85 still having problems
Thread Starter
Instructor
Joined: Oct 2009
Posts: 202
Likes: 9
From: Tucson
85 still having problems
I've been battling a problem in my 85 for a month now, and this is the second thread on it. I'm just out of options.
Overall the motor is sluggish. Its is ok at part throttle though sluggish. At WOT there is no power, and the motor detonates bad. The PCM throws no codes. Last weekend I completely removed the TPI, and installed new gaskets from the heads up. I check the reading on the TPS, and its within spec. I can disconnect the MAF, and the same thing happens. I replaced all of the vacuum lines. I checked the fuel pressure while driving. I checked the timing. It doesn't overheat. It sounds like a wicked vacuum leak, but I can't find one. What else can I check?
Overall the motor is sluggish. Its is ok at part throttle though sluggish. At WOT there is no power, and the motor detonates bad. The PCM throws no codes. Last weekend I completely removed the TPI, and installed new gaskets from the heads up. I check the reading on the TPS, and its within spec. I can disconnect the MAF, and the same thing happens. I replaced all of the vacuum lines. I checked the fuel pressure while driving. I checked the timing. It doesn't overheat. It sounds like a wicked vacuum leak, but I can't find one. What else can I check?
Le Mans Master
Joined: Feb 2005
Posts: 6,486
Likes: 566
From: Clearwater Florida
Have you checked your balancer and its timing mark for accuracy ? theres rubber between the hub and the outer ring and they have been known to slip ... this could cause your timing to be off substantially ...
Team Owner
Joined: Jan 2003
Posts: 20,335
Likes: 264
From: Summerland B.C. Canada
Race Director
Joined: Jun 1999
Posts: 14,924
Likes: 9
From: Merritt Ils Fl
Following what C409 said: Codes? Have you checked to see if timing is being added as throttle is opened? My SWAG is either your timing is way off(C409) or your EST system is not working.
SWAG........ Scientific Wild AZZ Guess.
SWAG........ Scientific Wild AZZ Guess.
Drifting
Joined: Jun 2010
Posts: 1,853
Likes: 8
From: Westerly RI
What about plugged cats? You could check to see if the exhaust pipe temp feels about the same both upstream and down stream of the cat. If the pipe is significantly warmer upstream, the cat is likely plugged. (My lawyer tells me I have to say, be careful of the hot pipes and don't just grab them to check the temp.)
Racer
Joined: Feb 2009
Posts: 261
Likes: 1
From: Riverside CA
What about plugged cats? You could check to see if the exhaust pipe temp feels about the same both upstream and down stream of the cat. If the pipe is significantly warmer upstream, the cat is likely plugged. (My lawyer tells me I have to say, be careful of the hot pipes and don't just grab them to check the temp.)
check that cat! mine was [U]wasted[U] beyond belief. i would wonder how it ever ran
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Advanced
Joined: Jan 2006
Posts: 71
Likes: 0
From: Highland Park IL
C409 is right on. The harmonic balancer can skip and you can not set the timing. If you are in a state that requires inspection you won't pass if the balancer skiped.
Drifting
Joined: Jun 2009
Posts: 1,287
Likes: 448
From: Upstate NY
What about plugged cats? You could check to see if the exhaust pipe temp feels about the same both upstream and down stream of the cat. If the pipe is significantly warmer upstream, the cat is likely plugged. (My lawyer tells me I have to say, be careful of the hot pipes and don't just grab them to check the temp.)
My 84 had the same problem this summer. It started and ran good up to about 3k rpm, but then it was like it just wouldn't rev higher -if I kept the pushing it the RPM would come up a little, but it sounded and felt like crap. I pulled the original CAT which had about 87,000 miles on it -you could not see light come throught it from a lead light held on the other side!
I bought a new Magnaflow CAT and I could see throught it without a light and the car runs great -RPMs come up much quicker and it goes right to red line no problem.
Drifting
Joined: Jun 2010
Posts: 1,853
Likes: 8
From: Westerly RI
At first thought you might say it's doubtful, as a you would expect a plugged cat would increase back pressure and degrade breathing. But it's fairly easy to check the pipe temps as I suggested, you might be able to rule out a cat problem that way.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Detonation is usually caused by timing too far advanced. You need to put #1 cylinder at top dead center and then see if the timing arrow points to TDC on the damper. If it is way off, you need to replace the vibration damper because they don't last forever and as they age they slip and eventually come apart with unpleasant results.
Thread Starter
Instructor
Joined: Oct 2009
Posts: 202
Likes: 9
From: Tucson
And the winner is...
PLUGGED CATALYTIC CONVERTER!
I pulled the cat this morning and it was nasty. I hogged it out and instant performance. The car runs awesome now! This must have been getting progressively worse for a while now.
I found a Magnaflow 93440 online for $110 shipped, so I'll plug it in when it gets here.
Most excellent thanks to all my brothers at corvetteforum! You've helped me out of a jam again!
PLUGGED CATALYTIC CONVERTER!
I pulled the cat this morning and it was nasty. I hogged it out and instant performance. The car runs awesome now! This must have been getting progressively worse for a while now.
I found a Magnaflow 93440 online for $110 shipped, so I'll plug it in when it gets here.
Most excellent thanks to all my brothers at corvetteforum! You've helped me out of a jam again!
Drifting
Joined: Jun 2010
Posts: 1,853
Likes: 8
From: Westerly RI
And the winner is...
PLUGGED CATALYTIC CONVERTER!
I pulled the cat this morning and it was nasty. I hogged it out and instant performance. The car runs awesome now! This must have been getting progressively worse for a while now.
I found a Magnaflow 93440 online for $110 shipped, so I'll plug it in when it gets here.
Most excellent thanks to all my brothers at corvetteforum! You've helped me out of a jam again!
PLUGGED CATALYTIC CONVERTER!
I pulled the cat this morning and it was nasty. I hogged it out and instant performance. The car runs awesome now! This must have been getting progressively worse for a while now.
I found a Magnaflow 93440 online for $110 shipped, so I'll plug it in when it gets here.
Most excellent thanks to all my brothers at corvetteforum! You've helped me out of a jam again!
