is it possible to have vac leak in climate control cause lean fuel condition?


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I am still trying to track down a lean fuel condition and I have checked and/or replaced almost everything. Again the vehicle is a 95 Jimmy W series Vortec 4x4 (OBD2 switchover year).
When I scan the data stream, I get a +25% on long term fuel trim. Heres what Ive done to eliminate the problem:
1. replaced the fuel pressure regulator and nut kit on the CPI unit 2. plugs/wires/cap/rotor 3. replaced all old looking vac hoses and tested them for leaks after (all good) 4. new fuel pump and filter 5. egr, IAT, MAP clean and gasket replace (TPS adjusted checked ok) 6. O2 sensor replaced and tested
The only other thing I can think of is that the clmate control switch has a leak (read:hiss) in it and needs to be replaced. Would a leak at this switch cause the lean fuel condition? I had a bad coil before also so I may try replacing that also (I have one kicking around already so why not..)
There is a slight hesitation off the line but its bareley noticable. Every once in awhile I get a random misfire code also. With all the lights off in the shop, I cannot see any arcing of the wires, cap, etc. Does this sound like it could also be the ignition module? As far as I know it times the spark/advance??
Thanks again! I appeciate all your help here guys! Andrew.
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<HTML> <HEAD> <TITLE>is it possible to have vac leak in climate control cause lean fuel condition?</TITLE> </HEAD> <BODY> <FONT FACE="Verdana">I am still trying to track down a lean fuel condition and I have checked and/or replaced almost everything. &nbsp;Again &#8211; the vehicle is a 95 Jimmy W series Vortec 4x4 (OBD2 switchover year).<BR> <BR> When I scan the data stream, I get a +25% on long term fuel trim. &nbsp;Here&#8217;s what I&#8217;ve done to eliminate the problem:<BR> <BR> </FONT><OL><LI><FONT FACE="Verdana">replaced the fuel pressure regulator and nut kit on the CPI unit </FONT><LI><FONT FACE="Verdana">plugs/wires/cap/rotor </FONT><LI><FONT FACE="Verdana">replaced all old looking vac hoses and tested them for leaks after (all good) </FONT><LI><FONT FACE="Verdana">new fuel pump and filter </FONT><LI><FONT FACE="Verdana">egr, IAT, MAP clean and gasket replace (TPS adjusted &#8211; checked ok) </FONT><LI><FONT FACE="Verdana">O2 sensor replaced and tested<BR> </FONT></OL><FONT FACE="Verdana"> &nbsp;<BR> The only other thing I can think of is that the clmate control switch has a leak (read:hiss) in it and needs to be replaced. &nbsp;Would a leak at this switch cause the lean fuel condition? &nbsp;I had a bad coil before also so I may try replacing that also (I have one kicking around already so why not..)<BR> <BR> There is a <B>slight</B> hesitation off the line but it&#8217;s bareley noticable. &nbsp;Every once in awhile I get a random misfire code also. &nbsp;With all the lights off in the shop, I cannot see any arcing of the wires, cap, etc. &nbsp;Does this sound like it could also be the ignition module? &nbsp;As far as I know it times the spark/advance??<BR> <BR> Thanks again! &nbsp;I appeciate all your help here guys!<BR> Andrew.<BR> </FONT> </BODY> </HTML>
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is it possible to have vac leak in climate control cause lean fuel condition?Do you have the proper fuel pressure for this engine? Look at the baro reading on the scanner does it coincide with your area, this can cause a lean condition that escapes diagnosis. I'd doubt if a leak in the hvac controls could skew your mixtrue with such small lines, how is the idle vacuum by the way?
face=Verdana>I am still trying to track down a lean fuel condition and I have checked and/or replaced almost everything. &nbsp;Again the vehicle is a 95 Jimmy W series Vortec 4x4 (OBD2 switchover year).<BR><BR>When I scan the data stream, I get a +25% on long term fuel trim. &nbsp;Heres what Ive done to eliminate the problem:<BR><BR></FONT> <OL> <LI><FONT face=Verdana>replaced the fuel pressure regulator and nut kit on the CPI unit </FONT> <LI><FONT face=Verdana>plugs/wires/cap/rotor </FONT> <LI><FONT face=Verdana>replaced all old looking vac hoses and tested them for leaks after (all good) </FONT> <LI><FONT face=Verdana>new fuel pump and filter </FONT> <LI><FONT face=Verdana>egr, IAT, MAP clean and gasket replace (TPS adjusted checked ok) </FONT> <LI><FONT face=Verdana>O2 sensor replaced and tested<BR></FONT></LI></OL><FONT face=Verdana>&nbsp;<BR>The only other thing I can think of is that the clmate control switch has a leak (read:hiss) in it and needs to be replaced. &nbsp;Would a leak at this switch cause the lean fuel condition? &nbsp;I had a bad coil before also so I may try replacing that also (I have one kicking around already so why not..)<BR><BR>There is a <B>slight</B> hesitation off the line but its bareley noticable. &nbsp;Every once in awhile I get a random misfire code also. &nbsp;With all the lights off in the shop, I cannot see any arcing of the wires, cap, etc. &nbsp;Does this sound like it could also be the ignition module? &nbsp;As far as I know it times the spark/advance??<BR><BR>Thanks again! &nbsp;I appeciate all your help here guys!<BR>Andrew.<BR></BLOCKQUOTE></FONT></BODY></HTML>
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Shep,
Sorry about not hitting you back on this sooner. My vac gauge was at my friends garage. Anyway, fuel pressure stands at 58 with key on engine off and about 52 while running. It holds above 52 for over an hour so I assume this is acceptable. There is no issue with startup other than the fuel trim swings.
