1996 Collector Edition Corvette

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wxo
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Re: 1996 Collector Edition Corvette

Post by wxo »

They are new Accel injectors with the same specs as the original ones. Most of the most of the off-idle stumbling was due to low fuel pressure from a defective fuel pressure regulator (Standard Products). Now with the new Holley adjustable fuel pressure regulator, 99% of the hesitation is gone, but there is still something not quite right. Still searching for the answer to that.
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wxo
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Re: 1996 Collector Edition Corvette

Post by wxo »

The answer is.......
Looking back at the history of this off-idle bog/hesitation/stumble, it was there from the time I first fired up the LT4. When I finally put a fuel pressure gauge on it, I saw that the fuel pressure was much lower than it was supposed to be. It turned out to be the faulty Standard Products fuel pressure regulator. I verified that when I installed the Holley adjustable regulator. I set it to stock specs according to my FP gauge, 44psi. Once more the problem was much improved, but the bog was still there. I tried going higher on the pressure and got it running quite well. It was very drivable now but I was significantly beyond the stock fuel pressure settings. The symptom now was a major hesitation that happened after up shifts where I would go a bit heavy on the foot feed to accelerate in the next gear. I decided to do some real road testing to see if even more fuel pressure would produce any changes in the bog. I took a big 5 psi swing at it to 55 psi and now the bog was gone. It was accelerating like crazy. However, just driving around the neighborhood in various gears produced a bog when loading it up in a higher gear at low speed. Now I knew exactly what to do. Up to 57 psi it went and that bog was gone. This car is now crazy fun to drive. :twisted: It just pulls strong gear after gear after gear. :mrgreen:
I took it down and had it inspected today in preparation for a license plate and legal driving.
Still a lot of things to deal with though. First thing is to flush out the cleaner in the cooling system and change one hose and the engine temp sensor and a new thermostat before filling it with fresh antifreeze. Headlights don't rotate. Gotta sort that out. AC doesn't work. That needs attention, too.
TBSS needs a shelter for the winter. Gotta get that done too.
Right now, though, I'm happy to have reached this point.
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Maverick
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Re: 1996 Collector Edition Corvette

Post by Maverick »

I had a ride in this great Vette. To me, it feels much faster than the Lincoln maybe in the 12s. But, WXO says the stock Vettes of that era aren't in the 12's. After thinking about it, I wonder if it feels that way because of the tires. No wheel spin. Where the Lincoln or Maverick tires would break loose, the Vette just MOVES. JERKS you back in the seat on shifts. :mrgreen:

Last Vette I rode in was a late 50s or very early 60s. Did not like the harsh ride and couldn't imagine a road trip in it. Don't know if it had stock shocks. WXO's Vette has a very comfortable ride and will be a fine cruiser. I hope the COVID mess is straightened out by next year and you guys can see it in Carlisle.

Love it!!!
Maverick
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wxo
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Re: 1996 Collector Edition Corvette

Post by wxo »

Now that I'm venturing out on the roads with the Vette, the F45 Real Time Damping System has come into focus and surprisingly, seems to be working fine. When I looked into it on the web, I found the following very interesting in it's complexity: (words that I hope don't come back to bite me later)

*** The 1996 Corvette Real Time Damping (F45):

The Real Time Damping System (RTD) optimizes ride and maintains ultimate handling capabilities through a driver-adjustable ride control system. Three settings, Tour, Sport, and Performance, each with a distinct range of ride firmness. RTD is designed to reduce impact harshness and improve: isolation, rolling smoothness,
high-speed stability (pitch/yaw), and wheel control.

RTD balances the vehicle by using sensors at each wheel, to measure movement. The data retrieved from the wheel sensors via the Powertrain Control Module is processed by a controller which calculates the degree of "valving" necessary to achieve optimum control of the vehicle. RTD adjusts the Delphi, bi-state ride adaptive gas, convertible specific shock absorbers in "real time" (10-15 milliseconds, or about a foot of roadway travel at 60 mph). Unlike C4 RTD, each shock is now individually adjusted.

RTD damping is electro-hydro-mechanical. Shock oil is forced through small orifices (valves) by movement of the shock piston and rod in the oil-filled shock body. The valve's resistance to oil flow provides the damping. The RTD's bi-state valve (continuously variable pressure control actuator) is mounted on the side of the shock.

Conventional shock absorbers are a compromise between performance handing and pleasing ride. While they can do one or the other very well, even the best hydraulic shocks are only adequate in how they address that compromise. The C5's continuously variable RTD has an additional bandwidth, through improvements in accuracy and speed of valve adjustment. However, all ride-adaptive systems using adjustable valves have limited bandwidth because of the slowness with which they change states along with the slow response of the fixed orifice valves.

