First, I want to explain why I have Vader listed in the subject, because I know he dis-likes to be singled out in a post. However, I feel this is his area of expertise and if he offers an explaination & answer, I'm sure all of us can benefit.
Here is the background. This is an 88 gta equipped with a Vortec supercharger which required wiring an auxilary electric fuel pump.
The symptoms:
The VATS system is circumvented with a resistor, but the system itself is still active. On restarts, hot or cold, the VATS systems resets its timer, requiring a 5 minute wait before you can re-crank the engine.
Randomly, in the run position, it seems like the injectors, spark ignition, & other accuators go into a self-test mode. This usually occurs with key on, engine off, but my son thinks this sometimes happens with the engine running.
The car is failing HC emissions. On the first test it was close to the limit, but slightly over. On 2 subsequent tests it was really high.
I think the problem is associated with the auxilary electrical fuel pump for the following reasons.
The ground screw was loose, & that maybe explains why the car got close to passing emissions the first time. After tightening the ground before the 2nd & 3rd test, HC emissions tripled. By totally disconnecting the electric pump ground & deactivating the aux. pump, I do not have any VATS problems after 12 starts, but can create a VATS problem after 1 start with the pump grounded.
The self test mode is random, so I can't offer status relative to the pump ground, but I suspect it's being influenced.
Now, here is the kicker. Power for the aux. electric pump is being tapped off the fuse box at the 10 amp fuse for ECM-Ign. In looking at the factory wiring diagram, this circuit feeds the VATS decoder module, the ECM & the ESC. The ECM & ESC could affect emissions.
Here are the questions?? Can we believe this aux electric fuel pump is creating some type of voltage noise to the electronics & disrupting their proper function?? If so why?
If so, what is the best fuse tap to use for powering up the aux. electric fuel pump? I'm definitely removing it from the ECM/Ign circuit, but I need another choice for a run & start circuit.
All comments & help are welcome.
Thanks, FJK
Here is the background. This is an 88 gta equipped with a Vortec supercharger which required wiring an auxilary electric fuel pump.
The symptoms:
The VATS system is circumvented with a resistor, but the system itself is still active. On restarts, hot or cold, the VATS systems resets its timer, requiring a 5 minute wait before you can re-crank the engine.
Randomly, in the run position, it seems like the injectors, spark ignition, & other accuators go into a self-test mode. This usually occurs with key on, engine off, but my son thinks this sometimes happens with the engine running.
The car is failing HC emissions. On the first test it was close to the limit, but slightly over. On 2 subsequent tests it was really high.
I think the problem is associated with the auxilary electrical fuel pump for the following reasons.
The ground screw was loose, & that maybe explains why the car got close to passing emissions the first time. After tightening the ground before the 2nd & 3rd test, HC emissions tripled. By totally disconnecting the electric pump ground & deactivating the aux. pump, I do not have any VATS problems after 12 starts, but can create a VATS problem after 1 start with the pump grounded.
The self test mode is random, so I can't offer status relative to the pump ground, but I suspect it's being influenced.
Now, here is the kicker. Power for the aux. electric pump is being tapped off the fuse box at the 10 amp fuse for ECM-Ign. In looking at the factory wiring diagram, this circuit feeds the VATS decoder module, the ECM & the ESC. The ECM & ESC could affect emissions.
Here are the questions?? Can we believe this aux electric fuel pump is creating some type of voltage noise to the electronics & disrupting their proper function?? If so why?
If so, what is the best fuse tap to use for powering up the aux. electric fuel pump? I'm definitely removing it from the ECM/Ign circuit, but I need another choice for a run & start circuit.
All comments & help are welcome.
Thanks, FJK
FJK,
Just because I have an electrical engineering background, does that make you believe I can help? (Well, I'll give it a stab...)
