Attn : Dan Martin
09-27-2001, 06:38 PM
#2
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Re: Attn : Dan Martin
Originally posted by bosco500
Is there a link anywhere that tells you how to check to see if all 6 cylynders are firing? Thanks for any help.
Is there a link anywhere that tells you how to check to see if all 6 cylynders are firing? Thanks for any help.
Do you suspect your engine is not firing on all cylinders? If so, what are the symptoms?
09-28-2001, 04:41 PM
#3
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Re: Re: Attn : Dan Martin
Originally posted by Daniel B. Martin
I'm not aware of such a link.
Do you suspect your engine is not firing on all cylinders? If so, what are the symptoms?
I'm not aware of such a link.
Do you suspect your engine is not firing on all cylinders? If so, what are the symptoms?
Also I got dyno'd at maxus and you could see the jumps in the dyno line. About every 400 RPM it would dip down.
09-29-2001, 08:24 AM
#4
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Posts: 4,601
Re: Re: Re: Attn : Dan Martin
Originally posted by bosco500
Honestly I have no idea what the problem is, but when I accelerate my car feels like its VERY hesitant to get up and go.. Its kinda like every 400 RPM it will lag and then pick back up. It does it over and over again until about 4000 RPM. Almost feels like a fuel problem, but I dont know. I installed the Walbro 255 lt./hr. fuel pump last week thinking it might help but it didnt. Any ideas?
Also I got dyno'd at maxus and you could see the jumps in the dyno line. About every 400 RPM it would dip down.
Honestly I have no idea what the problem is, but when I accelerate my car feels like its VERY hesitant to get up and go.. Its kinda like every 400 RPM it will lag and then pick back up. It does it over and over again until about 4000 RPM. Almost feels like a fuel problem, but I dont know. I installed the Walbro 255 lt./hr. fuel pump last week thinking it might help but it didnt. Any ideas?
Also I got dyno'd at maxus and you could see the jumps in the dyno line. About every 400 RPM it would dip down.
If you have no MIL then you might have a fuel problem such as ...
- bad fuel pump
- bad fuel pump relay
- bad fuel filter
- bad fuel injector(s)
- bad fuel pressure regulator
You might make a fuel pressure test to obtain more clues.
Another possibility to consider is tired Oxygen Sensors.
09-29-2001, 08:26 AM
#5
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Posts: 4,601
Fuel pressure test
A fuel pressure test is a standard diagnostic test. You will find instructions and a diagram or picture in the Chilton repair manual (page 5-3) and the Haynes repair manual (page 4-3,4).
Bleed the fuel rail pressure by pulling the fuel pump fuse (#32, 15 amps) and making several attempts to start the engine (it won't start). Install a T-fitting with a pressure gauge in the flexible rubber fuel line just downstream of the fuel filter. Install the fuel pump fuse. Start the engine. With the engine idling you should see the pressure maintain a stable 34 psi. Temporarily remove the vacuum signal hose from the fuel pressure regulator. The fuel pressure should increase to 43 psi. Reconnect the vacuum signal hose and operate the throttle to vary the engine speed between idle and 3000 rpm. The fuel pressure should vary between 34 and 43 psi.
Readings less than 34 psi could be caused by an obstructed fuel filter, a weak fuel pump, or a bad fuel pressure regulator. Readings greater than 43 psi could be caused by a bad fuel pressure regulator or an obstructed fuel return line.
After turning the engine off the fuel system should hold pressure for many hours. If the residual pressure bleeds off in only one hour that is a sign of a problem... bad fuel pump check valve, injectors with an internal leak, bad fuel pressure regulator, or an external fuel leak.
Bleed the fuel rail pressure by pulling the fuel pump fuse (#32, 15 amps) and making several attempts to start the engine (it won't start). Install a T-fitting with a pressure gauge in the flexible rubber fuel line just downstream of the fuel filter. Install the fuel pump fuse. Start the engine. With the engine idling you should see the pressure maintain a stable 34 psi. Temporarily remove the vacuum signal hose from the fuel pressure regulator. The fuel pressure should increase to 43 psi. Reconnect the vacuum signal hose and operate the throttle to vary the engine speed between idle and 3000 rpm. The fuel pressure should vary between 34 and 43 psi.
Readings less than 34 psi could be caused by an obstructed fuel filter, a weak fuel pump, or a bad fuel pressure regulator. Readings greater than 43 psi could be caused by a bad fuel pressure regulator or an obstructed fuel return line.
