I am having a problem with a 2000 Ford Explorer. It has a 4.0L engine and
200,000+ miles on the odome- ter. The vehicle originally came to our shop with
the.
Trouble Shooter Misfire, due to its potential contribution to excess vehicle emissions, is closely monitored by OBD II. Finding its cause when it occurs can be tricky. Misleading Misfire
Photo: Karl Seyfert
Karl Seyfert
appeared normal. A smoke machine was used to check for vacuum leaks (none were found). We had installed a set of injectors during the vehicle’s second visit because testing on a flow bench indicated the No. 1 injector was weak. Scan data since then has never indicated an injector failure, but I’ve noticed that the injector pulse width seems wider than normal at times, at approximately 4.5mS. The oxygen sensor is switching normally from .2 to .9 volt, indicating the PCM is in control of the fuel mixture. While consulting my service information, I found a Ford technical service bulletin that recommended valve spring replacement. A friend at a neighboring shop suggested that an intake manifold vacuum leak also might be to blame. There’s supposed to be a TSB on that problem, too. What do you think? Ignacio Gonzalez Address not given
I am having a problem with a 2000 Ford Explorer. It has a 4.0L engine and 200,000+ miles on the odometer. The vehicle originally came to our shop with the Check Engine light on and a DTC P0301 (cylinder No. 1 misfire) stored in the PCM’s memory. The spark plug wires and spark plugs looked pretty bad so we recommended a major tuneup. We cleared the DTC and returned the vehicle to the customer. The engine ran fine for a month or so before the customer returned because the Check Engine light was on again. This time a DTC P0304 (cylinder No. 4 misfire) was stored in memory. We suspected a defective ignition wire because the wire travels under the upper intake plenum to reach the No. 4 spark plug. After replacing the wire and clearing the DTC, we returned the vehicle to the customer. A couple of weeks later, he was back for the third time, this time with a DTC P0301 in memory. Inspection of the engine and related systems revealed a fuel pressure of 65 psi. Hot cranking cylinder compression ranged from a minimum of 130 psi to a maximum of 150 psi for the six cylinders. A relative (running) compression test also
Leaking intake manifold gaskets and/or valve springs have caused rough running and misfire complaints on some Ford 4.0L V6 engines (two designs were used). Before you begin disassembly based on TSB info, make sure you know which engine is under the hood.
6
December 2004
You’ve thrown a lot of information at me, Ignacio. Some of it may relate to the misfire problem and some may not. Let’s start with the TSBs. Explorers, Rangers and Mercury Mountaineers of this vintage are equipped with one of three engines: a 5.0L V8 and two different 4.0L V6s. One of the V6s has overhead valves, while the other has single overhead cams (SOHC). It’s important to know which engine your customer has before consulting the TSBs, because the bulletins may apply to one engine or the other, but probably not to both. The TSB involving the intake and exhaust valves (Ford TSB No. 02-3-2) applies to the 4.0L SOHC engine only. Affected vehicles set a DTC P0300 or P0301. When the DTC is set is very important, which is why it’s essential to consult the freeze frame data stored in the PCM before clearing any misfire DTCs. Once the freeze frame data is gone, there’s no way to recover it until the next time the problem occurs. In this case, the problem (misfire) must occur at an engine speed greater than 4800 rpm. This type of misfire (and the resulting DTC) occurs under heavy acceleration, due to higher-than-expected transient exhaust system backpressure,
Trouble Shooter
Editor & Publisher
John Lypen 248-312-2700 Executive Editor
Karl Seyfert, CMAT, LI, AF-SAE Managing Editor
Paul M. Eckstein Art Director
Harold A. Perry Detroit Editor
Tom Nash, AF-SAE 248-312-2708 Senior Writers
Bob Cerullo, AF-SAE Mike Dale, SAE Dan Marinucci, AF-SAE, L1 Mark Warren, AF-SAE, CMAT, L1 Contributing Writers
Sam Bell Bob O’Connor Paul Weissler Contributing Artist
Russell von Sauers Production Manager
Jennifer Herrmann Advertising Production Manager
Veronica Knight 248-312-2712 Circulation Manager
Dale Boehle 516-227-1401 Director of Brand Marketing
coupled with valve spring resonance points. In simpler terms: The exhaust valves may hang open slightly, causing the misfire. Install the updated parts to correct the problem, but bear in mind that this will correct an engine misfire problem above 4800 rpm only. If freeze frame data indicates your customer’s engine is misfiring at a lower rpm, look elsewhere. Intake manifold gasket leaks were handled under a full-on Ford campaign (TSB No. 00M12). Ford covered its 1997-2000 vehicles for six years or 72,000 miles, so your customer’s Explorer is unfortunately no longer covered. Once again, this TSB applies to the 4.0L SOHC engine only. Consult the TSB for information on updated gaskets and a camshaft chain tensioner, as well as installation instructions. Leaking intake manifold gaskets on this engine often produce rough running complaints when the engine is cold. The leaking gaskets admit unmetered air, diluting the mixture and causing a misfire. As the engine warms, the gaskets may swell enough to seal a little better and the engine smoothes out. The symptoms won’t return until
the engine is allowed to cool. If you don’t have a smoke machine to check the intake manifold gaskets, simple carburetor cleaner will do the job. While watching the short-term fuel trim (STFT) for each bank with your scanner, try spraying the carb cleaner near the intake manifold gasket mating surfaces (upper and lower gaskets). Watch for big changes in STFT, as the PCM attempts to compensate for the sudden addition of uninvited fuel. There’s one final thing you mentioned that may relate to the misfire DTCs: the abnormally long injector pulse width. You indicated that the injectors had been replaced, but not whether they were new. If the injectors are clogged or are receiving inadequate fuel pressure or volume, the PCM will respond the only way it knows how—by holding the injectors open longer. But this helps only if longer equals more. If only a trickle of fuel is making it through the injectors, it won’t matter how long they’re held open. An inadequate fuel supply caused by clogged injectors, a clogged fuel filter or a weak fuel pump means a leaner-than-normal fuel mixture. And that can lead to what? Repeat after me: misfire!
Lori Aemisegger 248-828-0000 Research Director
Catherine Smith Classified Advertising Manager
Donna Butera 800-858-3137 Associate Publisher
Dave Marlowe 248-312-2720 PUBLISHED BY HEARST BUSINESS PUBLISHING, INC., A UNIT OF THE HEARST CORPORATION Victor F. Ganzi President & Chief Executive Officer
George R. Hearst, Jr. Chairman
Frank A. Bennack, Jr. Vice Chairman
Richard P. Malloch President & Group Head, Hearst Business Media
William M. Wright Executive Vice President & Deputy Group Head, Hearst Business Media
William K. Baker Vice President & General Manager, Hearst Business Media
Robert D. Wilbanks Group Controller, Hearst Business Media
Kevin F. Carr President, Motor Information Systems
5600 Crooks Road, Suite 200, Troy, MI 48098
December 2004
7