What type of auxilliary pump are you using? If it is a vane or roller type (with a motor and brushes) the "noise" created by the motor could be affecting the ECM power quality to the point of creating confusion. That alone may be causing the anomalies you are describing. The most certain way to determine this would be to monitor the DC power source to the pump with an oscilloscope.
As for the "self-test" mode, that is usually a sign that the ECM thinks it is in the Field Service Mode. Again, electrical noise and marginal ECM grounding might create that circustance. I hope your ECM isn't damaged.
Connecting the auxilliary pump power to a different source may help reduce the noise on the ECM input power circuits. However, even if you move the power feed to a different circuit, it would probably be best to install a filter capacitor as close to the motor as possible. Probably a 47µF / 20+ WVDC electrolytic would suppress most of the transients created by the pump motor. Supressing or eliminating the noise at the source is generally the most effective means of clearing up any such problems.
I'm only guessing that the noise is related to the pump given your account of the phenomenon. There may be other issues affecting the overall HC readings, but a "confused" ECM certainly won't make fuel trim any easier. The O² sensor in particular is so sensitive that even low-level extraneous noise can affect it.
Just because I have an electrical engineering background, does that make you believe I can help? (Well, I'll give it a stab...)
What type of auxilliary pump are you using? If it is a vane or roller type (with a motor and brushes) the "noise" created by the motor could be affecting the ECM power quality to the point of creating confusion. That alone may be causing the anomalies you are describing. The most certain way to determine this would be to monitor the DC power source to the pump with an oscilloscope.
As for the "self-test" mode, that is usually a sign that the ECM thinks it is in the Field Service Mode. Again, electrical noise and marginal ECM grounding might create that circustance. I hope your ECM isn't damaged.
Connecting the auxilliary pump power to a different source may help reduce the noise on the ECM input power circuits. However, even if you move the power feed to a different circuit, it would probably be best to install a filter capacitor as close to the motor as possible. Probably a 47µF / 20+ WVDC electrolytic would suppress most of the transients created by the pump motor. Supressing or eliminating the noise at the source is generally the most effective means of clearing up any such problems.
I'm only guessing that the noise is related to the pump given your account of the phenomenon. There may be other issues affecting the overall HC readings, but a "confused" ECM certainly won't make fuel trim any easier. The O² sensor in particular is so sensitive that even low-level extraneous noise can affect it.
Vader, thank you for responding.
For the capacitor you mentioned, would this be wired in parallel with the ground side of the pump? Are these capacitors readily available at Radio Shack? Someone mentioned to me about using a diode in the voltage supply side of this circuit. Your thoughts & details if you agree. I planning on using the power window circuit for the power source. Any comments?
As for HC emissions, I'll be rolling the dice on Mon or Tue... kinda waiting for a cooler day, just in case this is a fuel tank venting problem ( which I still doubt). All I know is the canister purge system & AIR system appear A-OK to me. In fact, I notice the fuel tank is not building pressure as it did before, evidenced by large amount of hissing as the cap was released. Scan tool indicates 100% canister purge when off idle.
Assuming I pass emissions, I still need to reinstall that auxilary electrical pump so that it does not cause the functional problems I described. I'm not sure what type of pump it is, I think a vane style based upon its operating noise. It's a 1-1/2" dia, 8" long cylindrical pump.
Thanks, FJK
For the capacitor you mentioned, would this be wired in parallel with the ground side of the pump? Are these capacitors readily available at Radio Shack? Someone mentioned to me about using a diode in the voltage supply side of this circuit. Your thoughts & details if you agree. I planning on using the power window circuit for the power source. Any comments?
As for HC emissions, I'll be rolling the dice on Mon or Tue... kinda waiting for a cooler day, just in case this is a fuel tank venting problem ( which I still doubt). All I know is the canister purge system & AIR system appear A-OK to me. In fact, I notice the fuel tank is not building pressure as it did before, evidenced by large amount of hissing as the cap was released. Scan tool indicates 100% canister purge when off idle.
