HELP: Runs rough & dies @ light throttle

[jrtoffroad]

Hey guys, hopefully you can help me out. Haven't done any real diagnostic work yet, but need to get this resolved ASAP as this is my daily driver right now.

The car is a 91' ZR1 (of course) in a good state of tune (new O2 sensors, new plugs, fuel filter, newish plug wires, MSD coils, new inj's installed before I bought the car). The car has had secondaries removed and has the appropriate Mark H chip.

Okay, so here's the symptoms:
- Since I first got the car (when it had the secondaries installed) it would sometimes act like it didn't want to run at light throttle AFTER heavy throttle accelleration. For example: WOT up to higher revs then take your foot out of it suddenly and it feels like there's no power unless you're above say 1/2 throttle, above which it fells normal. If you put the clutch in the engine will idle. This would always pass quickly, after driving just a mile or so.

-Recently the car has started to run very poorly after the engine has not been recently run (does not seem to matter outside temp). On start up it will idle fine, but trying to drive up my road sometimes the engine will start running VERY rough and basically die if I give it any throttle UNLESS I exceed 1/2 throttle, then it picks up and seems to run normal. Sometimes it will work through this (with me having to give it heavy throttle a few times) while other times the engine will just die and need to be restarted. Upon re-start then engine pretty much always runs fine.

-After driving a few miles the engine seems to run normal at all throttle positions, unless every once and a while the engine exhibits the lack of power issue after heavy accel I 1st mentioned.

-Finally yesterday for the 1st time the engine just died as I pushed the clutch in to turn into my road (this was with the engine warm and seemingly running fine). It re-started immediately and ran fine. Oddly when I got into my driveway and when from reverse to 1st the speedo flashed to 220mph for a second.

I have never had a check engine light. Could I have any stored codes without one?

Sorry for the LONG post! My thoughts at this point are to check the Throttle Position sensor and the primary fuel pump. Not sure if it's any different with the chip I have, but the secondary pump only runs at heavy throttle inputs correct??

Any other thoughts??

THANKS guys!

[Kevin]

what were the injectors replaced with? stainless units or factory units

[jrtoffroad]

I don't recall the brand (will check my paper work when I get home), but they're not stock replacements. 99% sure they are stainless.

[GOLDCYLON]

Swap the primary fuel pump over to secondary. This will tell you if the pump is working once it gets out of loop. In other words it should not die. Replace the fuel filter as well for GP. If I was a betting man you are chasing a primary fuel pump failure. GC

[scottfab]

Sounds very much like the primary fuel pump in that many times they beging to stick then run fine over and over. Eventually total failure is coming.

Speedometer spazzing out briefly is not related.
all other pieces you previously replace not likely related.

[secondchance]

Check your MAP hose. If it is a rubber hose (no hard plastic between rubber fittings) it could be hose sqeezing shut under vacuum - worth a check before getting into fuel pump and injectors, etc...