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  #16 (permalink)  
Old 12-13-2010, 05:34 PM
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Repair the codes in the order they appear. A code 51 for a prom failure is exactly that a failed prom.Replace it with the latest update and retest.Plain and simple.
You can actually damage the ecm by installing the prom too roughly(actually easy to do).
If you vehicle has a factory vats system that could be part of the trouble .
the junkyard ecm may not be "learned " for the vehicle you are using it for.It wont start if that is the case.
If your ignition key has a little black pellet on it, that is for the anti theft system.
The code 12 is just to let you know 2 things
1 there is no distributor reference pulse (because engine is not running OK)
2 self test output is starting and working
If the code 51 was the original problem with the vehicle, put in a prom.
Go to CHEBBY, take the vin (on the registration) and the old prom number.

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  #17 (permalink)  
Old 12-13-2010, 05:47 PM
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Quote:
Originally Posted by Elkyblack
Well I know its not plugged exhaust because it has brand new exhaust.
I did not adjust tps or iac when I installed. Could it be that the ecm or prom is bad and isn't comunicating with the Iac? I am getting the 51 code. Also the temp gauge isn't working inside, would this cause system to malfunction as well.
The temp gauge has nothing to do with it as it has a completely seperate sensor from the computer
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Old 12-13-2010, 07:33 PM
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Quote:
Originally Posted by latech
Repair the codes in the order they appear. A code 51 for a prom failure is exactly that a failed prom.Replace it with the latest update and retest.Plain and simple.
You can actually damage the ecm by installing the prom too roughly(actually easy to do).
If you vehicle has a factory vats system that could be part of the trouble .
the junkyard ecm may not be "learned " for the vehicle you are using it for.It wont start if that is the case.
If your ignition key has a little black pellet on it, that is for the anti theft system.
The code 12 is just to let you know 2 things
1 there is no distributor reference pulse (because engine is not running OK)
2 self test output is starting and working
If the code 51 was the original problem with the vehicle, put in a prom.
Go to CHEBBY, take the vin (on the registration) and the old prom number.
Ok I actually went to Chevy today, and was told they discontinued the proms. Tbichips.com said they can burn me a completly stock replica of the oem prom for $56. The question is once I receive this prom what would be the procedures? Should I reset the Iac or will it set on its own? Is there anything special I should do, or should I just pop in this chip and start it up?
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Old 12-13-2010, 08:36 PM
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put it in and see how it does. If you have any questionable idle function hot or cold, you will probably have to perform a Minimum Air rate Adjustment.See how it does first, if you have to do the Min air rate post it here and well hook you up.No sweat.
Hint: the tps will be adjusted during the process ,so try it as is first just to see.
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Old 12-13-2010, 10:32 PM
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Did you ever check powers and grounds to ECM? I know I posted this already just didn't know if you did it. You have already spent a lot of money on parts that didn't fix anything. I am just trying to make sure all of the obvious is checked first. Check connectors and wiring, if you don't have a digital volt ohm meter get one and learn how to use it. You may find out that it is the prom that needs to be replaced but at least you will know without a doubt that everything else is working the way it is supposed to also.

Kurt
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Old 12-14-2010, 10:31 AM
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The suffix after the '299 shouldn't matter and most of those proms have been discontinued. If you know a pretty good parts guy you'll find that they can usually still find one in stock at a dealer if they search hard enough, but if they've already told you they don't have it, you're probably not going to get them to look.

I probably have a copy of a '299 prom (though I had a '91 K1500 Blazer with one in it), though I don't know if i have any chips floating around (often you can find them off older computer hardware, but it's easier to find the newer, larger chips used in the TPI and other port injected cars).

A 305 TBI ecm/prom should have started the 350 just fine, I'd bet that most people couldn't even tell that it had the wrong calibration in it (the 305 cars got smaller injectors so the calibration in the prom should be similar). Sounds like there is some other problem with that one.

