JimRockford

Hi,I’m hoping one of the resident third gen experts can help me out here. I have a 1990 Camaro RS with 305 tbi v8.and 700r4 automatic.it has only 95k Original miles on it. I got it from the original owner and I’ve been driving it for a year now. Just recently the car has started “bucking” only when accelerating into 3rd and then into 4th. It will buck almost like the engine is missing,if I accelerate harder the bucking stops.
The car doesn’t hesitate when pulling away from a stop and will go 80mph down the road so it’s not a fuel pump issue. Could it be an EGR valve problem? It idles smooth but will “hiccup” at idle every so offen,it does not do this under acceleration or at speed.. I’ve seen others claim the egr will do this. Or is it most likely the transmission?
If anyone here has had this exact issue before and can offer some help I would greatly appreciate the advice.

JimRockford

Really? Nobody else has had this problem before?

DynoDave43

iTrader: (11)

Does it still have the original plug wires? I had failing wires create a misfire under load in higher gears like that. Just a thought...

JimRockford

I’m not sure. What do the original factory wires look like? It seems to be doing it more now. I had hoped someone here had this issue before and knew what the cause was.

naf

iTrader: (7)

weak ignition can cause mis-fire under load at part throttle, while seemingly working fine under most other conditions.

If you have not, I'd replace all of the normal tune up stuff, plugs, wires, cap and rotor.

May not be your issue, but it's routine maintenance and will rule out a common cause.

JimRockford

I appreciate the input,but I want to diagnose and repair the part that is bad,not play the shotgun method and just throw money away replacing parts that don’t need to be replaced now and aren’t causing the problem. That’s the problem with mechanics and shops today...”sir,it’s your fuel pump” then you have them replace the pump and it’s still got the problem. Then it’s “sir,it’s your hei coil”,then that doesn’t fix it so then it’s “sir,it’s your tbi injectors”....before you know it you’ve thrown hundreds of dollars away using this shotgun guessing game method rather than simply diagnosing the problem and repairing it.

I realize nobody here can look at the car and accurately diagnose it for me. But I don’t want to just throw money away replacing all the parts on the car until I hit on the part that was the problem. I’ve read other threads here where some poor soul has bought and replaced 7 or 8 parts based on suggestions and they still didn’t solve it.

does anybody have tips to diagnose the hei coil or any other suspect parts so I can find the actual issue?

I love the body styles on these cars and all my previous third gens were early 80’s carbed models and none ever did this.
this is why I hate “modern” cars with computer bs,electric fuel pumps that require taking down the rear end and exhaust to replace,and other wonderful stuff that makes working on them a needlessly complicated nightmare.

unfortunately if you live in California you can’t jusf convert it to a carb and mechanical pump.

naf

iTrader: (7)

some may argue that replacing the plugs, wires, rotor and cap, which are routine replacement parts for a tune up, to be routine replacement parts

but either way, if I were determined not to replace any of these, I'd start with a spark tester and check for strong spark at each plug. ohm out each of my wires and carefully inspect the cap and rotor.

if you think it's the EGR disconnect it. test the valve by opening it by hand (reach under and force the diaphragm up). doing so should cause the idle to stumble. releasing it should allow it to clear.

you can then put a vacuum on it with a mityvac or equivalent to ensure the diaphragm is not leaking.

JimRockford

Car won’t run anymore. It started idling super rough and wouldn’t go faster than 10mph. Even at idle the engine now runs rough. I can still hear the fuel pump when I turn the key,sounds the same as it always had. I noticed the exhaust smelled of gas before it stalled. Not it won’t start again. Does this sound like leaking injectors?

naf

iTrader: (7)

consistent with weak ignition. as the plugs mis-fire more carbon builds up and the condition worsens.

pull your plugs and have a look. check them all, may be isolated to only a few. costs nothing but a few minutes. you've a throttle body injector? fuel delivery would affect them all nearly equally.

zed-028

clogged cat or muffler is a possibility. Ive had this exact symptom before - doesnt even need to be a full blockage, a partial will do it. drop the exhaust, wipe a few plugs off, get some starter fluid and see if she fires.

79Daytona

Dude I know what your going through I have a 92 Z28 5.7 TPI and it dose the same thing some times between third and going in to over drive and I have put in a new gas tank and fuel pump; injectors and a new disturber and plug wire and other small parts and I even checked the fuel pressure . The car had been setting for some time and it needed all the new part. Now its not doing it as bad as it was before but I'm running out of ideas what to try next..

DynoDave43

iTrader: (11)

Here are mine. Grey in color, 7mm, will say Packard Electric (or something along those lines) on them, and a date code IIRC.

cardo0

When was the last time the fuel filter was replaced? Even a clogged fuel filter can show good pressure at idle but its when you try to accelerate it staves the TBI from fuel.

I guess you should look at all the common maintenance items first - filters, plugs, fuel injector cleaner.