Need help ridding myself of a code 33 on my 88 C4
12-08-2013, 11:13 AM
#1
3rd Gear
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Need help ridding myself of a code 33 on my 88 C4
Hello to everyone...I have tried everything I know possibe to get rid of this 33 code. I installed a new MAF that didn't work...I installed new relays that didn't work....I also cut the connector off that plugs into the MAF and soldered a new connector on that did not work..I also checked the signal wire from the ECM we have power and ground.. my ECM is the #1227165..I have not changed that yet..the SES pops up a few minutes during driving....u know when the SES is going to come on BC the car basically hiccups then runs confused..I hooked the car up to a scan tool and it reads 6.0 grams per sec when warm....which is normal If I'm correct...any ideas would be helpful thanks for taking the time.....
12-08-2013, 12:17 PM
#2
Le Mans Master
Do you have the factory service manuals? And I've just got to ask, did you disconnect the battery to eliminate the code 33?
Part of testing...step 2 should be checking the fuel pump circuit by connecting 12 volts to terminal "G", there should be 12 volts at the sensor. If no voltage is present, make sure that the fuel pump is running. If not, repair the fuel pump circuit. I know this sounds funny, but it's part of the trouble shooting diagnostics. If I remember correctly I was throwing an intermittent 33, and then my fuel pump died.
BTW, mines an 87, but I think their basically the same.
Part of testing...step 2 should be checking the fuel pump circuit by connecting 12 volts to terminal "G", there should be 12 volts at the sensor. If no voltage is present, make sure that the fuel pump is running. If not, repair the fuel pump circuit. I know this sounds funny, but it's part of the trouble shooting diagnostics. If I remember correctly I was throwing an intermittent 33, and then my fuel pump died.
BTW, mines an 87, but I think their basically the same.
Last edited by rick lambert; 12-08-2013 at 12:19 PM. Reason: need to say my FSM and car are 19887
12-08-2013, 02:27 PM
#4
ok, there is a trick to what the SES lite and its code display is telling us...
information is useless and often confusing if its not interpreted correctly.
Code 33 only tells us that for a single second, the ECM saw higher than normal airflow. In its terms, a spike in voltage for what the TPS, inj, o2 and VSS were telling the ECM. ALl these things have input and they all must fall within a "window" to be normal. Anything that's out of that window, sets a code. 33 means the ECM saw a signal claiming there was too much airflow, but that does not necessarily mean that it is true ! If it were, the engine would run lean, get hot, and react to this in physical ways that we would see and feel as we drove. BUT, if its only a faulty signal, the engine will NOT react and run like crap, it will simply hiccup as it makes the electronic shift to OL operation so it can run on programming since it thinks there is a fault in the MAF. Its about perception...So we are looking for a faulty signal, probably not a faulty part.
Before going farther, what Rick was telling you is spot on correct. The MAF gets its 12v power supply thru the power relay, that gets 12 v (C993)from the fuel relay circuit. So, a code 33 can be set IF there are things effecting the fuel pump relay, the oil pressure switch or any of the wire between...especially c-998 which should be the 5v path TO the MAF.
Next, look for the voltage after start up in c-994 (drk blue wire). That's burn-off and IF that is ON while the fuel relay is sending 12v to the MAF there will be a code 33. Not likely the problem since you say it happens while driving and not at start-up.
To take this a step further, d/c the MAF burn-off relay and drive. Come back and see what codes are now present. You WILL have a new code (c-36) for the burn-off, BUT you might NOT have the 33 again. If that's true, the burn-off relay or its wire is faulty allowing voltage to leak to the MAF while running. This test is done after all codes have been cleared by d/c the battery briefly...
The dirty little secret of the Corvette electrical in a C4 is that the wire used was sub-standard and actually got some DOT attention because it failed the long term durability standard that the fed gov required for American made cars. A min of 10 yrs, most are designed well beyond that. The wire used in vettes, C4s was prone to insulation shrinking and drying that led to cracking and exposed bare wires. Personally I have had to chop out the entire left side fuel injection harness and solder in all new wire and plugs to solve a mystery misfire that would move from one cyl to another ! Took months to diagnose that and it came down to cracked insulation on EFI wires that were grounding each other or cross signaling each other. New wires, problem solved.
This is gently leading you to the next and hopefully last thing to look at...
Your 88 will have the jumper pole behind the battery. Those wires are all the power source wires for ALL the important stuff...EFI, dash, ECM etc...
Those all have a fusible link inline that's hidden under the battery tray. I have had these same wires cause a random misfire and some odd codes, (o2?) simply from the natural corrosion that grows on the contact surface. Take the jumper pole wires off, clean WELL with wire brush on a dremmel, and clean the pole too. Reassemble like it was all new and see if that helped. I ended some codes and some poor performance issues simply by cleaning the power source. Dirty contacts here will lead to low or unstable voltage to critical components.
While down there UNDER the battery tray/box, visually inspect ALL the wires in these many circuits. Being under the battery they are subject to ACID fumes and the wire WILL rot and corrode inside the insulation where it cannot be easily seen. If there is ANY indication of corrosion on ANY wire ends, green crud or discolored wire going to a connector, or insulation that's shrunk back from the end, GO DEEPER and continuity test or even cut some wire and solder in new. Your problem is definitely electrical, its a control or low voltage signal problem, and THIS area is where ALL the voltage originates from...so issues here will lead to issues elsewhere.
