but teach me how to fix. 
car bogging when accelerating
Thread Starter
Heel & Toe
Joined: Apr 2015
Posts: 15
Likes: 0
Car hesitation
Hello, I really need your help guys. My 85 vette is still having problems. I've replaced the fuel pump, filter, had the cat hollowed out, did plugs n wires, air filter, and o2 sensor. The car runs awesome when it's cold but when it gets to operating temperature it's completely boggs when you try n punch it. Please help, this is driving me crazy!
Race Director
Joined: Mar 2015
Posts: 15,926
Likes: 579
Hello, I really need your help guys. My 85 vette is still having problems. I've replaced the fuel pump, filter, had the cat hollowed out, did plugs n wires, air filter, and o2 sensor. The car runs awesome when it's cold but when it gets to operating temperature it's completely boggs when you try n punch it. Please help, this is driving me crazy!
and run it with the fuel gauge on it and see what the pressure is when it does it.
Last edited by antfarmer2; Sep 23, 2015 at 01:07 PM.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
Hello, I really need your help guys. My 85 vette is still having problems. I've replaced the fuel pump, filter, had the cat hollowed out, did plugs n wires, air filter, and o2 sensor. The car runs awesome when it's cold but when it gets to operating temperature it's completely boggs when you try n punch it. Please help, this is driving me crazy!
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
Hello, I'm still having some kind of restriction on my 85 corvette. It's ridiculous. It's has great fuel pressure, I had the cat hollowed out today cause they said it was clogged. Still same issue. Check engine light is finally on but probably because of the hollowing of the cat? Please help
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Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
Safety Car
Joined: Sep 2010
Posts: 3,752
Likes: 190
From: Indiana PA
Safety Car
Joined: Sep 2010
Posts: 3,752
Likes: 190
From: Indiana PA
You need to pull codes and go from there.
FYI, did this shop actually do a back pressure test to confirm it had a clogged cat? Removal of a functional catalyst is illegal last I checked.
Also, in a 1985 it has NO way to monitor if the catalyst is functional or not. So your check engine light is NOT on for that reason.
These cars have very simple computers any competent technician should be able to plug in to the ALDL with an OBD1 scan tool and read the sensor readings to determine if any are off of acceptable values.
IF it runs good when cold but not closed loop it is safe to assume the base engine is OK. Good compression any how. If no smoke from tail pipe the head gaskets are likely ok.
I'm theorizing that once into warm operation (closed loop) you are having issues with your fuel system operating correctly. Likely too lean.
Do yourself a favor, unplug the mass air flow sensor in the plenum after the air filter and see how the car runs. This will set a CEL but will (should) kick the car into open loop all the time and eliminate the MAF as an issue. The MAF and 02 sensors are critical sensors for proper engine operation once warm and into closed loop operation. Assuming 85's have a MAP sensor as well.
FYI, did this shop actually do a back pressure test to confirm it had a clogged cat? Removal of a functional catalyst is illegal last I checked.
Also, in a 1985 it has NO way to monitor if the catalyst is functional or not. So your check engine light is NOT on for that reason.
These cars have very simple computers any competent technician should be able to plug in to the ALDL with an OBD1 scan tool and read the sensor readings to determine if any are off of acceptable values.
IF it runs good when cold but not closed loop it is safe to assume the base engine is OK. Good compression any how. If no smoke from tail pipe the head gaskets are likely ok.
I'm theorizing that once into warm operation (closed loop) you are having issues with your fuel system operating correctly. Likely too lean.
Do yourself a favor, unplug the mass air flow sensor in the plenum after the air filter and see how the car runs. This will set a CEL but will (should) kick the car into open loop all the time and eliminate the MAF as an issue. The MAF and 02 sensors are critical sensors for proper engine operation once warm and into closed loop operation. Assuming 85's have a MAP sensor as well.
Safety Car
Joined: Sep 2010
Posts: 3,752
Likes: 190
From: Indiana PA
Once in closed loop ECM uses 02 sensor to fine tune air fuel ratio. IN open loop the ECM ignores the 02 and using engine sensor data inputs and programmed parameters.
BTW, to the best of my knowledge EVERY computer controlled engine runs in open loop at WOT.
BTW, to the best of my knowledge EVERY computer controlled engine runs in open loop at WOT.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
Closed Loop Control: simply means the ECM is no longer running a Pre written Script, but now relies on Critical Sensors in order to Control the Engines Fuel Schedule, etc. This may or may not be his issue! But as 93Rubi said; force the Computer into Open Loop and see how the Engine Runs, this may offer an answer to the OP's problem.
Instructor
Joined: Apr 2015
Posts: 153
Likes: 12
From: Savannah GA
I had a similar issue with my '95 after replacing intake gaskets and optispark. While re-checking my sensor connections, I discovered that I had not firmly reconnected the MAF sensor lead. I cleaned the connections and made sure the plug "clicked" onto the locking tab firmly. Problem solved!
Instructor
Joined: Nov 2009
Posts: 241
Likes: 4
From: rochester ny
I would get the car nice and hot and when it starts bogging down park it and ohm all the injectors. (If you want, ohm them when they're cold for comparison since it runs ok cold.) I'm willing to bet you have a few injectors that aren't firing when they are hot. This is a quick and easy way to possibly rule out the injectors.
I also agree with unplugging the maf and seeing if the problem goes away I've had these go bad and show similar symptoms before
I also agree with unplugging the maf and seeing if the problem goes away I've had these go bad and show similar symptoms before
Racer
Joined: Jul 2013
Posts: 405
Likes: 7
From: Raleigh NC
I would get the car nice and hot and when it starts bogging down park it and ohm all the injectors. (If you want, ohm them when they're cold for comparison since it runs ok cold.) I'm willing to bet you have a few injectors that aren't firing when they are hot. This is a quick and easy way to possibly rule out the injectors.
I also agree with unplugging the maf and seeing if the problem goes away I've had these go bad and show similar symptoms before
I also agree with unplugging the maf and seeing if the problem goes away I've had these go bad and show similar symptoms before