TPI throttle positioning sensor question
Thread Starter
Le Mans Master
Joined: Aug 2004
Posts: 5,019
Likes: 2
From: Russellville, Kentucky 1967 Sting Ray & 2001 C5
TPI throttle positioning sensor question
I have a street and Performance TPI system on my 327. Car runs fine but idles at 1k, a bit to high I think. I am trying to adjust the Throttle Positioning Sensor. Directions say to measure the blue and black wire for voltage with the ignition switch on.
I have no voltage to the sensor with the key on. I can measure voltage with it running, but zero in any position with engine not running but key on.
I have 'dynamically' adjusted it by moving it to decrease the idle RPM, but I don't know if that affects WOT or not...
Anyone have any suggestions?
I have no voltage to the sensor with the key on. I can measure voltage with it running, but zero in any position with engine not running but key on.
I have 'dynamically' adjusted it by moving it to decrease the idle RPM, but I don't know if that affects WOT or not...
Anyone have any suggestions?
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
http://www.corvetteactioncenter.com/...and+Idle+Speed
Thread Starter
Le Mans Master
Joined: Aug 2004
Posts: 5,019
Likes: 2
From: Russellville, Kentucky 1967 Sting Ray & 2001 C5
There is only one correct way to adjust idle (IAC valve ) and TPS. If TPS voltage is set wrong you may not get correct V for WOT performance
http://www.corvetteactioncenter.com/...and+Idle+Speed
http://www.corvetteactioncenter.com/...and+Idle+Speed
Perhaps a better question would be, where does the voltage at key on come from? It's not there
Race Director
Joined: Apr 2003
Posts: 17,699
Likes: 1,667
From: moraga ca
Your ecm somehow is wired to receive power when the key is in the engine start position and then when the engine is running. It should be wired to receive power in the ignition on position and then you will receive voltage at the tps.
Melting Slicks
Joined: Mar 2005
Posts: 2,350
Likes: 228
From: Northeast FL
Seems a bit odd. Mine was easy to adjust. Not to sound rude but are you sure the key is in the "On" position? If you don't have power with it "On" then it shouldn't have power when running as the power is from the same source and available when running.
Le Mans Master
Joined: Feb 2005
Posts: 5,146
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From: The Motor City
There should be voltage (approx. .53-.6) key on/motor off. I would first pull connector at the tps and check for voltage with vohm meter (key on/motor off) at weather pack connector and/or wiring itself to determine the problem (connector/wiring). If it is getting power at the wiring/connector, then with vohm meter attached and weather pack re-connected manually move the tps. The voltage should "sweep" higher (approx. 4.5 at WOT position), if it shows the voltage increasing but still shows zero at an idle position, then the tps has a dead spot.
Race Director
Joined: Jun 1999
Posts: 14,924
Likes: 9
From: Merritt Ils Fl
I assume this is a conversion on the 327 in the 67. Where did the system come from? The TPS gets a 5 volt reference signal from the ECM with the key in the "run" position, there should be no difference if the engine is running or not.
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Thread Starter
Le Mans Master
Joined: Aug 2004
Posts: 5,019
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From: Russellville, Kentucky 1967 Sting Ray & 2001 C5
Car runs, so I have to assume Street and Performance did something different in their system. I don't know if the Speed Density set up has anything to do with it or not...
Race Director
Joined: Jun 1999
Posts: 14,924
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From: Merritt Ils Fl
S&P must have provided some sort of documentation with the system that includes a wiring diagram. Suggest you start there. Apparently there are significant differences between the stock system and S&P.
Thread Starter
Le Mans Master
Joined: Aug 2004
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From: Russellville, Kentucky 1967 Sting Ray & 2001 C5
I guess I'll wait till Monday and call em.
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
They're pretty helpful folks so I would call them. They have some helpful pages on their web site also. Something doesn't make any sense though. It shouldn't need to be started to deliver power to the Run Circuit. Most ignition switches have two hot leads and the contacts in the switch deliver power for Start, Run and Acc when the rod connected to the key slides the contacts to make or break the circuit. Check your schematic to make sure the ECM is wired correctly. Frankly I don't know how it would start without reference voltages. You may need a different igniition switch - carbs only need to crank the starter and send juice to the coil - EFI needs a lot more.
