serious engine studdering all of a sudden

**jmatt07** · 06-19-2009, 04:46 PM

i have been driving the 98 ss all day. last winter i did h/c/i swap, also put 42# injectors in, mail order tune, longtubes, ory as well. anyway i have been drivin it all day today goin here and there. well we stop at the house for 20 min and then leave again. the whole way to restuarent. it was studdering really bad. like studdering when i accelerate and if im cruisin at a certain speed it will start studdering real bad. it seems like the only time it doesnt studder is if i drop it in a real low gear and ream it. it idles perfectly fine tho. all plugs are new, plug wires new and on tight. when we got to restuarant the ses light came on. any suggestions?

**cammed goat** · 06-19-2009, 05:35 PM

Check your MAF. Could be dirty, or loose. Check your wires and make sure none of them came in contact with anything in the engine bay which could cut any of the wires. How old is the fuel pump? These are things to start with.

**chuckie669** · 06-19-2009, 06:59 PM

If your SES light popped on, that's a good place to start. I had something similar, but mine was a wire that went bad.

**cuervo25_1** · 06-20-2009, 06:45 PM

By any chance wa fuel on one of those here and there trips? has it been raining alot there lately as well? could be water in the fuel from either when the filled the tanks at the gas station or cheap fuel that the station bought.Your o2 sensor could be on the way out. or any of the other above mentioned items.

**jmatt07** · 06-20-2009, 09:25 PM

well i got the code pulled at autozone and it said it was the passenger side o2 sensor. Actually, i wonder about the rain thing bc it poured while i was driving home and after i stopped at the house and left again thats when it started doing that.

**JoshieDoom** · 06-21-2009, 03:09 AM

Check the plug ins for the 02 sensors. Grease them up well with dielectric grease.

**0rion** · 06-21-2009, 08:21 AM

sounds like it's misfiring. Check and make sure you don't have a burned or cracked plug wire and if those are fine check fuel pressure.

**jmatt07** · 06-21-2009, 02:29 PM

well i spent some time today under the car cleaning the o2 connections and checkin for a burnt wire or anything. checked all the plug wires, theyre good.
maf is good and clean. i guess next thing is to check fuel pressure. the car seems to idle fine at a stop but when its studdering goin down the road i put it in nuetral and it idles down to 550rpm and almost dies then goes back up to 1000 then back down. it studders at pretty much any rpm. actually the only time i cant feel it studdering is when i put it in a low gear and its running at 4500 rpm or higher. does that mean it couldnt be a fuel pressure issue bc at higher rpm wouldnt the studder be worse bc it needs more fuel?

it really sucks bc my other broke down the other day as well so as of right now i have 0 vehicles to drive.

**cammed goat** · 06-21-2009, 03:42 PM

Did you replace that bad O2 sensor?

**jmatt07** · 06-21-2009, 09:15 PM

well the o2 sensor in it is brand new. i had check engine light on before for 02 sensors so i replaced them and it went out for a lil while and now its back on again.

**0rion** · 06-21-2009, 10:15 PM

did you ever get the car fully tuned?

**jmatt07** · 06-23-2009, 02:32 PM

No i havent had the car fully tuned yet. That couldnt be the cause of it could it? i drove it today and it was having the same problem and then all of a sudden it quit and was fine and then 10 min later it started again. idk what to do with this, i checked fuel pressure and is good. what left is there? replace the 02 again?

**cammed goat** · 06-23-2009, 03:26 PM

Originally Posted by 0rion

did you ever get the car fully tuned?

I agree with Orion. If you have more mods than your tune can handle, you gotta go deeper into the tune to get the results you want.

**rideon1200** · 06-23-2009, 03:55 PM

Once in awhile rather then replacing parts, its cheaper to take it to a shop and get it taken care of.

**jmatt07** · 06-23-2009, 05:05 PM

ya ive thought about that but last time i took it to a shop for a problem they had no idea what it was and then charged me a bunch of money for them to look at it.......

No one here has had this problem?

i know it needs the full tune but i dont even without that it shouldnt be doin what its doin. is it possible that its bad gas? i put used 42# injectors in it when i did h/c/i swap, i bought from mark @kyspeed, could one of the injectors be bad?

**cammed goat** · 06-23-2009, 07:11 PM

If it is an injector, try some fuel injector cleaner. Should work. If not, then you are gonna have to do some further diagnosing i.e. testing voltage in the harness and in the injectors. Do you still have the original injectors? You may have to reinstall the old injectors and run the car to see if the problem is still there or will go away. Have you looked at your MAF to see if it's dirty? If you have the metal mesh in your MAF, it should be silver. I know when I cleaned my MAF, it was grey, and after I cleaned it, the MAF was silver. What gap are you running in your plugs? When the car idles, does it surge? Or does it idle like it's coughing or choking itself? What octane are you running? Is the car knocking at all when running? Just some things to think about.

**jmatt07** · 06-23-2009, 07:54 PM

yes i cleaned the maf, it doesnt have the screen in it anymore. the plugs are about 2 weeks old tr6 with .35 gap. it idles perfectly fine at a stop but when its actin up on the road i coast with it in nuetral and the idle will drop 2 500 then come back up and go back down agian and then stabalize. im runnin premium which is 92 here. it feels like a misfire but only when im on the gas. its not knocking or anything.

ok i drove it to work today about a 15-20 min drive. of course, started stumblin and actin up unless i had the car at like 4000 rpm and it runs fine at that rpm, got it on the highway and was like running 5th gear at about 75mph for like 5 min, then put it in 6th and after that it ran great the rest of the way to work. i got of the highway and it ran smooth and strong. Then driving home it did same thing. ran crappy and stumbling and then ran great.
could i possibly have a crack in one of the plugs? i mean i put the new ones in 2-3 weeks ago and it ran fine for about a week b4 i started doing this.

**cammed goat** · 06-23-2009, 08:08 PM

You may have a faulty plug. Does your car have a rich exhaust smell at all? Now I'm beginning to wonder if you may have a faulty plug wire. I know when I changed my plugs and wires, one wire just fell off in my hand without me having to put any force to it. The wire was in my hand, but the boot was still on the plug.

**5abivt** · 06-23-2009, 08:09 PM

All I can offer based on a motor build... Check all your sensors. Unplug the sensors clean them and plug them back in.

**allbaugh_04** · 06-24-2009, 06:45 AM

Is there any way a plug could of gotten mixed with another one. I've heard of weird problems happening on changing out the injectors and not having a tune. However, you got a mail order tune, so IDK if that's your problem at all. Have you changed out your fuel filter lately, do you have cats?