Assuming I pass emissions, I still need to reinstall that auxilary electrical pump so that it does not cause the functional problems I described. I'm not sure what type of pump it is, I think a vane style based upon its operating noise. It's a 1-1/2" dia, 8" long cylindrical pump.
Thanks, FJK
FJK,
The capacitor should be wired in parallel across the power feed to the pump. In series, it would block any power to the pump.
A diode in series would have to be a VERY heavy one, 20A peak and 20 PRV minimum. Installed in the forward direction, it would do very little to filter the circuit. In reverse, all power would be blocked.
Another option with a diode would be to wire one in reverse polarity across the power leads of the pump to help with the possible ESD from any motor brush arcing that may be occuring. Between that and a capacitor, the power feed should be cleaned up fairly well. Perhaps a little better than a diode would be an MOV rated at about 22VDC, 10 Joules. That and a capacitor would really clamp down any transients. The ECM already has internal MOVs on its power supply circuits, but as I said, the best practice is to kill the noise at its source.
An audibly noisy pump is probably a vane type (like Bosch pumps).
The window circuit is probably as good as anything else, and hopefully isolated from ECM power a little better. The circuit breaker should be more than adequate for the pump.
As for the HC problem, usually that's a rich condition or a failing cat. It sounds like you're already on top of that problem, and have identified some possibilities. Good luck with the sniffer.
The capacitor should be wired in parallel across the power feed to the pump. In series, it would block any power to the pump.
A diode in series would have to be a VERY heavy one, 20A peak and 20 PRV minimum. Installed in the forward direction, it would do very little to filter the circuit. In reverse, all power would be blocked.
Another option with a diode would be to wire one in reverse polarity across the power leads of the pump to help with the possible ESD from any motor brush arcing that may be occuring. Between that and a capacitor, the power feed should be cleaned up fairly well. Perhaps a little better than a diode would be an MOV rated at about 22VDC, 10 Joules. That and a capacitor would really clamp down any transients. The ECM already has internal MOVs on its power supply circuits, but as I said, the best practice is to kill the noise at its source.
An audibly noisy pump is probably a vane type (like Bosch pumps).
The window circuit is probably as good as anything else, and hopefully isolated from ECM power a little better. The circuit breaker should be more than adequate for the pump.
As for the HC problem, usually that's a rich condition or a failing cat. It sounds like you're already on top of that problem, and have identified some possibilities. Good luck with the sniffer.
The auxilary electric pump affecting the VATS system & flunking emissions were separate issues. Finally passed emissions. The high HC was due to a leaky filler neck in the gas tank. No liquid leaks, just leaking fumes that were picked up by the test probes which go OVER the tailpipes & have a suction on them. The way I found this was by having emissions measured by a friend with a 4 gas analyzer, where the probe goes INSIDE the tailpipe. HC were 20 ppm. Then the probe was dragged around where the filler neck meets the fuel tank. HC were 1500 ppm & then the meter maxed out. Removing the tank & re-soldering the filler neck fixed the problem. Also leak checked the tank at 1 psi with soapy water. Removing & re-installing the fuel tank is another story in itself. Oh yeah, emission test fast passed on the dyno, HC's were 0.039 gm/mile, CO was 0.009 gm/mile.
Now, the car can go back to supercharged operation. Vader, if you're out there, I'm going to setup the auxilary fuel pump with a relay instead of direct wiring it. Also got that capacitor you spoke of & will wire it on the + side of the pump to ground.
Hope this post helps you guys avoid some problems I encountered & helps you trouble shoot 1 aspect of emissions test problems for high HC.
FJK
Now, the car can go back to supercharged operation. Vader, if you're out there, I'm going to setup the auxilary fuel pump with a relay instead of direct wiring it. Also got that capacitor you spoke of & will wire it on the + side of the pump to ground.
Hope this post helps you guys avoid some problems I encountered & helps you trouble shoot 1 aspect of emissions test problems for high HC.
FJK