1992 rough on acceleration

[Jeff Z.]

About a week ago I noticed when cruising on the highway at 65-70 if I hit the gas to accelerate there was an initial rough response. Now, the car is rough on idle and whenever I accelerate it's very rough and sluggish and the exhaust sound is not normal, very muffled and uneven. Any suggestions on how I begin to diagnose this problem?

Jeff (58610)

[Bill M.]

Re: 1992 rough on acceleration

I would start with the injectors. They are easy to get to and diagnose. Pull the connectors and check for resistance. They should all be in the range of 13 - 14 ohms. I found one of mine at about 2 ohms. I replaced all of them with rebuilts. That fixed the low-speed miss on my '92.

[Tom H.]

Re: 1992 rough on acceleration

Moisture in the opti spark distributor. Did you recently wash the engine ????

[Joe L.]

Re: 1992 rough on acceleration

Moisture in the opti spark distributor. Did you recently wash the engine ????

Tom-----


That's what I think, too. A leaking water pump could also be the source of liquid. Or, it might be that there's just enough atmospheric moisture.

I wonder if this 92 is an early one that somehow never got the distributor replaced on recall?

[Keith B.]

Re: 1992 rough on acceleration

could be a the Mass air flow, TPS, a bad opti will do that at any speed, just at different RPM. my two cents

[Edward J.]

Re: 1992 rough on acceleration

Jeff, The above info will put you all over the map( all above are common issues). As stated above the Opti spark dist. is a thorn in the side for 92 corvette owners, As are the water pumps when they leak. Water is the Opti.s enemy. To give you a little back ground on 92's dist. it was a sealed system not vented , so water/ moisture entered under the cap it game set match, no way to dry out. along with this issue, there was another problem also, some how the rotating assy. inside the dist. could form a vacuum and cause the dist. cap to collapse onto the dist. rotor, which again causes drivability problems. You really should bring to someone that knows corvettes to have it looked at. parts are not cheap for your corvette, so to start replacing you will find there $$$.

[Joe L.]

Re: 1992 rough on acceleration

could be a the Mass air flow, TPS, a bad opti will do that at any speed, just at different RPM. my two cents

Keith-----


No mass airflow on a 1992 LT1.

[Keith B.]

Re: 1992 rough on acceleration

Well then ignore that part. I would also hook it up to a good scanner that has the read outs from the ECM. and see if there is any erratic readings

[Jeff Z.]

Re: 1992 rough on acceleration

Thanks everyone. I suspected either injectors or the opti. I'm familiar with the opti issues on the '92 as I have read all about it. I've only had my '92 for a year and don't have a lot of the prior history. I did replace the plugs and wires this spring and I can tell you that the opti had not been touched recently.

I'm leaning to it being an opti issue, although the scanning for read outs is something I'll also do. The reason I'm leaning to it being an opti issue is that the low coolant light was coming on sporadically about a month ago. The coolant level was low seemingly from a small leak around the water pump. I got the coolant level back to normal and was preparing to replace the water pump gasket. It's been pretty hot here lately (engine temp running higher in traffic) and now what I'm wondering is if the gasket integrity has become even more compromised and finally some coolant has gotten into the opti.

A couple of questions. Since I do need to take the water pump off to address the leak, regardless of whether a wet opti is my issue, should I just replace the opti at the same time? If so, should I replace it with the distributor assembly that comes with a ventilation system hook up like the one that can be purchased through Corvette Central (part # 274583)? Second, I assume the leak from the water pump is at the gasket. But again, regardless, should I just install a new water pump?

Jeff (58610)

[Joe L.]

Re: 1992 rough on acceleration

Thanks everyone. I suspected either injectors or the opti. I'm familiar with the opti issues on the '92 as I have read all about it. I've only had my '92 for a year and don't have a lot of the prior history. I did replace the plugs and wires this spring and I can tell you that the opti had not been touched recently.

