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Car runs bad after it gets hot

DC/NH

Well-known member
Joined
Apr 1, 2002
Messages
48
Location
Deering,NH,US
Corvette
94 Polo Green 6 Speed Coupe
First I want to say I before putting it away for the winter I change plugs and wire in my 94 6 speed with 53k on it.

I have had the car for 5 year and since 21k.

It has always ran smooth and I have taken it on long trips. When I took it out in Spring after winters stoarge it started to skip so I put in some textron. That usally does thew trick but yesterday it ran real rough, smoked, bucked and I didn't think I would make it home. I got out and let it rest. Went back to start it up and everythinbg was fine. It never blew a code even when it ran rough.

My firend stays it may be O2 time and that I have 2 that I can change myself with the car up on ramps.

Questions are?

Do you think this could be it?

How many does a 94 LT1 have?

Where should I get them?

Are they easy to change?

Cheers,;help
 

LT4man

Well-known member
Joined
Jun 25, 2003
Messages
2,214
Location
Chicago
Corvette
96 Collectors Edition LT4
I would put some new gasoline in it and drive it some miles. Sounds like the gas got a little stale.

If it is not throwing any codes, I would not throw any money at it. You did a major tune-up before putting it away. I would think you would be OK!

SAVE THE :w
 

G Winter

Well-known member
Joined
Aug 21, 2004
Messages
2,177
Location
NW Iowa
Corvette
1990 red convert 6 sp
I agree with Greg, todays gas has a terrible shelf life.I don't know how injectors react to it but I know Sea Foam seems to do wonders for bad gas.
Sea Foam is a good product all around.


Glenn
:w
 

DC/NH

Well-known member
Joined
Apr 1, 2002
Messages
48
Location
Deering,NH,US
Corvette
94 Polo Green 6 Speed Coupe
My concern is when i started it up after a 1 hour rest everything was fine, smooth in fact. I didn't mention that it did this once at the end of last year and I pulled over waited about 15 minutes and started it up everything back to normal.

I think I will explore the O2 sensors becasue at 53k and 13 years its probably time and i don't think a waste of $$.

What brand and how many O2's does a 94 need?
 

John Robinson

Gone but not forgotten
Joined
May 3, 2005
Messages
1,555
Location
Muncie, Indiana
Corvette
1993 Polo Green Coupe
You might check the voltage on the TPS. I have had the TPS go bad without a code. Remember that the TPS basically tells the ECM how much fuel to put through the injector's. If it is not functioning right it could cause the ECM to make the engine run rich or lean. In which case the O2 sensor would go crazy. ;help

Throttle Position Sensor (TPS)
Copied from 1993 Service Manual
The Throttle Position sensor (TPS) is a potentiometer connected to the throttle shaft on the throttle body. It is a potentiometer with one end connected to 5 volts from the ECM and the other to ECM ground. A third wire is connected to the ECM to measure the voltage from the TP sensor. As the throttle valve angle is changed (accelerator pedal moved), the voltage output of the TP sensor also changes. At a closed throttle position, the voltage output of the TP sensor is low (approximately .5 volt). As the throttle valve opens, the output voltage should be approximately 5 volts.

By monitoring the output voltage from the TP sensor, the ECM can determine fuel delivery based on throttle valve angle (driver demand). A broken or loose TP sensor can cause intermittent burst of fuel from the injectors and cause an unstable idle, because the ECM detects the throttle is moving.

If the TP sensor circuit is open, the ECM will set a DTC 22. If the TP sensor circuit is shorted a DTC 21 will be set. A problem in any of the TP sensor circuits will set either a DTC 21 or 22. Once a DTC is set, the ECM will use a default value for TP sensor, and some vehicle performance will return.

A personal note, when my TPS failed it DID NOT set a code other than to tell me the ECM was bad.