FWIW, there is a whole series of TBI ecms that were used from the late 80's through the early 90's that are pin compatible with the '299, meaning that with the right prom installed you could just plug it in and it will run fine. The most common and best documented is the '7747 that was used in the late 80's through early 90's full size trucks (there is also a '6747 which is very similar but was only used in similar vintage TBI cars which had an additional sensor which is not as easy a swap). If I was going to replace both ecm and prom I would grab one of those (that is actually what I did in my blazer since I wanted to mess with tuning and didn't feel that there was enough information about the '299 and didn't want to reinvent the wheel). Besides the programming thing (and there are a lot of easily available programs for that one, like at one point I was burning some coolant and fouling the O2 sensor and needed to drive it so I found a copy of the similar vintage, mexican suburban code for the '7747 which did not have an O2 sensor rather than editing it out of my existing program) the other reason that I swapped to the '7747 was that I found that some scan tools didn't report back data from the '299.
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  #22 (permalink)  
Old 12-14-2010, 03:43 PM
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Quote:
Originally Posted by Silverback
The suffix after the '299 shouldn't matter and most of those proms have been discontinued. If you know a pretty good parts guy you'll find that they can usually still find one in stock at a dealer if they search hard enough, but if they've already told you they don't have it, you're probably not going to get them to look.

I probably have a copy of a '299 prom (though I had a '91 K1500 Blazer with one in it), though I don't know if i have any chips floating around (often you can find them off older computer hardware, but it's easier to find the newer, larger chips used in the TPI and other port injected cars).

A 305 TBI ecm/prom should have started the 350 just fine, I'd bet that most people couldn't even tell that it had the wrong calibration in it (the 305 cars got smaller injectors so the calibration in the prom should be similar). Sounds like there is some other problem with that one.

FWIW, there is a whole series of TBI ecms that were used from the late 80's through the early 90's that are pin compatible with the '299, meaning that with the right prom installed you could just plug it in and it will run fine. The most common and best documented is the '7747 that was used in the late 80's through early 90's full size trucks (there is also a '6747 which is very similar but was only used in similar vintage TBI cars which had an additional sensor which is not as easy a swap). If I was going to replace both ecm and prom I would grab one of those (that is actually what I did in my blazer since I wanted to mess with tuning and didn't feel that there was enough information about the '299 and didn't want to reinvent the wheel). Besides the programming thing (and there are a lot of easily available programs for that one, like at one point I was burning some coolant and fouling the O2 sensor and needed to drive it so I found a copy of the similar vintage, mexican suburban code for the '7747 which did not have an O2 sensor rather than editing it out of my existing program) the other reason that I swapped to the '7747 was that I found that some scan tools didn't report back data from the '299.
So its true that the 305 prom should have started the 350? I did forget to add that I put a different set of injectors on my TB. Because I took the top bridge thingy apart you know the thing with the spring inside and it looked shot. So I went to the boneyard and took the top off a 1993 Fleetwood. So would another number ecm really work?
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Old 12-14-2010, 06:36 PM
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Elkyblack, when did the problems first start to occur? Did it happen after replacing the injectors? Or did you replace them after the problem started?
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Old 12-14-2010, 06:51 PM
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Yes, a 305 ecm and prom will start a 350.

What makes you say it looked shot? That assembly is the pressure regulator and typically the only thing that goes bad in it is the diaphragm causing it to leak fuel.

The fleetwood should have had the same injectors and regulator as your truck, so that shouldn't have been a problem, but typically if you swapped the injectors, most people mess up the o-ring seals that are supported by the steel ring that was next to it, and most mess it up reinstalling it (quick check for this is to take the air cleaner off, turn the key on and let the pump pressurize the fuel system, usually if the rings are messed up you'll see a drip of fuel somewhere under the pod, sometimes at the injector nozzle, which usually isn't a leaning injector but a messed up o-ring
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Old 12-14-2010, 07:09 PM
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Well I just bought this truck, and when I bought it it was running but had the light flashing and needed a transmission, ok I replace the trans, now Im starting on this issue. It ran but had the hissing sound then it bog when I hit the gas when I got it, so I change the tps, Iac, and EGR hoping this would fix the problem. But nothing. So I decided to take apart to tb and thats when I discovered the problem that I described. I then changed the injectors and it ran the same.
Then I checked the codes and got the 51 code and went and change the prom and long story short its now not starting.
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Old 12-14-2010, 07:35 PM
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Maybe you should ditch the ecm and prom. Go and get a complete computer somewhere. Could be the whole works is fried now.
Might not be a bad Idea to see if you can retrieve a live data stream just to see if the puter is functioning,also recheck the trouble codes.
Have you also rechecked the fuses?
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Old 12-29-2010, 10:07 PM
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Did you ever solve the problem?
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Old 12-30-2010, 06:03 AM
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Actually I did. I went to the boneyard again and found another ecm
with the same service number, change the Iac again and she fired up and ran like a top. Im still puzzled, but hey she runs lol!!!
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Old 01-02-2011, 03:10 PM
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Glad to know you got it going!
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