Intermittent drivability problem due to fretting corrosion -- a casestudy

I'm posting this information in case you may run across a similar problem.

PROBLEM
1998 Cadillac DeVille with Northstar control system and with
intermittent MIL, sometimes flashing. Vehicle was taken to dealership
and P0303 code extracted (cylinder 3 misfire). Number 3 fuel injector
replaced and all is quiet. MIL turns on, again, sometimes flashing.
Vehicle taken to an independent shop, P0308 (cylinder 8 misfire) code.
"Motorvac" treatment given, problem goes away. MIL turns on, sometimes
flashing. Vehicle taken to dealer, DTC P0308 present. On way to
dealer, MIL turns off. Customer states the problem often goes away.
Tech performs power balance test and recommends replacing #8 injector.
Customer refuses, claims dealer incompetent. Customer pays $150
diagnostic fee and leaves. Since "customer" is a family member, I get
to look at the car, next.

EXPERIMENT
Scan tool (OTC Enhanced Monitor with Pathfinder 99 firmware) showed
P0308 in history, both long-term fuel trims were negative (as expected
on a hot engine -- although one was more negative than other). Vehicle
appeared to be running well when examined. Ignition on cylinder 8
'scoped and compared to "known-good" (I used #6 since this was
convenient and PCM was not complaining about this cylinder). Both
cylinders were firing at about 10 kV. "Good" is between 10 kV and 15
kV. Decorative top cover was removed , tape from #8 and #6 fuel
injectors' wiring was unraveled and current peak and duration measured.
Both injectors were drawing 1 ampere, pulse width was about 3.2 mS
(scan tool showed 3.3 mS was commanded).

Pathfinder 99 allows individual injectors to be turned off. With engine
off, idle air control motor was disabled and engine was started.
Selectively turning off injectors showed approximately identical RPM
drop (before fuel control kicked in). Engine was turned off. Idle air
controller was reconnected and new DTC ("cannot control idle rpm") was
cleared. Although the power balance test was not done "by the book,"
its outcome convinced me that, at the moment of the test, no problems
existed in #8 cylinder.

HYPOTHESIS
System appeared to be in very good control of fuel delivery, although
slightly different long term fuel trim (LTFT) readings hint at a
possible air leak (injector O-ring, intake manifold, etc.). Misfire was
not present. Initermittent problem is symptomatic of electrical
connectivity issue, characteristic of fretting corrosion (due to
microvibration inside electrical connector and oxygen ingress causing
oxide formation -- do a web search if you're interested in details).

REPAIR
#8 fuel injector connector was disconnected and injector's pins and
connector clips cleaned with Caig Labs' "Deoxit D5" (a very good contact
cleaner/lubricant) and reconnected. Connection reopened, recleaned and
final connection made.

FOLLOW-UP
Vehicle has been running flawlessly for three weeks. Family member told
next time P03xx code present, all injectors will have connections
cleaned. Total time spent on job: 2 hours.

If you want to contact me on details, please replace the digits with "o."

Cordially,

Bohdan Bodnar

GM has a TSB stating exactly what you did to the injector connector, mild
corrosion being the culprit, btw, good work!!!
"Bohdan Bodnar" > wrote in message
...
> I'm posting this information in case you may run across a similar problem.
>
> PROBLEM
> 1998 Cadillac DeVille with Northstar control system and with intermittent
> MIL, sometimes flashing. Vehicle was taken to dealership and P0303 code
> extracted (cylinder 3 misfire). Number 3 fuel injector replaced and all
> is quiet. MIL turns on, again, sometimes flashing. Vehicle taken to an
> independent shop, P0308 (cylinder 8 misfire) code. "Motorvac" treatment
> given, problem goes away. MIL turns on, sometimes flashing. Vehicle
> taken to dealer, DTC P0308 present. On way to dealer, MIL turns off.
> Customer states the problem often goes away. Tech performs power balance
> test and recommends replacing #8 injector. Customer refuses, claims
> dealer incompetent. Customer pays $150 diagnostic fee and leaves. Since
> "customer" is a family member, I get to look at the car, next.
>
> EXPERIMENT
> Scan tool (OTC Enhanced Monitor with Pathfinder 99 firmware) showed P0308
> in history, both long-term fuel trims were negative (as expected on a hot
> engine -- although one was more negative than other). Vehicle appeared to
> be running well when examined. Ignition on cylinder 8 'scoped and
> compared to "known-good" (I used #6 since this was convenient and PCM was
> not complaining about this cylinder). Both cylinders were firing at about
> 10 kV. "Good" is between 10 kV and 15 kV. Decorative top cover was
> removed , tape from #8 and #6 fuel injectors' wiring was unraveled and
> current peak and duration measured. Both injectors were drawing 1 ampere,
> pulse width was about 3.2 mS (scan tool showed 3.3 mS was commanded).
>
> Pathfinder 99 allows individual injectors to be turned off. With engine
> off, idle air control motor was disabled and engine was started.
> Selectively turning off injectors showed approximately identical RPM drop
> (before fuel control kicked in). Engine was turned off. Idle air
> controller was reconnected and new DTC ("cannot control idle rpm") was
> cleared. Although the power balance test was not done "by the book," its
> outcome convinced me that, at the moment of the test, no problems existed
> in #8 cylinder.
>
> HYPOTHESIS
> System appeared to be in very good control of fuel delivery, although
> slightly different long term fuel trim (LTFT) readings hint at a possible
> air leak (injector O-ring, intake manifold, etc.). Misfire was not
> present. Initermittent problem is symptomatic of electrical connectivity
> issue, characteristic of fretting corrosion (due to microvibration inside
> electrical connector and oxygen ingress causing oxide formation -- do a
> web search if you're interested in details).
>
> REPAIR
> #8 fuel injector connector was disconnected and injector's pins and
> connector clips cleaned with Caig Labs' "Deoxit D5" (a very good contact
> cleaner/lubricant) and reconnected. Connection reopened, recleaned and
> final connection made.
>
> FOLLOW-UP
> Vehicle has been running flawlessly for three weeks. Family member told
> next time P03xx code present, all injectors will have connections cleaned.
> Total time spent on job: 2 hours.
>
> If you want to contact me on details, please replace the digits with "o."
>
> Cordially,
>
> Bohdan Bodnar
>
>



