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Stall problem??

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red86

Guest
The car-1986 coupe tuned port injection manual
The problem- The car stalls when I first take off almost like its short on fuel, than it runs fine. However its just resently started to cut out shortly after taking off. Replaced ICM.The MAF was replaced before I got the car. Checked the fuel pressure tested at 38 pounds. When I got the car it had been sitting for a couple of years and the fuel pump relay and overdrive relay were both missing replaced both those and drained the fuel put new fuel in and replaced fuel filter. It acts like its starving for fuel but once shes going it runs like a rapped ape. Could it be the TPS or MAP? Its so close to running like it should but I'm new to the Corvette scene and hoping someone out there could give some words of wisdom:) Thanks
 

corvette66

Well-known member
Joined
Nov 3, 2003
Messages
519
Location
Mattawan MI
Corvette
1969 427
So if you are sitting still... and mash the trottle to the floor it will bog down for a moment, then slowly start to pick up?
you might want to try bumping the distributor a few deg either way. see how that does before spending money on the expensive electronics. Maybe try a better fuel and advance the distributor a bit. Usually when the TPS goes bad the car will stall at idle. Or idle bad. Can you hear any vacuum leaks? try putting a rubber hose/tube to your ear, and run the other end around all the vacuum ports, works like a stethescope. I used to have an 86 that had reaaly bad pick-up. turned out to be a vacuum leak. I found it with a piece of syphon hose :)
 
R

red86

Guest
I foregot to mention I checked the timing it was at 7*. I only use Chevron Supreme and it only stalls for just a moment, until recently. It now actually boggs down and cuts out when I take off in first. I also noticed that if I crank the wheel and get on it it almost dies like there is a fuel shut off or something.
 
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red86

Guest
Could this be my fuel pressure regulator? When the car is idleing the rpms float between 700 and a 1000 rpm usually calming down to 700.TPS? After driving a while it holds at about 800 but it seems to move around. Its never consistant. This is driving me nuts. Its so close to being right. It wants to run but there is diffently something not right.
 

corvette66

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Joined
Nov 3, 2003
Messages
519
Location
Mattawan MI
Corvette
1969 427
The tps would be a good start considering the fact that they are fairly inexpensive. The tps has a metal slider type contact. It could have a short or sort. But when the sensors start to fail usually they will trip the check engine light. especially a TPS or IAC. Stalling problems are always magnified when cranking the wheel simply because it's dragging the motor with the power steering pump, much like the AC will. Once you find the stalling problem the steering will be fine. AC work???
 
R

red86

Guest
When I say turn sharp I mean I was trying to do a donut and the car practically shut off. It completely fell on its face like there was some kind of fuel shut off relay tripping or something. As far as the AC working thats another issue. When I plug in the connector under the hood on the passenger side the fan (defrost) turns on regaurdless if the car is on or not so I have to run the car without heat or ac until i figure it out. I started to hear a tick under the hood. At first I thought it was a sticky lifter but I discovered that the tick is comming from the fuel injection system. You can match the ticking with the pulsating of the injectors:confused. Also when I did the fuel pressure test I noticed that there was no built up pressure in the rail when I went to bleed it off also when I shut the car off the the pressure gauge immediatly started to drop. Is this normal? I was expecting it to hold pressure. Could this be a injector problem? Its also sometimes hard to start. Sometimes it fires right up other times it crank crank crank...... than it fires up??? I tried to take it through DEQ but failed. The car passed everything with flying colors except the CO at cruise. It makes no sense the limit for CO idle is 1.2 and the car got a .03, but the cruise limit is 1.0 and I got a 1.55. How can it be so low at idle but fail at cruise. Could the injectors be pouring too much fuel in at cruise? Oh yeah there is no check engine light and it is not throwing any codes.
 

John Robinson

Gone but not forgotten
Joined
May 3, 2005
Messages
1,555
Location
Muncie, Indiana
Corvette
1993 Polo Green Coupe
I realize this is for a 93 TPS car but the principal is the same for your car.

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.


 
S

speedmaster4

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

yup...seen several TPS that were bad, no code displayed...good chance this is your prob...