[Reference material provided by GM Media Archives. Rev. 09/25/95 & H. Halverson: The History of Corvette Electronic Ride Control Systems]

RTD occupies '97 Service Manual Sections 3-139 to 238. The system is complex. You will know if it isn't working as one of 26 DTC's will set. Practically speaking, the more seat time you put in the more atuned you will become to the subtle differences in settings.

Previous C4's had this:

The Selective Ride Control system is controlled by it's own computer. As delivered, it used special Bilstein shock absorbers. The 4 shocks are only part of the system however. There are dampening adjustment motors and position feedback sensors at each shock that monitor the rotary position of an actuator shaft and if their outputs are not what the computer expects to see, you get a SRS trouble light.

The computer also looks at the vehicle speed sensor plus checks itself. You get the SRS trouble light if there are problems with those systems as well.

The shocks have variable diameter orifices that control how fast the shocks can move up and down. The orifice size is controlled by adjusting a shaft that extends through the top of the shock absorber. The shaft is turned left and right by the actuator mounted on the top of the shock. There is a dampener adjusting motor on each shock that cranks the shaft left or right plus a sensor that reads the position of the shaft and feeds that information back to the SRS system computer.

Based on the input from the driver's select ride switch, the vehicle speed sensor and the position feedback sensor, the computer sends battery voltage to the dampening adjustment motor to move it to the appropriate position.

Power on Checks and System Monitoring

Immediately after receiving power (when you turn the ignition key) the SRC computer does a power on check and if it finds a problem, it lights the Selective Ride System light on the DIC (Driver's Information Center). If all is OK, it does not light the light and presets the shocks to a 60 degree initial position (the full range is 0 to 160 degrees). If things go badly after the initial power on sequence, the light will come on when the problem occurs and go off when the computer is satisfied that things are OK. A trouble code is stored for later retrieval if the problem is intermittent.

Suspension Control

As the speed changes, the computer looks at what kind of ride you have selected and cranks the shaft around to what it thinks is the proper match of shock travel and dampening versus speed based on the selection you made with the three position selective ride switch located within easy reach of the driver's position.

The system is designed such that the dampening rate increases with vehicle speed and decreases as you slow down. In effect, it monitors the degree of stiffness requested by the driver and the speed of the vehicle. It then sends either + or - battery voltage to the dampening motors on the shocks and monitors how the shocks are responding to the commands using the position sensor information.

The result is a constantly changing suspension setup, tuned to the conditions present at the time, instead of a compromise solution tuned to one standard set of conditions. In other words: an active suspension.

Troubleshooting the FX-3 Suspension

If you have a service manual, there is a section that explains how to retrieve any stored trouble codes from the SRS computer which is the first step in repairing the system plus there are troubleshooting charts that walk you through a logical repair procedure based on conditions observed or measured.

On the the early model, all digital dash C4s (which were made through 1989), plus any other mid model year C4s that had a 12 pin ALDL connector, you ground pins A & B on the ALDL connector under the dash just to the right of the steering wheel and count the flashes on the SRS light to see if any trouble codes have been stored. On all C4's with a 16 pin ALDL connector (except the 1996 model), you ground pin G and the trouble codes for the SRS computer will be displayed on the LCD screen that doubles as your trip odometer and speedometer. The appropriate service manual describes exactly how to extract the codes for either system as well as explaining what the codes mean.

Without the computer codes, you are shooting in the dark if you try to troubleshoot a FX-3 problem but a couple possibilities are bad grounds or battery wires going to the dampening adjustment motors or bad ground/signal leads coming from the position sensors to the computer. So, first you should check all connectors associated with each shock and make sure they are not corroded or dirty. Wiggle each of them in turn and see if the problem goes away. If it does, you have a bad connection to deal with.

Another possibility is the driver transistors in the SRS computer itself. If the computer commands the dampening motor to move but the driver transistors are bad or leaky, nothing will happen (or not enough will happen), the expected results will not be fed back by the position sensors, and the SRS trouble light will come on. Changing the actuators or shocks will not correct this sort of failure, you must repair or replace the computer itself.

Lastly, if you install a High Energy Ignition and coincidentally begin to have problems with your Selective Ride System, the wiring from the HEI is cross talking into the SRS wiring. Reroute the wires from the HEI so that it does not run parallel to any OEM wiring and try relocating the HEI control box to a different location to minimize the problem.

