[Gmecm] SER# 1227747 ACSU promID Idle Problems
dgilbert78 at juno.com
dgilbert78
Fri Dec 8 18:27:35 UTC 2006
Hello: Have been following your problems a little. The IAC count should
never be at zero, if it gets to zero it will loose control of the idle.
You do want it however to be as low as possible without ever going to
zero. I had a lifter valley leak that was bleeding air into two cylinders
adjacent on Pass side of a 355. The way i discovered this was by pulling
the plugs after engine had been running for awhile. The leaking ports had
more carbon deposited on the plugs than the non leaking ones.(sucking
oil) Cleaned plugs and re installed and after awhile they were carboned
up again. Pulled the intake and the gasket mating surfaces had oil on
them, and should not have had any. Installed new gaskets and a skim of
red RTV. Snugged the intake bolts and beat on the manifold carb flange
with a rubber mallet. Tightened intake bolts a little and beat on it
again. Repeated the process until reached torque specs, this resolved the
problem. Also On the TBI units they have a habit of having the MAP port
carbon up. A vacuum gauge will only show a complete plug. The TBI needs
to be pulled and the MAP vacuum port verified that it is completely open,
use choke cleaner and a rod to make sure all carbon is gone. If the port
is highly restriced it will act like a carbed acclerator pump problem for
the vacuum to the MAP is delayed and lags behind vacuum demand, engine
will hessitate on quick throttle opening. Well hope some of that info
helps you in some small way. Good luck
Darryl...
On Fri, 8 Dec 2006 08:40:45 -0600 "David Allen" <davida1 at hiwaay.net>
writes:
> OK Didn't know the manifold was new! It shouldn't have carbon in it
> at all. Unless the casting is defective and there is a cross-leak
> in the EGR ports.
> AFAIK the MAP sensors are all the same IF the connector plugged
> in. The 1-bar, 2-bar and 3-bar versions are keyed different in the
> connector. As far as I know all non-turbo / non-supercharged
> engines have a standard 1-bar sensor. So the 93 'Burban sensr
> should be the same.
> Re-tightening the manifold could very well stop an internal
> manifold gasket leak, but it could also warp the manifold and cause
> worse problems.
> If the ECM is closing the IAC off all the way (down to 0) that
> tells us the idle is above the target idle RPM. The only way it can
> become above the target idle RPM is if there is air entering the
> engine from some unknown source.
> Have you disconnected abd plugged the brake booster port yet? It
> can cause a huge leak that originates under the dash in the car
> where you can't hear it.
> Maybe when you shift into gear and back to P/N, you hold the
> brakes then release them. This causes the booster to do something
> "wrong" and aggravated the leak?
> Just another crazy thought...
> David
>
>
> ----- Original Message -----
> From: "Dave Thomas" <Dave.Thomas at us.festo.com>
> To: <gmecm at diy-efi.org>
> Sent: Friday, December 08, 2006 8:25 AM
> Subject: Re: [Gmecm] SER# 1227747 ACSU promID Idle Problems
>
>
> > First of all, let me thank you for the great hints. Especially,
> the under
> > the manifold leak, I have been racking my brain on how to check
> for that
> > problem. In regards to the crumbs, hopefully, the new engine,
> new
> > manifold, and new EGR valve would not have an issue like this but
> I have
> > seen crazy stuff happen before. I will pull the EGR valve and
> look for any
> > obstruction. I might put the old one back on the engine. The Map
> sensor
> > or vacuum line may be a problem too. Do you know if the MAP
> sensor has the
> > same calibration as a slightly newer unit from a 1993 Chevy
> Suburban with
> > TBI. I own the suburban and it runs fine. I almost hate to swap
> parts
> > because you know what will happen.
> >
> > The truck sat for two years and I am unaware of the problems it
> had before
> > it quit running. However, after I got the vehicle it fired right
> up after
> > replacing the battery and I was able to move it around in the
> yard, seems
> > like it cut off some then but the big problem was the engine was
> so caked
> > with oil that the oil on top of the head could not drain back to
> the pan,
> > so when the oil reached the height of the valve guide, the oil
> would push
> > through to the exhaust on the back two cylinders and it would
> begin smoking
> > like a freight train. Then it would stop smoking and run for
> awhile
> > longer. This was evident from the wet exhaust ports on the heads
> on
> > cylinders 7 and 8.
> >
> > One other thing, I just thought of, is that the Edlebrock
> Manifold
> > (EDL-3704) only required 25 ft-lbs or torque to tighten while the
> manual
> > said to use 35 ft-lbs of torque. Maybe I could tighten the intake
> to 35
> > ft-lbs to stop a internal leakage after I check the vacuum on the
> valve
> > cover.
