ECU & PROM Identification

[1967Ragtop]

Good Morning,

I'm hoping someone out there can help me determine if the PROM in my ECU is the correct one. The ECU looks to be a remanufactured GM unit and the large blue label has it listed as number 7-7747 and DC Code of 1012MT. There is another sticker on the side of the metal case where I see a sticker with the number 122937774706632 REMFG and after removing the little cover, I can see a peel and stick label has been applied to the board. It reads 07774700122830057 REMFG.

If this is the correct computer for my truck, and who knows what the previous owners have done to it, should it have a PROM that reads AMUC?

It's an 87 V10 305 TBI with a TH400 Transmission and a 3:42 gear in the back end. I use WinALDL to monitor things and I keep getting a rich flag and it won't pass emissions. I guess I'm hoping someone put the wrong PROM in it and that's the cause.

Thanks in Advance,
Mark

 

[Sgt Gus]

Well, you likely have the right ECU. 7747 is common. To dig into chip, prom info and files, gearhead-efi would probably be your best bet. HOWEVER, I would start elsewhere.
Did PO put an adjustable fuel regulator? And did you check the fuel PSI?
There is alot of troubleshooting to tbi using search feature. Also, a resource page for downloading emissions and other manuals.
Kind regards,
Gus

 

[gmbellew]

Is there a sticker anywhere behind the glove box that also has the original PROM code on it? Not 100% sure, but seems like I remember that on my 90 burb. But I agree with above, sounds like the computer is probably right.

If you are running rich, is the ECM pulling fuel (as evidenced by the long and short term fuel trim)? Things have to be SUPER rich before it will actually throw a rich code. And even then, I don’t think it will ever throw that at idle.

 

[1967Ragtop]

Here are a few photos.

 

[YakkoWarner]

Also, is WinALDL showing you fluctuation on the O2 sensor readings? The ALDL data stream isn't fast enough to track the O2 sensor in real time, but if it never changes or only very slightly over several minutes it could mean your O2 sensor is not reporting accurately. If you pull a couple plugs, do they look black and sooty (which they should if the engine is truly running rich). If they look clean and have a normal brownish tinge to them, there is a good chance the O2 sensor is throwing a false reading to the ECU.

 

[gmbellew]

If you are monitoring data in winaldl, what are the BLM and INT numbers? That is the actual fuel trims. There is a rich/lean flag that should vary from rich to lean as the computer adjusts as fast as it can based on O2 feedback. Just failing emissions isn’t enough to throw a code. If it is failing emissions, I’d look at tune up parts, catalytic converter status, etc. but I’d monitor the fuel trims first and see what’s up first. CTS and MAP play into fueling also, with refinements coming from the O2 once you are in closed loop. So looking at the info from those will be insightful also.

 

[1967Ragtop]

Wow! That's a lot of responses in a short amount of time.

No adjustable fuel regulator, but both tanks have new sending units/pumps in them and the switching valve works as it should.

I do use WinAlDl and from what I gather, nothing looks too lean or too rich, but to be honest, I've never done datalogging. I've only watched the values as it was idling. It's never thrown a code for being too rich (I think), but I guess the thing that had me worried was seeing a steady check next to #44 O2 Lean while on the Error Codes screen (Maybe it did throw a code?) and a reoccurring check would appear and disappear next to Rich Flag when viewing Flag data. If that flag is related to the adjustments made by the 02 sensor, whose signal does seem to update every second or two, I guess things are operating as they should.

The plugs actually looked pretty good. None of them looked black or sooty. They had a nice brown appearance to them and the truck runs really good, but it does seem to burn a lot of fuel.

And after replacing the cat and bumping up the idle to 1050, it passed emissions earlier today. Before making any changes the HC's and CO were both too high for the Delaware standards. Not knowing the history of this truck gave me the idea that maybe someone replaced the PROM with either a custom one or possibly one from a larger motor that would demand more fuel. When I got it, it had a Holley TBI unit on it and they flow more air and fuel than the stock one I replaced it with.

This computer stuff is a bit foreign to me, but if this seems to be operating as it should, let me know.

Thanks again for the help,
It's greatly appreciated.
Mark

 

[YakkoWarner]

If you are monitoring data in winaldl, what are the BLM and INT numbers? That is the actual fuel trims. There is a rich/lean flag that should vary from rich to lean as the computer adjusts as fast as it can based on O2 feedback. Just failing emissions isn’t enough to throw a code. If it is failing emissions, I’d look at tune up parts, catalytic converter status, etc. but I’d monitor the fuel trims first and see what’s up first. CTS and MAP play into fueling also, with refinements coming from the O2 once you are in closed loop. So looking at the info from those will be insightful also.

Also depends on how the inspection rules for the individual state - here in Texas they used to do a tailpipe sniff on pre-ODB2 vehicles but having a check engine light on was an automatic fail even if the tailpipe readings were in spec.