Perdels
Post Fiend
Joined: Sep 2003
Posts: 6,096
Likes: 26
From: Mesa AZ
A faulty fan clutch or worn out serpentine belt can sometimes throw perdel readings off as well. Some CPS types will also skew the perdel readings...
Perdel is just a reading of relationships....so it simply measures how evenly each cylinder is contributing to the rotational operation of the engine. If all the injectors are evenly worn out....then the perdel readings won't show any differences. Once an injector is performing much better or worse compared to its neighbor (in the firing order), then the perdel test might be able to detect that.
Lead Driver
Joined: Jun 2003
Posts: 8,298
Likes: 24
From: Damon (South East Texas)
This is true. I replaced my stock crankshaft damper with a Fluidampr and it lowered my perdel percentages. Reading perdels can point to a cylinder/s that are contributing less than others, but other testing must be done to pinpoint the source of the problem.
Postmaster
Joined: Jun 2010
Posts: 2,555
Likes: 8
From: Longview, TX
I'm chasing a vibration at idle too. Enough for change to rattle a tad, but not horrible. I'm not concerned about it, just aware. My thoughts are this order : 1) crank shaft pulley 2) torque converter 3) engine mounts 4) injection.
I'm not sure reading perdels would single out any of the issues, just point to AN issue.
I'm not sure reading perdels would single out any of the issues, just point to AN issue.
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Hotshot
Joined: Jan 2011
Posts: 18,849
Likes: 179
From: Puget Sound
Perdels can be weird. I thought it was PERcent DELineation, but I never found this in writing.
I have seen a Perdel of 6 on a smooth-idling truck and a rough-idling truck, so you have to take all the symptoms together. The rough-idling had a black CPS and was smoking, but it was a loose injector. The smooth-idling truck had a gray CPS. I've had a reasonable idle with a true reading of 2 or 3.
Here's more fog for the bank: You can have a "bad" injector that shows a difference in the idle when you unplug it - while it's weak, it's not necessarily dead. Observation, CCT, and a cold buzz test combined can help point to a bad injector... but putting new O-rings and copper washers on the sticks, plus rotating their position and conducting the same tests is the only way I know to verify. This is assuming it passed the buzz test. A weak-sounding buzz test means first check UVCH and test again (assuming good oil). You can see how this is as much art as science. It's all about not throwing a grand in there to "test" a theory that the sticks are bad.
If you still have that rolling idle, that's tuning... I learned that one.
I have seen a Perdel of 6 on a smooth-idling truck and a rough-idling truck, so you have to take all the symptoms together. The rough-idling had a black CPS and was smoking, but it was a loose injector. The smooth-idling truck had a gray CPS. I've had a reasonable idle with a true reading of 2 or 3.
Here's more fog for the bank: You can have a "bad" injector that shows a difference in the idle when you unplug it - while it's weak, it's not necessarily dead. Observation, CCT, and a cold buzz test combined can help point to a bad injector... but putting new O-rings and copper washers on the sticks, plus rotating their position and conducting the same tests is the only way I know to verify. This is assuming it passed the buzz test. A weak-sounding buzz test means first check UVCH and test again (assuming good oil). You can see how this is as much art as science. It's all about not throwing a grand in there to "test" a theory that the sticks are bad.
If you still have that rolling idle, that's tuning... I learned that one.
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Post Fiend
Joined: Sep 2003
Posts: 6,096
Likes: 26
From: Mesa AZ
Post Fiend
Joined: Sep 2003
Posts: 6,096
Likes: 26
From: Mesa AZ
5% or less is acceptable according to Ford. 5-10% is cause for investigation and over 10% usually results in getting an injector replaced. Again, according to the dealer.
Hotshot
Joined: Jan 2011
Posts: 18,849
Likes: 179
From: Puget Sound
In my personal experience, I have used the CCT when I knew I had a bad hole and I wanted to isolate which one was the likeliest suspect... and it works for this. When my injector prairie-dogged, it disrupted the fuel to the cylinders that fire before and after it, so in my case... a series of three bad Perdels in firing sequence pointed at the one in the middle. The firing order includes 6, 8, 1, and all three were bad in the CCT - the culprit was #8.
The graph below was a poor-flowing #1 at idle:
The graph below was a poor-flowing #1 at idle: