[Gmecm] SER# 1227747 ACSU promID Idle Problems

[Programmer]

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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