[Gmecm] SER# 1227747 ACSU promID Idle Problems
David Allen
davida1
Fri Dec 8 13:58:14 UTC 2006
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
>
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> | <gmecm at diy-efi.org> |
> | cc|
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> | Subject|
> | Re: [Gmecm] SER# 1227747 ACSU promID Idle Problems |
> | |
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>
> 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
>>
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>> To|
>> | <gmecm at diy-efi.org>
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>> |
>> cc|
>> |
>> |
>> |
>> Subject|
>> | Re: [Gmecm] SER# 1227747 ACSU promID Idle Problems
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>>
>>
>>
>> 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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>>>
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