Help needed - EVAP system causing high idle
Help needed - EVAP system causing high idle I’m at a bit of a loss here. 1989 Camaro with complete (gas tank to radiator) 2002 LS1 swap including emissions.
When the wires to the fuel tank evap system are connected, idle is at 1500-1700. Disconnecting purge solenoid connection to manifold (the only connection from evap to the vacuum system I know of) makes no change. I don’t see any possibility of a vacuum leak.
individually unplugging any one of the evap systems to the tank brings idle back to normal aside from the ora/bla low reference wire. Disconnect that one and it just cranks. Disconnect the whole thing and idle is normal.
Voltages measured (ign on):
Evap Solenoid (pink) - 12.2V (eng ctrl fuse)
low reference (ora/bla) - 32.2 mv (C1 23)
5V reference (gray/bla) - 5.07V (C1 46)
Fuel tank pres signal (dk grn) - 1.62V (C2 64)
Canister vent sol control (wht) - 12.2V (C2 45)
I have the dk grn/wht from the engine bay canister purge solenoid going to C2 34
It all functions, no MIL codes. Just high idle if the rear is fully connected. Any thoughts?
When the wires to the fuel tank evap system are connected, idle is at 1500-1700. Disconnecting purge solenoid connection to manifold (the only connection from evap to the vacuum system I know of) makes no change. I don’t see any possibility of a vacuum leak.
individually unplugging any one of the evap systems to the tank brings idle back to normal aside from the ora/bla low reference wire. Disconnect that one and it just cranks. Disconnect the whole thing and idle is normal.
Voltages measured (ign on):
Evap Solenoid (pink) - 12.2V (eng ctrl fuse)
low reference (ora/bla) - 32.2 mv (C1 23)
5V reference (gray/bla) - 5.07V (C1 46)
Fuel tank pres signal (dk grn) - 1.62V (C2 64)
Canister vent sol control (wht) - 12.2V (C2 45)
I have the dk grn/wht from the engine bay canister purge solenoid going to C2 34
It all functions, no MIL codes. Just high idle if the rear is fully connected. Any thoughts?
Teching In
Joined: Aug 2018
Posts: 23
Likes: 1
What are your fuel trims doing while the EVAP system is activated? As far as I know the only way it would be getting air would be through the manifold purge solenoid. I wonder if it is stuck open. Maybe try pulling the line and plugging to inlet to the solenoid?
I liked your idea of unplugging the line - running with the manifold port open made it run just about the same. Perhaps 1800 at idle. Unfortunately, putting a plug on the port still was idling at 1500 - 1700.
Confused again.
Teching In
Joined: Aug 2018
Posts: 23
Likes: 1
I would download the torque app for your phone it is only $5 on google play store and get a $10 OBD2 Bluetooth adapter off ebay. Helps a lot with troubleshooting this stuff. Will allow you to see throttle position, fuel trims O2 readings etc.
Trying out that app.
Fuel trims:
LTFT1 - 9.4%
LTFT2 - 5.5%
I don’t see the short term or live trims doing anything.
But - this is where it gets strange. My throttle position sits at 24% Unplugging the TPS sensor does nothing. The wires at the fuel evap connection change it. Disconnecting the 5v reference sets it back to 0% reconnecting it jumps the TPS to 42% disconnecting and then reconnecting evap canister vent brings it back to 21-24% disconnecting low reference spikes the reading to 100% disconnecting fuel tank press. drops it to 0%
(EDIT: these voltages were varying oddly with these random combinations. I couldn’t get them to reproduce. The fuel pres seems to be the main culprit.)
This is so strange. I’m going back through wiring diagrams to see if I missed something like a separate 5v reference or something strange.
Fuel trims:
LTFT1 - 9.4%
LTFT2 - 5.5%
I don’t see the short term or live trims doing anything.
But - this is where it gets strange. My throttle position sits at 24% Unplugging the TPS sensor does nothing. The wires at the fuel evap connection change it. Disconnecting the 5v reference sets it back to 0% reconnecting it jumps the TPS to 42% disconnecting and then reconnecting evap canister vent brings it back to 21-24% disconnecting low reference spikes the reading to 100% disconnecting fuel tank press. drops it to 0%
(EDIT: these voltages were varying oddly with these random combinations. I couldn’t get them to reproduce. The fuel pres seems to be the main culprit.)
This is so strange. I’m going back through wiring diagrams to see if I missed something like a separate 5v reference or something strange.
Last edited by MORK; Aug 19, 2021 at 12:22 PM.
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DBC. I double checked all of my TPS and EVAP to ECM connections and they look to be in the right place. I’ll take another look at the grounds - hopefully nothing has snapped or gotten loose back there - that part of the harness is no fun with how tight it is.
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Verdad Gallardo Grounds still tight - found one ground to firewall I relocated to the cylinder head and even made up another chassis ground strap for good measure. Same result.
At least I can rule out the grounds for the time being.
At least I can rule out the grounds for the time being.
