What are tags?
Intermittent stumble, intake backfire on '94 Suburban
Hello Guest		   
  • Login
• Register…
• Start blog		   • Who, Where, When
• What can I do?
• What to Read?		   • Polls
• Avatars
• Interests		   • Cities and Countries
• Random blog
• Users search		   • Search
• Games
• Tests
• CarGuru		   • Сообщества
• Talxy Chat
• Horoscope
• Online		  
Зарегистрируйся!
CarGuru > Technology > Intermittent stumble, intake backfire on '94 Suburban 3 March 2005 17:13:04
  Recent blog posts: 
hi!i here new
hi!i here new

who that pass a pay test but…
who that pass a pay test but positives did not come. why?

1994 mazda mx 13 stuck in third…
i have a 1994 mazda mx 13 with the 2.2L engine and automatic transmission and around 190K miles on it. a…

1995 chysler concorde stuck in…
any chance i can fix this problem

Burle!!!
Burle!!!

4e za dephizit zapisei
4e za dephizit zapisei

xaxaxa ug ne projdet!!!
xaxaxa ug ne projdet!!!

izvenite ja uxoju...XYWE.
izvenite ja uxoju... XYWE.

kuda delis' vvse moi zapisi ?
kuda delis' vvse moi zapisi ?

  Forums:   
    topic feeds

• CarGuru  all topics, blogs and comments

• Driving

• Formula-1

• Indycar

• Nascar

• Other sport

• Technology

• 4 x 4

• Volkswagen

• Mercedes

• Acura

• Alfa-romeo

• Audi

• BMW

• Chrysler

• Dodge

• Ford

• General Motors

• Jeep Willys

• Honda

• Hyundai

• Mazda

• Nissan

• Peugeot

• Pontiac

• Porsche

• Saab

• Saturn

• Toyota

• Volvo

• Buy / Sell

• Open discussion

• Anonymous
  Discuss: 
2000 Mercury Cougar
I just bought this 2000 Mercury Cougar at a used dealer ship & sorry to say have had nothin' but…

cheer Shah Rukh Khan
Mark wrote on 10 Oct 2008 11:11:06 GMT: http://narrow.dosti­i.net -- Jbilou, have a liquid…

Weird brake noise
It's my 2001 Impala, 70K. When braking, I can hear kinda "bell ring" noise, like a jack…

basic Hall-effect distributor…
Given that the basic Hall-effect distributor will require one wire for ground, a second wire for voltage…

Re: Cars are running by water?
"srividya" <mahesh.srividya62@­gmail.com> wrote in message…
  Recent forum topics: 
Chicago Speedway/Sportsman's…
http://www.chicagotr­ibune.com/sports/chi­-090105-sportsmans…

Re: RACER Magazine Issues For…
You mean they are worth something? I just tossed a bunch of mags, Racecar Engineering, On Track…

A buck?
I have a twenty in my pocket right now. Could I have gotten the team? -- - dillon I am not invalid…

2008 predictions scored
Well, since I told Mike he needed to score his pre-season predictions, I guess I'd better do mine…
  Recent forum comments:
RE: Sources: Petty to close shop…
Agreed: he seems to be angry enough at the folks who took over that he's no longer got any association…

RE: Sources: Petty to close shop…
"Martin X. Moleski, SJ" <moleski@canisius.e­du> wrote in…

RE: Sources: Petty to close shop…
On 1/3/09 21:47, in article YqV7l.2927$BC4.1417­@nwrddc02.gnilink.ne­t…

RE: Sources: Petty to close shop…
"John McCoy" <igopogo@ix.netcom.­com> wrote in message…

RE: basic Hall-effect distributor…
N8N <njnagel@hotmail.co­m> wrote: Explain to me this "orange box." It sounds…

RE: basic Hall-effect distributor…
Nathan M. Gant wrote: The 'orange box' could care less how many cylinders you have. All it does is…

RE: basic Hall-effect distributor…
Nathan M. Gant wrote: The Orange Box is made for a reluctor pickup, not a Hall Effect. Now, it might…

RE: basic Hall-effect distributor…
N8N wrote: If he is talking about getting the first Chrysler electronic ignition used in the early…

RE: basic Hall-effect distributor…
Nathan M. Gant <ngant17@peoplepc.c­om> wrote: Okay. No. The output signal tells the…

RE: basic Hall-effect distributor…
Nathan M. Gant wrote: What will feed the coil the primary voltage it needs? What will control the…
  Moderators:
 Administrator
 Protorioris

Intermittent stumble, intake backfire on '94 Suburban

Guest 3 March 2005 17:13:04
 Symptoms: When warmed up, random intermittent stumble, most noticeable
on acceleration, sometimes with backfire through intake manifold.
Feels like the whole engine suddenly shuts down for 1/4 - 1/2 second,
repeated a few times over the course of ~5 seconds, then no problem for
another few minutes. Never happens at idle. Tachometer "twitches"
+/-100 rpm or so irregularly, continually. Slightly rough idle; has
never stalled. No diagnostic trouble codes (except DTC 12, "system
OK") are in evidence when I get the engine to blink them out on the
"Check Engine"-type light.