BUT...first ...FIRST...put a pressure guage on the test port on the fuel rail (harbor fright sells a cheap but functional one for abt $15)...pressure should jump up to abt 40 psi when ign is switched ''on''. hold 10 psi after 12 hr with key ''off''...a dying fuel pump will sometimes give symptoms described above.
 
R

red86

Guest
I did the fuel pressure test it gauged at 38lbs but it instsntly lost all pressure when I turn the car off.
 

Robertwav1

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Joined
Jan 7, 2003
Messages
821
Location
Ocala, Florida
Corvette
1993 Blue
I'd suspect the regulator, since you have hard starts sometimes. Do you notice any black smoke at all comming from the exhaust when you have those hard starts? I don't like the fact that you're losing pressure so fast and nothing at the rail. There is a check in the fuel pump which could cause your problem but then no trace of smoke would be noticed if there is no fuel. Just something else to check or look for.
 
R

red86

Guest
I have not noticed any black smoke. I do notice a strong gas smell sometimes though. The car sat for awhile before I got it and I'm wondering if maybe one of the injectors may be bad. It Does'nt seem to have to power it should., When i on the freeway in fourth or any gear and get on it there is a rattleing sound coming from the engine. No its not pinging, its diffenly a rattle sound. I've noticed it before when I'm reving the engine by hand. Could this be a bad fuel pump? Also when I get on it when i'm going through the gears it seems to be lugging or holding back its wierd.
 

corvette66

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Joined
Nov 3, 2003
Messages
519
Location
Mattawan MI
Corvette
1969 427
"I'm wondering if maybe one of the injectors may be bad"

If one of the injectors is bad, or not working at all, put new spark plugs in it and run it for a few miles. Pull them out, and look to see which one is quite noticably different. Also if the injector is bad to the point where it won't spray (clogged), the motor should have a slight lope, or shake, due to the off balance caused by one cylinder not running right. If you do indeed locate one, try pulling the plug wire off and see if it runs any different. If there is no diference then you have a pluged injector for sure. Then you could always disconect the plug wire run it for a while and then pull the plug out stick a swab in it and see if it is wet.

Someone else might have a better way to check, but these are the "poor mans" tools. :D
 

Robertwav1

Well-known member
Joined
Jan 7, 2003
Messages
821
Location
Ocala, Florida
Corvette
1993 Blue
I have not noticed any black smoke. I do notice a strong gas smell sometimes though. The car sat for awhile before I got it and I'm wondering if maybe one of the injectors may be bad. It Does'nt seem to have to power it should., When i on the freeway in fourth or any gear and get on it there is a rattleing sound coming from the engine. No its not pinging, its diffenly a rattle sound. I've noticed it before when I'm reving the engine by hand. Could this be a bad fuel pump? Also when I get on it when i'm going through the gears it seems to be lugging or holding back its wierd.

The gas smell is a good indicator. Check the regulator. I don't know how yours is configured but it may have a vac hose on the back of it...pull it off and sniff for fuel, there shouldn't be any...if theres a trace, the diaphragm inside is bad. Do the easiest things first ... you have to start somewhere. The rattling could be anything form am exhaust rattle to a bad cat.
 
R

red86

Guest
The gas smell is a good indicator. Check the regulator. I don't know how yours is configured but it may have a vac hose on the back of it...pull it off and sniff for fuel, there shouldn't be any...if theres a trace, the diaphragm inside is bad. Do the easiest things first ... you have to start somewhere. The rattling could be anything form am exhaust rattle to a bad cat.

What do you mean bad cat? Funny you reply with all of this. My brother and I did all the test on the fuel pump EGR and the fuel regulator. We think we had narrowed it down to bad cat/bad injectors. Than on the way home I started losing power than I get on the freeway and I'm in 4th gear peddle to the floor doin 65. I pull off the nearest exit pop the hood my Headers are glowing look under the car cat is glowing but the rest of the exhaust is fine. BAD CAT???
 

Robertwav1

Well-known member
Joined
Jan 7, 2003
Messages
821
Location
Ocala, Florida
Corvette
1993 Blue
All the indicators are there! I would now take it to a reliable exhaust place and see what they think. Your gettin close. ;)
 

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