94 Truck dilemma

[Ward]

It would be usefull to know some of the actual values , such as MAP, it
should be 35-40 kpa with about a 5 kpa increase going from park to drive. 

How did you establish the degree of rich ? ST/LT values ? 
The LT (BLM) may be off by a considerable amount and still be near stoch.
Its the ST, (intigrator) value that you should be concerned about, It should
be with in +/- 2 units to be +/- 0.2 AFR ratio points.
 
The start up drill is very different for a cold start vs a warm re-start.
the cold start closed loop delay timer is set to 120 seconds, and the warm
re-start Cl timer is set to 30 seconds. 

If the 10 sec's is the break point for problems, is not due to closed loop
control and the ST/LT info is of no use.


Also which engine ? there are 4 engines ?

Ward




On Mon, 24 May 1999 23:46:14 EDT, EFISYSTEMS at aol.com wrote:

>  Hi People,
>           I have spent an entire day trying to diagnose a problem, to no 
>  avail.  When the engine starts it runs fine for approx 10 seconds,then 
> starts 
>  running extremely rich.....I then rev it up to "clean" it out and block 
>  learns and integrators are reasonable (123-125) then gradually returning
to 
>  idle all numbers stay within reason and again will idle fine now for
about 
>  3-4 seconds then whammo rich again, I was fortunate enough to have the
exact 
>  year and truck to start swapping parts with.....here is a list of what I

> have 
>  checked or changed....
>  Fuel Pressure      steady at 13 when problem is occuring or not
>  TPS voltage         steady, no intermittent highs or lows
>  Map Voltage        steady, no intermittent highs or lows......even tried

>  another
>  Coil                     coil was tried from other truck....supply
voltage 
> 13+
>  Tach lead disconnected from coil to verify no shorting of tach
>  Throttle Body and injectors were exhanged for the other truck
>  BHMX (matching)computer chip tried from other truck
>  Computer tried from other truck
>  Distributor tried from other truck
>  EGR checked for leaks and even blocked off at one point to verify idle 
> problem
>  Temp sensor checked on scanner to verify no intermittent jumps
>  Knock circuit checked on scanner to verify no intermittent jumps
>  Timing verified and verified 10 degree jump with rpm(wire pulled) still 
>  changed dist later
>  Spark plugs changed....compression checked ,all within 20 lbs of each
other.
>  Another shop had already replaced cap, rotor, wires, and plugs... to try
to 
>  fix problem.
>  Customer had just come from muffler shop and had new o2 sensor, y pipe
and 
>  cat back system installed since previous shop had told him he had a
plugged 
>  cat.
>  Stored data on the scanner of 75 frames prior to engine stumble and 25
after 
>  ....looked at every frame and compared all data points to see what
voltages 
>  had moved or even if vss had somehow gone crazy......
>  All this and no codes on the scanner (unless you let it idle poorly so
long 
>  it sets the high map voltage code)
>  The above is not in the order of which things were changed...just trying
to 
>  recall from a very frustrating day.
>  At the end of the day I got the idea it has to be some sort of a
grounding 
>  problem and the only grounds I know of on the engine are the two small
ones 
>  near the thermostat, the two on the passenger rear of engine(one goes to
the 
>  chassis from the engine and one goes to the frame)and the main battery 
> ground 
>  cable......All seems ok.....but maybe there's more I am missing
here......I 
>  then unhooked the battery for a few minutes (last ditch effort) and truck

>  started and ran normally this time for 7-8 minutes,,,not 
> seconds..........One 
>  last thing is this truck has had lots of stereo put in it and lots of 
>  capacitors for noise......if anyone can give me a spot to look tomorrow I

>  would sure appreciate it and get back to the group with my 
>  findings......Thanks in advance.
>  -Carl Summers





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