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Discussion Starter #1
Ok I will try not to be too long winded, but........

I have completed a swap from a 305 to a rebuiilt 350 in my 92 GMC K1500.

Original system was a TBI, so I went with the TBI for the 350.

Problem is this: engine runs well and smooth at idle, and will accelerate moderately well, but when you give it approx half throttle it bogs and backfires through the throttle body. I understand that some of the sensors used on the 305 will not work on the 350, so to that end I have replaced the knock sensor with a new 350 one.

I also invested in a laptop cable and downloaded a copy of WINALDL to check for any inconsistancies in sensor readings. However I am unable to get a good data as my ECM # is 16146299 and that does not appear in the WINALDL list.

Has anyone had any experience with this type of ECM?, and what did you use to check your data?

Truck Specs

Block - 1975 Chevy 350 - 4 bolt - .030 over
Crank - Stock OEM
Pistons - KB Hypereutectic
Oil Pump - Z28
Heads - Vortec 64 cc
Cam - Speed-Pro RV cam - 194/214 @ .050 ( I think)
Lifters/Rockers - Stock OEM
Intake - Edelbrock Performer TBI - #EDL-3704
Headers - Edelbrock Shorty Headers
Throttle Body - Holley Two Barrel TBI model 321- - 670 cfm
Distributer - Stock OEM (from the 305)
Cap/Rotor - MSD
Coil - MSD GM Blaster
Ignition - MSD 6A
Exhaust - 3" Y Pipe - Single High Flow Cat - Dynamax Cat Back Duals
Fan - Flex-A-Lite Electric Puller
PROM - Hypertech 350 Street Runner #122121
ECM - 16146299 AWHC
Trans - 700R4
Axle - 3.73 Positraction

If there is anything I've forgotten, let me know.

Thanks
 

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Sounds like you did your home work well. I dont see any problems with your set up. I would get on thirdgen.org and go to the TBI forum and post upi your problems as the guys over there know there stuff. Great site for anything TBI/TPI. Good luck!
 

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could you have missed a 305 sensor that should of been replaced with a 350 sensor ? are the 305 & 350 Distributer - Stock OEM (from the 305) the same ? or could it be the non stock Cap/Rotor - MSD Coil - MSD GM Blaster Ignition - MSD 6A ? or could it be the Vortec heads be it ? could it be the cam upgrade or the Intake - Edelbrock Performer TBI - #EDL-3704 the computer is not recognizing ? or can these be changed with the programing ?




just ideas




Mustangsaly
 

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No mention of the fuel pump...? Sounds like the fuel pressure is falling off when demand is up...? You would get the same issue using the stock TBI from the 305 on the 350 it would put it into a lean condition... But good you went with an aftermarket unit but it may need some sort of calibration too...? (TPS not set correctly or...?)
 

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Hates: Liver. Loves: Diesel
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Uh... aren't the injectors different? I could be wrong, but I thought the 350 injectors were bigger. Could be you're just running out of capacity.
 

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Oh, I just re-read... you're using vortec heads. The TBI heads from the 305 are incredibly restrictive. You've basically upped your VE by a large amount when you went to the vortecs.

The stock TB only flows about 390, but your combo looks good for about 275 hp. Now I really think you're running out of breath and/or gas.
 

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The ECM for my 93 Caprice also didn't appear on the list, but using the (?) 4288 format as the WINALDL choice worked just fine. Try it next before trying the others.

I second the comment on the fuel pump, but more specifically I'll ask what injectors you are using and what is the fuel pressure?
 

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I did a very similar engine upgrade to a 90 c1500, except i started with a 350.
I had almost identical upgrade components. I had a host of issues, ranging from a mild engine hunt at 40 degrees outside, to fuel loading at anything over 1/3 throttle. I found that the prom programming is quite difficult to get correct. I sent my reprogrammed prom back at least 5 times (each time with block learn numbers at 200 rpm intervals) TRY that while driving around town!!
Anyway, I have heard of programmers with dyno's (and the test vehicle of course), doing 10-100 runs or reprograms before getting it right. Especially with non stardard upgrades.

My goal was more power and still retain all of the nice things that go with fuel injection, like good cold starts and better fuel economy (?) sounds simple enough, but i never could get the combos right. We build lots of crazy stuff, and I have never had so much trouble with anything.
After a year or so I finally found a doner totalled 99 3/4 ton vortec, robbed engine and all. Everything including the ecm and all wiring, dash, inner fenders, doors, door panels, header panel transmission. We even moved spot welded brackets over.
What started as a little rebuild, turned into quite a challenge.
Sorry for the rant.
I now have what i wanted, lots of umph, and decent fuel
 

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I re-read your post again.
How long has the new combo been together. It takes a while for the ecm to learn its new parts. I would get it up to highway speed for at least several five minute runs. Fuel is determined by your tps and your map sensor. (and other things like temp) It is then further corrected by your O2 sensor. It sounds like the fuel curve is too rich at a certain engine vacuum, and is loading up faster than the ecm can correct it. If the sensors are working correctly, and the computer has learned what it can, you will need a closer prom match.
Have you tried the stock prom? It should be able to a 10-15% change in cylinder volume. The cam may freak it a little, but it is worth a try. Again it will need a little "learning" time. My stock one did better than the one I ordered all customized.
When I did my truck I never even replaced the glove box liner for access.

Brian
 

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Discussion Starter #11
Many thanks for the responses people!

53_belair - Thanks it’s been on drawing board for quite awhile, and I will follow up on your suggestion and take a look at thirdgen.org

Mustangsaly – I was thinking the same thing, I will cross-reference part # on all the sensors to see if there is a difference between the 305 and the 350 ones.

Bumpstick – I have a fuel pressure gauge that I am going to install this weekend, that should tell me if I’m in the 9 – 15 lb range.

Curtis73 – Yes the vortec heads require more flow, that’s why I went to the Holley Two Barrel 670 cfm

Halfprice5 – I was thinking of picking up a stock 350 chip, just to see what kind of difference it makes. I would prefer to tweak this thing myself, it can’t be all that difficult, plus it’s a good learning experience! LOL

kdrolt – I have been using the 4288 format, and I was able to extract some of the raw data, but it won’t datalog, and it won’t show either RPM or MPH. See previous comments on fuel pressure and injectors.

Sudden Psycho 31 – The engine has been together and in the truck for about a month now, and I’ve put about 150 KM on it while trying to get things sorted out. One thing I’ve noticed is that the engine does not heat up to normal temp unless it sits and idles for a while. It has a new 180 thermostat, but it may be sticking open (I will replace it this weekend as well) I also as mentioned above I will be getting a stock 350 chip, just to see what it does.
I was hoping to use the WINALDL to see what all the sensors are doing, in hopes that I could pin the problem down that way, but maybe I will have to go back to old voltmeter system!

Thanks again for all the replies!
 

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