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Engine light and engine studder

2K views 14 replies 7 participants last post by  JJLT1 
#1 ·
I have an '86 with the stock 305. Recently, I have noticed the car is difficult to start when it's warm (although not all the time) and every now and then, the engine will studder for a while as if it's misfiring and down on power. When it starts the studder the engine light illuminates. This past weekend I drove about 20 miles to a store, and the engine started doing this as I got close. I managed to get to the store, came out about 15 minutes later and tried to start the car. It was hesitant to start and turns over very slowly as long as I floor the gas. The minute I let off the gas the engine shuts down. I have to then feather the gas pedal in and out until the engine 'catches' and returns to normal and the check engine light turns off.

Not sure what is happening as my ODBII will not read the code but it seems to be happening more often. Not being a mechanic, although I get my hands dirty with different things (brakes, plugs, wires, starters, etc.), any thought on what I should look for before I take the car in?

Thanks in advance.
 
#2 ·
You can "read" the codes using a paperclip. Turn the car off, and then insert a paper clip, bent into a U shape, into the two top right holes on your ALDL connector. Turn the key to on ( Not Started), and watch your check engine light. It should flash the codes, repeating each code 3 times. First code should be a 12 ( 1 flash, followed by 2 flashes). This is normal, indicating that the ECM is working. After this 12, any other codes stored will flash in sequence. If you see 12 again, you are back to the beginning.

Post up any codes you see, and we'll try and help.
 
#4 · (Edited)
Code 21 is an Open Circuit or Misadjusted TPS on the carb. Code 45 is a rich condition. The 45 is being triggered by the TPS. From the service manual:

To check the TPS , tuen key on and check voltage of TPS connector B to C. If under 2 volts, can be faulty ECM or connections. If over 2 volts, start engine and let it dle. Connect Dwell meter to "Green" terminal near carb. Read 6 cyl scale. Jumper TPS Connector B and C, and read dwell. If under 10 degrees, replace ECM. If over 10 Degrees, Check TPS Terminal connections. If OK, Check resistance on TPS. A to B and A to C. Any over 20,000 ohms, replace sensor. Both Under 20,000 ohms, adjust TPS. If unable to adjust, replace TPS.

HTH
 
#5 ·
Great info but I failed Latin in college. It is Latin?

Seriously, thanks for the info. As it seems to be over my skill level, I'll forward this to the local shop. The car has been eating more gas than normal and this is probably due to the issues that you list.
 
#6 ·
Sorry for confusing you. There's a small Sensor in the Carb ( Throttle Position Sensor- TPS). It senses how much the throttle is open, and adjusts the timing and carb mixture accordingly. It sounds like the sensor is showing near Wide Open Throttle, and is adjusting the timing and rich conditions. Take it to someone that knows Quadrajet Carbs, and they can fix it probably by replacing that sensor. It requires taking the top off the carb, so it is not necessarily a real simple fix without the tools and knowledge. However, is could be something as simple as spraying with some carb cleaner to free up the sensor's movement.

For a picture, look at post # 11 in this thread.
http://www.google.com/imgres?imgurl=http://www.hotrodders.com/gallery/data/500/Q_Jet.jpg&imgrefurl=http://www.hotrodders.com/forum/modifying-electronic-controlled-quadrajet-150264.html&h=450&w=600&sz=64&tbnid=L1gfM55OWFH3dM:&tbnh=101&tbnw=135&prev=/images%3Fq%3Dquadrajet%2BTPS%2BPicture&zoom=1&q=quadrajet+TPS+Picture&usg=__sodhr120w0rdAitcj1VyAUMjneI=&sa=X&ei=75CHTY3ZNYeosAOUt6T1AQ&ved=0CBwQ9QEwAg
 
#9 ·
TPS was my first thought too. I know there may be budgetary concerns but if I had such a setup I'd be planning for a TBI replacement down the line. I never liked computer controlled carbs because they can be so touchy. I hated the carb on my 81 Camaro.

:nanawrench:
 
#10 ·
I too would bet on the TPS being the root of your trouble. I had a problem with mine two years ago. Rich mixture, lazy response and pinging with any kind of load, even with higher octane fuel. Unlike the newer OBD II systems, the old system won't post a TPS trouble code until it's way out of range, 5 volts IIRC. I replaced it with one I had from a spare carb and it was fixed instantly. I picked up 3 mpg, crisper response and no more pinging, even on 87 octane, Intermittently, I had four different codes, mostly what I'd call "results" codes, such as the code 45. After replacing the TPS, no more codes of any type.

Bill
 
#12 ·
intermittent problems are the worst,, it sounds like its working more than not??
one thing you can check is the connection,,unplug the connector on the front drivers side of the carb,,
see if its cracked/broke,,check for corrosion,,look at the wires see if any are rubbed through,,pull on the wires at the plug??
its one of those things you dont think about,,you just grab it check it,,then get the volt meter out..
just unpluging it a couple of times might help..
its worth a try,,dont cost anything,,25 years of vibration can do things,,goodluck swimman..:texas:
 
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