throttle return interference; '89 Caprice
May 13th, 2019, 5:42 PM
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throttle return interference; '89 Caprice
My very-low mileage '89 Caprice has a behavior that makes it difficult to drive with smoothness and finesse.
I suspect that problem is rooted in the emission controls. When releasing the accelerator pedal, it will not return to normal idle speed.. in order to operate the vehicle well. For example, if I am proceeding down a road at 30 or 35 mph, and take it out of Drive, the engine speed is immediately high... like a fast idle when cold. If I continue to coast to the stop sign about a quarter-mile away, the idle speed has returned to normal by that point. My adamant argument is that the engine should immediately drop to a normal idle speed... but there is definitely "something" that severely slows down the normal return to idle speed.
It feels like there's a hydraulic door-closing mechanism on the throttle control. The car is totally stock, having just turned 80,000 miles. There is no carpet or floor mat interference with the gas pedal.
The reason that I suspect emission controls... is that it's claimed that cars make the most pollution when decelerating... which is a high intake manifold vacuum condition... which, relatively-speaking, "starves" the fuel-air mixture for air. Air is needed to reduce oxides of nitrogen and whatever. So the thing that the car builder engineers have focused on, to try to meet the EPA standards, is to "monkey" with the engine performance when decelerating.
I'm not in favor of dirty air....... but I am even more in favor of being able to properly control my automobile. Because of this too-high engine speed when decelerating, it makes this car "borderline dangerous", having to stomp on the brakes too hard.. because the drive train is actually "fighting" the brakes.... and handling truly suffers.
This car has great handling potential, given its F41 sport suspension. Interestingly, I have a second '89 Caprice with almost triple the accumulated road mileage... and it behaves in the same bad manner. This bad car behavior doesn't happen nearly as much when in Direct Drive... but it does in OverDrive. I do appreciate the great gas mileage..... but it's very tiring to drive it.
I wonder if it my engine's EGR system.. that is allowing excess air into the intake manifold when decelerating... causing the engine to rev too much... which, since it's in gear, tends to keep driving the car (at the rear wheels) when I'm trying to slow down or stop.
In that common situation, the rear wheels are fighting the brake system............. or, with the brakes not applied, it causes the vehicle to keep going at the same 'whatever' speed... almost like cruise control was "on".... yet when in neutralL..... where the car should naturally slow down, and the engine speed slow down. That's how it "feels" to the driver: extremely aggravating.
"Somebody" must know about this in detail. My GM shop manual does not address this problem, not even "potentially". For the record, the '89 Caprice is the first year of fuel injection [throttle-body].
Is it possible that it is the fuel injection system which is engineered to prevent normal return-to-idle speed... at least for "x" amount of time... like in the scenario I painted in this thread. There must be a way to solve this problem.
I suspect that problem is rooted in the emission controls. When releasing the accelerator pedal, it will not return to normal idle speed.. in order to operate the vehicle well. For example, if I am proceeding down a road at 30 or 35 mph, and take it out of Drive, the engine speed is immediately high... like a fast idle when cold. If I continue to coast to the stop sign about a quarter-mile away, the idle speed has returned to normal by that point. My adamant argument is that the engine should immediately drop to a normal idle speed... but there is definitely "something" that severely slows down the normal return to idle speed.
It feels like there's a hydraulic door-closing mechanism on the throttle control. The car is totally stock, having just turned 80,000 miles. There is no carpet or floor mat interference with the gas pedal.
The reason that I suspect emission controls... is that it's claimed that cars make the most pollution when decelerating... which is a high intake manifold vacuum condition... which, relatively-speaking, "starves" the fuel-air mixture for air. Air is needed to reduce oxides of nitrogen and whatever. So the thing that the car builder engineers have focused on, to try to meet the EPA standards, is to "monkey" with the engine performance when decelerating.
I'm not in favor of dirty air....... but I am even more in favor of being able to properly control my automobile. Because of this too-high engine speed when decelerating, it makes this car "borderline dangerous", having to stomp on the brakes too hard.. because the drive train is actually "fighting" the brakes.... and handling truly suffers.
This car has great handling potential, given its F41 sport suspension. Interestingly, I have a second '89 Caprice with almost triple the accumulated road mileage... and it behaves in the same bad manner. This bad car behavior doesn't happen nearly as much when in Direct Drive... but it does in OverDrive. I do appreciate the great gas mileage..... but it's very tiring to drive it.
I wonder if it my engine's EGR system.. that is allowing excess air into the intake manifold when decelerating... causing the engine to rev too much... which, since it's in gear, tends to keep driving the car (at the rear wheels) when I'm trying to slow down or stop.
In that common situation, the rear wheels are fighting the brake system............. or, with the brakes not applied, it causes the vehicle to keep going at the same 'whatever' speed... almost like cruise control was "on".... yet when in neutralL..... where the car should naturally slow down, and the engine speed slow down. That's how it "feels" to the driver: extremely aggravating.
