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]

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.php?main_page=product_info&cPath=0&products_id=7&zenid=7bafdb946b5302390cfd0cfa83c0b2b1

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/tech/howto/idx.php/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

[secondchance]

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

Any difference in how rough the motor is running depending on engine temp?
Reason I am asking is, at least in my case, my 94 would run just fine until engine temp hit around 190 or so.
At first, I thought it was open loop/closed loop issue. It turned out, at least in some cases, injector would run fine until it heated up at which point it would start to short out internally.
Also, #3 and 4 are not on the same coil. I think #4 and 7 and #3 and 2 are correct pairing for coils.

[Tony91]

I let it warm up but maybe I didnt let get warm enough, I 'll try again later, gonna do some reading on pulling the plenum..

[secondchance]

I let it warm up but maybe I didnt let get warm enough, I 'll try again later, gonna do some reading on pulling the plenum..

Check these link also.
http://www.corvetteactioncenter.com/tech/howto/idx.php/78/002/article/

http://www.corvetteactioncenter.com/forums/zr-1-general-technical-discussion/14366-plenum-removal-procedure.html

Since 2002 I must have pulled the plenum 4-5 times. Good news is that it gets easier every time.:mrgreen:

[tccrab]

Some GREAT pics and very clear/concise info in these threads here on the forum:
http://www.zr1netregistry.com/forum/showthread.php?t=7614
http://www.zr1netregistry.com/forum/showthread.php?t=9123


There's lots more where this came from, just click on the search button and type in "Plenum Pull".

TomC
"Crabs"

[flyin ryan]

If you know somebody that has or you yourself can get your hands on a Tech 1A, it will let you drop injectors one at a time. Same idea as what you just did, rough running when dropped or no change, either way it will help you key in on an injector problem or a bad hole as well, although sounds like you have your cylinders figured out to some degree already. I'm posting this to help you regarding your injectors, specifically.

[Tony91]

So I got home today I took it got it nice and warm and started to miss. I started on the even side, couldn't get to #8 (motor was hot). Not much of a difference, started on the oddside pulled #1 and no difference at all. Again worked down to #5 not much difference and again I couldn't get to #7. So I think the injector in #1 is the problem. I guess I better start my shopping list!

[Tony91]

Not no more!!!:razz: I tore it down and cleaned up the nest, installed new FIC injectors and wires, buttoned it up and nothing:icon_scra. I figured out I was getting gas but no spark. After some digging around it turned out that one of the connectors on the coil pack was not all the way in, turned the key and it fired right up!! I do have to say thank you to all that helped-KUDOS!! especially Jeff whom I made quite a few calls:worship:

[Paul Workman]

Not no more!!!:razz: I tore it down and cleaned up the nest, installed new FIC injectors and wires, buttoned it up and nothing:icon_scra. I figured out I was getting gas but no spark. After some digging around it turned out that one of the connectors on the coil pack was not all the way in, turned the key and it fired right up!! I do have to say thank you to all that helped-KUDOS!! especially Jeff whom I made quite a few calls:worship:

Congratz!!! Very gratifying, I'll bet. And that dreaded "plenum pull"? Twas no bik deal either, huh?

Now...You can come over and help me eliminate possible causes of my miss. Mine is wicked - indications are a valve or that it ingested something, but Marc H is not at all sure it is a valve. :icon_scra Got a laundry list of things to check out before pulling the engine and yanking the heads...:rolleyes:

P.

[secondchance]

:thumbsup:

[Tony91]

The plenum pull was not that bad and youre right once it started what a good feeling! I took it out this morning and it ran good and strong, the temp was running higher than normal gonna let it cool down and check the level