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LT1 mechanic's advise needed, long story, but a good read.

  
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LT1 mechanic's advise needed, long story, but a good read.

 
sly94coupe sly94coupe
New User | Posts: 1 | Joined: 08/07
Posted: 08/27/07
02:42 PM

so there I was... cruising, on a Saturday about twilight, through Pacific
Beach CA, with the top off and the windows down. smiling at the two bikini
clad cuties in the convertible VW next to me. When "IT" happened to me for
the first time! I depressed the accelerator pedal, and the car surged and
hesitated and convulsed like the village drunk in a gutter, while it made an
awful sound from the exhaust like a nitrous fed popcorn popper. this whole
dramatic display of discontent without throwing up the Check Engine light.
WOW, the embarrassment, not about the girls... you can find those anywhere,
but a corvette on the side of the road with the hazards on and the hood
pointed straight to the sky, like a flag, a big white flag! I was ashamed to
bring discredit to my corvette driving brothers!!  
So after about 15 mins of me staring at my LT1 the same way a monkey looks
at a math problem, I began unplugging and replugging every electrical
connector I could get my paws on, to ensure proper connectivity. then I
attempted to start my car, successfully to find it running as it usually
would.... I immediately headed for home.  then just as my destination came
in sight, my gleaming white corvette does "IT" all over again, but only
above 3000 rpms, then as I drive a little farther, it starts doing "IT" at
2500 rpms. and then at 2000 then 1500, and you get the picture, as my
optispark equipped disaster limps into the driveway like a three legged
giraffe, I kept thinking "what could cause such an odd problem, without
throwing any trouble codes?" then the strangest thing occurred.. a little
orange gleam of hope lit up on the driver info center, "SERVICE ENGINE
SOON".
So I scream into the house, shouting "I need a paperclip NOW!" And sure as
breakfast. I bent that unsuspecting little shiny innocent paperclip up into
a 1994 corvette OBD 1 code reader and inserted my shiny new tool into the
number 4 and 12 ports in the black pluggy thingy under the dash, then I
proceeded to put the key into the ignition, then give it a little twist...
then there they were... DTC CODES! 4 of them, wow... I was SO hopeful to
find that my trusty On Board Diagnostic would tell me what to fix to make my
little white corvette as good as new. DTC #12: of course, means nothing, DTC
#97: VSS Output Circuit, DTC #42: Ignition Control Circuit Shorted. DTC #48:
Mass Air Flow Sensor Circuit. Oh yea.. Somewhere amongst all of this
nonsense my digital speedometer decided it would be fun to let me guess how
fast I was going, rather than doing its only natural duty. Oh the joy of a
LT1 corvette with 143000 miles. Well . I took my car to my good buddy's shop
and convinced him to allow me to occupy a hoist and borrow some tools for a
bit, then away to work I went. and oh boy was it fun. I replaced the VSS,
Then checked the wires to the PCM for continuity, they were good, then on to
the MAF, I again checked the wires, they were good, I gave the MAF sensor
itself to a mechanic at the shop and asked if he would test it for me, it
was good, so on to the ignition. again here I go with my gigantic yellow
FLUKE meter, only to discover that all wires are Perfect! Being as I had it
all torn apart, I replaced the plugs, wires, and ignition coil, and changed
the engine and trans oil and their respective filters, and a fuel filter for
good measure, while cleaning the manifold and injectors free of carbon
buildup. Couple of hours and a few scraped knuckles later, I pack up shop,
thank Mike for all his help, and away I go, out for a little test drive, as
soon as the under-hood temp raised, it started acting up, doing "IT" again.
not the engine coolant temp, it was at 215 before I hit the freeway, then
down to 195 as soon as I was to speed, ass soon as I hit traffic... again we
went with the popcorn popper action. I popped the hood for 15 min or so,
looked for any loose connections, fired it up to find the coolant still over
200, but the car running great, wonderful, outstanding, until heat builds
under the hood again. So now I know my limits. As I am a "less than wealthy"
active duty Marine, I don't have another car to drive, so I carefully plan
my trips to and from work at the cooler times of the day when there is no
traffic.
A few days later, im driving down the I-5, and my car freaks out! It stalled
dead from 2200 rpms, all the lights in the car flashed and all *** broke
loose at 85 mph in the cockpit of my little white corvette. Buzzers were
going off radio was beeping and cutting in and out, all the lights in the
Driver Info Center were flashing all the dash and interior lights were
blinking. So again I am furious with my 12000 dollar paperweight with 315/35
r 17 tires. I waited until the urge to set my pretty little white corvette
on fire diminished to a simple curiosity of "W T ***  then I reattempted
to start the car to find yet another orange light of hope. DTC #36:
Distributor Ignition System High Pulse., I tried to restart the car again,
it fired up, ran fine all the way to work. then last night, after work, I
walk to my car only to find it dead, no voltage. Battery has no charge. with
no reason, the battery simply bled out and died. As I stare at this
disastrous yet beautiful white corvette, I recall my child hood. memories of
my dad and grandpa, (both GM Prototype builders, with a lot of experience at
the Milford proving grounds) speaking of this wonderful new LT1, with its
reverse flow cooling and optical ignition thingy, wonderful stuff, as we did
donuts in the K-Mart parking lot in a Mock built go-fast Caprice, 2 years
later to be known as the resurrected "Impala SS". Don't get me wrong I love
GM and I will never buy anything else. But *** what the *** is wrong with
this car? Please help, I beg you, if you have any inclination of what could
be troubling my baby. Please help us.  