"Somebody" must know about this in detail. My GM shop manual does not address this problem, not even "potentially". For the record, the '89 Caprice is the first year of fuel injection [throttle-body].
Is it possible that it is the fuel injection system which is engineered to prevent normal return-to-idle speed... at least for "x" amount of time... like in the scenario I painted in this thread. There must be a way to solve this problem.
Last edited by Maynard G. Krebs; May 13th, 2019 at 5:49 PM.
May 16th, 2019, 4:51 PM
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Irish Alley..... the throttle control springs seem just fine.
If I coast between an eighth-mile and a quarter-mile, the idle speed is back to normal. But when driving, one cannot let off the gas for a typical curve and then get back on it gently... but the throttle is not idling, but is so high that the drive wheels are fighting the brakes and the front wheels.... ruining the good, natural handling that this car should have.
If I coast between an eighth-mile and a quarter-mile, the idle speed is back to normal. But when driving, one cannot let off the gas for a typical curve and then get back on it gently... but the throttle is not idling, but is so high that the drive wheels are fighting the brakes and the front wheels.... ruining the good, natural handling that this car should have.
May 19th, 2019, 2:54 PM
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My engine won't return to idle quickly enough.
I have two stock 1989 Caprices, with 305 throttle-body injection, & F41 sport suspension.
It takes much too long for the idle speed to return to normal... once the accelerator pedal is released.
My guess is the emission controls deliberately slowing down the engine revs when decelerating (and pumping air into the intake manifold).
I figure that this is done either via the EGR system, OR a modified fuel injection pump that has a strong retarding mechanism that slows down the engine speed returning to normal idle.
The bottom line.. is that such behavior prevents smooth driving for good handling.... such as when wanting to get back on the gas lightly after releasing accelerator when approaching a slight curve.... and wanting to gently 'power out of it' ---- but that cannot be done. Often the drive wheels are fighting the driver's efforts to slow the vehicle down when needed. It's an abomination... as it is.
It takes much too long for the idle speed to return to normal... once the accelerator pedal is released.
My guess is the emission controls deliberately slowing down the engine revs when decelerating (and pumping air into the intake manifold).
I figure that this is done either via the EGR system, OR a modified fuel injection pump that has a strong retarding mechanism that slows down the engine speed returning to normal idle.
The bottom line.. is that such behavior prevents smooth driving for good handling.... such as when wanting to get back on the gas lightly after releasing accelerator when approaching a slight curve.... and wanting to gently 'power out of it' ---- but that cannot be done. Often the drive wheels are fighting the driver's efforts to slow the vehicle down when needed. It's an abomination... as it is.
July 24th, 2019, 9:38 PM
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... found the answer / reason . . . .
I discovered that the throttle-body EFI, beginning in 1989 Caprices, is about totally controlled by the on-board computer.
Indeed, the accelerator does not direct the car to provide more fuel, but rather merely controls the amount of opening of the amount of AIR entering the induction system / the intake manifold. This would be totally okay..... if it wasn't for the fact that these Caprices have the on-board computer using the EFI to primarily provide good starting and running, all the while providing great fuel mileage, but MAINLY to reduce emissions.. at the decided cost of driver control-ability via use of the gas pedal. It really feels like I'm driving a computer... with tires on it. In short, I find that to be no fun to drive... whether mildly.. or enthusiastically. The car's engine is reluctant to rev up normally.... and worst of all, utterly reluctantly to "rev down" when the accelerator is released.... making it borderline dangerous to drive, IMO. Some drivers might not notice this phenomenon...... but I despise it.
Therefore, I have decided to sell both of my '89 Caprices with the optional F41 sport suspension option. One has only 81,000 miles [no rust, no rot]..... and the other about 228,000 miles. Both run fine, no accident damages, clean interiors.
e: jerrychase_at_large@yahoo.com
Indeed, the accelerator does not direct the car to provide more fuel, but rather merely controls the amount of opening of the amount of AIR entering the induction system / the intake manifold. This would be totally okay..... if it wasn't for the fact that these Caprices have the on-board computer using the EFI to primarily provide good starting and running, all the while providing great fuel mileage, but MAINLY to reduce emissions.. at the decided cost of driver control-ability via use of the gas pedal. It really feels like I'm driving a computer... with tires on it. In short, I find that to be no fun to drive... whether mildly.. or enthusiastically. The car's engine is reluctant to rev up normally.... and worst of all, utterly reluctantly to "rev down" when the accelerator is released.... making it borderline dangerous to drive, IMO. Some drivers might not notice this phenomenon...... but I despise it.
Therefore, I have decided to sell both of my '89 Caprices with the optional F41 sport suspension option. One has only 81,000 miles [no rust, no rot]..... and the other about 228,000 miles. Both run fine, no accident damages, clean interiors.
e: jerrychase_at_large@yahoo.com