Correct. Today I’m going to try some continuity tests on the TPS - I know the evap wires are good, they are new and in the correct pins - just ran them last week.
Before I found out I had to go full emissions legal, I had even ran the purge on a separate push button just to manually remove any built up fuel smell, it would just drop the idle 50-100 rpm and then settle back to normal. It actually worked great - just hit the button a mile from home, it would suck up from the charcoal can, and bingo. Garage smells clean.
Before I found out I had to go full emissions legal, I had even ran the purge on a separate push button just to manually remove any built up fuel smell, it would just drop the idle 50-100 rpm and then settle back to normal. It actually worked great - just hit the button a mile from home, it would suck up from the charcoal can, and bingo. Garage smells clean.
All TPS wires are in the correct pins in the ECM, no shorts or grounding out. The sensor itself works perfectly but the ECM only sees the signal when the evap wires are disconnected.
it seems like the fuel tank pressure signal is the the source of the problem. I can connect the rest of the evap wiring and idle and throttle position is normal. Connect the pressure signal and the TPS jumps to 27% and idle is 1500 - -1700. The wire measures 1.06v which fluctuates a small amount.
it seems like the fuel tank pressure signal is the the source of the problem. I can connect the rest of the evap wiring and idle and throttle position is normal. Connect the pressure signal and the TPS jumps to 27% and idle is 1500 - -1700. The wire measures 1.06v which fluctuates a small amount.
Last edited by MORK; Aug 19, 2021 at 11:51 AM.
Is it possible that the fuel pressure sensor is bad? Or that possibly a few wires were crossed and/or pinched?
Is there a reason that you need a functional EVAP system? Unless you are in California and need it to pass the CARB stuff, I'd just delete it. That's what I did on a few LS swaps that I converted to stand alone. Just disable the codes and tell them not to display.
Engine bay looks extremely clean, very nicely done. But one thing that I noticed is where there is normally a blocked off spot in the intake right behind the TB, there is some sort of open hole. Is the picture playing tricks on me or?.
What are you doing for PCV? Do you have that hooked up like stock, or is that somehow connected to the EVAP?
Is there a reason that you need a functional EVAP system? Unless you are in California and need it to pass the CARB stuff, I'd just delete it. That's what I did on a few LS swaps that I converted to stand alone. Just disable the codes and tell them not to display.
Engine bay looks extremely clean, very nicely done. But one thing that I noticed is where there is normally a blocked off spot in the intake right behind the TB, there is some sort of open hole. Is the picture playing tricks on me or?.
What are you doing for PCV? Do you have that hooked up like stock, or is that somehow connected to the EVAP?
It’s possible that the pressure sensor is bad. However, it’s voltage reading is dead on what it should be (Fluctuates between 0-5v depending on pressure)
Colorado requires all engine swaps to be checked off through a very intensive process now. (It’s actually a carb state now as well) They do a deep dive into the ECM with a dedicated tech that makes sure no parameters have been tuned or altered. Essentially, I have to have 100% of the donor cars systems intact and fully functioning. I had a separate ECM tuned for all the bolt ons with the emissions tuned out.
This last wire is the only remaining piece to the puzzle.
Good eye on the manifold. I had considered faking an EGR port for visual inspection when the motor was 98 spec, it’s an LS6 manifold. PCV routes through the catch can.
Colorado requires all engine swaps to be checked off through a very intensive process now. (It’s actually a carb state now as well) They do a deep dive into the ECM with a dedicated tech that makes sure no parameters have been tuned or altered. Essentially, I have to have 100% of the donor cars systems intact and fully functioning. I had a separate ECM tuned for all the bolt ons with the emissions tuned out.
This last wire is the only remaining piece to the puzzle.
Good eye on the manifold. I had considered faking an EGR port for visual inspection when the motor was 98 spec, it’s an LS6 manifold. PCV routes through the catch can.
Very interesting. Well I'd suggest tracing that wire from the back to the BCM or ECU where ever it ends up terminating. Maybe you pinched a wire somewhere and it's grounding out. Could be why when you connect it that it makes the TPS read higher since I think they are all on a common ground signal.
All of the evap wires (tank press, low reference, evap solenoid, 5v reference, vent solenoid) are brand new wiring straight to the ECM and match multiple wiring diagrams and pinout confirmations.
The TPS wires have been checked for continuity and for shorts to each other or grounding out.
Everything operates as normal until I connect the tank pressure wire.
The TPS wires have been checked for continuity and for shorts to each other or grounding out.
Everything operates as normal until I connect the tank pressure wire.
Talking to a friend and he mentioned that my ~1.37V from the gas tank pressure signal wire is almost exactly 27% of the 5V max which happens to be the throttle percentage it is overriding…
Talking with the tuner and shop I got the ECM from to see if there’s a chance that pin could be wrong or if we should try another 411 ECM with the stock 2002 Camaro tune.
Talking with the tuner and shop I got the ECM from to see if there’s a chance that pin could be wrong or if we should try another 411 ECM with the stock 2002 Camaro tune.