Engine surging at 4000 RPMs

[sccdmc]

The car my son bought had the PCM stolen. robertisaar steered us to a
PCM that finally started the fuel pump and injectors. It ran fine for about 10-15 min., then it started acting like it was hitting a rev limiter at 4000rpm. Kind of a quick surging. I unhooked the neg. terminal for 15 min. It didnt change. Any ideas of what it could be. 16149396 is the PCM that seemed to work. It came out of a 93 3.1 Lumina. My sons car is a 91 Z34. Thanks!

[55trucker]

When you installed the replacement ECM (from the 3.1 engine)...did you include the mem-cal needed for the 3.4 DOHC engine? Altho the ECM itself is somewhat universal the plug-in chips are not. Some of the chip codes for the DOHC are AYSZ (this is my chip, 91 DOHC engine, auto trans), BBUK, BCDT, BCFA.

[Superdave]

3.1 code and 3.4 DOHC code are extremely different. you need to put the DOHC chip in that ECM for it to run correctly.

[robertisaar]

3.1 code and 3.4 DOHC code are extremely different. you need to put the DOHC chip in that ECM for it to run correctly.

right, the 3.1 has most of its power down low, while the LQ1 doesn't make much until 4000, then it screams like a banshee.

that could be why it feels like a rev limiter, because the engine is sucking in so much air, but the ECM isn't giving it anywhere near enough fuel, meaning no power and lots of detonation

[Superdave]

Not only that but the DOHC has a ton more spark advance then the 3.1.

[SofaKingWeToddDid]

maybe the 'surging' is the power band? when my engine was out of tune it wouldnt even have power till 4000rpm!! lol then it would go like hell! that could be taken as a surge...