GM TBI Question

ajbirkennewaccount

Well-Known Member
Joined
Mar 21, 2005
Location
Raleigh
I have a 79 Jeep J20 that the PO converted from carb to TBI. He did a great job from what I can tell (which isn't much!).

Chevy 1227747 computer and with a 28 pin reprogrammable chip from moates.

I am getting intermittent rough running after warming up and pulled a 51 code

CODE 51
Trouble Code 51 indicates that the ECM sensed a fault in the MEM-CAL. On power-up, the ECM does a checksum of the MEM-CAL to ensure the MEM-CAL integrity is good. If the calculated sum does not match the sum in the MEM-CAL, the ECM will hardcode 51 and enter Back-Up mode, since the ECM cannot know where in the MEM-CAL the fault lies.
Code 51 is set when:
? the actual MEM-CAL checksum does not match the value in the MEM-CAL
Possible causes include:
1. Incorrectly installed MEM-CAL module
2. Defective MEM-CAL module
3. Defective ECM

I don't know Sh*t about TBI. I'm wondering if the 28 pin chip came loose since it had to be soldered in?

What will happen if I just go buy a new 1227747 computer and plug it in?

Thanks in advance. I think it's great that it can be reprogrammed, but I'm not really sure I want to buy all the junk needed to reprogram etc. I just want to drive the darn thing and not have it run like crap.

Thanks in advance!!!

Adam
 
It'll need a new prom chip too if you get a new computer. The reman computers don't come with a prom. Are you sure the po soldered the prom to the ecm circuit board or is it attached to the stock prom socket. It'll throw a code 51 if the prom is bad or if its loose. The 28 pin chips can be made to fit the 24 pin socket but it doesn't fit good in my opinion. The way I set mine up was to remove the stock socket and solder in a 28 pin zip socket. Then a stock prom or a reflashable 28 pin can be made to work.
 
Thanks for the response. I think the chip was just loose. It has the quick switch so you can switch chips easily and it wasn't seated all the way. The po removed the old socket and soldered on the 28 pin socket.

Hopefully that's it!
 
Sounds like it. That's the same thing I did to my old ecm. I removed the original socket and soldered on the zip socket with the lever. If it was loose that'll cause your code 51 and it'll go to limp in mode which runs just good enough to pull off the highway and wait for a tow, LOL

You can cut a square of foam like from a seat cushion and put it between the chip and the metal cover to help keep it seated in the future.
 
Sounds like it. That's the same thing I did to my old ecm. I removed the original socket and soldered on the zip socket with the lever. If it was loose that'll cause your code 51 and it'll go to limp in mode which runs just good enough to pull off the highway and wait for a tow, LOL

You can cut a square of foam like from a seat cushion and put it between the chip and the metal cover to help keep it seated in the future.

BAM! nice call. I like it when stuff is simple. I really should learn more about this setup though!
 
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