> >
> > Regards,
> >
> > David Thomas
> > Food & Packaging SBD Engineer
> > Festo Corporation
> > Phone: (704) 527-1427
> > Fax: (704) 527-7935
> > email: dave.thomas at us.festo.com
> >
> >
> >
> >
> >
> >
> >
>
> > "David Allen" <davida1 at hiwaay.net>
> 12/08/2006 09:01 AM
> >
>
> >
> >
> >
> > Please respond to
> > "David Allen" <davida1 at hiwaay.net>
> >
> > |--+------------------------>
> > | | |
> > |--+------------------------>
> >
>
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> > |
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> |
> > |
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> |
> > |
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> To|
> > | <gmecm at diy-efi.org>, <Dave.Thomas at us.festo.com>
>
> |
> > |
>
> cc|
> > |
>
> |
> > |
>
> Subject|
> > | Re: [Gmecm] SER# 1227747 ACSU promID Idle Problems
>
> |
> > |
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> |
> > |
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> |
> > |
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> |
> > |
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> > |
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>------------------------------------------------------------------------
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> >
> >
> >
> >
> > This may have already been addressed but... If the EGR valve
> pintle (the
> > piece that closes and opens the exhaust flow) is stuck, even a
> little, it
> > will cause similar idle stalling.
> > Sometimes the act of changing the EGR valve will dislodge some
> carbon
> > from inside the manifold passage. Then a crumb will immediately
> hold-open
> > the new EGR valve. Essentially this is causing a huge internal
> vacuum leak
> > betweent he manifold and exhaust.
> > Pull the valve and look for any junk in the pintle.
> > I guess you have checked for bad intake gaskets? Pull the PCV
> valve out
> > of the valvecover and plug the valvecover hole. Locate the other
> > valvecover hole (where the vent hose goes to the air filter) and
> place your
> > thumb over it. If you feel vacuum (in spite of the PCV valve not
> being
> > connected) then your intake gaskets may be blown/ torn on the
> bottom edge,
> > drawing air from inside the block where the carb-cleaner test will
> not
> > catch it.
> > Also a slow response from the MAP sensor due to a plugged or
> collapsed
> > vacuum hose is devastating to a TBI system. The ECM will not
> compensate
> > immediately for changes in air pressure and the engine will run
> lean or
> > rich under transient conditions.
> > If this was running before the engine was repaced, then likely
> something
> > "happened" during the engine remove / install.
> > Hope this helps!
> > David
> >
> > ----- Original Message -----
> > From: "Dave Thomas" <Dave.Thomas at us.festo.com>
> > To: <gmecm at diy-efi.org>
> > Sent: Thursday, December 07, 2006 11:00 PM
> > Subject: Re: [Gmecm] SER# 1227747 ACSU promID Idle Problems
> >
> >
> >> Here is what I have observed today. Replace ACSU prom with AMUR
> prom.
> > Ran
> >> pretty good until closed loop mode. Same problem with stalling
> when
> >> putting into gear the second time. (I.E. put vehicle in gear,
> watch Idle
> >> air counts go to zero, return to park or neutral, vehicle rpms
> raise, but
> >> IAC stays at 0, try to put vehicle back into gear and the vehicle
> cuts
> > off.
> >>
> >> I cannot for the life of me get the car to run to set the minimum
> air
> > idle
> >> setting which I believe to be 425 rpm +/- 25 rpm, with vehicle in
> gear.
> >> This is after I ground the diagnostic pins on the ALDL connector,
> wait 10
> >> seconds for the IAC motor to zero out, remove ground from ALDL
> and start
> >> engine. As I turn the idle screw down where the rpm's are around
> 500
> > rpm,
> >> the vehicle just stalls out. Recrank engine, truck runs fine
> until you
> >> place into gear, the IAC counts start counting down, if it stops
> before
> >> reaching 0, the car stalls out everytime with the new prom
> calibration,
> >> which has idle at operating temp set to 500 rpm. The old prom
> ran at 525
> >> rpm. I checked the vacuum, at one point the engine was surging
> up and
> > down
> >> and the vacuum gauge was sweeping back and forth between 15" HG
> and 17"
> >> HG.. I have a trouble shooting guide which says to look at the
> ignition
> > if
> >> vacuum varies between 1 and 2 " HG. Can the coil or ignition
> module be
> >> heating up and just dropping out at low idle speeds?
> >>
> >> I plugged the EGR,AIR vacuum port, the vapor canistor vacuum port
> and
> >> plugged my vacuum gauge into the port on the rear fitting of the
> > manifold.
> >> This left the PCV valve port, Map port, and vacuum booster
> connected to
> > the
> >> system. I then squirted TBI cleaner and WD40 around the base of
> the
> >> Throttle body, all vacuum lines and capped ports, fitting where
> vacuum
> >> booster is connected to the manifold and no leak has shown.
