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
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