Quote:
Originally Posted by mwebb
newer GM products use DFCO as the time to test EGR of course on many of those systems the MAP sensor is just a tag along klingon for the purposes of the EGR test and has little to zero fuel trim authority
i do not see any thing related to that EGR test
in your stuff ? maybe that system is too primitive ?
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Can you post this EGR test logic? I'd like to take a look at it, as I've never seen this particular strategy for the EGR diagnostic.
DFCO would seem to me to be a very poor time to test for EGR operation due to the relatively low exhaust pressure, that is if the MAP you're talking about is actually taking pressure measurement only from inside the intake manifold.
I have seen systems with a pressure transducer that measures the pressure in the EGR delivery tube as compared to the pressure inside the intake manifold. Basically the algorithm looks for an approximate offset in pressure that coincides at each point tested. If the manifold pressure changes by 10% (and EGR is in operation), then it expects the pressure in the EGR delivery tube to change by approximately 10%, give or take a window for slop.
Are you saying a test like this (above) happens during DFCO?
It's hard to imagine since DFCO is often very brief, and as soon as DFCO is initiated, the IAC starts reacting by opening up to reduce manifold vacuum.
I'd just like to take a look at that logic.
The code in my truck is indeed "primitive", though the EGR diag is pretty much the same as what GM used in the larger codes all the way up to the 1998 model year. It basically tests the O2 integrator offset during a steady load cruise condition once above 45 MPH.
Here are the calibration qualifiers for the EGR test on my truck:
Quote:
;---------------------------------------------
; ERR 32 >> EGR <<
;---------------------------------------------
LD52B FCB 30 ; 30 SEC DIAG CYCLE TIME ENABLED IF IN MAP WINDOW
LD52C FCB 80 ; 40 Kpa LO LOAD DISABLE
LD52D FCB 208; 87 Kpa HI LOAD DISABLE
LD52E FCB 17 ; 6.6% LO TPS LIMIT (ENABLED IF IN TPS WINDOW)
LD52F FCB 64 ; 25% HI TPS LIMIT (ENABLED IF IN TPS WINDOW)
LD530 FCB 250; 98% EGR ON THRESHOLD
LD531 FCB 25 ; 2.5 SECs EGR ERR DELAY TIMER
LD532 FCB 3 ; 3 COUNTS FAIL COUNT THRESHOLD
LD533 FCB 10 ; 3.9% TPS, CHANGE TO DISABLE TEST
LD534 FCB 28 ; 2.8 Secs TEST DURATION
LD535 FCB 4 ; 4 COUNTS, INTEGRATOR DIFF FOR EGR OK
LD536 FCB 45 ; 45 MPH REQUEST TO ENABLE TEST
LD537 FCB 255; 99.6% EGR D.C, DECREMENT FOR TEST IN WORK (454cid TYPICALLY 50%)
;---------------------------------------------
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