 
55Guy 55Guy
New User | Posts: 27 | Joined: 07/06
Posted: 08/28/07
05:24 AM

Did you replace the Optispark unit?  

 
tsakovs tsakovs
New User | Posts: 1 | Joined: 09/07
Posted: 09/04/07
11:37 AM

Hi,

I've been Googling to find someone else who has a similar problem as mine.  I have a 95 Impala SS with an LT1 and have just finished replacing the Opti, coil, waterpump and the ECM.  My origianl problem was typical for the Opti... Whenever it got 'damp' outside the car would NOT start until it dried out.  That problem is now fixed, finally, but I've run into a new problem VERY similar to the one here.

The car will run fine cool.  I can even let it run in my driveway for an hour or more without seeing this problem.  But once the engine has gone above operating temp after being at speed for a while - even if the coolant temp comes back into normal temp range - the engine will sputter and usually it dies.  Many times at highway speeds.  Slow moving or stopped traffic makes it 10x worse!

Once the engine cools down significantly I can then restart.  Sometimes with more sputtering and sometimes not.  I've found a way to speed recovery by using the OBD1 "paperclip" tool in the OBD connector.  This causes the cooling fans to start without the motor being ON which cools the engine down more rapidly.

The odd thing is that the temp of EVERYTHING on the engine is very very hot, way too hot to touch.  Under normal conditions I can at least touch the intake manifold for more than a few seconds.  When it dies I cannot touch anything.

Since my PCM is located under my filter's air box I am 'kind of' ruling that out since it's not being affected by the temp.  I'm 'thinking' that it might be a temp sensor or switch... but I'm not getting ANY trouble codes!  Maybe I got a BAD ECM from Autozone...?  How would I know this?

I'd hate to have to bring it to a dealer or even worse a repair shop who will have to guess at my expense!

Any insight into this problem would be MOST appreciated.

Thanks,
Tony S.  

 
jcatz jcatz
New User | Posts: 3 | Joined: 11/07
Posted: 11/03/07
04:51 PM

I have never had any overheating problems with 96 Lt1. I drain the entire coolant from engine by removing the knock sensors on each side of the engine.the dex-cool will have sludge issues if you mix non distilled water with dex-cool. also mixing regular sil. based anti freeze. not that you did it but some service jocky did. do not add sealant pellets. temperature should not vary, once at operating temp. open vent on thermostat housing vent trapped air. if lots of air possible head gasket. bad head gasket will prevent water pump from pumping coolant. can't pump air or exhaust gases. also test replace coolant cap no pressure in system coolant will boil, crate air, pump can't pump.. good troubleshooting......  

 

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