As long as you are dirty, go ahead and get underneath and take the ground bundle of harness wires off the block or bellhousing bolt and clean all those as well. There will be 4 or 5 blk wires on one bolt. These are ALL the important ground wires for the ECM and all the EFI control devices and display. The harness grounds are more important than the battery cable ground. The grounds drop out of the harness main trunk by the brake booster and come from a rather cheesy splice into the harness...another potential source of trouble with very little black tape protecting the bare harness wire from corrosion....Another unique "cost cutting" measure by some GM executive...."lets limit the use of black tape for each vehicle to 8" or less and that will save us approx $1847.96 over the production run". Gotta love the bean-counters...
Moving on......things to look at,
burn-off power/relay
fuel relay/ pump circuit
oil pressure switch
wire insulation health
jumper pole wire/contact quality
Borrow an ECM to eliminate that as the source of the 33...I seriously doubt that it IS the ECM, but it still has to be looked at to be eliminated as a suspect.
Good luck !
information is useless and often confusing if its not interpreted correctly.
Code 33 only tells us that for a single second, the ECM saw higher than normal airflow. In its terms, a spike in voltage for what the TPS, inj, o2 and VSS were telling the ECM. ALl these things have input and they all must fall within a "window" to be normal. Anything that's out of that window, sets a code. 33 means the ECM saw a signal claiming there was too much airflow, but that does not necessarily mean that it is true ! If it were, the engine would run lean, get hot, and react to this in physical ways that we would see and feel as we drove. BUT, if its only a faulty signal, the engine will NOT react and run like crap, it will simply hiccup as it makes the electronic shift to OL operation so it can run on programming since it thinks there is a fault in the MAF. Its about perception...So we are looking for a faulty signal, probably not a faulty part.
Before going farther, what Rick was telling you is spot on correct. The MAF gets its 12v power supply thru the power relay, that gets 12 v (C993)from the fuel relay circuit. So, a code 33 can be set IF there are things effecting the fuel pump relay, the oil pressure switch or any of the wire between...especially c-998 which should be the 5v path TO the MAF.
Next, look for the voltage after start up in c-994 (drk blue wire). That's burn-off and IF that is ON while the fuel relay is sending 12v to the MAF there will be a code 33. Not likely the problem since you say it happens while driving and not at start-up.
To take this a step further, d/c the MAF burn-off relay and drive. Come back and see what codes are now present. You WILL have a new code (c-36) for the burn-off, BUT you might NOT have the 33 again. If that's true, the burn-off relay or its wire is faulty allowing voltage to leak to the MAF while running. This test is done after all codes have been cleared by d/c the battery briefly...
The dirty little secret of the Corvette electrical in a C4 is that the wire used was sub-standard and actually got some DOT attention because it failed the long term durability standard that the fed gov required for American made cars. A min of 10 yrs, most are designed well beyond that. The wire used in vettes, C4s was prone to insulation shrinking and drying that led to cracking and exposed bare wires. Personally I have had to chop out the entire left side fuel injection harness and solder in all new wire and plugs to solve a mystery misfire that would move from one cyl to another ! Took months to diagnose that and it came down to cracked insulation on EFI wires that were grounding each other or cross signaling each other. New wires, problem solved.
This is gently leading you to the next and hopefully last thing to look at...
Your 88 will have the jumper pole behind the battery. Those wires are all the power source wires for ALL the important stuff...EFI, dash, ECM etc...
Those all have a fusible link inline that's hidden under the battery tray. I have had these same wires cause a random misfire and some odd codes, (o2?) simply from the natural corrosion that grows on the contact surface. Take the jumper pole wires off, clean WELL with wire brush on a dremmel, and clean the pole too. Reassemble like it was all new and see if that helped. I ended some codes and some poor performance issues simply by cleaning the power source. Dirty contacts here will lead to low or unstable voltage to critical components.
While down there UNDER the battery tray/box, visually inspect ALL the wires in these many circuits. Being under the battery they are subject to ACID fumes and the wire WILL rot and corrode inside the insulation where it cannot be easily seen. If there is ANY indication of corrosion on ANY wire ends, green crud or discolored wire going to a connector, or insulation that's shrunk back from the end, GO DEEPER and continuity test or even cut some wire and solder in new. Your problem is definitely electrical, its a control or low voltage signal problem, and THIS area is where ALL the voltage originates from...so issues here will lead to issues elsewhere.
As long as you are dirty, go ahead and get underneath and take the ground bundle of harness wires off the block or bellhousing bolt and clean all those as well. There will be 4 or 5 blk wires on one bolt. These are ALL the important ground wires for the ECM and all the EFI control devices and display. The harness grounds are more important than the battery cable ground. The grounds drop out of the harness main trunk by the brake booster and come from a rather cheesy splice into the harness...another potential source of trouble with very little black tape protecting the bare harness wire from corrosion....Another unique "cost cutting" measure by some GM executive...."lets limit the use of black tape for each vehicle to 8" or less and that will save us approx $1847.96 over the production run". Gotta love the bean-counters...
Moving on......things to look at,
burn-off power/relay
fuel relay/ pump circuit
oil pressure switch
wire insulation health
jumper pole wire/contact quality
Borrow an ECM to eliminate that as the source of the 33...I seriously doubt that it IS the ECM, but it still has to be looked at to be eliminated as a suspect.
Good luck !