I have a 1986 Camaro with a 305 TPI engine. It has a miss at all RPMs at any temperature. When coasting at around 45 MPH, the tach reads about 2000 RPM, and the car jumps foreward and backwards, with the RPMs jumping up and down and I believe I can hear it backfire. Increasing the idle stops the backfiring, but not the missing.

I'm not sure what exactly is wrong, I have replaced the plugs, wires, cap, rotor, and ignition coil, I have replaced the fuel injectors (they didn't look good when I pulled them out) and I have adjusted ignition timing. I also checked that the CEL bulb didn't burn out, and read the codes, but only got a 12.

Now, here's something that strikes me as being odd, the vacuum line going to my EGR solenoid had been snapped off for the longest time without throwing a code. And replacing the line didn't do anything to the miss.

Does anyone have any ideas of what I could look at next?

 

If the egr is stuck open it will cause a idle surge and a lean miss. Have you checked your fuel pressure ?

 

I do get surging from time to time that sometimes evens out after a minute or two. I haven't checked my fuel pressure in a couple of years, but I'll do that.

 

Alright, I checked fuel pressure. It reads 44 psi. I also pulled the vacuum hose for the pressure regulator and didn't see any fuel in it, and I didn't smell any noticeable amount of fuel in it.

Also, after driving it a but, add hard starting to the list of symptoms. The missing seems to go away above 1500 RPMs while driving, with the backfiring occurring at just under 1500 while coasting. It doesn't backfire while idling, and the missing smooths out just above 1500 RPMs at idle.

I feel that I should add that last night, when I had the EGR solenoid out, it was open, which would provide vacuum to the EGR valve. Are these usually open by default? I guess I could take it back out and apply voltage to it to see if it closes.

 

the egr solonoid goes to ported vacuum and is normallay open, with every thing you replaced im thinking it might be a crack inbetween the distributor poles or the pickup coil or bad ecm.

 

This may also be an intake manifold or runner gasket leak affecting just one or two cylinders. I am thinking of this since the miss seems to get better at higher throttle opening. Maybe try going around the runner connections at the base with brake cleaner while listening for a response from the engine.

 

The ECM activates the EGR solenoid to disable the EGR under certain conditions.

 

Alright, I put my old cap and coil back in, and it misses less, but still stumbles while coasting around 45 mph, under 1500 rpm, and it still misses at idle. I replaced the runner gaskets, both upper and lower, yesterday while I was swapping out injectors. the mating surfaces were clean and flat, and the runners torqued to spec. I'll get some cleaner and check for leaks just to be on the safe side though.

 

I took the car to the local automotive school and let the teacher look at it. He had me unplug the battery wire going to my ignition and then turn the engine over. He said that he could hear that one of my cylinders doesn't have compression.

So I guess I'm either looking for a new car or a new engine.

 

To narrow it down to a cylinder you can do a cylinder drop test and if this is the case do a compression check on that cylinder.

 

I'm thinking it's probably time to do an overhaul on all of my cylinders.

 

Cranking compression test. That's old school. Why do I never think of that? Too used to pulling out the gauge I guess. Yeah, low compression on one cylinder makes sense. Before you scrap the motor though, I have brought back many with a quick ball hone cross hatch, new rings and pistons and a good valve job. Cheaper than you might think. You can even roll new rod bearings in while you're there and the motor will run a long time.

Compression loss on a small block chevy, unless a cylinder has been hydro-locked somehow, is almost always an exhaust valve. Generally #7 or #8 as they get the least cooling. Crappy OE valves and too high combustion temps.