As for vac readings. 18-19in Hg at idle with no wide swings indicating any engine damage, blown gaskets or major timing issues. I replaced the MAP sensor and pigtail because there was an intermittent ground inside the sensor. I do, however, still have +25% on long term fuel trim. Short Term checks out flat with no issues. TPS is operating perfectly and my propane test on all intake gaskets, EGR, etc showed no variation in rpm. It would appear that the vac reading and leak tests came back normal but I may have missed something. I am starting to suspect a bad pintle in the EGR although I did test it previously when it was cleaned out and serviced and it checked out ok in 3 positions. The main drivability issue now is hesitation under 2-3k rpms on take off (feels like a bad rotor or ign miss). All wires check out ok, no sparks arcing when I kill the lights in the garage. Has anyone had this kind of issue with a faulty ignition module??
Im going to disable the secondary ignition and fire the poppets into a jar or something to check for anything whacky. At that point if I cant find anything I think I will fill the engine bay with quad mix and grow daisies out of it.
Thanks! Andrew.
in article 1179000903 snipped-for-privacy@sp6iad.superfeed.net, Shep at snipped-for-privacy@capital.net wrote on 5/12/07 4:13 PM:

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<HTML> <HEAD> <TITLE>Re: is it possible to have vac leak in climate control cause lean fuel condition?</TITLE> </HEAD> <BODY> <FONT FACE="Verdana">Shep,<BR> <BR> Sorry about not hitting you back on this sooner. &nbsp;My vac gauge was at my friend&#8217;s garage. &nbsp;Anyway, fuel pressure stands at 58 with key on engine off and about 52 while running. &nbsp;It holds above 52 for over an hour so I assume this is acceptable. &nbsp;There is no issue with startup other than the fuel trim swings.<BR> <BR> As for vac readings. 18-19in Hg at idle with no wide swings indicating any engine damage, blown gaskets or major timing issues. &nbsp;I replaced the MAP sensor and pigtail because there was an intermittent ground inside the sensor. &nbsp;I do, however, still have +25% on long term fuel trim. &nbsp;Short Term checks out flat with no issues. &nbsp;TPS is operating perfectly and my propane test on all intake gaskets, EGR, etc showed no variation in rpm. &nbsp;It would appear that the vac reading and leak tests came back normal but I may have missed something. &nbsp;I am starting to suspect a bad pintle in the EGR although I did test it previously when it was cleaned out and serviced and it checked out ok in 3 positions. &nbsp;The main drivability issue now is hesitation under 2-3k rpms on take off (feels like a bad rotor or ign miss). &nbsp;All wires check out ok, no sparks arcing when I kill the lights in the garage. &nbsp;Has anyone had this kind of issue with a faulty ignition module?? &nbsp;<BR> <BR> <BR> I&#8217;m going to disable the secondary ignition and fire the poppets into a jar or something to check for anything whacky. &nbsp;At that point if I can&#8217;t find anything I think I will fill the engine bay with quad mix and grow daisies out of it.<BR> <BR> Thanks!<BR> Andrew.<BR> <BR> <BR> <BR> in article 1179000903 snipped-for-privacy@sp6iad.superfeed.net, Shep at snipped-for-privacy@capital.net wrote on 5/12/07 4:13 PM:<BR> <BR> </FONT><BLOCKQUOTE><FONT SIZE="2"><FONT FACE="Arial">Do you have the proper fuel pressure for this engine? Look at the baro reading on the scanner does it coincide with your area, this can cause a lean condition that escapes diagnosis. I'd doubt if a leak in the hvac controls could skew your mixtrue with such small lines, how is the idle vacuum by the way?<BR> </FONT></FONT></BLOCKQUOTE><FONT FACE="Verdana"><BR> </FONT> </BODY> </HTML>
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Sound like you could use a diagnostic smoke machine... they are perfect for finding any and all leaks. Check out www.ntshoptools.com for the best deal in smoke machines.
Gene
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