496ho misfire and intermittently stalls when starting up
07-05-2015, 03:04 PM
#1
496ho misfire and intermittently stalls when starting up
I have a 2005 496ho and my problem is that it sometimes dies directly after starting up. After trying two or three times it starts and idle fine with the gear in neutral. Happens both cold and warm, but more frequent when warm. Putting down the throttle when starting doesn't help.
When in gear it idles fine the first minute or so then it starts to misfire, not very bad, but constant. Increasing the throttle slowly the misfire increase up to 2500-2800 RPM when the misfire disappear and it runs normal, no beeps or warnings. Going back off plane it idles fine for a minute then it starts to misfire again. I pulled the plugs today and they didn'tīt look good, the porcelain color goes from brownish color to black at cylinder 7 and 8. The plugs are NGK Iridium TR55IX with about 100 hours on them. When checking the plugs before both the NGKīs and the previous AC Iridums (which ran fine when changing after 300 hours) the porcelain on all plugs has always been white. Iīm going to order a scan tool tomorrow but I thought someone here maybe have an idea or guess what can cause this issue. My guess, since the plugs are dark, it should be on the ignition side, maybe a bad sensor. Which sensor controls the spark, crank or cam?
Thanks for any input!
When in gear it idles fine the first minute or so then it starts to misfire, not very bad, but constant. Increasing the throttle slowly the misfire increase up to 2500-2800 RPM when the misfire disappear and it runs normal, no beeps or warnings. Going back off plane it idles fine for a minute then it starts to misfire again. I pulled the plugs today and they didn'tīt look good, the porcelain color goes from brownish color to black at cylinder 7 and 8. The plugs are NGK Iridium TR55IX with about 100 hours on them. When checking the plugs before both the NGKīs and the previous AC Iridums (which ran fine when changing after 300 hours) the porcelain on all plugs has always been white. Iīm going to order a scan tool tomorrow but I thought someone here maybe have an idea or guess what can cause this issue. My guess, since the plugs are dark, it should be on the ignition side, maybe a bad sensor. Which sensor controls the spark, crank or cam?
Thanks for any input!
07-05-2015, 04:52 PM
#2
Banned
iTrader: (9)
Possible IAC and a dirty flame arrestor and bad and or completely dirty IAC Muffler. the 496 flame arrestor holds contaminations deep that are hard to see - clean from the inside out with brake cleaner or cleaner while off. A dirty flame arrestor especially for the 496 causes rich conditions.
Do you have DTS if so NO IAC or IAC MUFFLER
Scan the engine and look for Fault codes and low rpm parameters
Do you have DTS if so NO IAC or IAC MUFFLER
Scan the engine and look for Fault codes and low rpm parameters
Last edited by BUP; 07-05-2015 at 07:46 PM.
07-05-2015, 07:53 PM
#3
Registered
may want to have fuel pressure checked,also,make sure the rubber line from the manifold to the fuel pressure regulator is connect and not dry rotted.also check all your grounds,,seems to be a rash of bad connections lately.
07-07-2015, 02:03 PM
#4
Thanks for Your inputs! :-)
I donīt think I have a dirty flame arrestor since it runs strong wot and no soot at the transom but I will check and clean it anyway. I have read a lot of threads about the IAC problems and that it, from what I understand, also can cause problems at rpmīs over idle, I suppose it will throw a fault code when I scan the engine. Bad ground I havenīt thought of will check that along with the rubber hose to the fuel pressure regulator. Iīm still leaning towards a spark issue because of the sound of the misfire, but I have been wrong before. I will get the scan tool this weekend, will be interesting to see what it will show.
I donīt think I have a dirty flame arrestor since it runs strong wot and no soot at the transom but I will check and clean it anyway. I have read a lot of threads about the IAC problems and that it, from what I understand, also can cause problems at rpmīs over idle, I suppose it will throw a fault code when I scan the engine. Bad ground I havenīt thought of will check that along with the rubber hose to the fuel pressure regulator. Iīm still leaning towards a spark issue because of the sound of the misfire, but I have been wrong before. I will get the scan tool this weekend, will be interesting to see what it will show.
07-07-2015, 06:06 PM
#5
Banned
iTrader: (9)
Actually the ECM really has the end control for spark. Ok going back thru I thought you change spark plugs already to the AC delco's as you were saying " the previous AC Iridium". I would change the spark plugs if not already new.
Also make sure your rubber hose to the IAC is all connected and not split or cracked.
Also make sure your rubber hose to the IAC is all connected and not split or cracked.
