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Help Please! Won't rev past 4800 when hot

When my '93 3.6 Turbo gets hot, it won't rev past 4800 RPM. The car starts perfectly, and drives perfectly, however after a few (2-3) full boost pulls to near red-line, it won't pull again and its like hitting a rev limiter at around 4800. Then after driving for a while and everything cools down, it will let me fully rev again once or twice then bam, it won't rev again. Any thoughts?


Last edited by skierlawyer; 09-12-2010 at 06:40 PM.. Reason: Additional info added
Old 09-12-2010, 06:36 PM
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Can you describe what it does at 4800? Could be a bad coil or CDI box that just can't keep up anymore...
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Old 09-12-2010, 06:55 PM
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It abruptly stops accelerating. It will maintain its speed and stay right at 4800 but won't go any faster, its like hitting a rev limiter.
Old 09-12-2010, 07:38 PM
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What boost are you running? Could it be that you are hitting the overboost?
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Old 09-12-2010, 08:55 PM
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Anything boost related, or even something like a faulty-seating wastegate, should allow you to rev past 4800 if you tip-toed up to it. Please let us know if- when it is exhibiting the problem, you can slowly tip in the throttle in first gear (trying to avoid boosting) and go past the 4800 ceiling.

Ignition woes- cap/rotor/wires/plugs, CDI and coil, all get worse with heat, all get worse with RPM, and all seem to do worse under a load. It is much harder to light off a boosted cylinder than the same one at idle. One of your fuel pumps/relays may be heating up and quitting on you and you are only running on one during the problem. A clogged fuel filter would not be an intermittent problem IMO. Good luck man.
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Old 09-12-2010, 09:07 PM
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Greetings:

Similar situation. My car was starving for fuel. A quick way to diagnos. I have a 7th injector-I turned it on and off when it was acting bad/stall. By turning it on, I had a rush in power. That tells me, fuel/pressure was not there. The fuel head was clogged. I didn't drive much-not good. I use mmo regulary now. Never had a problem since then. GL.
P.S.---CHECK everything..What he said^^^^^
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Old 09-13-2010, 06:33 AM
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Check your cat

I hade a similar problem with my 86 930 ... The rear bumper was hot, turned out to be a plugged up cat converter.
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Old 09-13-2010, 09:49 AM
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well first thing is a 3.6 turbo doesnt have a cd box, it has an ignition control unit kind of like a a 911 dme but just for ignition. i believe the rev limiter is built in to this. it also controls your timing and has boost/vacuum reference. being that your car isnt "breaking up" rather its feeling like a soft touch rev limiter id venture to say the control unit is a possible cause. if a fuel filter was going bad or if you were starved of fuel the car would act different then you describe, same with the plugs/cap/rotor/wires, these would feel more like a missfire
Old 09-13-2010, 09:03 PM
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check your gas filter
Old 09-13-2010, 09:21 PM
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check you fuel pump the one in the front
Old 09-13-2010, 09:24 PM
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Its not the fuel filter, changed that 3000 miles ago. Both fuel pumps sound like they are both working at idle. I am bringing it to Eisenbud's in Denver on Monday and hopefully they can figure it out. I will post the results.
Old 09-13-2010, 09:50 PM
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Quote:
Originally Posted by skierlawyer View Post
It abruptly stops accelerating. It will maintain its speed and stay right at 4800 but won't go any faster, its like hitting a rev limiter.
+1 on "bad coil". I'm told the Bosch CDI boxes tend to either work or not.

I just had a "hard" 6,000 RPM misfire on the dyno - when poking around, noticed black stuff puking out of the coil.

Thinking back, it may have been doing it for a while and I just thought it was the rev limiter and not noticed it was too low...
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Old 09-19-2010, 06:33 PM
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I think I found the problem

It seams that the issue is that a large rubber boot on the left side of the engine gets loose and leaks when the rubber gets soft from lots of heat. I am going to better secure it with some screws and hope that that will fix it.
Old 09-22-2010, 05:09 PM
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OFF THE BOOST PIPE NOW...
 
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Are you talking about the large 90* boot? Avoid the screws and try new clamps.

Besides, screws won't stop it from leaking.

Quote:
Originally Posted by skierlawyer View Post
It seams that the issue is that a large rubber boot on the left side of the engine gets loose and leaks when the rubber gets soft from lots of heat. I am going to better secure it with some screws and hope that that will fix it.
Old 09-22-2010, 05:41 PM
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I've seen those 90 degree rubber hoses get soft and mushy on the bottom side right after the air flow meter housing from oil sitting there. I don't know if the hose I saw do that was oem or aftermarket.

Oil in the air cleaner housing, air flow meter, intake hose and plumbing, turbo, and on into the intercooler would be likely coming from the breather hose puking out blowby oil mist into the air filter housing and that would probably be from a motor that is worn.

Recircualting blowby oil mist and combustion gases back into the intake is good for the air we breathe but it increases the chances of detonation and lowers the efficiancy of the intercooler as it becomes internally coated with oil film.

Old 09-22-2010, 08:47 PM
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