bad hesitation?
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Junior Member
Joined: Sep 2002
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From: Grand Rapids MI
bad hesitation?
I have a 86 Z28 TPI 305 and when I push the throttle whether its in park or driving around it has a real bad hesitation, what could the problem be I am new to computer cars so I dont know much about them. I do know know that this car has been doing this for years. Also were not real strict on emissions around here and I would like to remove all the smog equipment but I dont know what it will do to the computer. Thanks for any info you can provide me.
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Joined: Jan 2000
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APB,
Going lean on throttle tip-in is not uncommon on our TPI systems, but it usually can be adjusted out.
Start looking at the throttle body for wear and cleanliness, and check the TPS voltage. You may also need to check the minimum air position of the throttle plates. A check of the base timing and CTS accuracy could also help identify some of the issues at play.
Check the vacuum at idle. A reading below 17" Hg may be compounding any other problems.
Another thing that helps is to replace the thermostat with a 180°F unit (no lower unless you are into ECM reprogramming). The lower coolant temperature helps keep the system from leaning the mixture at idle to the point of inducing hesitation.
If that doesn't improve the hesitation, inspect the intake tract between the MAF and throttle body for leaks.
As for the emissions equipment, unnless you need the space under the hood, there should be no real reason to remove any of the components:
* The A.I.R. system doesn't take any more than 1-2 HP at peak RPM, so it isn't realistically a factor. I have to chuckle a little at those engines that have had the A.I.R. removed in the interest of some "free power" while still using mineral oil. Dyno documentation proves an increase of almost ten HP (9.8) by changing to synthetic lubricant, while the best-case gains for A.I.R. pump removal might be 2 HP.
* The EGR system can actually help produce more power by keeping head temperatures down and allowing more timing advance.
* All the rest of the systems are generally passive, taking no engine power and not affecting power at all. Systems like EVAP and PCV actually provide benefits and take no power.
* Even a cat converter, which can be restrictive to exhaust flow, can be replaced with an effective, high-flowing version that keeps the car smog-legal and frees up some top-end power.
Before you go randomly disabling systems and removing components, do a little homework to determine what the results might be. Solve the hesitation problem first, then decide what you want to remove. Changing the hardware now will only complicate the problem by introducing more random elements.
Going lean on throttle tip-in is not uncommon on our TPI systems, but it usually can be adjusted out.
Start looking at the throttle body for wear and cleanliness, and check the TPS voltage. You may also need to check the minimum air position of the throttle plates. A check of the base timing and CTS accuracy could also help identify some of the issues at play.
Check the vacuum at idle. A reading below 17" Hg may be compounding any other problems.
Another thing that helps is to replace the thermostat with a 180°F unit (no lower unless you are into ECM reprogramming). The lower coolant temperature helps keep the system from leaning the mixture at idle to the point of inducing hesitation.
If that doesn't improve the hesitation, inspect the intake tract between the MAF and throttle body for leaks.
As for the emissions equipment, unnless you need the space under the hood, there should be no real reason to remove any of the components:
* The A.I.R. system doesn't take any more than 1-2 HP at peak RPM, so it isn't realistically a factor. I have to chuckle a little at those engines that have had the A.I.R. removed in the interest of some "free power" while still using mineral oil. Dyno documentation proves an increase of almost ten HP (9.8) by changing to synthetic lubricant, while the best-case gains for A.I.R. pump removal might be 2 HP.
* The EGR system can actually help produce more power by keeping head temperatures down and allowing more timing advance.
* All the rest of the systems are generally passive, taking no engine power and not affecting power at all. Systems like EVAP and PCV actually provide benefits and take no power.
* Even a cat converter, which can be restrictive to exhaust flow, can be replaced with an effective, high-flowing version that keeps the car smog-legal and frees up some top-end power.
Before you go randomly disabling systems and removing components, do a little homework to determine what the results might be. Solve the hesitation problem first, then decide what you want to remove. Changing the hardware now will only complicate the problem by introducing more random elements.
