This might be a little long, but I'm stumped and confused.

97 vortec 5.7 , mild cam( not sure specs apply) , gm vortec to tbi intake, egr block off, re worked stock heads with hardened internals. Block is thirty over, line bored , balanced a blue printed. 9 to 1 compression.

When I had a carb on it it was rated right at 375 horse at the flywheel.

I've searched and searched. Rebuilt throttle buddies, ultimate upgrades, tried big block injectors , he'll I have a bb throttle body I was thinking about trying.

Problem - when the vehicle is cold it sputters , actually more of a bog down. It's only at low pedal pressure, punch it and it will work itself out... I've tried every sensor known to man, I've tried tps adjustment , fuel pressure regulator adjustment, ..

The minutes the vehicle goes into closed loop, it runs like it should. It runs like all the money and time I have in it. I'm sure there is more info you might need, and I'm pretty sure you will want some data logging info. I'm working that, I've been a carb guy my entire life. It just seems so backwards then what I'm used to..

Any help would be appreciated .

 

When cold check the engine coolant temp sensor resistence, see if its close to the outside air. A scanner really helps here, as it shows what the ecm is seeing.
Are you running an open element air cleaner? Is it really cold where you are at?

 

No open air cleaner. I've tried one, tb spacer, and everything else I cold throw at it. It's kinda my sleeper, looks stock but runs. I know if I just went back to a carb setup it would fix it. I just refuse to give up on this. I live in south georgia so 9 months of the year this problem last 5 to 8 minutes.

I'll go check the resistance of the temp sensor.

 

2.64 ohms on a 20k scale which is 264 ohm completly cold with 60 degree ambient temperature outside

 

My 91 truck ran the same way. Ran perfectly in closed loop but had a slight off idle bog in open loop. Ended up being a bad O2 sensor. It was an in range fault so the O2 sensor never showed up as a fault code.

 

Okay, my o2 sensor is attached on the driver side header. ( headmen long tube ) it's approximately 2 inches below the point at where the four tubes become one. I'm currently running a single wire 02 . Recommend replacing it, or going to a 3 wire?

 

Again, pretty new to the Whole ecu tuning and all that, but to my understanding the computer doesn't even use the signal from the o2 sensor until it is in closed loop. Not saying it won't work, but seeing as how the problem is in open loop I'm not sure the o2 sensor shouldn't play that much importance or be helpful to my problem. Again, not trying to argue or dispute your ideas, cuz believe you and me im going to try them.

 

264 ohms is way off for a cold CTS. It should read about 3,700 ohms at 70 degrees and about 180 ohms at 210 degrees. Retest to verify your results and if your first reading was correct, replace the CTS.

You're right to think that in open loop the ECM runs without benefit of the O2 sensor and the secondary fuel correction system of which it is a part. That's why the problem clears up in closed loop. A scan check would probably reveal high BLM and Integrator numbers. However, an O2 sensor that is stuck low or high can affect even open loop drivability and may not set a code. However, if this were the case, your vehicle probably wouldn't achieve closed loop.

 

Ill replace the cts for good measure. I'm slightly confused on your ohm numbers. I've tested 3 different brand straight out if the box and they register 2.90 to 3.13 ohms? Havnt check while at operating temperature. I'm also going to wire in a universal 3 wire o2..then we shall see what happens.. thanks

 

Never mind about the ohms reading.. I was set at the wrong scale... the new ones are within your pecans.. I'm replacing it and the o2 tonight.. see what we come up with. Thanks again

 

My open loop/closed loop problems were when I was driving. Through the data link plug, the CEL can be activated to indicate if it's in open or closed loop. Flashes fast and flashes slow. Sorry but I can't remember the sequence to do it. While driving, I would notice when it was open or close and that's when I noticed the bog happening. I had already replaced my CTS figuring that was the problem but it didn't help. The bog finally went away when I changed the O2. I still use a single wire O2.

 

Alky, If I remember my factory GM correctly, to get the CEL to function as you describe, you jump pins A & B of the ALDL with the engine running. This places the system in road test mode. The CEL flashes slow in open loop, fast in closed loop. The Helms factory shop manual details the procedure.

 

That sounds like what I did. Just couldn't remember how I did it.

 

Just got a new toy yesterday. The new Snap On Solus Ultra w/Euro. It won't be much better than my old MT 2500 on these early GM systems but it will make my life much easier on almost everything else.