 

LT4man

Well-known member
Joined
Jun 25, 2003
Messages
2,214
Location
Chicago
Corvette
96 Collectors Edition LT4
My concern is when i started it up after a 1 hour rest everything was fine, smooth in fact. I didn't mention that it did this once at the end of last year and I pulled over waited about 15 minutes and started it up everything back to normal.

I think I will explore the O2 sensors becasue at 53k and 13 years its probably time and i don't think a waste of $$.

What brand and how many O2's does a 94 need?

My 96 LT4 has 90,000 miles. I bought it new. It has four (4) oxygen sensors and they have never been replaced. I tell you this, because even after replacing them, your problem could still be there. Even as a maintenance item, they are not necessary to replace.

I owned an auto & truck repair shop for 20 years. I have never liked throwing parts at a car to see what works. Just my opinion.

Just as a point of information, your sensors were designed and built by Robert Bosch. Chevy uses them for a reason. They are very dependable.

SAVE THE :w
 

G Winter

Well-known member
Joined
Aug 21, 2004
Messages
2,177
Location
NW Iowa
Corvette
1990 red convert 6 sp
One other thing to look at. There is a chance that you have a converter getting plugged.

Glenn
:w
 
S

speedmaster4

Guest
you also have typical early symptoms of fuel pump failure...our numerous probs with GM in-tank fuel pumps have led to the conclusion that the pumps are good for 10 years OR 100k miles, whichever comes first...it's an under $100 DIY fix, get the short 'wiring harness' with the new pump also.
 

DC/NH

Well-known member
Joined
Apr 1, 2002
Messages
48
Location
Deering,NH,US
Corvette
94 Polo Green 6 Speed Coupe
I went to drive the car again for a distance. The car drives around locally and "cool" just fine. Yesterday was a hot & humid day. At the 25-mile point it started to get rough again and worse by the mile, NO CODES at all. I shut the car off at a gas station went in get a drink and wait. Started it up and it was fine temp was about 165. As soon as the temp got to 220 wham it started again. I wanted to nurse it home so I stopped again. When I was stop and shut the car off the temp went to 250 and I lifted the hood and there was some steam/smoke. I closed the hood and it started to rain so I waited it out. After the rain past I started it up, ran great so i cruised home. The temp never got to 220 so i never had a problem.

No codes ever blown, I have changed the wires and plugs last year, it only has 53K on it and has been babied, garaged over the winter (I live in NH). Every year when i start her up I use Textron in the gas.

I am about to make an appointment to a Dealer but i hate to get ripped off and maybe over changed with some ECM thing when it could be something else.

Does this additional info help key anything among you?
 

Ghost~3~

Well-known member
Joined
Oct 18, 2003
Messages
81
Location
So.San Francisco Ca.
Corvette
1985 Blue Coupe
I had a "Seeping" Heater control valve on my '87, Don't know if your's used one of them as it's 9 year's Newer than mine??? On mine it's located on the far right side of the fire wall next to the fender. That was LAST year on mine and I have
right at 70K showing on the mileage.

Ever had that thermostat changed?? I've seen some Break and get cocked sideway's, and at LOW speed will pass enough water, But at HIGHER speed's
thing's tend to get somewhat HOT.

Figured I'd suggest these possibilites, as I just changed out the Water Pump & Stat as a part of Preventative Maintenance, as I had the Intake Plenum Off to
replace a bad EGR Valve anyway.
 

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
I do not think that it is an 02 sensor problem but that is easy enough to check with a simple voltmeter. Do a search on the forum an you will find plenty of info on how to check the O2 sensor. You can also check it with the on board diagnostic feature of the ECM.

How is the coolant level? What color is the smoke?

Something is breaking down when it gets hot. It could be electrical or mechanical. Go back to basics instead of blaming the Electronics.
Do you have fuel?
Do you have air?
Do you have compression?
Do you have spark?
Are they all getting to the right place at the right time?

Until these questions are answered throwing money at it is a crap shot.
 

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