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Can anyone help

fedcop90vette

Member
Joined
Apr 29, 2007
Messages
22
Location
Delaware
Corvette
1990 Black Coupe
I have a stock 90 vette, I started having problems with the car getting real cammy and shaking,at idol, I got the car home and it stalled and I couldn't get it started again. I had the car towed to a local chevy dealer. They told me I had a miss in the number 1,2,8 cylinder,they did a complete tune up,distrib cap,points,plugs,wires etc. They took the old plugs out and they were black. I just bought the car so I really don't know when the last tune up was done before this.


After the tune up,they said I still have the same problem. At this point they thought maybe a bad valve,stuck valve. They removed the valve covers and checked everything out,rocker arms,valves,etc, everything was fine. Oh yes there were no codes present during the diagnostic check. The mechanic is at a bit of a loss.

Does anyone have any suggestions,solutions? has anyone had this problem before?

Any help would be greatly appreciated. The car has 92,000 miles.

Thanks
 

Notorious

Well-known member
Joined
Oct 9, 2005
Messages
53
Location
Confederate States of America
Corvette
Highly modified '95 A4 coupe
Judging from your symtoms, I'm guessing the plugs are black from a rich condition. Assuming this is the case and they missed that fact from a simple plug read, it's time to cut your losses and take it to someone who knows what they're doing.
 
S

speedmaster4

Guest
to start, you need a mechanic...based on your narrative, the ''person'' at the dealership who worked on your car is not a mechanic...walk up to the next three c4 vette owners that you can approach, explain that you are a new buyer, and ask them ''who'' they take their vettes to.

first step to troubleshoot any efi vehicle is to cut the list of possible culprits in half --do that by checking the fuel pressure...pressure should go to abt 40 psi as soon as the key is put in ''run'' position (don't need to actually start the engine) and drop very slowly when the key is turned ''off''...after 12 hours in ''off'' position, fuel pressure should still show 10 psi.

if fuel pressure is satisfactory, remove all spark plugs, remove ''bat'' power from distrib, and do an old-fashioned ''compression test'', to rule out basic mechanical problems -- occasionally those still do occur.

next check the egr valve (my first guess at your source of trouble, but really a guess -- check fuel pressure and compression to save tail-chasing before anything else is attacked)
 

fedcop90vette

Member
Joined
Apr 29, 2007
Messages
22
Location
Delaware
Corvette
1990 Black Coupe
Thanks

Notorious and Roadmaster you have the same thought that I have! I found a Corvette specialist in Dover (delaware),I'm going to pick the car up and have it taken there! This is my 3rd vette that I've owned (81 coupe,94 coupe) and I have never been so frustrated! And the man calls himself a Corvette mechanic..I should arrest him!!!

Thanks for the replies so far I'm writing them all down for future reference!!
 

vetteboy86

Well-known member
Joined
May 26, 2003
Messages
2,760
Location
IN
Corvette
1986 Black "Indy 500 Pace car replica"
I've been there and done that. If you spend some time researching things on these boards you will probably find out alot if info. More info right now is needed. It would be nice to get the car back and go from there. I think there has even been instances were plugged cats can do this type of thing. Basically like the guys said before you need to start somewhere. Even if you had a dead cylinder the car would start and run!
 

fedcop90vette

Member
Joined
Apr 29, 2007
Messages
22
Location
Delaware
Corvette
1990 Black Coupe
Thanks

Vetteboy86,I use to live in another state where you could take you car to someone who knew what they were doing! The car will start now and run,very rough,almost like you have a competiton cam inside,lots of shake,no power..injectors were good,no tapping,no metal sounds,no clonking etc. There was no warning light and no code from the ecm.

Yes you are correct there is alot of info on this site, and alot of good people. Learning more each day!

Thanks
 

wishuwerehere82

Well-known member
Joined
Sep 6, 2003
Messages
2,314
Location
Rochester, NY
Corvette
Red '82 Coupe,Sebring Silver '98 Coupe
Sounds like your IAC motor is stuck on full rich to me. But you would be throwing codes for rich O2 sensor.
 

fedcop90vette

Member
Joined
Apr 29, 2007
Messages
22
Location
Delaware
Corvette
1990 Black Coupe
Thanks

Wishuwerehere82,thats the biggest mystery,no codes given....thanks for the suggestion!
 

wishuwerehere82

Well-known member
Joined
Sep 6, 2003
Messages
2,314
Location
Rochester, NY
Corvette
Red '82 Coupe,Sebring Silver '98 Coupe
Wishuwerehere82,thats the biggest mystery,no codes given....thanks for the suggestion!
The problem with computers is that they only do what they are programmed to do. They manage the systems they have control over.

If you pull off a spark plug wire, the computer never knows. Likewise with a bad fuel pump, pressure regulator, spark control module, fuel filter etc. Because the computer assumes that they are working.

The dealerships are pretty useless on anything that is "outside the box" , so taking it to a Corvette speciallist is really a must in a situation like this.
 

gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,547
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Check the EGR!!!!! There bad to get a Chunk of Carbon in them and be stuck WIDE OPEN!!!!!!! Like a BIG Vacuum Leak!!!! And then the Oxy's will tell the ECM that it's is REAL Lean,and then the ECM will tell the Injectors to Dump the Fuel to it!!!
This can show up as Random Missing,and it gets worse before it gets Better,the rougher they run the more Carbon gets knocked loose in the EGR passages!!!!

