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Running Compression Waveform help
Posted to Technical Discussion Forum on 4/5/2015 43 Replies

Good Morning everyone,

Some good friends of mine were looking at a used van. They asked me to look it over and tell them what I thought. It had a leaky radiator, and worn ball joints, but otherwise was very clean, 87k miles on the clock. Idles smooth as glass, and starts up very quickly.

Test drive revealed it was very sluggish under a load and up semi steep grades. As in it wont go over 60mph uphill. Scan Data revealed the Catalyst and 02 monitor had not run to completion yet. No Dtc's were set, but Test id's 57, 58 and 72 are all failing.

2005 Dodge Grand Caravan SE Plus, Engine/Propulsion Scan Data

I told them I think it would be better to pass on this van. Friends go back, tell the dealer what had been found, and he knocks off 300 clams and that was good enough to seal the deal, sigh. It passed a smog inspection, which I thought was unusual.

But anyhow, a week later the MIL is on with P0404 EGR Valve Performance/Rationality. I suspected a restricted exhaust from the get go. So...in goes the pressure transducer, Wps500 Range 2, so 1v = 10 psi. I dont get to do this often, so I was pretty excited.

Heres what I got...

Doesnt seems to reveal much at idle...

2005 Dodge Grand Caravan SE Plus, Engine/Propulsion Waveform

Marked up for your viewing pleasure.

2005 Dodge Grand Caravan SE Plus, Engine/Propulsion Waveform

2005 Dodge Grand Caravan SE Plus, Engine/Propulsion Waveform

(Notice Cursor 2 is reading 1.65v, thats 16psi in the exhaust plateau)

2005 Dodge Grand Caravan SE Plus, Engine/Propulsion Waveform

.lsm File

2005 Dodge Grand Caravan SE Plus, Engine/Propulsion Waveform

I found some other captures in the archives that help illustrate a restricted exhaust, (thanks Shannon Lindsey.) See the pressure pulses (Exhaust Plateau) between the compression towers that rise as rpm's increases?

File ID: [2005 Volkswagen Jetta 2.5, Engine/Propulsion Waveform]

How about another? See the trend?

File ID: [2005 Ford Escape XLT, Emissions Waveform]

Here is a snap throttle with no restriction. (known good)

File ID: [1994 Honda Civic DX, Engine/Propulsion Waveform]

Now the Van in question again...See the resemblance? Looks, and feels awfully like a restricted exhaust to me.

File ID: [2005 Dodge Grand Caravan SE Plus, Engine/Propulsion Waveform]

What do you guys think?

It makes sense too, that an EGR Valve with too much pressure behind it, will flow more than expected and set a rationality code as a result. Can this P0404 really be related to the excessive exhaust back pressure?

Oh btw, at some point the EGR Valve was replaced, and a battery disc performed to reset the EGR learned adaptive values, and the code just returned.

Appreciate all the feedback, Im certainly out of my element doing this kind of testing.

Kevin from California

Files Referenced:

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car Vehicle Data

2005 Dodge Grand Caravan SXT 3.8L

Engine3.8 L
Trans4-speed Automatic (Electronic)