97 vortec K3500, fresh stock cam engine shorty headers no cats 2.5 inch

[suspectracing]

Engine runs great in open loop. pulls like a train. all senors are new and look good on the scanner. when it switches to closed loop after the o2 get hot, it runs like crap and misfires randomly on wide open throttle and and at part throttle does not pull good. I have talked to market place tuners and they say because you cannot record the data stream on 96 to 98 they could only guess what might work. Is there a way to figure out what open loop is and then convert that to closed loop or just make it stay in open loop? I have been chasing this for months.It has been to a number of shops with zero result. Yes the fuel pressure is correct under load and idle Everything looks great till you get it off open loop and put it under load. new bosch injectors new PCM with stock tune. all sensors are reading correct and the PCM throws no codes. It thinks all is good. Help?

[blindsquirrel]

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[gtstorey]

Is that tunable at all with hpt? Not on the supported vehicle list.

[2xLS1]

You need Tunercat OBD2 to tune 96,97 Black Box PCMs. Just unplug the O2 sensors to keep it in open loop. You will have codes if you have no way of turning them off. And I have never had trouble using HPT scanner on 96,97s. Just limited PIDs.

[suspectracing]

You need Tunercat OBD2 to tune 96,97 Black Box PCMs. Just unplug the O2 sensors to keep it in open loop. You will have codes if you have no way of turning them off. And I have never had trouble using HPT scanner on 96,97s. Just limited PIDs.

Unplugging the O2's does not work. It still misfires. I cannot believe that this has never happened to anyone else. I am very close to tossing a Qjet and HEI on it and figuring a way to get the transmission to shift.

[suspectracing]

I have been told by two turners that 96 to 98 PCMs in this 7.4 chevy trucks do not allow and data to be down loadeded to a file. I can see it in real time but I cannot save it to a file.

[gtstorey]

Can’t be tuned with HP Tuners but you can read limited number of sensors/channels.

[suspectracing]

Can?t be tuned with HP Tuners but you can read limited number of sensors/channels.

I guess this problem cannot be solved by a mere mortal. No one knows how to keep it in open loop where is runs and shifts great. I have a 97 K3500 Chevy with a fresh Vortec 7.4 that pulls like a train for about 1.5 miles when the computer goes to closed loop, that can't be fixed. I love computerized cars a lot, but this one has everyone stumped. I do not want to spend another 1200 bucks in the hope that I can fix it and I don't want to spend the same dough on a carb and transmission software/hardware. Everything that one can see with a very good scanner says all is good. STFT and LTFT look good, O2's cycle right, All the sensors look great. But it only runs right for 1.5 miles. no codes.

[gtstorey]

Probably can be fixed but not with HPT. Check out Tunercat as mentioned above. Not sure what you expect from a HPT forum when it’s a non HPT supported vehicle.

If it’s running that badly on shorty headers and cat delete it’s probably not tune related anyway.

[2xLS1]

Here is the table in Tunercat OBD2 for a 97 Black Box PCM that needs to be changed to keep it in open loop via coolant temp enable rather than fixing the actual problem. I guess I must not be a mere mortal since I could solve the keeping it in open loop. Although with no O2 sensor activity with O2s unplugged it also cannot go into closed loop but I guess you seem to know better. Like I said before it takes Tunercat OBD2 to edit 96 and 97 Black Box PCMs. Good luck fixing your problem.

[edcmat-l1]

I have been told by two turners that 96 to 98 PCMs in this 7.4 chevy trucks do not allow and data to be down loadeded to a file. I can see it in real time but I cannot save it to a file.

You're talking to the wrong turners. It can be data logged. There are numerous aftermarket OBD2 data logging tools out there. They're not difficult to find. You should be able to data log it with HPtuners and EFIlive both.

[Fast4.7]

You're talking to the wrong turners. It can be data logged. There are numerous aftermarket OBD2 data logging tools out there. They're not difficult to find. You should be able to data log it with HPtuners and EFIlive both.

I also suggested OBDLink to him on another forum. OBDLink is what I used to datalog both my 97 Express and my 03 Dakota before either one could be tuned with commercially available software. Both had piggy back controllers on them for years.