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speedracer67's Avatar
 
Join Date: May 2015
Posts: 2
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Porsche Crest 85.5 944 wont rev past 3000rpm and im stuck

last post on something like this was in 03 had to make a new post.

after chasing around a running issue i'm stuck with no real idea besides a new chip/ check the DME for bad solder joints. what I have done:
new FPR, checked the fuel filter its fine and the pump runs strong
new TB and TPS,
new speed and reference sensors - those helped because i had completely lost my tach and the car ran horrible and now i have my tach back and the car is significantly easier to creep around my driveway - not street legal rn.
I opened my AFM and did the unthinkable.. so i have a new used one on the way. already preparing myself to check the potentiometers track on the resistor - wont muck that up twice. and this is assuming that it wasn't leading itself to my problem either.

now, my throttle cable does have slack and doesn't seem to fit - seems to be several inches longer than needed - i compared the max rpm with both the factory throttle cam and a aftermarket quick response- the quick response only lent itself to a slight rise in the max attainable rpm.

other mods: Bursch test pipe because my cat had clogged and almost burnt the car down, maybe the O2 sensor is leading to an unfavorable AFR if it was damaged? the car also after fires... off the throttle... BOOM.

i would greatly appreciate any conversation over this with someone more knowledgable than i. thanks in advance.
Old 05-06-2015, 05:26 PM
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Join Date: Oct 2007
Location: Phoenix, AZ
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I would get the proper throttle cable.

Get the car idling, pop the hood and use your hand to throttle cam. Does it rev up properly then?

Is the car running well? How do the spark plugs look? Compression tests? The list goes on....
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Old 05-06-2015, 06:26 PM
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i have it i just need to get to installing it. im currently in finals week

manually operating the throttle body i haven't noticed a difference i will have to check again after the new AFM . i get the butterfly is open about a quarter of the way and the car after fires and i back off. i know that the cable right now maxes out about a 75% of the way to full open. i had a friend visually check while i operated the pedal. i should have ran the test the other way around aswell*

i should run a compression test i have just put it off. the car ran when i got it after i got the clutch serviced and an oil change it started to do this jerking motion under throttle.

it runs well and idles well, ive got new plugs a new distributor new wires and a new coil. the previous plugs were all pretty clean no evidence of blow by oil or coolant.

it revs smooth now that i replaced the reference and speed sensors with the new TPS it used to be real jittery and liked to hesitate. its just acting like im hitting red line just over 3000rpms
Old 05-06-2015, 06:38 PM
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Unplug the O2 sensor and see if that changes anything. It sounds like you're running super rich. I would put a fuel pressure gauge on the rail and see what's going on.
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Old 05-06-2015, 08:50 PM
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Sometimes broken valvesprings will cause a higher RPM miss, though usually not that dramatic if only in one cylinder. I've seen people chase what they thought was an eletrical missfire for ages, only to find out one of the dual valvesprings was broken.
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Old 05-07-2015, 02:48 PM
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Comeau Racing
 
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If the car runs fine up to 3,000 rpm, it sounds like you might have an obstruction in the exhaust. I had a car that wouldn't rev past 3200 rpm. Ran fine below that. Great idle. The cat had come apart. You may have pieces of your cat in the muffler section? Test by unbolting last section of exhaust and rev it.
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Old 04-28-2016, 09:22 AM
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