problem with many J tech computers in 99-00 jeep and chryslers.
Those engines are pretty sensitive to spark plug condition. But its a good chance you are spot on with the TPS guess, but its a guess, as you know because it wont give a data stream, real nice, thank you chrysler.
I would suggest to hook up the DMM to the TPS and perform a sweep test. Be sure to move the throttle at a slow enough rate to allow the meters sampling rate to catch any glitch that may be present.
OR use a DSO and do a sweep with the sensor hooked up and the key on. Real time display of the Oscilliscope is a great tool.
I also have had chrysler PCMs fail and have a plethera of driveability problems, cured only by a junk yard PCM.
One other thing to consider would be dirty injectors.If they dont spray a good pattern , it can make a car run real poor. Seafoam in the fuel and some drive time will help that a lot.
Bucking and jerking can also be a cam sensor signal dropping in and out, but without a live data stream to indicate cam and crank signal being present or not, it is a crap shoot.
I have a (rarely used) GB Instruments GDT-11 multimeter in my toolbox.
You have to understand that I have "just enough knowlege to be dangerous" when it comes to electronic diagnosis. :embarrass
So I'll type what I *think* is right, and you can confirm or deny that ... OK?;)
I do understand that it's resistance that I'll be measuring, so the red lead will go in the center (red) outlet on the multimeter "V(Ohm)mA".
I'm fairly sure that I'll want the switch pointing to one of the five indicator scales in the lower left (Ohms) Here's the part I'm really not sure of -- "200"?
I suppose that I could call the tech line to get the correct specification range?
Both of the leads will, of course be used to probe 2 of the 3 TPS connectors ... But which 2? I'm thinking that polarity is not a concern.
I also understand your advice to move the potentiometer slowly and smoothly throughout it's range ... thanks for that.
I will have to look up the sweep resistance and pinout specs, and can for you if you like. I am off for a few days though so I cant get the exact specs for you till later in the week.
HOWEVER... the 2000 ohm scale should be what you use. I am thinking it should read in that range somewhere.
Not sure on pinouts, but ones own logic should be able to decipher it.
You cant hurt the TPS hooking a meter to it, so find the 2 pins that have the constant resistance across them , no matter where the tps is turned to, and you have the static circuit, or the power on circuit. The lead that is left will be the posistion value circuit that is hooked to the "wiper" or arm of the device. You can have the one lead on the posistion value (variable part or wiper) pin and the other lead on either one of the static (constant ohms value) circuit and you will be good to go for the test.
OK ... I never had the chance to look at her car again, as she had it booked in at the local Chrysler dealership.
The prognosis is that the cam sensor is somehow out of synch with another sensor or something inside the trans bellhousing. :confused: The trans would have to come out ... yada yada ... $2000.00 +
She's considering jacking up the radiator cap, and driving a new car under it ...
"Buy a GM car with a 3.8" was my advice.:thumbup:
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