Need help ecu prob

[sdime94]

I hope you don't mind me posting a question on this site I have a 91 jimmy and I was wondering if you could tell me the best chip for it. It has been bored .60 over and has a comp stage 2 cam and had the heads rework. Now haveing problem after the ecu takes over. If you unhook the batter and what for the ecu to reset and hook it back up it runs great for the frist 15 min and then the ecu kicks in.

[turbodog]

Originally Posted by sdime94

I hope you don't mind me posting a question on this site I have a 91 jimmy and I was wondering if you could tell me the best chip for it. It has been bored .60 over and has a comp stage 2 cam and had the heads rework. Now haveing problem after the ecu takes over. If you unhook the batter and what for the ecu to reset and hook it back up it runs great for the frist 15 min and then the ecu kicks in.

SyTy ECU and memcal is distinctly different from all other Jimmy's. You would do best in a forum for regular sonoma's and jimmy's. I will offer that the timing you describe is probably the ECU trying to go 'closed loop' after the O2 sensor heats up. try disconnecting the O2 and see if it runs better, longer (you will get a 'check engine' light). This is not a solution, just a step in the troubleshooting process.

[sytyguy]

Like Rick said, disconnect the O2 and see if it helps. The ECM should default to stoichiometric O2 mVs and act like all is well with the AFR. If this remedies the problem, it could indicate a faulty O2 or a serious closed loop fueling issue. Do you have a rich or lean condition when in closed loop? (Do you smell fuel and foul plugs or do you have to keep you're foot in the gas to help it run?)

FWIW, when I upgraded the cam in '90 Jimmy DD, I had to make some noticeable adjustments to the VE maps to compensate for the altered rpm range. You may have to do the same.

Check the O2 and we'll go from there.