I clean or replace the EGR ,start them up and shut them off without the EGR on to blow whats loose out of them 2-3 times!!!
(Just start and shut off,It will take off like a Run away Detroit Diesel with out any throttle!!);LOL

And then I take 2 EGR gaskets and sandwich a Stainless Steel screen between them on the exhaust side to keep the carbon busted up small enough to go through the EGR without getting stuck!!!!!:upthumbs Its Spring,I've done this to about 4 GM cars and trucks in the last month!!
 

wishuwerehere82

Well-known member
Joined
Sep 6, 2003
Messages
2,314
Location
Rochester, NY
Corvette
Red '82 Coupe,Sebring Silver '98 Coupe
Check the EGR!!!!! There bad to get a Chunk of Carbon in them and be stuck WIDE OPEN!!!!!!! Like a BIG Vacuum Leak!!!! And then the Oxy's will tell the ECM that it's is REAL Lean,and then the ECM will tell the Injectors to Dump the Fuel to it!!!
This can show up as Random Missing,and it gets worse before it gets Better,the rougher they run the more Carbon gets knocked loose in the EGR passages!!!!

I clean or replace the EGR ,start them up and shut them off without the EGR on to blow whats loose out of them 2-3 times!!!
(Just start and shut off,It will take off like a Run away Detroit Diesel with out any throttle!!);LOL

And then I take 2 EGR gaskets and sandwich a Stainless Steel screen between them on the exhaust side to keep the carbon busted up small enough to go through the EGR without getting stuck!!!!!:upthumbs Its Spring,I've done this to about 4 GM cars and trucks in the last month!!
I bet you're right!
 

Notorious

Well-known member
Joined
Oct 9, 2005
Messages
53
Location
Confederate States of America
Corvette
Highly modified '95 A4 coupe
Wishuwerehere82,thats the biggest mystery,no codes given....thanks for the suggestion!
There are any number of problems that can cause a rich condition w/o throwing a code.
 

fedcop90vette

Member
Joined
Apr 29, 2007
Messages
22
Location
Delaware
Corvette
1990 Black Coupe
Thanks

I will check the EGR, Junk you have such a great reputation, thanks for your help! I will keep everyone posted on what happens. Thanks all!
 

SPANISHVETTS

Well-known member
Joined
Nov 5, 2002
Messages
1,143
Location
El puerto de Santa Maria Spain
Corvette
before 60,63&82 now 90 383 Stroker & 91 ZR1-Sold
Listen to Bro Junkie.

After the EGR the Cats are the next suspect.

If you do not have to meet emission standards you could block off the EGR. I would block it off first any to test it with out having to remove the plenum.

The L-98 is minimal in the computer control department. Our ECMs are just fuel management systems with a knock sensor. 99% of our electrical problems are bad ground wires and 90% of our mechanical problems are old fashion problems that any SBC mechanic with 1/2 a brain should be able to sort out.

Ask the standard questions:
Does it have fuel?
Does it have Air?
Does it have compression?
Does it have Spark?
Are they all getting to the right place at the right time?

These questions are always the same whether you are working on a 1 cylinder moped or one of our race cars.

Unless C4C5 works at the dealership keep your car at least 4 blocks away from their shop.:eek:hnoes
 

gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,547
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Listen to Bro Junkie.

After the EGR the Cats are the next suspect.
The Cats certainly could be a Player,Dose the cat's,header pipe and manifolds Look as if they've been Extremely Hot???;shrug
 

fedcop90vette

Member
Joined
Apr 29, 2007
Messages
22
Location
Delaware
Corvette
1990 Black Coupe
MEMCAL

Chevy told me my memcal/chip is bad and GM doesn't make them anymore,any suggestions where to get one?
 

wishuwerehere82

Well-known member
Joined
Sep 6, 2003
Messages
2,314
Location
Rochester, NY
Corvette
Red '82 Coupe,Sebring Silver '98 Coupe
Chevy told me my memcal/chip is bad and GM doesn't make them anymore,any suggestions where to get one?
Is this the same Chevy that just got done banging you for a tune up?

Here's one source.
http://www.tunetyme.net/westersgarage.html
[SIZE=+0]Chevrolet / Pontiac [/SIZE]
[SIZE=+0]1984-1992 CAMARO, FIREBIRD, CORVETTE[/SIZE]
[SIZE=+0]All TBI and TPI Applications 2.8V6, 305V8 and 350V8 and all customized versions of each engine or transmission combo, camshaft choice, intakes, injector changes, etc. [/SIZE]
[SIZE=+0][SIZE=+0][SIZE=+0]TBI PROM $[/SIZE][/SIZE][SIZE=+0]2[/SIZE][/SIZE][SIZE=+0]79.00 or TPI Memcal[/SIZE][SIZE=+0] $345.00[/SIZE]
 

SPANISHVETTS

Well-known member
Joined
Nov 5, 2002
Messages
1,143
Location
El puerto de Santa Maria Spain
Corvette
before 60,63&82 now 90 383 Stroker & 91 ZR1-Sold
Get the Vette out of Chevy and into a real Vette mechanic.

Memcal errors are almost always Voltage or Ground related. Has the ¨Mechanic¨ bothered to check the Alternator output?

The national debt is at $9 trillion; most of it due to Old Vettes being repaired at the Chevy dealership! :eyerole

One of the Navy boys here had a F body that GM said had a bad ABS module and pump. The estimate was over $2000. We found a chaffed power wire where it passed through the frame to the module. 10 min. work, a bit of Solder and some shrink wrap. Total cost of $2000 GM repair. About $0.08.:W

Any Idiot can read a code scanner; a real mechanic knows what is behind the codes.
 

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