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dead spot when excelerating

 
vinnycampo
I love my Chevy Chevette!
Posts: 2
Joined: 08/13
Posted: 08/15/13 02:16 PM

I have a 1982 corvette with a cross fire injected engine.  When I excellerate the engine there is a dead spot that causes the engine to bog down for a second or two.
I have had this problem since I purchased the car but realy poses no problem except for the fact that it does not excellerate smoothly as it should.  Is this a common problem for a crossfire?  Is there an easy fix for it?  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 08/15/13 08:22 PM

well.. this one is going to be tougher than the 84 crossfires..

as it really needs a scan tool  with the 5 pin ALDL connector adaptor...   a monitor 2000 with the proper connectors and cartridge will really help.. and they are cheep sometimes..

OTC2000
notice the grey rubber device in the upper left corner..  that takes the 12 pin cord end and allows it to fit into the 5 pin ALDL connector.. so you can see the live data stream with the scan tool.. this makes diagnosing easy...

otc monitor 2000...  

there are many versions of the OTC 4000E

Otcmonitor4000e

not all come with the proper 12 to 5 pin aldl adaptors.


A0fe3b0e 5527 4C17 B8e9 2F0bcaf6fd96 Zpsbe7bd807  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 08/15/13 08:51 PM

check the vacuum hose connections on the back of the throttle bodies.. note that the center vacuum ports are blocked off.. as they are only used to sync the throttle linkage with a pair of vacuum gauges calibrated in inches of water..

84Crosfirevacuumcal


there are a few things to check once you verify the vacuum hose connections are intact and not leaking...

engine off.. open the throttle part way..  wiggle the individual throttle shafts while looking down the bore or at the lever end.. make sure that there is NO PLAY in the shaft to housing bore ...

a tight fitting throttle shaft would be like this..(O)..

a loose fitting throttle shaft would be like this.(O )   or ( O)

what happens with this is the throttle closes to a different angle each time.. as it opens..  the computer looks at the changes in voltage from the TPS.. the throttle position sensor..

when the shaft bores are worn.. the shaft and throttle blades actually can open before the TPS starts changing voltage .. so the computer does not start widening the injector pulse width to match the fuel needs of the engine..

this is where the scan tool comes in handy... as you can look at the TPS sensor voltage with the scan tool.. and operate the throttle several times.. the TPS voltage needs to come back to the EXACT same fraction of a volt..  somewhere between 0.50 and 0.98 volts at idle...  there is an exact spec for this.. i don't recall what it is right now...

there is another thing that can only be checked with a scan tool..

the IAC counts..   Idle air counts..  these are the big HEX devices screwed into the fronts of the throttle bodies. they are stepper motors controlled by the ECM..  they control the idle speed and act as dash pots as you slow down..

with the engine warmed up.. the coolant temp above 190F.. foot off the gas pedal...  TPS should be less than 1.0 volts..

and the idle air control counts should be between 20 and 50..

if they are less than 20.. the computer is trying to slow the engine down.. if they are more than 50.. the computer is trying to speed the engine up..   if you don't have them within the 20 to 50 range at idle.. you will have idle issues..


next.. see the MAP sensor.. please verify the hose is NOT collapsed or leaking..  its been so long since i have been under the hood of a C3 crossfire.. that i have forgotten.. but most later versions are hooked up with only SHORT pieces of vacuum hose and a rigid nylon tube.. this reduces the amount of expansion and contraction in the hose.. so the changes in manifold signal to the MAP sensor are faster and more accurate..

over behind the EGR vacuum solenoid is the ground connection for the ECM.. the ONLY one.. there are several other grounds around the engine bay that MAY also need cleaning..

these are most of the ground locations on the 82 and 84 crossfire motors..

82 84Crossfiregroundconnection  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 08/15/13 09:04 PM

plan on several hours to identify and clean all the grounds..

you won't believe how much better cars run when the grounds are all intact .. hint.. grounds are actually half the circuit and the side that supplies electrons..

i have a test.. if you have a digital volt meter.. this is only a starting point test..

engine running.. headlights on...   digital volt meter set to 20 volts DC scale..

1.   battery Negative post to the battery positive post.. 14.1 to 14.8 volts.

2.  Battery Negative post to the engine block... 0.04 volts DC max..

3.  Battery negative post to the body grounds.. firewall/brake booster bracket.. something like that.. 0.02 volts DC max.

4.  engine block to body...  0.02 volts DC max.

since your C3 battery as i recall is mounted behind the seats inside the car..  you can use a single side  of a jumper cable pair to perform these tests..  # 2, 3 and 4 .  


you will also want to change the inline fuel filter..  probably inside the frame rail behind the right front tire.. but i am not that sure on a C3..  all my books are stored away right now.. so i am going by memory..  

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