aa8jzdial Posted February 21, 2006 Share Posted February 21, 2006 Very odd symptom. 1990 Legacy, 150k miles, manual 2 wd. When driving switching climate control from a/c to heat causes a definate misfire. Also occasionally see the cel toggle on and off when doing this. What sort of spike could be introduced? Something involving the deenergization of the a/c clutch solenoid maybe? Is there a counter emf diode that may have failed? Also, son say's he thought it may also occur when going from "off" to "heat" although I haven't seen it yet. Not a huge issue if the pulse doesn't work it's way back to the ecu. Anyone else ever see this odd situation? tnx rick w. mi. Link to comment Share on other sites More sharing options...
nipper Posted February 21, 2006 Share Posted February 21, 2006 This is easy, but weird. The heater controls are vaccum actuated. Aparently you have a vacume leak under the dash, then when you switch to heat, is leaning out the fuel mix and causing the missfire and the CEL light. This should be easy to find, as its under the dash between the heater control and heater door motor. nipper Link to comment Share on other sites More sharing options...
OB99W Posted February 21, 2006 Share Posted February 21, 2006 Nipper may well be right about the vacuum leak, especially if the misfire is continuous and not just a one-time event when the switching occurs. On the other hand, if you want to concentrate on possible electrical problems, I wouldn't look to defective back-emf-suppression diodes as the first choice. Rather, I'd suggest checking that all chassis ground connections are good (tight, low resistance). Since you seem aware of electrical/electronic terminology, I assume that you could use a multimeter and check for volage drops across connections, etc. A bad ground or two can sometimes cause "interesting" (and varied, depending which grounds are bad) symptoms. Link to comment Share on other sites More sharing options...
aa8jzdial Posted February 21, 2006 Author Share Posted February 21, 2006 Thanks for the insight gentlemen. I feel more comfortable with electrical/electronic issues. My batting average with vacuum problems is poor at best. Either way it is going to take a bunch of digging in the shop manuals and laying under the blasted dash. Thanks again guys. rick w mi Link to comment Share on other sites More sharing options...
OB99W Posted February 21, 2006 Share Posted February 21, 2006 [...]Either way it is going to take a bunch of digging in the shop manuals and laying under the blasted dash.[...]You may need to get under the dash, but many of the ground connections tend to be on the other side of the firewall (in the engine compartment). Link to comment Share on other sites More sharing options...
nipper Posted February 21, 2006 Share Posted February 21, 2006 Thanks for the insight gentlemen.I feel more comfortable with electrical/electronic issues. My batting average with vacuum problems is poor at best. Either way it is going to take a bunch of digging in the shop manuals and laying under the blasted dash. Thanks again guys. rick w mi Fisrt thing i would do is remove the HVAC control, and find out what cacum line goes to the heater door motor. Remove that line, place your finger over the vacum port. With the car running turn on the heat while your blocking the port. If you get no missfire, you found your problem. BTW, when the heat is on, are you getting hot air out of any other vents or the defrosters? nipper Link to comment Share on other sites More sharing options...
aa8jzdial Posted February 22, 2006 Author Share Posted February 22, 2006 The misfiring is not continuous at all. Just one real quick misfire. Not sure if it is vacuum related. Seems the sputtering might last for a few seconds or so as someone else mentioned. Are the hvac controls best removed by popping off the control panel? Haven't been there on this vehicle yet. As typing this it occured to me that if a/c related, removing the a/c clutch might help isolate the trouble. Phooey. The clutch has been disconnected since who knows when. Certainly tends to knock out the counter emf issue. This is not a burning issue as the cars is fine other then this. As it is approaching 10 degs outside I may procrastinate just a bit. Still would be nice to collect a few more thoughts though for if and when the weather warms up. again, tnx all rick w mi Link to comment Share on other sites More sharing options...
nipper Posted February 22, 2006 Share Posted February 22, 2006 The misfiring is not continuous at all. Just one real quick misfire. Not sure if it is vacuum related. Seems the sputtering might last for a few seconds or so as someone else mentioned. Are the hvac controls best removed by popping off the control panel? Haven't been there on this vehicle yet. As typing this it occured to me that if a/c related, removing the a/c clutch might help isolate the trouble. Phooey. The clutch has been disconnected since who knows when. Certainly tends to knock out the counter emf issue. This is not a burning issue as the cars is fine other then this. As it is approaching 10 degs outside I may procrastinate just a bit. Still would be nice to collect a few more thoughts though for if and when the weather warms up. again, tnx all rick w mi be interesting to see if it goes away when the weather is warmer (not because your not using heat) nipper Link to comment Share on other sites More sharing options...
OB99W Posted February 23, 2006 Share Posted February 23, 2006 I found an interesting piece from "Motor" magazine: http://www.findarticles.com/p/articles/mi_qa3828/is_199810/ai_n8811652 This relates to a '93, so the wiring info may not be accurate for a '90, but the concept might be applicable. Here's an excerpt from the article (what appear to be "typos" are probably due to scanning using optical character recognition): -------------------------------- Subaru Engine stumble with a/c on. Zexel air conditioner-equipped 1993 Legacy models that stumble when the a/c compressor cycles can be fixed by doing a little ECM rewiring. First, start the engine and get it up to operating temperature with the alc on. Then, pull and replace the a/c relay in the main underhood fusebox several times to try to duplicate the condition. You may vvind up doing this 20 times or more. If you can't make the stumble happen, try doing the same thing with the la/c main fan relay If you get the stumble this time, disconnect the battery ground cable, then the green fuel pump relay connector (B30). Connect about 10 inches of 14gauge wire to the yellow 14-gauge wire at tenll 2 with a Scotchlok connector. Don't cut the wire at the relay! Route this new wire carefully to the ECM by pulling connector B48, then cutting the yellow/red wire at terminal 15 about 3 inches from the connector. Use another Scotchlok to connect the other end of the new wire to the yellow/red wire, then reconnect it to terminal 15. -------------------------------- Link to comment Share on other sites More sharing options...
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