Ok, this may be a tough one.

I am experiencing a misfire on my 91 camaro TBI. I replaced wires, cap, rotor, and it didnt help. Sometimes on acceleration it stuters badly, and almost dies. At idle it shakes around and misfires intermitantly.

Here is the weird thing. I have a manual cooling fan switch. I noticed that the missing is MUCH worse when the cooling fan is on.

That got me to wondering about my grounds. Where do the fuel injectors and/or ignition system ground to? What could be causing this embarassing stutter? Please help me.

Incase you need to know, it is a 305 with LT4 cam, vortec heads, power plus intake, holley 670 TBI with stock injector pod. Im not sure if any of that is important, but im desperate.

 

I'm pretty sure the ignition system is wired to the ECM, which has three grounds. I'll see if I can scan in some wiring diagrams

 

OK, here you go. Sorry it's such a big picture, but you can't read anything on it otherwise. All the grounds are in red. This is for a stock 91 5.0 TBI

 

If you figure this out let me know. i was getting trouble code 22 and 44. 22 was my throttle position sensor bad, and 44 was a loose vaccum hose. now the ecm is clear of errors, but when i try to accelerate it spits and sputters until et gets up to speed. and idles rough. If you figure this out please let me know and i will do the same. My elecric fan also quit a week earlier.. Robbie

 

actually, I figured some of it out. It still runs rough at idle, but it may just be the cam.

What i did was I combined all the wires that ground on the passenger side head and ran them to the battery (they looked frayed and crappy). That didnt seem good enough so I spliced in another wire that grounded to the firewall.

Heh. I know it sounds a little shoddy, but it worked. No more stumbling acceleration, no more weird cooling fan stuff.

I also pulled a touch of timing and it improved, however this probably might not help you too much.

 

Take it out run it and then pull the plugs. Look for evidence of a faulty cylinder. If the plugs look good(all burning evenly) I would look at EGR. Bad vacuum control to it, or possibly junked up with carbon so it can't close. You mention it's better with the ground fixed, but is it back to where it was?

 

No it still runs a little bumby. But tons better than before.

Also my car doesnt have EGR anymore.

 

Sound like your gettin low spark. Did you check your coil??? I'm no master mechanic, but thats what it sounds like to me.

 

Have you checked fuel pressure and volume?
I will bet the pump is going out.

 

check your timing. Thats just what it sound like to me.