> >>
> >> Also checked the fuel pressure at the outlet of the fuel filter.
> It was
> >> dead nuts on 13 psi.
> >>
> >> I'm not sure why I can't get the min. idle air to 400 rpms? Any
> >> suggestions?
> >>
> >> Once again, Thanks for reading and any suggestions,
> >>
> >> David Thomas
> >> Food & Packaging SBD Engineer
> >> Festo Corporation
> >> Phone: (704) 527-1427
> >> Fax: (704) 527-7935
> >> email: dave.thomas at us.festo.com
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >
> >> "Programmer" <lwester at lincsat.com>
> > 12/07/2006 07:39 PM
> >>
> >
> >>
> >>
> >>
> >> Sent by:
> >>
> >> gmecm-bounces at diy-efi.org 12/07/2006 07:38 PM
> >>
> >> Please respond to
> >> gmecm at diy-efi.org
> >>
> >> |--+-------------------------------->
> >> | | |
> >> |--+-------------------------------->
> >>
>
>>-----------------------------------------------------------------------
-------------------------------------------------------------------------
--|
> >
> >> |
> > |
> >> |
> > |
> >> |
> > To|
> >> | <gmecm at diy-efi.org>
> > |
> >> |
> > cc|
> >> |
> > |
> >> |
> > Subject|
> >> | Re: [Gmecm] SER# 1227747 ACSU promID Idle Problems
> > |
> >> |
> > |
> >> |
> > |
> >> |
> > |
> >> |
> > |
> >> |
> > |
> >>
>
>>-----------------------------------------------------------------------
-------------------------------------------------------------------------
--|
> >
> >>
> >>
> >>
> >>
> >> Diagnose from the latest calibration first...but your "0" IAC
> count is
> >> definitely indicating unmetered or uncontrolled air.
> >>
> >> Lyndon.
> >>
> >> ----- Original Message -----
> >> From: "Dave Thomas" <Dave.Thomas at us.festo.com>
> >> To: <gmecm at diy-efi.org>
> >> Sent: Thursday, December 07, 2006 8:41 AM
> >> Subject: Re: [Gmecm] SER# 1227747 ACSU promID Idle Problems
> >>
> >>
> >>> PCV Valve - Brand new from GM
> >>> EGR Valve - Brand new from GM ( I also tried removing the vacuum
> hose
> > and
> >>> plugging the vac hose to eliminate the switch leaking)
> >>> I plan on checking the fuel pressure, exhaust backpressure and
> install
> >> new
> >>> AMUR prom. I am going to try to reset the min. air at idle, and
> I have
> >>> diacom that I will try to record some data. I also plan on
> rechecking
> >> the
> >>> MAP sensor and test the vacuum with a pressure gauge to see if
> there are
> >>> any inconsistencies.
> >>>
> >>> I have not replaced the fuel pressure regulator, but I would
> expect the
> >>> fuel pressure test should show any problems with it.
> >>>
> >>> Thanks for your suggestions,
> >>>
> >>> David Thomas
> >>> Food & Packaging SBD Engineer
> >>> Festo Corporation
> >>> Phone: (704) 527-1427
> >>> Fax: (704) 527-7935
> >>> email: dave.thomas at us.festo.com
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>> "Programmer" <lwester at lincsat.com>
> >>> 12/07/2006 10:30 AM
> >>>
> >>>
> >>>
> >>>
> >>> Sent by:
> >>>
> >>> gmecm-bounces at diy-efi.org 12/07/2006 10:26 AM
> >>>
> >>> Please respond to
> >>> gmecm at diy-efi.org
> >>>
> >>> |--+------------------------>
> >>> | | |
> >>> |--+------------------------>
> >>>
> >>>
>
>>>----------------------------------------------------------------------
-------------------------------------------------------------------|
> >
> >>
> >>> |
> >>> |
> >>> |
> >>> |
> >>> |
> >>> To|
> >>> | <gmecm at diy-efi.org>
> >>> |
> >>> |
> >>> cc|
> >>> |
> >>> |
> >>> |
> >>> Subject|
> >>> | Re: [Gmecm] SER# 1227747 ACSU promID Idle Problems
> >>> |
> >>> |
> >>> |
> >>> |
> >>> |
> >>> |
> >>> |
> >>> |
> >>> |
> >>> |
> >>> |
> >>>
> >>>
>
>>>----------------------------------------------------------------------
-------------------------------------------------------------------|
> >
> >>
> >>>
> >>>
> >>>
> >>>
> >>> PCV valve correct ?
> >>> EGR leaking ? (IS this the correct EGR valve from GM ?)
