rough idle
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Joined: Mar 2001
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From: las vegas, nv.
rough idle
Here we go again! Bone stock '87 IROC 350 TPI. One day I'm sitting at a stop sign, and suddenly the idle goes rough, like someone pulled the plug or something. Since then, I've boorowed diagnostic equipment like noid lights, fluker meter, etc. Everything is in spec, even the fuel pressure. The car is acting like it has dropped a cylinder. I've run three cans of Outlaw injector cleaner through it to no avail. Any ideas, guys??
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Joined: Jan 2000
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Bob,
If you are certain the ignition system is functioning and you have good compression on all holes, you need to perform a power balance test to locate the offending cylinder(s). I had a similar problem with my TPI and the test isolated the dead holes.
To perform a power-balance test, start the engine, allow it to reach operating temperature, then unplug the IAC electrical connector while the engine is idling. Unplug the electrical connector from one injector and monitor the engine RPM as it is disconnected. The drop in idle RPM should be relatively equal through the firing order. Replace the electrical connector and go on to the next injector. You need to realize that the ECM will sense the RPM drop and attempt to compensate by adjusting the IAC, which is why it was disconnected in the first place.
Compare the RPM drop at each cylinder. Don't forget to replace the IAC connector. If one or more injectors caused little or no change in RPM, it is not flowing fuel at the correct rate. NOTE: This test will not be accurate if the ignition system is not in good order or compression is low on a cylinder.
This test allowed me to identify two defective injectors, and test results after removal of the injectors confirmed that - two of them had very poor spray patterns and low flow rates. The engine had 18,000 miles and I had already tried several types of injector cleaner in the fuel tank with no improvement.
As always, if you discover a bad injector, I would recommend contacting Cruzin' Performance.
------------------
Later,
Vader
------------------
"Fear is how I fall, Confusing what is real..."
Adobe Acrobat Reader
[This message has been edited by Vader (edited May 27, 2001).]
If you are certain the ignition system is functioning and you have good compression on all holes, you need to perform a power balance test to locate the offending cylinder(s). I had a similar problem with my TPI and the test isolated the dead holes.
To perform a power-balance test, start the engine, allow it to reach operating temperature, then unplug the IAC electrical connector while the engine is idling. Unplug the electrical connector from one injector and monitor the engine RPM as it is disconnected. The drop in idle RPM should be relatively equal through the firing order. Replace the electrical connector and go on to the next injector. You need to realize that the ECM will sense the RPM drop and attempt to compensate by adjusting the IAC, which is why it was disconnected in the first place.
Compare the RPM drop at each cylinder. Don't forget to replace the IAC connector. If one or more injectors caused little or no change in RPM, it is not flowing fuel at the correct rate. NOTE: This test will not be accurate if the ignition system is not in good order or compression is low on a cylinder.
This test allowed me to identify two defective injectors, and test results after removal of the injectors confirmed that - two of them had very poor spray patterns and low flow rates. The engine had 18,000 miles and I had already tried several types of injector cleaner in the fuel tank with no improvement.
As always, if you discover a bad injector, I would recommend contacting Cruzin' Performance.
------------------
Later,
Vader
------------------
"Fear is how I fall, Confusing what is real..."
Adobe Acrobat Reader
[This message has been edited by Vader (edited May 27, 2001).]
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