Thread Starter
Junior Member
Joined: Sep 2002
Posts: 11
Likes: 0
From: Grand Rapids MI
bad hesitation
what is the tps, and cts and what do I check them with also how would I richen up fuel to the motor if it is lean. As far as the smog equipment goes the main reason I want to eliminate it is for room, but your right I will definately wait till I figure this problem out first. Just wanted to know if it would affect the computer. I found a couple other suggestion that maybe I should try O2 sensor and alternator what do you think? Thanks
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Joined: Jan 2000
Posts: 19,668
Likes: 314
APB,
The TPS (Throttle Position Sensor) is located on the right side of the throttle body:
Adjustment is relatively easy, but will require a digital voltmeter (DVM). You'll find having one very beneficial on our cars, so you might as well at least get a cheap one now.
Throttle Position Sensor (TPS)
Tools needed:
1. Digital Volt-Ohm-Meter (VOM)
2. Breakout jumper wires or probes (make your own)
- OR -
3. AutoXray, Diacom, or similar scanner will replace the VOM and jumper wires.
Turn on ignition, but don't start the engine.
With a diagnostic scanner: plug in the scanner and read the TPS voltage. It should be 0.54Volts +/- 0.07 VDC.
Connect the VOM to the TPS electrical connector terminals ‘A' and ‘B'.
With a breakout jumper: Disconnect the electrical connector from the TPS. Install the breakout in-line, between the TPS and wiring harness connector. Connect the meter probes to terminals 'A' and 'B' on the connector. (‘B' is the positive connection, ‘A' the signal ground, or negative.)
With probes: If you have very slender probes on your VOM, you can back-probe the TPS connector while it is attached to the TPS. If you have made probes of large dressmakers pins or a similar item, you can back-probe the connector as well. Connect the meter probes to terminals 'A' and 'B' on the connector.
Turn on the ignition to read the TPS output voltage at the idle position. The reading should be 0.54VDC +/- 0.07VDC. The ideal is the center of the range, 0.54VDC for a stock engine. To adjust the output voltage, loosen the two Torx screws holding the TPS to the throttle body, and slightly rotate the TPS up or down, reading the voltage until it comes into specification. Tighten screws. Using the throttle lever, rotate the throttle to WOT (wide open throttle). The TPS voltage should be over 4.0 volts. Close the throttle again, and then slowly open it to WOT, observing the voltage reading. It should increase progressively and in a linear fashion. If it sticks or jumps or falls off at all while doing this check, the TPS sensor may be failing and could be a cause of stumbling and driveability problems.
After achieving the desired setting, turn off the ignition switch. Remove all jumpers or the scanner and reconnect the TPS connector as required.
The TPS (Throttle Position Sensor) is located on the right side of the throttle body:
Adjustment is relatively easy, but will require a digital voltmeter (DVM). You'll find having one very beneficial on our cars, so you might as well at least get a cheap one now.
Throttle Position Sensor (TPS)
Tools needed:
1. Digital Volt-Ohm-Meter (VOM)
2. Breakout jumper wires or probes (make your own)
- OR -
3. AutoXray, Diacom, or similar scanner will replace the VOM and jumper wires.
Turn on ignition, but don't start the engine.
With a diagnostic scanner: plug in the scanner and read the TPS voltage. It should be 0.54Volts +/- 0.07 VDC.
Connect the VOM to the TPS electrical connector terminals ‘A' and ‘B'.
With a breakout jumper: Disconnect the electrical connector from the TPS. Install the breakout in-line, between the TPS and wiring harness connector. Connect the meter probes to terminals 'A' and 'B' on the connector. (‘B' is the positive connection, ‘A' the signal ground, or negative.)
With probes: If you have very slender probes on your VOM, you can back-probe the TPS connector while it is attached to the TPS. If you have made probes of large dressmakers pins or a similar item, you can back-probe the connector as well. Connect the meter probes to terminals 'A' and 'B' on the connector.
Turn on the ignition to read the TPS output voltage at the idle position. The reading should be 0.54VDC +/- 0.07VDC. The ideal is the center of the range, 0.54VDC for a stock engine. To adjust the output voltage, loosen the two Torx screws holding the TPS to the throttle body, and slightly rotate the TPS up or down, reading the voltage until it comes into specification. Tighten screws. Using the throttle lever, rotate the throttle to WOT (wide open throttle). The TPS voltage should be over 4.0 volts. Close the throttle again, and then slowly open it to WOT, observing the voltage reading. It should increase progressively and in a linear fashion. If it sticks or jumps or falls off at all while doing this check, the TPS sensor may be failing and could be a cause of stumbling and driveability problems.
After achieving the desired setting, turn off the ignition switch. Remove all jumpers or the scanner and reconnect the TPS connector as required.
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