Help! 90 Convertible running very bad!

[skitch]

My 90 model is not running good at all. Almost not running. It will start up, but it acts like its flooding. Gas fumes are very strong, and it won't stay running. I drove it the other day and notice a severe lack of power , got it home and opened up the shop, it wouldn't even start back. THe next day it started , but running very bad. Any ideas?
Thanks
Skitch

 

[stang-etr96]

How long had it been sitting since being started or run? Bad gas, fouled plugs ????

 

[skitch]

It never sits more than a week or so. New plugs about 3 months ago and gas is good. I just filled it up , I noticed it was slugish before I got gas.

 

[Kenny]

Just a guess. Wifes car (Saturn) did that. Had a bad MAP sensor. So rich cat got red and internal meltdown. New cat new sensor ran fine.

 

[G Winter]

It could be a pressure regulator gone bad. Unhook the vacuum hose to it and see if there is gas in it or if you can smell gas in it.

Glenn

 

[lobobuzz]

What a bummer... good luck with figuring the issue out, Skitch.

 

[Kenny]

It could be a pressure regulator gone bad. Unhook the vacuum hose to it and see if there is gas in it or if you can smell gas in it.

Glenn

That's a good suggestion

 

[boomdriver]

I forget if that yr had a mass air sensor or if it has the "manifold air-pressure" sensor.
It sounds like a bad MAF or MAF relay. That will make it evil acting at best, barely runs, burps, chokes and backfires and will not take throttle. If it dies it will not restart. Might start up in an hour or day... The gas smell might be the unburned or excess fuel. When the Mass Air sensor fails, it has no clue how much fuel to use, so it just dumps it in. Usually so rich that it can;t run. I am sure that the MAP system has similar symptoms because both systems measure the air flow so the correct fuel amounts can be added for a combustable mixture.
It has a fail-safe mode in the ECM that it SHOULD set after it runs with a major sensor malfunction for a minute or so.. Then it should go to a programmed operation that will allow it to run semi normally to get it home. Also known as the "limp-home mode". If it is NOT going into limp home mode, then that is a clue that the problem may be something other than a sensor.
Is it setting a trouble code? Ck Eng lite on? Establish what the code is. There are list of trouble codes and what each one means.

I had an injector wire short out once, that made the whole bank short and stick open. That dumped so much gas so fast that it actually flooded the crankcase with gasoline. When it first fired after much screwing around, it squirted liquid gasoline out of the exhaust. It took 3 oil changes and five showers before I stopped smelling gas.

 

[G Winter]

I forget if that yr had a mass air sensor or if it has the "manifold air-pressure" sensor.
It sounds like a bad MAF or MAF relay. That will make it evil acting at best, barely runs, burps, chokes and backfires and will not take throttle. If it dies it will not restart. Might start up in an hour or day... The gas smell might be the unburned or excess fuel. When the Mass Air sensor fails, it has no clue how much fuel to use, so it just dumps it in. Usually so rich that it can;t run. I am sure that the MAP system has similar symptoms because both systems measure the air flow so the correct fuel amounts can be added for a combustable mixture.
It has a fail-safe mode in the ECM that it SHOULD set after it runs with a major sensor malfunction for a minute or so.. Then it should go to a programmed operation that will allow it to run semi normally to get it home. Also known as the "limp-home mode". If it is NOT going into limp home mode, then that is a clue that the problem may be something other than a sensor.
Is it setting a trouble code? Ck Eng lite on? Establish what the code is. There are list of trouble codes and what each one means.

I had an injector wire short out once, that made the whole bank short and stick open. That dumped so much gas so fast that it actually flooded the crankcase with gasoline. When it first fired after much screwing around, it squirted liquid gasoline out of the exhaust. It took 3 oil changes and five showers before I stopped smelling gas.

The 90 has MAP not MAF

Glenn

 

[John Robinson]

Don't forget the TPS

I know this is for a 93 but I believe the principal is the same for any TPS system

Hope this sheds some light on the tps for you

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.

I used a couple of straight pins through the wires to hook the meter on

 

[vetteboy86]

I know it is an obvious question, but is the SES light on? If it isn't, that does not mean that there are not any codes. The light may be malfunctioning. It is very easy to retrieve codes. If you do not know the procedure we can walk you through it.

