gulf_coast_228

I might as well be chasing a ghost. My 1992 Firebird GTA has a stutter in the rpm that's most noticable when accelerating. It's faint at idle, but present when I'm up to speed. If I'm at idle in park and I rev the engine I do not hear or feel the stutter. It's very noticable when getting onto the interstate. It can be heard and felt when I'm up to speed there. This is also affecting performance. I've checked fuel pressure and it's normal.. the needle doesn't budge even while it stutters. Holds good pressure when I turn the key. New injectors (From FIC). New plugs, cap, and rotor. New filters. Timing appears good at idle and holds steady. No SES light or error codes. Has been happening for over a month. I'm at a real loss as to what this could be...am I missing anything? Any help is appreciated!

gulf_coast_228

I should add that I took the car to a shop a few weeks back and they thought it was my EGR valve opening and closing at the wrong times. The EGR valve on it was just replaced a little over a year ago. Still, could that cause this? Could it be a loose or worn timing chain?

gulf_coast_228

Does anyone have any idea what this might be? Anything else I can test?

JTNKTZ

iTrader: (10)

Sounds like your rockers are loose to me. I had the same problem. Happens only under load and high RPM's.

gulf_coast_228

Would this also cause a ticking sound upon acceleration? I figured that might be a slight exhaust leak but if loose rockers tick like under load like that then this might just be it!

netfreak

I don't want to scare you but I had something like that happening with mine, quite similar to what you're describing. Seemed that during regular acceleration it felt like I was losing fuel to the engine, but the problem would disappear at WOT and never happened in park or neutral. Did a standard tuneup and checked a few things but no change. My 700R4 nuked itself weeks later.

gulf_coast_228

Before I dig into this over the weekend is there anything I should know? Did some reading on adjusting the rocker arms and looks like my best bet will be to adjust them with the engine idling. Everything is stock and hasn't been adjusted since the car was bought. If there's a safer method please let me know. Since I'm not sure if this is indeed the issue should I look for anything specific? I'm very new at messing with the rocker arms so any advice is appreciated!

gulf_coast_228

Still looking for a solution.. yesterday I pulled the spark plugs one at a time to see if maybe a plug wasn't firing but it doesn seem like that. The skip is audible at idle now and appears random. I honestly don't think it's anything with one cylinder. I don't know if it matters but wondered if maybe a vacuum leak would cause the miss so I pulled the vacuum hose from the vacuum canister to the intake and all that happened was the engine revved up. Maybe it's not vacuum. I'm lost. Will try to look at the rocker arms soon but honestly I have no idea what I'm looking for. If something is loose I dunno if that would make a random stutter that gets worse under load.

gatorcola

Any relation of the stutter to rpm?

Is your egr solenoid ok?

gulf_coast_228

I would assume the EGR solenoid is okay, since it's only about a year old since it was replaced. The stutter doesn't seem dependent on RPMs, as it happens in idle while parked, in drive with the brake held down, while accelerating, and while maintaining a high rate of speed (70-75 on interstate at about 2k RPMs). It's much worse on acceleration at all speeds. There's a real lack of power too, like the car just really doesn't want to go. Of course with it stuttering it's no wonder. No error code on the EGR however.

gulf_coast_228

Just as an update to my situation; last night I took the valve covers off and none of them were making any sort of tapping sound so I'm assuming that's good. I'm starting to think it's timing related since the car's at 200,000 miles on it's original timing chain, so that will be replaced today. Another thing that supports my theory is last night I disconnected the EST and drove it around about a mile or two. The engine was weak and sounded bad but it did not stutter/miss at all! Not even when accelerating which is when it's worst.

When the timing chain is replaced I'll post the results here. Hopefully this resolves the miss and stutter.

Also, where is my EGR solenoid? I looked for it last night but honestly I'm not even sure what it looks like.

Engine: 350 TPI 5.7 V8

rgarcia63

Follow the vaccum hose from the EGR valve underneath the plenum it will be connected to the EGR solenoid.

gulf_coast_228

Replaced the timing chain with no effect on the miss/stutter. Why would it be the EGR system? When I took it to the shop to diagnose they said it was my EGR valve and simply stopped up the EGR valve vacuum hose and blocked off a small vacuum line on the bottom of the intake. I still had the problem. Without vacuum to the EGR system could it still cause this problem?

91interceptorZ

iTrader: (3)

I don't know if this is it.....but it could be two seperate problems....When you said when your in park or neutral you don't feel it.....but when you up to speed you can feel and hear it...I bet ya it really shows up around 65-70mph.....my question for you is....what type of drive shaft do you have....steel or aluminum.....the reason I ask is many people are chasing a problem like your....and at least some of it if not the whole problem is the driveshaft...if you have a steel one....throw it in the trash and get an aluminum line....the steel lines (as shown in car craft) actually bend when your up to speed.....even if they are balanced and good u-joints....The steel line is just not designed right....I can post two serperate threads if you need so you can read up on their problem...sounds pretty close to yours....they tried all sorts of stuff...I kept saying driveline...finally they put a new aluminum line in, and they posted that it fixed the problem completely....just some thoughts.

gulf_coast_228

I'll definately look into that. I'm wondering if this is a driveshaft issue wouldn't it get worse as I go faster? The miss is at its worst when accelerating. When I'm up to speed it almost goes completely away with exception of high speeds (interstate travel) where I can feel it miss just enough to notice. It's still worth looking into anyway though.. maybe eventually replace with a good performance shaft.