After turning the engine off the fuel system should hold pressure for many hours. If the residual pressure bleeds off in only one hour that is a sign of a problem... bad fuel pump check valve, injectors with an internal leak, bad fuel pressure regulator, or an external fuel leak.
09-29-2001, 08:28 AM
#6
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Posts: 4,601
Oxygen Sensors - tired versus dead
There are two degrees of failure.
1) The Oxygen Sensor is "dead".
The signal from the Oxygen Sensor is outside the normal range, or completely absent. The Engine Control Module (the computer) turns on the Malfunction Indicator Light and stores one or more Diagnostic Trouble Codes. This failure mode is obvious because of the dashboard warning light.
A dead Oxygen Sensor is a severe failure and should be repaired promptly.
2) The Oxygen Sensor is "tired".
The Oxygen Sensor still works but it responds slowly to changes in the oxygen concentration in the exhaust stream. There is no MIL or DTC. This failure mode is less obvious. The symptoms are increased fuel consumption, decreased engine power, and a feeling of sluggishness. The throttle response is not crisp, like it was when the car was new. An Oxygen Sensor may become tired due to high mileage or being "poisoned" by exposure to various substances including leaded fuels, anti-freeze, anti-seize, RTV sealants, and the residue of burned engine oil. A "tired" Oxygen Sensor is still doing its job, but not performing well.
A tired Oxygen Sensor is not a severe failure and the car may be operated safely.
You may have your Oxygen Sensor(s) tested. There are electronic testers made for this specific purpose. In addition, a technician with an automotive oscilloscope can test Oxygen Sensors. The signal from a healthy sensor varies from a low threshold (around 0.2 volts) to a high threshold (around 0.8 volts), and it sweeps back and forth between those extremes about 10 times per second. If the scope trace shows the Oxygen Sensor signal failing to reach either extreme, or oscillating between them at a frequency slower than 10 cycles per second, that is evidence of a "tired" sensor.
I've read that a bad Oxygen Sensor can sometimes be rejuvenated by removing it, clamping it in a vise, and heating the sensing tip red hot with a propane torch. This is said to burn off a crust of deposits which interfere with its operation. I've never tried this torch trick myself, so cannot vouch for it's effectiveness. If you have a sensor which is already dead, you have little to lose.
For more information about Oxygen Sensors see:
http://www.volksparts.com/o2sensors.htm
http://members.aol.com/carleyware/library/o2sensor.htm
1) The Oxygen Sensor is "dead".
The signal from the Oxygen Sensor is outside the normal range, or completely absent. The Engine Control Module (the computer) turns on the Malfunction Indicator Light and stores one or more Diagnostic Trouble Codes. This failure mode is obvious because of the dashboard warning light.
A dead Oxygen Sensor is a severe failure and should be repaired promptly.
2) The Oxygen Sensor is "tired".
The Oxygen Sensor still works but it responds slowly to changes in the oxygen concentration in the exhaust stream. There is no MIL or DTC. This failure mode is less obvious. The symptoms are increased fuel consumption, decreased engine power, and a feeling of sluggishness. The throttle response is not crisp, like it was when the car was new. An Oxygen Sensor may become tired due to high mileage or being "poisoned" by exposure to various substances including leaded fuels, anti-freeze, anti-seize, RTV sealants, and the residue of burned engine oil. A "tired" Oxygen Sensor is still doing its job, but not performing well.
A tired Oxygen Sensor is not a severe failure and the car may be operated safely.
You may have your Oxygen Sensor(s) tested. There are electronic testers made for this specific purpose. In addition, a technician with an automotive oscilloscope can test Oxygen Sensors. The signal from a healthy sensor varies from a low threshold (around 0.2 volts) to a high threshold (around 0.8 volts), and it sweeps back and forth between those extremes about 10 times per second. If the scope trace shows the Oxygen Sensor signal failing to reach either extreme, or oscillating between them at a frequency slower than 10 cycles per second, that is evidence of a "tired" sensor.
I've read that a bad Oxygen Sensor can sometimes be rejuvenated by removing it, clamping it in a vise, and heating the sensing tip red hot with a propane torch. This is said to burn off a crust of deposits which interfere with its operation. I've never tried this torch trick myself, so cannot vouch for it's effectiveness. If you have a sensor which is already dead, you have little to lose.
For more information about Oxygen Sensors see:
http://www.volksparts.com/o2sensors.htm
http://members.aol.com/carleyware/library/o2sensor.htm
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