 

[skitch]

I know it is an obvious question, but is the SES light on? If it isn't, that does not mean that there are not any codes. The light may be malfunctioning. It is very easy to retrieve codes. If you do not know the procedure we can walk you through it.

Thanks guys. I have been reading the Service Manual and checking for codes. There are no codes present.Learning alot about the ecm codes though. I believe you guys have some good ideas and I will check the MAP sensor if I can find it.The cars is running very rich, but it will idle fine. It wont take any fuel when I give it the throttle.

 

[skitch]

Well its not the MAP, just replaced that and no change. Looks like I'll be checking the Fuel Pressure Regulator next.

 

[boomdriver]

just pull the vacuum line and see if its wet with gas. A good fuel pressure regulator has a rubber diaphram between the cap that has the vac, and the actual fuel flow. When that diaphram breaks or leaks, it allows gas to be sucked into the vac system and basically floods the intake/plenum with gas. If the diaphram is intact, the vac line to the regulator will be dry and have no gas smell.

Could this be as simple as dirty injectors? If injectors get dirty or sticky they can dump too much gas with each pulse. Fuel is regulated by the time the injector is open, so when they get dirty they can stick or slow down. These things operate on mili-second pulses, so cleanliness is critical. Lucas injector cleaner works, and one of the dura-lube mfg has a treatment that did also work. Most injector cleaners are junk and may even damage the rubber in some fuel systems. Beware the cheap stuff !
Some people still use Marvel Mystery Oil once or twice a yr in the tank. Not sure if cats appreciate that or not....

 

[sstearns2]

Well its not the MAP, just replaced that and no change. Looks like I'll be checking the Fuel Pressure Regulator next.

Does it still have the original fuel injectors? You can check the resistance between the pins on the fuel injectors. It should be 16 ohms if I remember right. The resistance goes down as the ethanol in the 'new' fuels eat the coils and eventually the injector stops working. There are lots of threads on new fuel injectors.

The new injectors are ethalol proof.

You might want to pull the throttle body off and clean the inside of it and the idle air controller attached to it. It should really be done every once in a while.

Another thought is the PCV valve on the drivers side valve cover could be stuck open. It's cheap to change that.

Anyhow, just some thoughts. My guess is that a couple fuel injectors have gone bad.

Scott

 

[skitch]

I did pull the vacuum line off the pressure regulator and it was dry. I was planning on putting new injectors in soon anyway.Anyone have suggestions where to get them?

 

[skitch]

I have used Lucus injector cleaner in this car before. It stii has the factory injectors also. I did notice it started idling rough in the past. I was considering replacing the injectors also.

 

[John Robinson]

Save your money

Before throwing parts at your problem run down all the things that you can do without spending a fortune on parts.

Check all the vacuum lines for leaks

Check the egr to make sure it is not hanging open

Check the egr solenoid valve

Again check the TPS

Check the grounds to make sure they are not sending false signals to the ECM

As already suggested do the volt check on the injectors.

Make sure all the electrical connectors are clean inside and making good contact.

One of the problems with the codes we get is that the code can only suggest a possible problem in a circuit. For instance I was getting a code for a lean right bank 02 sensor. That did not mean the sensor was bad just that the exhaust gas was lean. The cure was a new fuel filter that would allow the ecm to have all the fuel it needed to respond to the engine throttle therefore the 02 sensor no longer sensed a condition caused by a low volume of fuel and it did not need to be replaced.

Just because it is a Corvette does not mean it is some sort of exotic car. The fact is that it is just that a car with the same requirements as any other car when it comes to diagnosis and care. No Mystery here.

 

[sstearns2]

I agree with not just throwing parts at the car, but if it has the original injectors then it's just a matter of time before they give you problems even if they are not causing the current issue.

There are lots of opinions on injectors... I used these. Great price and the motor runs great...

Corvette, Camaro, Firebird, GTO Only - L98 CORVETTE, CAMARO, F'BIRD - 1986-1992 Corvette, Camaro Pontiac T/A Bosch Design III 22lb Fuel Injector - Fuel Injector Connection

Scott

 

[skitch]

I will do more checks. I already checked the vacuum lines and all. Like I said, there are no codes in the ECM. I was going to replace the injectors anyway because of a rough idle condition thats been going on for awhile. But it ran fine off idle. Are those injectors the same ones on Ebay? Seems like a good deal.