91interceptorZ

iTrader: (3)

yeah....the shaft should be replaced anyway...even if it's not the problem...just a good idea...you can replace it with a stock aluminum 4th gen line.....but you don't really feel driveline vibration untill 65mph or so....so it sounds like it's engine...but do line anyway.........have you replaced key parts...cap rotor plugs wires, etc....could be bad injector....also do a compression check...you might have a dead hole.

gulf_coast_228

The plugs, cap, rotor, wires, and injectors have been replaced and are no more than a year old. Same with the EGR valve. Injectors about a month. I'm dreading the results of the compression test. If it ends up being a cracked block or something I'm screwed.

91interceptorZ

iTrader: (3)

could be....or low compression (bad rings), or bad head gasket.....try the compression test I think...I don't know where else to start....

mpb74

sounds like your valves need to be adjusted, or you have a bad lifter.
either one will cause it to have a skip.

91interceptorZ

iTrader: (3)

agree....you might check the rockers for adjustment....and it could be a collapsed lifter.... gotta start somewhere...just start by checking rockers,lifters, and compression...then go from there I'd say....

gulf_coast_228

Okay... checked the rockers today to make sure they were all tight and they were. Followed instructions found on this site to make sure I was doing it right, as well as referencing my Haynes manual to make sure I was checking the intake or exhaust. They were all good.
I'm starting to think about the EGR thing. What should I look for, what can I test? I honestly can't do a compression test myself so I'll have to have a local shop do it, and can't do that until the weekend.

I recorded a video (actually it's just audio, too dark for video) and around 10 seconds in you can hear it stutter. I tried to get one while accelerating but it didn't turn out well enough to hear. Here's the link: http://www.youtube.com/watch?v=23jTs7K5ixM

I'm starting to doubt it being valve-train related.
I want to add that there is no smoke from the exhaust, not when idle, moving or accelerating.
I do have a question for anyone willing to answer though... my oil pressure seems to have dropped slightly since I changed out the timing chain. Now at idle when the engine warms up it sits slightly above the 15 mark on my gauge, but when driving it's steady at the 30 (if not very slightly below that)... is this normal? I'm worried it might be a bit low, and might have something to do with this issue.

As always, advice is welcome. Thanks for the help so far, I'll keep on checking things..it's got to be something.

z28_fire

Did you ever figure it out?

gulf_coast_228

Unfortunately no. I still have no idea what's causing it but the odd thing is for the past few months it hasn't stuttered hardly at all, then this past week it started again. It's not as bad but still there. Soon I'll be replacing the intake gaskets so we'll see. Next is to check the spark plugs I guess. If it wasn't so random it would be easier to diagnose.

naf

iTrader: (7)

Most of the things you've chased down are not going to cause a 'random' miss.

Fuel pump going out, but you've already verified correct pressure WHILE it was missing, correct?

A bad EGR could cause a problem if it's opening when it shouldn't and/or sticking. IF it's been disconnected you can rule it out in most cases.

Most likely problem would be a weak spark, especially if your miss is on the left bank where the O2 sensor is. A miss there confuses the ECM into going too rich, which will compound the problem.

Ohm out each of your plug wires. If any one of them is significantly off, replace it. Check each of your plugs. Inspect for condition and gap, 0.035 is good on gap. Check your coil. Inspect your cap and rotor. DO NOT assume because some of the above was recently replaced that it is still functioning at 100%. Been there.

If you cap/rotor/wires/plugs are more than a year old consider replacing them.

The above won't cost anything unless you identify a part that needs replacing anyway. If the miss persists I'd recommend using a scanner to see what the ECM sees when it reoccurs.

I can't imagine how bad intake gaskets could cause such an intermittent problem without other symptoms. Same with the timing gear, though. Rockers, as well, shouldn't need to be touched unless someone else's hands have been foolishly playing with them.

There have been a lot of darts thrown at a solution for your issue in this thread but in my opinion few are even hitting the wall. Disappointing in a way.

z28_fire

That is some great information. I will try these as well.

88gta_hiflyer

iTrader: (1)

I agree that your ignition system could still be your problem. I had a similar problem with my 88 GTA and it turned out to be something simple. Look closely at the wires on and around your ignition coil. These get brittle over time and break. Start with the connectors on top of the coil and follow the wiring as far as you can. Could be worth a shot.

z28_fire

So, I took it out today for a long ride after replacing the fuel filter along with some other items, and it was fine at high speeds. Once down to lower speeds it started to sputter a little. I opened the hood and heard a ticking sound. My biddy said it sounds like my injectors. What do you all think?

Saculia

iTrader: (1)

Check to make sure that you don't have lose ground wires. I have had a similar problem before with a loose alternator ground.
I think the problem you are experiencing is spark related.

naf

iTrader: (7)

An ignition related mis-fire will be most pronounced at lower rpms and higher loads.

Not sure why you replaced the fuel filter when you stated your fuel pressure was steady even when stuttering?