PROM GUIDE

GM MEMCALs

The MEMCAL is a large brown and blue 'T' shaped plastic carrier that plugs into a special 50 pin socket inside the ECM. Half of the MEMCAL is an EPROM [27C128 - 128Kbits - 16K bytes, 150ns or better] that contains the computer software and look-up tables for a specific vehicle. The other half of the MEMCAL is that neat little board covered in "squishy stuff" and a couple of chips beneath it. That is the Electroninc Spark Control [ESC] module for that vehicle. The ESC "listens" to the knock sensor and sends a yes/no signal to the ECM to indicate the presence of knock. As you can imagine, an incorrect PROM can cause a car to run bad, or not at all. An incorrect ESC module can tell the ECM that knock is there when it in fact isn't, or worse yet, NOT tell the ECM when knock is present.

Memcal from a Saudi Syclone

The following is a list of MEMCALs that have been used in the Syclone and/or Typhoon. The Scan ID is the 16-bit number that is transmitted to a scan tool as a PROM ID . The Delco ID is the letters/numbers that are on the Delco sticker on the MEMCAL. The Part Number is the AC Delco (GM) part number for that MEMCAL.

Scan ID

Delco ID

Part Number
3051 AXXA 3086 16163085
3961 AYBM 4052
3961 AYBM 4053 16164052
3971 AYBN 4175 16164174
8581 AWXJ 9137 16159136
831 BBZA 1576 16181575
841 BBZB 1580 16181579
0 DOAC 6502

The AXXA 3086 was in the early Syclones. GM issued a "campain" PROM, AYBM 4052, to address some driveability issues. The AYBM 4053 is the same as the AYBM 4052, only it has a different Date Code and Sequence Number. The AYBN 4175 has been found in both late Syclones and early Typhoons. No details on the AWXJ 9137 have been obtained and it has been discontinued by GM. The BBZA 1576 has been found in '93 Typhoons with the BBZB 1580 being the current GM MEMCAL for the Typhoon. The DOAC 6502, also known as the 'NM8', belongs to the MEMCAL of the Saudi Syclone and Typhoon and is designed to run leaded fuel without an Oxygen (O2) sensor.

The graph above shows the timing characteristics of all the stock chips where the timing figure for each RPM band is an average over the (0 - 190kPa) pressure range for that band. Note how the BBZB1580 gives more timing overall, particularly lower in the RPM range.

The above graph shows the timing figure for the maximum Manifold Air Pressure (MAP) reading of 190kPa. This timing advance is applicable when at Wide Open Throttle (WOT) and the boost is at normal or above normal maximum levels. Note that the currently available and late market chips are running between four and eight degrees less timing at WOT, presumably as a safety measure to reduce the risk of detonation (And failure within the warranty period... ?)

Compatible ECMs

GM put the Sy/Ty ECM [part 1227749] in only a few vehicles. This is the list of vehicles that contain the 1227749 ECM... again, from the Snap-On book.

Don't confuse the ECM with the MEMCAL that is plugged into the ECM. Any of the above ECMs will work in a Sy/Ty, but only a Sy/Ty MEMCAL will work properly in a Sy/Ty.

Aftermarket PROMs

This is a brief table of some of the aftermarket PROMs seen. Please note that vendors are constantly upgrading their products, so don't assume that the following is exactly what will be in a PROM you would receive from that vendor today. No conclusions about the vendor's ability to engineer a PROM are made, simply that facts, as seen, are reported here.

Vendor Part Ref. PROM
ID		 IC Pump
On		 RPM fuel
shutoff		 MPH boost
disable		 Max Retard
(degrees)		 EGR enable
Dynotech - 3961 140 F 5328 116 12.7 176 F
ATR SY137 (pit bull - street) 3961 66 F 5723 200 12.7 176 F
ATR SY138A (strip) 831 166 F 5723 200 15.5 140 F
ATR SY138E (strip 40lb) 831 66 F 5723 200 15.5 140 F
Kenne-Bell 8026 (street) 65535 186 F 7447 120 0.0 305 F
Kenne-Bell 8026-40 (street- 40 lb) 65535 186 F 7447 120 0.0 305 F
Kenne-Bell 8027-40 (strip-40 lb) 65535 186 F 5553 254 6.3 176 F
Superchips - 831 185 F 5119 116 12.7 140 F
JET Custom Lee Howie 3961 185 F 5328 116 12.7 176 F
Hypertech - 3961 140 F 5328 116 12.7 176 F
Conley Magnum 831 66 F 5723 200 15.5 140 F

Disclaimer
It is generally understood that it is not illegal to dump a PROM and tell people what the general make-up is, as long as an exact copy is not made for personal or commercial use (Sold or given away). This page is here to help buyers make informed decisions.

This page does not claim to be all-inclusive and all-knowing and information shown is supplied "as is" with no confirmation given on the accuracy.

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