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infinit Q45 doesnt acclerate or go over 45mph


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mikekane0982
New User

Apr 21, 2010, 8:06 PM

Post #1 of 4 (1951 views)
infinit Q45 doesnt acclerate or go over 45mph Sign In

i have an 1992 infiniti q45 , It has a V8 with 159000 miles on it,tranny and motor run good ,no noise and shifts fine.but I replaced the cats some coils,fuel filter,maf sensor,spark plugs, My car had this problem in december and I replaced all that I just listed.but now it slowly has gotten worse then before.It has good gas pressure.the fuel pumps good.Theirs no check engine light on.The newest symptoms are it doesnt accelerate at all.I cant get it to go over 1800 rpms if I try it bucks or has no response.and the longer the drive the worse and worse it gets.I eventually cant go no more.It comes to a crawl to 30 mphs at 1500rpms.It has a rough idle but its not that bad.If I rev it in park I can get it to go up to 4000rpms but quickly goes done to 700 rpms and then wont go back up unless I take my foot off the gas.Sometimes it runs alittle better but not often enough to count.No one can figure it out since theirs no check engine light.And Im sick of getting ripped off.So please help me out in anyway.Has anyone had these similiar problems?Does anyone know what it could be?


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Apr 22, 2010, 5:39 AM

Post #2 of 4 (1944 views)
Re: infinit Q45 doesnt acclerate or go over 45mph Sign In

You just said it has a rough idle. Rough suggests it isn't burning fuel properly which probably killed the cats to begin with unless they plain rusted out.

No load revving as even a test is a good way to make scrap metal out of that engine. I'd do a compression test on this and check for exhaust restrictions,

T



mikekane0982
New User

Apr 22, 2010, 4:10 PM

Post #3 of 4 (1934 views)
post icon Re: infinit Q45 doesnt acclerate or go over 45mph Sign In

i had the cats done in december because they were bad .i also had the maf sensor fuel filter and coil done at the same time.it ran better but not 100%.it slowly got to the point it is at now.it used to sometimes not let me rev past 5000rpms while driving , it acted like it was getting stuck or like it cant go any further.and while it was acting like this , if it was a long drive it would slowly get worse.it would get down to 2000rpms and have that problem.it would slowly lose power.shorter rides were better.but now it wont go past 1800 rpms.if i try to press the gas it bogs down and sometimes bog down so much it turns off other times it feels like it cant go no where.like somethings holding back.it sounds like burrrrrrr when i press the gas.it also backfires in the intake sometimes if i hold the gas down.what can it be?could the old cats clog the mufflers and when i replaced them it freed up some flow but since it didnt fix the problem the new cats got over heated and now are clogged and its 10 times worse?


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Apr 22, 2010, 5:06 PM

Post #4 of 4 (1923 views)
Re: infinit Q45 doesnt acclerate or go over 45mph Sign In

Mufflers don't usually clog up but it's possible. At miles and age with the running rough history I'd be diagnosing for timing, valve timing, and exhaust restriction - perhaps again with even new converters. It's older and some miles on this. High RPMs without load is pushing it with about any engine. Back firing suggests valve timing, regular timing, burnt valves especially intake, weak valve springs or more.

Compression test and testing for restrictions would be good information. Checking each spark plug in comparison to others could be telling as well. Anytime an engine isn't running smoothly and well it is usually dumping unburned fuel to converters that can overheat, plug up even if relatively not that old.

As said they can rust such that connections are beyond repair but burning out from inside is usually from them working too hard for too long and checking again for restrictions would help,

T







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