Running rough

[Tony91]

Recent new member. hoping to get some answers. I have a 91, its been runnig fine I took it out this morning and on the way back home I heard a noise ( not a knocking sound more like a ticking popping sound) now its running rough. I was able to limp home pulled in the garage and reved it up it feels like it is missing. I just fueled up with 100 octane would that have anything to do with it? any suggestions? Thx

[A26B]

Do you have a service manual?
Did you get a SES light on the display?
Start by pulling stored codes. Write them down, if any.
If no codes, while running, remove plug wire, one at a time. Note which cylinder does NOT cause a change in idle speed/roughness.

[Kb7tif]

sounds like running on 7 cylinders, I bet an injector might be the culprit, if the injectors are stock its a very good chance. the ticking/poping sound might be the dual mass flywheel responding to the miss.
That nice fuel, (i like it too) might have helped with the stock injectors

[Tony91]

Thanks for the help, I do have a service manual,not sure if any codes are showing I dont have a scan tool. I was kinda hoping it wasnt the injectors, but I suspected it might be. I guess that would entail the dreaded plenum pull. If injectors whats the best source? and what gaskets do I need?

[tccrab]

If it's a miss, my bet is bad injectors.
Are yours originals?
Replacement injectors, a lot depends on how much you want to spend.
I DO NOT recommend replacement originals, nor will anyone else here.
The original Multecs were not designed for gas with ethanol and there an internal seal that degrades quickly and eventually shorts the coils. Interestingly enough, the originals are the most expensive by far of all of your choices.
Your three choices most common choices by price are:
RC Engineering
Accell
MSD's from FIC.

Gaskets.
All you will need is a set of plenum gaskets, get 'em here at Jerry's:
http://jerrysgaskets.com
Jerry is a member here and a GREAT guy, and his stuff is the BEST.

Pulling the plenum is fairly easy if you're reasonably handy. There's LOTS of pics and info available here on the forum, just do a search on plenum pull.

Good luck!!

TomC
"Crabs"

[Tony91]

Tom,sorry I didn't get back sooner spent the rest of the day with the family and thanks for the info. I think the injectors are original, besides injectors what gaskets are needed and I notice quite a few people change plug wires, should that be done as well?

[VetteMed]

Originally Posted by Tony91

Tom,sorry I didn't get back sooner spent the rest of the day with the family and thanks for the info. I think the injectors are original, besides injectors what gaskets are needed and I notice quite a few people change plug wires, should that be done as well?

Plug wires can only be changed when the plenum is pulled, so it's a good opportunity to change a fairly inexpensive part. Some folks (myself included) also used the injector swap as an opportunity to put in new ignition coils, though it could be argued convincingly that this is overkill if they work fine.

[Tony91]

Thanks for all the great advice!! I'm hoping to get out there later today and start by pulling spark plug wires to see what cylinder is missing. I guess if I'm gonna have to pull the plenum I will clean things up under there as well and check the vacum connections as well.

[tccrab]

Tony:

The only gaskets you'll need is plenum gaskets, here's a link:
http://jerrysgaskets.com/store/index...fd0cfa83c0b2b1

Since the spark plug wires and coils can only be accessed with the plenum off, now is the time to replace them if you have any doubts at all.
See JeffVette on this forum for these, tell him I sent ya.

While you're under there, now's a good time to test all the vacuum secondary components. Make sure all the connections are leak free, and that all the components are working correctly.
Here's all you'll ever need to know (and more) about vacuum secondaries:
http://www.corvetteactioncenter.com/...0/002/article/

And finally, make sure to re-torque the oil box breather bolts and also the injector housing bolts. They tend to loosen with time.

Good luck!

TomC
"Crabs"

[Tony91]

ok, I started it up ran fair, started to pull plug wires1 at a time I could hear the idle drop on most cyclinders. #3 had the least amount of change, than #4 had the next least. I had to pull #3 off several time to listen if there was any change in the motor. Still think its injectors? I really appreciate all the support and feedback.
Tony