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Fuel pump Prom programming


rogold99

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Maybe KDirk or one of our other resident experts can answer this. I have read on other posts that a PROM is programmed for the fuel pump prime cycle time when the ignition key is turned on. I think mine is set for 2 seconds, and I would like to change it to a longer run for easier cold starting. My questions are 1. Is it possible to check by using the CRT to what PROM I am using, and 2. Does anyone here offer a new or used PROM with an updated programming for sale, or possibly reprogram the PROM I have?

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I've not looked into this, but the fuel pump prime time is probably represented as one or two bytes in the code. Problem is knowing what data to change, and what unit of measure it is in.

Perhaps Padgett may have some insight on this, though the BCM firmware has never been disassembled to my knowledge. ECM has been well documented.

If the address of the prime timing value can be identified, I could change it and burn a new EPROM. Reprogramming the original is a waste of time; 25 year old UVEPROMS are too flaky to erase and reuse in my experience.

A new 28 series EEPROM can be substituted and is inexpensive as a blank, so no reason not to start with a fresh part.

KDirk

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Guest Mc_Reatta

Believe function is totally controlled by ECM only, so there might be documentation of how to change. I would expect value to be a number of CPU clock cycles that add up to 2 seconds or so real time. So value could be raised to max allowed by number of bits designated for this in memory.

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My ed99 shows 2204, looks like the TSB is calling for a 1094. So I should be looking for a ECM with a different PROM. I do have a few spare ECM's I robbed out of the recent "U-Yank-It" cars. Should these numbers be printed on the PROM somewhere, or will I have to install the ECM's to check? Thanks for the help.

Edited by rogold99 (see edit history)
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The ECM will have a sticker on it that shows what the factory installed PROM letter code. The MEM-CAL inside will also have a square silver sticker on the EPROM (within the blue/brown MEM-CAL housing) that shows the letter code. Go by this one, not the one on the outer shell of the ECM as it the MEM-CAL may have been changed at some point.

Problem is, I do not believe the numeric identifier is shown on either the sticker on the ECM casing, or the PROM sticker inside the MEM-CAL, so you will need to either:

1. Get an ECM from a 1989 Reatta known to have the revised MEM-CAL -or-

2. Find a ROM image of the 1989 "1094" MEM-CAL EPROM that can be burned to a chip. Then you have the undue pleasure of having to remove the old EEPROM from the MEM-CAL carrier and install the newly burned chip. Been there and done that, and frankly, it is a dog of a project. The factory EPROM is soldered into the carrier, and thus needs to be VERY carefully removed by breaking the solder joints without destroying the contacts in the carrier.

Then (this is what I have done anyway) solder in a new 28 pin DIP IC socket (with machined pins, cut shorter than stock to reduce the sockets mounted height) onto the carrier contacts. The soldering has to be done very precisely with a fine tip rig so that you do not bridge adjacent contacts with solder. Then the new chip (EEPROM) can be put in the socket, the blue cover snapped on and the whole thing can be buttoned up and tested. I should also mention that the backup logic (small circuit board with pins mounted next to the chip) needs to be pushed away slightly to clear the socket.

Yes, the new chip can just be soldered in sans socket without any clearance issues, but I like to have it easily serviceable later on if a new program should need to be burned in, thus the need to socket the chip within the MEM-CAL. This makes it easy to pull, put in the burner and erase/reprogram it should I ever want or need to.

KDirk

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Thanks for the info KDirk. I just checked my spare ECM's , one had the 2204 again, and one had a 1304??. I looked up the GM part #16141300 (from the TSB) on GMPartsdirect for $41.70 plus shipping, I may call them to see if it is still available. Or search Ebay and the interweb until something pops up. I guess in the meantime I could run 12V from the battery, thru a switch hidden under the dash and connect it to the fuel pump prime connector under the hood. Sounds kinda redneck I know, but it would save wear and tear on the ignition switch.

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I *think* the one marked 1302 may be the ED99 1094 but would need to install to be sure:

[TABLE=width: 961]

<TBODY>[TR]

[TD][/TD]

[TD]ASSU</SPAN>[/TD]

[TD][/TD]

[TD=align: right]1989</SPAN>[/TD]

[TD=align: right][/TD]

[TD=align: right]16141300</SPAN>[/TD]

[TD=align: right]1228253</SPAN>[/TD]

[TD=align: right]1302</SPAN>[/TD]

[TD=align: right]1094</SPAN>[/TD]

[TD] EB</SPAN>[/TD]

[TD]LN3</SPAN>[/TD]

[TD=align: right]3.8</SPAN>[/TD]

[TD][/TD]

[TD]AUTO</SPAN>[/TD]

[TD]F79</SPAN>[/TD]

[/TR]

</TBODY><COLGROUP><COL span=5><COL><COL span=9></COLGROUP>[/TABLE]

If so, I have the .bin. I also have all the equipment to program but have been having very poor success with the 20+ year old UVPROMs lately so if the new one is available U$50 is not expensive. Otherwise as mentioned you need to replace the old PROM (a 27C256) which is a pain.

Edited by padgett (see edit history)
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Thanks Padgett and Dave, I rechecked my ECM'S, the one is a ASSU 1302, not 1304 as I previously posted (sticker is hard to read). So I will try a swap this weekend and see what happens. Should I swap the whole ECM or just try the PROM first?

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  • 2 weeks later...

Well I did the swap (prom and the ECM) and the car does start a lot better. The pump runs longer now, maybe 3 seconds instead of 2 seconds, but it does the trick. The ED99 readout on the CRT data does read 1094 after the swap. Thanks to all for the assistance!

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