Car bucks while accelerating


Chase3203
01-07-2010, 11:24 AM
Hello all, well yesterday I was driving my 2000 crown victoria police interceptor and noticed that it was bucking (almost jerking back and forth) while i was slowly accelerating. I had a misfire on cylinder 6, but it was checked out and fixed. I've noticed that the bucking occurs when the acceleration was slow and stops when I accelerate strongly. Any help would be appreciated.

Blue)(Fusion
01-07-2010, 11:46 AM
Check the EGR system. It is common for the DPFE sensor to accumulate water in it and give false information to the ECU which them commands the EGR valve differently than it should.

Remove the DPFE sensor located on the rear of the passenger side cylinder hear. Remove the electrical connector, two hoses, and two bolts. Tap it several times in your hand to remove the water from it. I even let it sit upright for an hour or two to let it air dry a bit. Reinstall it (ensuring the hoses are connected to the correct ports), and then try driving it again.

If that fails to work, check the EGR valve for blockage and a working diaphragm. With the engine running, if you apply vacuum to the port on the top of the EGR valve, the engine should sputter and run rough until it compensates for the EGR gasses.

danielsatur
01-07-2010, 11:58 AM
Your car wants some Air + fuel!
Replaced Air, fuel filter, clean MAF/iACT sensors, and throttle body.

knelleken
01-11-2010, 06:44 PM
sounds like a bad cop (coil on plug)

Blue)(Fusion
01-11-2010, 06:56 PM
Your car wants some Air + fuel!
Replaced Air, fuel filter, clean MAF/iACT sensors, and throttle body.

He's getting air and fuel. He says it's bucking when the engine is under light load and it is fine under heavy load. A lack of air or fuel would cause problems at the higher RPMs as well as the lower RPMs.

sounds like a bad cop (coil on plug)
Not quite. Like with the air/fuel thing, a bad COP would be noticeable at all power settings, not just low load cruising.

I've had this problem myself and the issue was the with the EGR system.


Replaced Air, fuel filter, clean MAF/iACT sensors, and throttle body.
You should clean your MAF, TB, and plenum and replace any dirty filters, though. Always helps to eliminate the obvious when diagnosing a problem.

danielsatur
01-11-2010, 07:03 PM
A bad COP, EGR, Intake, or PCV system will throw a misfire, or lean codes.

A bad or dirty MAF, IACT, Air filter, and fuel filter could cause that bucking feeling while Wide open throttle.

You need alot of Air + Fuel for 235hp, the MAF/IACT sensors are used for metering Air.

1) Visual inspect your old air filter, and air duct work, it's probably contaminated with oil from a bad PCV system.
The oil will contaminate the MAF/IACT sensors giving a false signal to the ECU/PCU for Air/fuel mix.

Blue)(Fusion
01-11-2010, 07:13 PM
A bad COP, EGR, Intake, or PCV system will throw a misfire, or lean codes.
Not always. If you look at the Mode $06 data, you will see you need a certain number of misfires for a code to be stored or the CEL to illuminate. In my case, it bucked occasionally under light loads (maintaining speed on flat terrain) but no codes were set because it did not happen often enough.

A bad or dirty MAF, IACT, Air filter, and fuel filter could cause that bucking feeling while WOT!

You need alot of Air + Fuel for 235hp, the MAF/IACT sensors are used for metering Air.

I agree completely. However the OP says that the bucking feeling goes away when he accelerates hard. I am not saying these are not possible causes - they should not be overlooked, regardless. And the 2000 CVPIs were only 215HP.

I've noticed that the bucking occurs when the acceleration was slow and stops when I accelerate strongly.

Chase3203
01-11-2010, 09:32 PM
Thanks for all of the feedback I will clean out the throttle body and check my filters. The car sat for 2 years when I first bought it and I didn't change air or fuel filters but I am getting that done next week. Do you got any diagrams to help with disassembling the DPFE and other things?

danielsatur
01-11-2010, 10:03 PM
2-Years sitting around, picture a Briggs & stratton engine X 8-cylinders sitting around for a couple of years!

I would due some spring cleaning 1st.

Chase3203
01-11-2010, 10:40 PM
What do you recommend?

Blue)(Fusion
01-11-2010, 11:01 PM
Yeah sitting around for two years is a long time.

Change ALL fluids and filters ASAP! That would be a good start. I'd run some Seafoam through the gas tank and the PCV valve, too. That will help take off any varnish in the fuel tank and carbon from the cylinders. Change plugs and wires.

danielsatur
01-12-2010, 12:44 PM
New Air filter, fuel filter, clean throttle body, and clean MAF/IACT sensor with CRC MAF sensor cleaner.

Also some Injector cleaner, and fresh gasoline.

Chase3203
01-12-2010, 01:43 PM
sounds like a bad cop (coil on plug)That's what I thought was causing my misfire at first.

Yeah sitting around for two years is a long time.

Change ALL fluids and filters ASAP! That would be a good start. I'd run some Seafoam through the gas tank and the PCV valve, too. That will help take off any varnish in the fuel tank and carbon from the cylinders. Change plugs and wires.I'm planning on changing out air and fuel filters this week and getting a transmission fluid change as well. I changed my plugs a while back, but not the wires. Where is the PCV valve?

New Air filter, fuel filter, clean throttle body, and clean MAF/IACT sensor with CRC MAF sensor cleaner.

Also some Injector cleaner, and fresh gasoline.First thing I did when I got it was injector cleaner after running the tank out almost to empty. Also where are these sensors? Any diagrams would help.

danielsatur
01-12-2010, 02:40 PM
The MAF/IACT sensor is mounted on the Air box/filter, it meters the air flow going into the engine.

Yea! You need some more gas

Do a Google ''youtube auto MAF sensor cleaning''

Don't use carb cleaner, use CRC MAF sensor cleaner.

Chase3203
01-13-2010, 09:23 AM
Thanks I'm going to try your suggestions. The bucking actually hasn't been showing itself lately and the car runs really smooth now. I'm still gonna swap out those filters though for sure and the fluids.

junk yard doggie
01-14-2010, 08:23 PM
Does that sea foam eat fuel varnish? I need to get something to clean up that varnish in tank.

I Think I fixed the miss in my car. I changed plug wires to an good old set I had laying around. They are apparently better than the newer set I had on the car. I had the plug wires on and off a million times trying to fix some other things, they must have gotten broken in the process. The car seems to run perfect with no miss. I will do some more test driving tomorrow. and post the results.

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