> >>> The updated PROM ACSU to AKAJ to AMUR had several related TSB's
> ...and
> >>> these
> >>> updates fixed those concerns.
> >>> TSB 88-180-6E AKAJ
> >>> TSB 88-T-109
> >>> TSB 88-T-25
> >>> TSB 88-87-657-109
> >>> TSB 88-88-657-108AMUR
> >>>
> >>> Lyndon.
> >>>
> >>> ----- Original Message -----
> >>> From: "Dave Thomas" <Dave.Thomas at us.festo.com>
> >>> To: <gmecm at diy-efi.org>
> >>> Sent: Tuesday, December 05, 2006 6:34 AM
> >>> Subject: [Gmecm] SER# 1227747 ACSU promID Idle Problems
> >>>
> >>>
> >>>>
> >>>>
> >>>>
> >>>> I have a 1987 GMC V1500 4WD truck with a 700R4 transmission.
> The Prom
> >> ID
> >>>> is ACSU. I have replaced the original engine with a GM Factory
> Crate
> >>>> Replacement for VIN K engines. All stock except for an
> Edelbrock
> >>> EDL-3704
> >>>> manifold. I am having some problems with the idling of the
> engine and
> >>>> stalling when put into gear. I have noticed on a cold start
> that
> >>>> everything seems to be fine with the exception of BLM of ~154.
> As the
> >>>> unit
> >>>> warms up to temperature, I notice the engine will start to
> reduce the
> >>> idle
> >>>> speed trying for a idle speed of ~625 rpm. At this point the
> IAC
> > counts
> >>>> are hovering around 40 counts. When I put the truck in gear,
> the IAC
> >>>> counts start reducing along with the rpms until the rpm reaches
> ~525.
> >> At
> >>>> this point, the IAC counts are usually at 0. When the vehicle
> is
> >> shifted
> >>>> back into park or neutral, the idle will raise back up but the
> IAC
> >> counts
> >>>> will remain at 0. When the vehicle is put into gear the second
> time,
> >> the
> >>>> engine will stall and die. I have tried setting the minimum
> Idle on
> > the
> >>>> throttle body to allow the IAC to remain open, however 3-5
> counts is
> > the
> >>>> best I have ever achieved but this did not correct the
> stalling. Also,
> >> I
> >>>> have tried the service procedure for checking minimum idle air
> at 425
> >>> rpms
> >>>> in gear with the IAC unplugged. I cannot achieve this number
> without
> >> the
> >>>> vehicle stalling. I have sprayed TBI cleaner around the
> intake
> >> manifold,
> >>>> tbi gakset, all vacuum connections and I have not seen the idle
> raise
> >>>> showing a vacuum leak. Also, after stalling the vehicle is
> very hard
> > to
> >>>> start and keep running unless you rev the engine up above 1500
> rpm and
> >>> let
> >>>> of the throttle very slowly. Also, occasionally the engine
> will surge
> >> up
> >>>> and down (50-100 rpms) but not too extreme.
> >>>>
> >>>> We replaced the rotor, cap, wires, spark plugs, knock sensor,
> O2
> > sensor,
> >>>> new EGR valve, PCV valve, cleaned the throttle body, and all
> new
> >> gaskets
> >>>> during the engine swap. The MAP sensor, throttle position
> sensor,
> >>>> ignition
> >>>> module, coil, EGR switch, are from the old engine. I have
> also
> > swapped
> >>>> the IAC motor with one that is known to be good with no change.
> The
> >>>> original engine was gunked up and not allowing the oil to flow
> back
> > from
> >>>> the head, after some time of running, oil would enter the
> exhaust valve
> >>>> guides on the number 7 and 8 cylinders causing the spark plugs
> to foul.
> >>> I
> >>>> haven't checked the back pressure from the exhaust system/ cat
> but it
> > is
> >>>> suspect. I also plan to check the Fuel pressure to see if the
> unit is
> >>>> functioning within specifications (9-13 psi). I have ordered
> an
> > updated
> >>>> prom with the bin file AMUR which seems to be the latest eprom
> however
> > I
> >>>> don't really expect this will fix the problem.
> >>>>
> >>>> TPS = 0.66 volts at idle
> >>>> Map at idle was in spec.
> >>>>
> >>>> Everything seems to be working fine but obviously something is
> not.
> >>>>
> >>>> Any information greatly appreciated,
> >>>>
> >>>> David Thomas
> >>>> Food & Packaging SBD Engineer
> >>>> Festo Corporation
> >>>> Phone: (704) 527-1427
> >>>> Fax: (704) 527-7935
> >>>> email: dave.thomas at us.festo.com
> >>>>
> >>>> _______________________________________________
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