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Hard to start,runs rough at high speed.


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David'scorvette
New User

Feb 19, 2017, 11:31 PM

Post #1 of 4 (304 views)
Hard to start,runs rough at high speed. Sign In

I have a 1991 5.7 liter corvette ZR1 with the LT5 engine. It has 35,000 plus miles and has been rebuilt once, suppossedly. It has 4 cams and 32 values,fuel injected and should crank right up with out any gas, but it will not start with out feeding it gas,an a lot of it. Also when you get the on it the car vibrates terribly. I have an other Vet,a 1996 with a LT1 engine with over 128,000 miles on it, an it will smoke the ZR1. Can you help me? Two shops have not helped at all. Their best idea was to change the fuel injectors, but that's about $750.00 to a $1,000 bill an I want more than a maybe before I fork out that kind of dough. Can you help? Is there a diagonstic test I can perform or have performed for me? Any help would be very appreciated. Thank you for your time and trouble!


Hammer Time
Ultimate Carjunky / Moderator
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Feb 20, 2017, 5:33 AM

Post #2 of 4 (291 views)
Re: Hard to start,runs rough at high speed. Sign In

If you don't trust the diagnosis that you have been given, then go get a second opinion. We can't begin to second guess a mechanic that has actually checked the vehicle without seeing what he has seen.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Discretesignals
Ultimate Carjunky / Moderator
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Feb 20, 2017, 6:42 AM

Post #3 of 4 (281 views)
Re: Hard to start,runs rough at high speed. Sign In

You should definitely ohm check the injectors to see if they are shorted. The old multecs were common for shorted injector windings. They should all be 11.8-12.6 ohms. Current ramping the injectors with a oscilloscope would also reveal shorted injectors.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


kev2
Veteran
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Feb 20, 2017, 9:02 AM

Post #4 of 4 (269 views)
Re: Hard to start,runs rough at high speed. Sign In

Fuel pressure test then with KOEO observe pressure drop,
You say will not start without giving lots of gas- do you mean-
1) actually pouring fuel into throttle body?
2) holding accelerator pedal open or pumping.


Not a great in depth system but have you look at codes? -


PS: 8th character of vin# is J - or am I wrong?


(This post was edited by kev2 on Feb 20, 2017, 10:10 AM)






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