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In article >,
Bohdan Bodnar > wrote:

> I'm posting this information in case you may run across a similar problem.
>
> PROBLEM
> 1998 Cadillac DeVille with Northstar control system and with
> intermittent MIL, sometimes flashing. Vehicle was taken to dealership
> and P0303 code extracted (cylinder 3 misfire). Number 3 fuel injector
> replaced and all is quiet. MIL turns on, again, sometimes flashing.
> Vehicle taken to an independent shop, P0308 (cylinder 8 misfire) code.
> "Motorvac" treatment given, problem goes away. MIL turns on, sometimes
> flashing. Vehicle taken to dealer, DTC P0308 present. On way to
> dealer, MIL turns off. Customer states the problem often goes away.
> Tech performs power balance test and recommends replacing #8 injector.
> Customer refuses, claims dealer incompetent. Customer pays $150
> diagnostic fee and leaves. Since "customer" is a family member, I get
> to look at the car, next.
>
> EXPERIMENT
> Scan tool (OTC Enhanced Monitor with Pathfinder 99 firmware) showed
> P0308 in history, both long-term fuel trims were negative (as expected
> on a hot engine -- although one was more negative than other). Vehicle
> appeared to be running well when examined. Ignition on cylinder 8
> 'scoped and compared to "known-good" (I used #6 since this was
> convenient and PCM was not complaining about this cylinder). Both
> cylinders were firing at about 10 kV. "Good" is between 10 kV and 15
> kV. Decorative top cover was removed , tape from #8 and #6 fuel
> injectors' wiring was unraveled and current peak and duration measured.
> Both injectors were drawing 1 ampere, pulse width was about 3.2 mS
> (scan tool showed 3.3 mS was commanded).
>
> Pathfinder 99 allows individual injectors to be turned off. With engine
> off, idle air control motor was disabled and engine was started.
> Selectively turning off injectors showed approximately identical RPM
> drop (before fuel control kicked in). Engine was turned off. Idle air
> controller was reconnected and new DTC ("cannot control idle rpm") was
> cleared. Although the power balance test was not done "by the book,"
> its outcome convinced me that, at the moment of the test, no problems
> existed in #8 cylinder.
>
> HYPOTHESIS
> System appeared to be in very good control of fuel delivery, although
> slightly different long term fuel trim (LTFT) readings hint at a
> possible air leak (injector O-ring, intake manifold, etc.). Misfire was
> not present. Initermittent problem is symptomatic of electrical
> connectivity issue, characteristic of fretting corrosion (due to
> microvibration inside electrical connector and oxygen ingress causing
> oxide formation -- do a web search if you're interested in details).
>
> REPAIR
> #8 fuel injector connector was disconnected and injector's pins and
> connector clips cleaned with Caig Labs' "Deoxit D5" (a very good contact
> cleaner/lubricant) and reconnected. Connection reopened, recleaned and
> final connection made.
>
> FOLLOW-UP
> Vehicle has been running flawlessly for three weeks. Family member told
> next time P03xx code present, all injectors will have connections
> cleaned. Total time spent on job: 2 hours.
>
> If you want to contact me on details, please replace the digits with "o."
>
> Cordially,
>
> Bohdan Bodnar

Good to see you back!

Thanks, Neil! I've been messing around, on and off for about 1/2 year,
with a voltage drop problem in a 1995 Ciera that is more difficult to
find than to diagnose. The PCM's power circuit is on the same line as
the turn signals; there's an abnormal drop in that circuit whenever the
turn signals are on, thus causing RPMs to rise and fall in time
(instrument panel, SRS, PCM power, turn signals are all on the same
circuit). The problem is not in the ignition switch (that was an
expensive guess on my part -- time and money). What I really need is
several hours without interruption so I can go in with a portable
'scope, jumper wires, etc.

I'll write this up once I figure out exactly what the failure mechanism is.

Bye,

BB
aarcuda69062 wrote:

>In article >,
> Bohdan Bodnar > wrote:
>
>
>
>>I'm posting this information in case you may run across a similar problem.
>>
>>
>>
>Good to see you back!
>
>

Cool,
Yet another problem fixed by Deoxit D5.
For the past few months, I have been using it to clean ANY connector I
remove, no matter how shiny, before returning to service.

--Don
Don Byrer
Electronics Technician/Friendly but Sarcastic Pilot
FAA Airways Facilites/Tech Ops, RADAR/Data/Comm @ CLE
Amateur Radio KJ5KB
Instrument Pilot Commercial Student
PP-ASEL 30 Jan 2005 "-IA" 25 Mar 2005