HELP: Runs rough & dies @ light throttle - ZR-1 Net Registry Forums

jrtoffroad · 06-22-2012

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 · 06-22-2012

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

jrtoffroad · 06-22-2012

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 · 06-22-2012

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 · 06-22-2012

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 · 06-22-2012

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...

06-22-2012	#1
jrtoffroad Join Date: Sep 2010 Location: Colorado Springs, CO Posts: 75	HELP: Runs rough & dies @ light throttle 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!

06-22-2012	#2
Kevin Join Date: Jun 2005 Location: pittsburgh Posts: 4,632	Re: HELP: Runs rough & dies @ light throttle what were the injectors replaced with? stainless units or factory units __________________ It's not the car, it's the people - Doug Johnson 90 r/r "KEYS ON" nick named "T.L.B"

06-22-2012	#3
jrtoffroad Join Date: Sep 2010 Location: Colorado Springs, CO Posts: 75	Re: HELP: Runs rough & dies @ light throttle 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.

06-22-2012	#4
GOLDCYLON Join Date: May 2007 Location: Peoria, AZ Posts: 9,155	Re: HELP: Runs rough & dies @ light throttle 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 __________________ GOLDCYLON - 91 ZR-1 #2014 GOLDCYLON - 90 ZR-1 #2794, 4L60e (Formerly Schrade's) GOLDCYLON - 11 CTS-V Arizona State Director 91 WHITE/BLACK #2014. 380 P&P&PCed,Ported Heads, Jeal Long tubes, Corsa Exhaust/FIKSE FM-5s /LED TLs, LED Headlights, Front Wilwood 6 piston narrowlite calipers and rear Wilwood caliper street shop mod,CNCed Coolant Pipes,TPI Cvr,Filter cover,Stainless Bolts, DRM/DOM PROM /ZFDOC mod build #102,DRLs,BMAD with stainless Debris Screen,Coplan Air Blaster, Pioneer APP Radio 4,Brey-Krause HB,Sub Bar,Fire extinguisher seat mount,DRM Coilovers,LEDs everywhere,Compass mirror (orange),V1 DIC hidden display, Homelink sun visor, Carbon Fiber top x3 and APSIS Carbon Fiber interior, APSIS CF Steering Wheel/NAPA Leather, Banski trailing arms, Guldstrand front suspension,urethane bushings from Prothane (total suspension) ZFDoc drive shaft safety loop, raptor shift light (orange),AO engineering louver front plate, Console seat cushion, 96CE seats with black custom Sheepskins, ss billet catch can,Viper remote entry/alarm,Cragar Rear Louvers,LED side louver lights, Dewitts Radiator with SPAL fans and a Woods 160 T-Stat 90 RED/BLACK #2794. 4L60e Automatic Stage V by RPM Transmission, TCI Dedicated TCM, OBX Stainless Headers, Corsa Exhaust, SAN Secondaries and Haibeck PROM, Exotic Muscle Coil overs, LED Interior Lights, LED Tail Lights, LED Headlights, 94 Sport seats with black custom Sheepskins , Cragar rear louvers, GS Front calipers, Banski Trailing arms, APSIS Carbon Fiber steering wheel, Front and Rear Baer Eradispeeds, DRLs, Guldstrand front suspension,urethane bushings from Prothane (total suspension), Dewitt's Raditor with Dual SPAL fans and a Haibeck 170 T-Stat 11 RED/GREY CTS-V

06-22-2012	#5
scottfab Join Date: Jan 2009 Location: Portland Oregon metro area (Washington side) Posts: 3,207	Re: HELP: Runs rough & dies @ light throttle 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. __________________ Scott Vett owner since 1979._It's about the car and the people

06-22-2012	#6
secondchance Join Date: Aug 2006 Location: McLean, VA Posts: 3,723	Re: HELP: Runs rough & dies @ light throttle 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...