vmi_vette

My 92 started to stumble on acceleration today. It is most noticeable when the car is in 5th or 6th and I do a part throttle accel at low rpms (engine load at low rpms). The optispark and water pump were replaced before I bought the car 20k miles ago. The spark plugs and fuel regulator were also replaced at that time. I have not replaced the fuel filter since I have had the car, so I think I will do that right now.

Any ideas on what might be causing this? Could it be either a clogged fuel filter, bad optispark, bad coil, bad alternator (just replaced two months ago, but already had to get a new one under warranty - piece-o-crap AutoZone rebuilt unit only put out 80 amps instead of 120), or bad wires? Since I am only getting the problem under acceleration and not steady-state rpm or load I think I might have to rule a few of these out, but not sure. It is an Arizona car, so the engine bay stays dry.

No codes have been throw yet.

Thanks for the help.
:confused:


[Modified by vmi_vette, 8:49 PM 2/17/2003]

Wadoka

When mine did it, changing the fuel filter and the plug wires fixed the problem. Since I did both at the same time, I don't know which one did the trick.

vmi_vette

Thanks for the reply. I think I will tackle the cheap parts first. I will get a fuel filter tomorrow, and see if that works. Then on to plug wires.

don hall

Let's hope it is not your opti-spark unit. The opti can fail at any time, regardless of mileage. Hesitation at low RPMs can be the result of a faulty opti. If your fuel filter is restricted, you would notice a loss in performance more so at the higher RPMs. If replacement of the filter solves your problem, you should inspect your fuel tank for any contamination (rust) that might exist. Most performance problems are not associated with fuel filters. When a filter becomes clogged, it can be attributed to the fuel supplier not changing filters at the pump, and the fuel, water and all, by-pass the filter into your tank.
Your alternator should not be a performance factor, as the amps required by the electronics will be supplied by the battery until the batt runs "dry". You can easily check the out-put of the alt with the gage button, and see if it reads 14+ volts with the engine on.
My suggestion would be to analize what components you can to solve the problem, but don't wait until you are stranded before having the opti tested.

gpagaduan

sounds like wires and coil to me. I had mine diagnosed by the dealer. Changed one bad wire and it did the trick. How's your fuel mileage?

vmi_vette

Good points. I am starting to leaning towards wires or optispark also. How do you get an optispark tested?

My fuel mileage is around 18.7 (half freeway/half city). This morning I had no problem when I did I full throttle accel from a stop through the first two gears. However, when I stuck it in 6th gear at 50 mph and gave it some gas to load the engine, it stubbled really bad.

Boy, do I wish I had a good engine data scan software package like Datamaster. That was the next thing on my list to buy when I had some extra money.

Nathan Plemons

I'm gonna lean towards tune up items. They are fairly cheap and a good idea anyway. My car highly modded doesn't miss a beat if you floor it from 1000 rpm's in 6th gear. It doesn't really go anywhere but it doesn't complain about it. Meanwhile my friend's camaro complains VERY badly. We're gonna try a tune up for him and see what happens.

Read this thread and see if any of it sounds familiar http://forums.corvetteforum.com/zerothread?id=492217 :cheers:

vmi_vette

Nathan,
Thanks. I am leaning more and more towards plug wires. Not sure if I should get OEM or MSD 8.5 superconductors though. This car is a daily driver, so I don't want to wait for parts.

Nathan Plemons

I love the MSD 8.5 wires. They are the best I have ever used for quality and durability. For exampele every other plug wire I've ever touched has pulled apart on me. I've never had an MSD pull apart and I've had them on and off several times.

The problem with the MSD's is that they don't fit the stock wire looms. If you can deal with that I would highly recommend them because there are none better. They also really do only have 50 ohms of resistance per foot.

vmi_vette

Nathan,
Did you modify the factor looms with a dremal, or did you buy new looms. Where did you purchase the MSD wires and looms, if you got new one. I am thinking I could buy some looms from the dealer and modify them, but I need to look at them first.

Thanks for the info.


[Modified by vmi_vette, 7:00 AM 2/18/2003]

Nathan Plemons

I've got headers too so I dont' even have wire looms. I'm sure you can get some at a local parts store but mine are just held out of the way with tie wraps.

John Row

Unfortunately, the only way to test an opti is to replace it. Save this option as your last resort. Usually the opti is indicated by hi-RPM miss and jumpy idle (although anything is possible :rolleyes: ).

Do tune-up parts first.