Most SD systems use a fixed, .62 voltage (idle retun signal) for the TPS and there's no adjustment.
Idle is controlled by the ECM and the Target number is based on Coolant Temp Signal and Load (a/c - Park/Neutral/Drive). There's nothing to adjust. For something different, you'll need to burn it in. If you want to see what's going on, scan it, post the Data - there's a good chance it's working the way it's suppose to (except for the wiring).
Most SD systems use a fixed, .62 voltage (idle retun signal) for the TPS and there's no adjustment.
Idle is controlled by the ECM and the Target number is based on Coolant Temp Signal and Load (a/c - Park/Neutral/Drive). There's nothing to adjust. For something different, you'll need to burn it in. If you want to see what's going on, scan it, post the Data - there's a good chance it's working the way it's suppose to (except for the wiring).
Race Director
Joined: Jun 1999
Posts: 14,924
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From: Merritt Ils Fl
Funny how some things will eat at what little brain you have left. Ignition switch has four positions, Acc.--Off--Run--Start.. Electrically there is no difference in voltages in the Run position if the engine is running or not. TPS should have its reference voltage unless S&P does some very strange things in their ignition circuits.
Le Mans Master
Joined: Feb 2000
Posts: 9,715
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From: Kempner Texas
I measure mine with one DVM touched to the blue wire and the other to a metal engine ground. Just did it most recently on my son's 96 a few months ago. TPS plugged IN.
Jake
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Thread Starter
Le Mans Master
Joined: Aug 2004
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From: Russellville, Kentucky 1967 Sting Ray & 2001 C5
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Sure - assuming it's adjustable and the ECM is programmed for that; idle range is .56 volts +/- .06 volts or .5 to .62 volts. Below that, it usually conks out. Above it, the IAC pintle will be retracted and a typical TPI will idle somewhere around 1200 to 1500 rpms. If the ECM is set up for a fixed .62 volts, then that's where you want it. I'd still scan it and you might also want to see that the IAC is working: Slightly depress the accelerator and start it. Let it run for 10 seconds. Off for 5 seconds. Restart normally (foot off the pedal) and note the RPMS. Turn it off. Restart again. Idle rpms should be higher than what you noted; but return to that # in a couple of seconds. If so, the ECM is using the IAC to control idle speed and you could assume that the TPS signal is providing the idle voltage.
Thread Starter
Le Mans Master
Joined: Aug 2004
Posts: 5,019
Likes: 2
From: Russellville, Kentucky 1967 Sting Ray & 2001 C5
Sure - assuming it's adjustable and the ECM is programmed for that; idle range is .56 volts +/- .06 volts or .5 to .62 volts. Below that, it usually conks out. Above it, the IAC pintle will be retracted and a typical TPI will idle somewhere around 1200 to 1500 rpms. If the ECM is set up for a fixed .62 volts, then that's where you want it. I'd still scan it and you might also want to see that the IAC is working: Slightly depress the accelerator and start it. Let it run for 10 seconds. Off for 5 seconds. Restart normally (foot off the pedal) and note the RPMS. Turn it off. Restart again. Idle rpms should be higher than what you noted; but return to that # in a couple of seconds. If so, the ECM is using the IAC to control idle speed and you could assume that the TPS signal is providing the idle voltage.
Team Owner
Joined: Jul 2004
Posts: 28,431
Likes: 3,284
From: Hartford WI
There is only one correct way to adjust idle (IAC valve ) and TPS. If TPS voltage is set wrong you may not get correct V for WOT performance
http://www.corvetteactioncenter.com/...and+Idle+Speed
http://www.corvetteactioncenter.com/...and+Idle+Speed
This is all assuming that the timing is spot on and that you have the IAC working and the passages are clean and not sooted up.