I'm leaning to it being an opti issue, although the scanning for read outs is something I'll also do. The reason I'm leaning to it being an opti issue is that the low coolant light was coming on sporadically about a month ago. The coolant level was low seemingly from a small leak around the water pump. I got the coolant level back to normal and was preparing to replace the water pump gasket. It's been pretty hot here lately (engine temp running higher in traffic) and now what I'm wondering is if the gasket integrity has become even more compromised and finally some coolant has gotten into the opti.

A couple of questions. Since I do need to take the water pump off to address the leak, regardless of whether a wet opti is my issue, should I just replace the opti at the same time? If so, should I replace it with the distributor assembly that comes with a ventilation system hook up like the one that can be purchased through Corvette Central (part # 274583)? Second, I assume the leak from the water pump is at the gasket. But again, regardless, should I just install a new water pump?

Jeff (58610)

Jeff------

You can tell if the car has a "1st design" Optispark. Using a mirror, look at the bottom of the aluminum base of the distributor. If there are no holes, then it's the 1st design which was supposed to have been replaced on recall. If there are 3 holes, then you have the 2nd design. However, there can be the same problems with the 2nd design over time. Later 1992's had the 2nd design originally installed.

You cannot use the stock-type 3rd design which is vacuum ventilated unless you make several other changes to the engine. However, you can use 2nd design modified to include vacuum ventilation (like 3rd design) and that's what I recommend you use. That may be what the Corvette Central unit is.

I think you should replace the waterpump. 1992 uses a waterpump that is unique to that year but it's still available from GM and Delco. If you are going to replace the waterpump, I think I'd go ahead and replace the distributor at the same time. It's actually quite a bit more work to replace the distributor and the Optisparks are not cheap, but if even if the distributor is now OK, when it does go bad, you'll have to remove the waterpump again to replace it.

Addendum----

The correct modified 2nd design Optispark for your 1992 is their #274590. The 274583 is for 1993-94 (although I do not understand why there is a difference since 1992-94 Optisparks were the same)

The OEM-quality waterpump is GM #12529560 aka Delco #251-537

[Bill H.]

Re: 1992 rough on acceleration

Before you do anything, pull the codes. You don't need a scanner. You can pull them right on your dash display using a paperclip. If you're not going to have the car judged, I'd look at the MSD opti. It's billet aluminum and has an o-ring seal on the cap vs GM's paper gasket. The cost is about the same as the GM and the vent kit from CC. The one on my 92 has 30k on it and it's been wet numerous times. BTW, if you plan to do the opti youself, buy a power steering pump pulley puller/installer. Removing the pulley saves a bunch of time, gives you access to the left side of the opti and eliminates having to loosen up the p/s unit. The puller costs $26.

[Bill M.]

Re: 1992 rough on acceleration

Jeff------

You can tell if the car has a "1st design" Optispark. Using a mirror, look at the bottom of the aluminum base of the distributor. If there are no holes, then it's the 1st design which was supposed to have been replaced on recall. If there are 3 holes, then you have the 2nd design. However, there can be the same problems with the 2nd design over time. Later 1992's had the 2nd design originally installed.

Here's a picture of the vented '92 opti:

[Jeff Z.]

Re: 1992 rough on acceleration

Thanks for all the great feedback. Joe, can you explain a little more how to access the codes on the dash with a paperclip? I'm not familiar with this process. Also, what's the best resource for "decoding" the codes?

[Bill H.]

Re: 1992 rough on acceleration

Thanks for all the great feedback. Joe, can you explain a little more how to access the codes on the dash with a paperclip? I'm not familiar with this process. Also, what's the best resource for "decoding" the codes?

Actually, that was me Jeff. I have a detailed write up on a pdf. that I can email you, PM me your email address. It's very easy to do. It's also described in the FSM but my pdf. is a bit easier to understand. If you don't have a FSM (Factory Service Manual), get one. You can't properly work on a C4 without one. The important thing with the FSM's is that they have diagnosis flow charts. If you pull a code 32, that code and the chart will help you find out what's causing it. The FSM's on CD are inexpensive on ebay, like $25, the Helm's paper version is $105 (recommended).