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04-13-2011
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#1 |
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Join Date: Apr 2011
Location: Ontario
Posts: 7
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car pulsates under load when in power mode
I just bought a 1991 corvette zr1 and i dont find any difference when i switch from normal to power mode. in normal mode the car drives fine. when i switch to power mode, the light comes on. car still feels like 210 hp and when i accelerate heavy, the car pulsates and vibrates. when i let off and drive normal, the pulsation goes away.
im thinking its the secondary injectors that may be the problem as i continue to read in the other posts. I would like to be sure before i invest in them. Also, if it is the injectors, is there anybody you can recommend with a decent price? Im from Canada if that makes a difference. Maybe the local parts shop can order from a major supplier. sorry, one last thing... any advice or tricks to do an oil change? and is it true the zr1 takes 12 litres? thanks in advance! 
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04-13-2011
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#2 |
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Join Date: Mar 2009
Location: Orlando, FL
Posts: 1,828
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Re: car pulsates under load when in power mode
Being a 1991, injectors are certainly a likely explanation. If they are original, I'd bet on one or more being faulty.
Many aftermarket brands available - Accel, RC Injectors, FIC (sells reconditioned Bosch units, popular because they're about half the price of the others). Oil change tricks? Elevate car, remove drain plug, drain oil. Reinstall drain plug, change oil filter, refill with oil. Takes about 9 quarts for a typical oil change. There is oil that remains in the oil cooler plumbing, 3-4 quarts, which cannot be drained easily.
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2004 Z06/Z16 LeMans Commemorative Edition 1991 ZR-1 #302 White/Gray (sold) 1991 ZR-1 #1147 Red/Saddle (sold) |
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04-13-2011
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#3 |
   
Join Date: May 2007
Location: Peoria, AZ
Posts: 9,155
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Re: car pulsates under load when in power mode
As stated bad injectors.
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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 |
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04-13-2011
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#4 |
 
Join Date: Dec 2003
Location: Arcadia,OK
Posts: 3,394
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Re: car pulsates under load when in power mode
One more note on the oil change. Make sure about doing one or the other.
1. Draining hot: best to drain overnight if possible (My Personal Favorite), 3 or 4 hrs minimum. 2. Draining cold: Drain until slow drip, button up & fill to full on dipstick. If new filter, check again later when cold & top off. The LT5 is slow to return oil from the top end to the pan. Doing a standard, quick hot drain & refill can easily result in overfill.
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Jerry Downey JERRYS LT5 GASKETS & PARTS http://www.jerrysgaskets.com 1994 ZR-1, Black/Black, Lingenfelter Aerobody, 416cu in, 3.91 gears, coil-over susp, Brembo brakes, etc. 2016 Black-Red, 3LT-Z51 Auto 8-speed. |
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04-13-2011
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#5 |
Join Date: Dec 2003
Location: Grand Island NE
Posts: 1,512
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Re: car pulsates under load when in power mode
You will never get in that much as 3 quarts are left in the oil cooler. 8.5 or 9 is about what mine takes.
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Dennis Fierstein 90 ZR-1 #2562 Atomic-Z ZR-1 Net Registry Chairman of the Board ZR-1 Net Registry Treasurer |
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04-13-2011
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#6 |
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Join Date: Feb 2011
Location: Medford, NJ
Posts: 77
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Re: car pulsates under load when in power mode
I'm acutually exeriencing a similar issue where I can't tell much of a difference between "Normal" and "Power" modes. If the issue lies in the secondary injectors, would that throw of a code, or a warning light? Is there a way to check if the secondary injectors are bad without pulling the plenum?
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04-13-2011
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#7 |
Join Date: Oct 2004
Location: Folsom CA
Posts: 1,655
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Re: car pulsates under load when in power mode
From Marc Haibec's website:
http://zr1specialist.com/HAT%20Web/a...Resistance.htm A word of caution, DO NOT force your volt meter probe leads into the female pins of the ECM plug. Save yourself the agony that only took me 2 years to diagnose and repair on my ZR-1. Shoving the probe leads into the pins serves to stretch out the female connector and then they won't make good contact with the male pins in the ECM. Causes all kinds of mysterious intermittent problems. Back-probe the pins instead, simply pull the rubber plugs out with needle nosed pliers. When you look carefully at the ECM plug you will see what I mean. Good luck!!! TomC 'Crabs
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TomC '90ZR1 #792 Honorary Pirate [B]If it ain't FUN, you're doing something terribly WRONG. [/B] |
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04-14-2011
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#8 | |
Join Date: May 2007
Location: Westminster, Maryland
Posts: 3,689
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Re: car pulsates under load when in power mode
Quote:
I had a similar problem with my 1994 when I bought it. The first easy check is when you turn the ignition key to ON without starting the car, do you hear the Secondary Vacuum Pump run for a few seconds and then turn off? The pump is located just forward of the coolant overflow bottle, near the pass side headlight. If the pump doesn't run at all, it needs to be replaced before you can do any other analysis. If the pump runs-stops-runs-stops-etc, then you have found that there is a vacuum leak that you will need to fix before you do any other analysis of the injectors. Another quick way to test the vacuum pump is to find the thin plastic vacuum tubing that runs from the vacuum pump to the engine. Right near the alternator, there is a connection that you can separate. With the ignition key on, pull that vacuum line connection apart and by putting your thumb over the end of the tubing coming from the pump you can easily check its operation. Post up and let us know if you vacuum pump is working. Jim |
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04-14-2011
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#9 |
Join Date: Dec 2004
Location: Jacksonville, FL USA
Posts: 4,645
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Re: car pulsates under load when in power mode
Hi and welcome to our corner of the asylum!
 I would ask do you know when the fuel filter was last changed out? They are out of the way & get overlooked. No SES light when you try to make it accelerate? Then the light goes out when you relent? Check CCM as it may store that soft DTC. It sure sounds like it's starving for gas when you want the secondaries, but why? 2* injectors check Ohm readings hot. Ohm okay = good coils, but could be clogged tips. 2* injectors for fuel flow, could be injectors or fuel pumps. 55 PSI on rail is top of the range, FSM says 48 - 55 PSI. Check regulator hose for fuel, if fuel present regulator is N/G. Pump socks clogged? 2* vacuum system could have: a vacuum leak or bad actuators. Collapsing air intake duct from filter housing to air horn. These are some of the things you could look at. Not trying to make work for you. Are the injectors OEM, if so they maybe the most likely cause of the trouble.  Tom
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1990 ZR-1, Black/grey, #2233, stock. ZR-1 Net Reg Founding Member #316 & NCM member |
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04-14-2011
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#10 |
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Join Date: Dec 2003
Location: Arcadia,OK
Posts: 3,394
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Re: car pulsates under load when in power mode
On the oil change and the stated capacity of 12 qts.
After tearing down several LT5's, I come to the conclusion that there may be a qt of oil in the oil cooler. The rest is in all sorts of little nooks & crannies in the cylinder heads, lifters, oil filter housing. etc. , that just never drains down. The appx 12 qt capacity is for a new, completely dry engine & filter. I've cleared my oil cooler before with an oil change and doesn't even come close to 11qts.
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Jerry Downey JERRYS LT5 GASKETS & PARTS http://www.jerrysgaskets.com 1994 ZR-1, Black/Black, Lingenfelter Aerobody, 416cu in, 3.91 gears, coil-over susp, Brembo brakes, etc. 2016 Black-Red, 3LT-Z51 Auto 8-speed. |
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