One final thought: like most electrical problems with a C4, check the connectors first and make sure they are free of corrosion and making good contact before you go on to more exotic solutions. In the absence problems caused by a HEI system, poor connections and/or grounds are where most of the SRS problems originate.
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wxo
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LT4 engine noise

Post by wxo »

I would like your ideas regarding the source of the slightly muffled knocking noise in my engine. It is loudest on startup and eventually goes away. The following video was recorded before I got the fuel pressure sorted, so ignore the fuel pressure gauge and focus on the background engine noise. If you skip forward to about 3:30 on the timeline you will be able to hear it more clearly.
https://youtu.be/xudlQpYHL6E
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GMJohnny
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Re: 1996 Collector Edition Corvette

Post by GMJohnny »

If the noise goes away when the motor warms up and you have consistent oil pressure
warm or cold, I’d get some miles under my belt before I tore anything apart. I’m not
sure if this car has it or not, but my Oldsmobiles have always had a damper in the
exhaust manifold to help build heat when the motor is cold. Mine flaps like crazy until
the heat heats up a spring and the flap opens. Annoying, but it goes away when warm.
I’d look for something stupid like that. I’d also put a stethoscope to the motor to hear
where the noise comes from when cold. It’s been my experience that motors don’t fix
themselves, so if it was a rod or a main, the noise wouldn’t go away. Anything loose
wouldn’t quiet down. I’d guess that it’s a stuck lifter somehow or maybe a valve not
returning all the way based on sludge or something being stuck when cold, heat makes
it free up. My vote would be to start worrying about it after 2000 miles and another oil
change are on the car.

GM
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wxo
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Re: 1996 Collector Edition Corvette

Post by wxo »

GM, I've had my share of tearing into this car. Everything is difficult. I'm content to leave well enough alone for now. I'm not too concerned about the sound since it goes away. I thought it might be the AIR pump which runs when the engine is cold, but I pulled the fuse and it didn't change the sound. I'm just driving it around town and listening and feeling out the car now. I didn't realize how noisy a convertible is. The leather seats themselves make a lot of noise. Oh, well, it will get better with time.
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Basement Paul
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Re: 1996 Collector Edition Corvette

Post by Basement Paul »

Any chance it's noisier just because it's in the rich cycle to keep it running when it's cold? My S10 is noisier when it's cold and I bet your TBSS is too. Unless I'm hearing it wrong...

-BP
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Maverick
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Re: 1996 Collector Edition Corvette

Post by Maverick »

I’m not sure if this car has it or not, but my Oldsmobiles have always had a damper in the
exhaust manifold to help build heat when the motor is cold. Mine flaps like crazy until
the heat heats up a spring and the flap opens.
It sounds like something like that to me. "Puff, puff, puff, puff, ..." at the rate of a single cylinder cycle. Only on the right side. I couldn't pick it up at the tail pipes. No way its bearing noise. The engine sounds really smooth and quiet when warmed up. I thought it was a cyl miss that disappeared when warm. IR thermometer on the header runners might eliminate the miss theory. :mrgreen:
Maverick
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wxo
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Re: 1996 Collector Edition Corvette

Post by wxo »

BP, I believe you are thinking of the piston slap noise that is related to aluminum engine blocks. Yes the TBSS does it and Maverick's 521 had piston slap also. The LT4 is an iron block with aluminum heads.
This noise is louder on the passenger side and has a poit, poit, poit sound imbedded in the background. That's why I checked the AIR pump for the AIR INJECTION REACTOR system that runs when the engine is cold. Anyway I'm just looking for ideas. Maybe if something breaks I'll find out what it is. :shock:
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wxo
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Re: 1996 Collector Edition Corvette

Post by wxo »

Maverick wrote: IR thermometer on the header runners might eliminate the miss theory. :mrgreen:
I put the IR thermometer on the exhaust manifolds today. Readings were very different from cylinder to cylinder during the warmup cycle. Maybe the cylinders heat up at different rates. I don't know. In addition, there is very limited area on each exhaust port to measure the temp. The exhaust manifolds are covered with shields and the center two manifold ports are siamesed. It was inconclusive.
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wxo
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Re: 1996 Collector Edition Corvette

Post by wxo »

Maverick and I discussed this issue this morning and he came up with a good diagnostic suggestion. Upon cold start, I will disconnect each injector in sequence to observe any changes in the noise. It will be interesting to learn the results. It may point to a particular weak cylinder or at least point us in another direction for the source.
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wxo
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Re: 1996 Collector Edition Corvette

Post by wxo »

The noise goes away when I pull the injector connector on #8 cylinder.  That is the cylinder where I struggled so much to change the spark plug because it is so tight in there.  I think it would be prudent to go back in there and revisit that spark plug.
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wxo
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Re: 1996 Collector Edition Corvette

Post by wxo »

While putzing today, I decided use a flashlight to take a look inside the right side valve cover through the oil filler hole. What a great surprise! It is immaculate in there after 103k miles.
IMG_3865.JPG
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Maverick
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Re: 1996 Collector Edition Corvette

Post by Maverick »

NICE!!!
Maverick
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