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It's New, But Is It Improved?Posted 8/13/1998By Kevin Caple
Have you ever come across a car that has a rough idle that is hard to diagnose? Recently I received a call on a car that had a fresh tune-up, good fuel and good fuel pressure. Scan data showed sensors read correctly, except MAP was a little high due to the rough idle (low vacuum). The block learn/integrator or long-term/short-term fuel trim looked a little low, possibly due to the MAP being high, yet the car "felt" lean. Replacing the O2 sensor with a known good part made no change. All the grounds were good when voltage drop was tested. Adding propane or carb spray to the intake helped the engine smooth out, but there were no vacuum leaks. Sure enough, playing a hunch, the tech pulled off the electric solenoid-style EGR and found a piece of carbon holding the pintle just off its seat. Now it all made sense. With exhaust gases being introduced back into the intake at idle (in this case the EGR was just barely open), the O2 sensor read rich because there was not much oxygen in exhaust gas. Remember, the O2 sensor is just looking at oxygen content, and low oxygen = rich mixture = take away fuel. Of course, the MAP sensor may have read a little high, but that's attributed to the rough idle. When the ECM saw higher MAP voltage, it thought the engine was under a load and added more fuel. Then the 02 sensor said way too rich and BLM/INT went lower yet. On the old diaphragm EGRs, it wasn't so bad. If you put your fingertips under the diaphragm and if it was finger-burning hot to the touch, it was a pretty sure bet the pintle was not seated tight. Next came the electric solenoid-type valves that offer very accurate EGR operation, but no easy way to tell if the pintle is seated without removing the valve and pouring solvent into the passageway to see if it leaks. Here's the "new and improved" part of the story - the linear feedback-style EGR, which is basically an electric solenoid EGR with a TPS-type device built into it, called a pintle position sensor (PPS). On a scan tool, the commanded EGR position can be monitored. The PPS will show that the EGR is doing what it has been commanded to do. If the PCM/ECM is commanding 50 percent EGR, it would expect the actual position to be reported back as 50 percent. If these don't closely match, a trouble code will be set. In this case, even if a code was not set, a scanner could be plugged in to show 0 percent commanded EGR, but actual EGR position of about 8 percent. Then you'd know there's a stuck-open EGR before opening the hood! A tip of the hat to the engineers on this one. It is truly new and improved from a diagnostic standpoint.
What ... Still No Pedal?Posted 8/13/1998By Jeff Boskowitz
You've had it. You worked like a dog to get that clutch job done on that miserable 4x4, only to go through two gallons of brake fluid and you STILL don't have a pedal. The customer drove into the shop complaining that when he towed his boat out of the water, he could feel the clutch slipping. All you need to do is replace it. Once inside, you notice the slave cylinder is leaking as well. No problem. As long as you're in there, you can replace that too. Now that you've got it back together, just bleed it and get on to the next job. Simple, right? Ford's hydraulic clutch system may be one of the most frustrating things you'll ever have to work on. Relax, elevated blood pressure doesn't help ... but patience does. The key to getting a pedal quicker on the 4x4 is to make sure the components being bled have the air pockets in a position to be expelled from the bleeder when opened. In most cases, this requires the back of the vehicle to be lifted about six inches. Another trick that works well is to bleed the system in two parts instead of trying to fight the master and the slave together. Look for the check valve where the line attaches to the slave. Remove the line, depress the valve and have an assistant slowly push the clutch pedal to the floor, not releasing until the valve is sealed. Repeat until the fluid is free of bubbles. This ensures all the air is out of the master and line first. Leave the valve closed and have your assistant lightly push on the pedal. If it is firm, there is something to work with when bleeding the slave. Reconnect the line to the slave and again, opening the bleeder first, slowly depress the pedal, being sure to seal the bleeder before the pedal is released. Continue until fluid is free of air. Check operation. A word of caution: Any air left in the slave at this point, even though the clutch does work, will eventually migrate back up the line and into the master, causing poor release and a mushy pedal ... again!
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Copyright (c) 1996-2008. Automotive Service Association. All rights reserved.
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