New member needs help

Scot Sealander Sealand at clarityconnect.com
Fri Nov 20 15:19:12 GMT 1998


J Norris wrote:

> I finally broke down and got a Diacom and recorded the event.  When it 
> happened at WOT, my O2 reading dropped to 0 and my integrator climbed 
> to 180 while my inj. pulse width was 9.5ms or so.  

There is some good information there if you know how to use it. Keep
reading.


> My TPS voltage was .55 at idle and 4.98 at WOT.  The ECM will not go
> into open loop PE mode at this high of a voltage.  At this high 
> setting, the ECM was trying to maintain a 14.7:1 air fuel ratio.  I 
> readjusted the TPS to 4.63 volts max and BINGO!  The ECM goes into open 
> loop rich condition.

"Trying to maintain" is clear.  But look at that O2 volts!  Look at the
integrator.  The ECM is seeing a lean condition *WHILE IN CLOSED LOOP*.
It is trying to so something about it (maxing the int), but it can't do 
enough.
 

> Now, the million dollar question is could the high TPS voltage at
> WOT cause the lean condition I am experiencing? 

It can at minimum contribute to it, and it probably the cause.  The ECM
listing has high and low voltage limits for the raw A/D value the TPS 
supplies.  The exact values for these limits and associated test 
conditions will vary with the particular calibration used. 

So here is the important thing. If the A/D result it is out of the
"normal" range, it IMMEDIATELY sets the TPS bad flag, but may not set
the error code if the bad value isn't present long enough.  If the TPS is 
flagged bad, a substitute default value is used, and this value is not 
enough to set PE mode.  So it stays in closed loop, and *will not* enter 
PE mode. 


> The fuel pressure is fine (37 psi at idle 45 psi at WOT) but I never 
> had an opportunity to check it while the seemingly lean condition was 
> occurring.  

The psi delta is right.  The 45 psi sounds familiar, didn't someone just
post that there injectors shut down at 45 psi?  Lean at WOT?  Hmmm.  Got
those kind of injectors?


>From another post:

> Its an aftermarket chip but the stock one reacts the same way.  

They should.


> Everyone I talked to says that there is no reason the ECM should leave 
> PE mode at that voltage. 

Are we still talking TPS voltage above 4.9 or so? If so:

Everyone?  Now you know who NOT to ask. :-)  Big grin!  As said earlier,
the ECM *will* leave PE if the TPS is so high that it is out of the
normal range.  


> Something else my be causing it.  The guy who made my prom, Fastchip,
> suspects the MAF.  He said the ECM will substitute values it thinks 
> airflow should be when the MAF is bad.  He also told me that swapping 
> out MAF's is the only way to tell.

BTW, what are your MAF airflow values at WOT?  

Ok, now are we still talking lean at WOT?  I thought I read that AFR was
correct once the TPS was reset to the proper range.  If it was, then the 
MAF is probably Ok.

I still see some concern for the lean condition when not in PE.  There
may be a simple explanation, but if it runs right with the TPS set where
it belongs.....use it.
 
If I don't understand this correctly, keep typing!

Scot Sealander    Sealand at clarityconnect.com




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