Just replaced the O2 sensor (first replacement in 203,000 miles),
ignition module and ignition coil. New plugs, wires, cap, rotor
installed 23,000 miles ago. Spark plugs have always been clean when
inspected and continue to look excellent. Bending and jiggling the
coil wire manually at idle doesn't cause anything. Pickup coil
inside distributor had been replaced along with ignition module 30,000
miles ago to cure the only no-start in 203K miles. The pickup coil has
a metal shield around it that can be rotated back and forth about a
half inch or so by hand. Pickup coil resistance is in-spec. Generous
dose of "dry gas' fuel additive dumped into a full tank several
weeks ago to remove water if there were any present.

Using a relatively slow laptop oscilloscope (and sampling even more
slowly at about 20 samples/second so I can stop a trace and save it
just after I notice a stumble), I find the Throttle Position Sensor
seems to be behaving the same during episodes as when normal. The MAP
output during normal operation seems to behave like I'd expect. Fuel
pressure downstream of new filter is OK and constant at 12 psig through
episodes. EGR can be worked open and shut using a vacuum source with
engine off.

I haven't even narrowed it down to fuel or ignition yet. Is there
any way to know if the 2 throttle body injectors are actually spraying
fuel at all times, for instance by measuring their current flow?
(I'm not buying a borescope, lights, and video camera to film the
spray pattern as I drive down the highway at 55. : )) Some way to
monitor the injector pressure itself?

How does an engine backfire through the intake, anyway? There's
always a flammable mixture in there so the ignition source must be
provided somehow during an episode. The service manual, when referring
to stumble on acceleration, points one toward fuel system first, then
ignition. When addressing backfires (exhaust or intake), fuel
disappears off the list of things to check. All I can imagine is both
valves open at some point with unburned fuel in-between and therefore a
combustible path between glowing carbon cinders in the exhaust system
and the intake manifold.

I don't think my laptop scope is fast enough to get at the details of
either the primary or secondary ignition waveforms. I've heard that
one can tell if a given cylinder is running rich or lean from the
secondary voltage waveform. ! I could buy a supposedly suitable scope
for about $600 from Picotech, with a little extra for current clamps
and secondary voltage pickups. I'm almost thinking that this would
be preferable to replacing parts one by one, if I could convince myself
I'd find the culprit and replace only it.

I imagine the Powertrain Control Module would be the most expensive
thing that would cause this problem; I don't know how much they sell
for. Can I set up the ignition system to run self-contained within the
distributor for a test drive to see if the problem goes away? Other
suggestions to troubleshoot the problem?

Add comment
Guest 28 February 2005 03:28:25 [ permanent link ]
 I would recommend you perform a "leak-down" test - don't bother with a
compression test - because it sounds as if you could have an intake
valve that is letting compression get by.

Add comment
Guest 3 March 2005 17:13:04 [ permanent link ]
 The problem is intermittent. Wouldn't a valve problem (except if it
were sticking open) be evident all the time? How would one diagnose an
intermittently sticking valve anyway?





sallycode@sbcglobal­.net wrote:> I would recommend you perform a "leak-down" test - don't bother with
compression test - because it sounds as if you could have an intake> valve that is letting compression get by.

Add comment
 

Add new comment

As:
Login:  Password:  
 
 
  
 
Пожалуйста, относитесь к собеседникам уважительно, не используйте нецензурные слова, не злоупотребляйте заглавными буквами, не публикуйте рекламу и объявления о купле/продаже, а также материалы нарушающие сетевой этикет или УК РФ.

CarGuru > Technology > Intermittent stumble, intake backfire on '94 Suburban 3 March 2005 17:13:04
see also:
RSC warning system, my final thread and…
Re: Favorite car in rFactor?
rasFactor
пройди тесты:
{censored}
see also:
I have a 1992 Chevy Cavalier great ...
cooling fan(s) in 91 mazda miata
1992 cabrio trans swap
  Copyright © 2001—2008 Car-Guru
Idea: Miсhael Monashev
Помощь и задать вопросы можно в сообществе support.car-guru.com.
Сообщения об ошибках оставляем в сообществе bugs.car-guru.com.
Предложения и комментарии пишем в сообществе suggest.car-guru.com.
Информация для родителей.
Write us at:
If you would like to report an abuse of our service, such as a spam message, please .