With my 85 tpi 305 iroc, it has been missing on the lower rpm's. When you have it just idling it is fine. When you put it in gear and drive it, it misses on the lower rpm's and you can hear through the exhaust. The cap,rotor,plugs, and wires where changed like 6 months ago. They all look good and im not getting any codes. Could it be something else.

I also noticed when i have the timing lite on it, and i hit the gas it will retard then advance.
THANK YOU

 

Well, i pulled some plugs today and they looked fine. im confused on what could cause this. i hope it isn't the injectors.

 

The reason it retards is because of the sudden increase in air pressure in the manifold relative to the RPM when you open the throttle blades. As soon as you hold the blades steady and the RPM catches up, the timing will start to advance again.

As far as the missing, yeah, it could be your injectors. On mine, I believe I've traced it to the valve lifters on the #2 cylinder that feel like a miss at idle up to about 1200 rpm and then it smooths out. Next week, I'm going to change those lifters and hopefully prove my hypothesis.

Try this little experiment- with the engine idling, pull off one injector plug at a time and see how the engine responds. The RPM should drop when an injector becomes disconnected. Replace the connector and then move on to the next one. When you get to a point where disconnecting an injector causes no response in the engine, you've found your problem cylinder. What you do next is swap plugs with the injector next to it and see if the problem jumps over to that cylinder. If that happens, you have faulty wiring. But if not, then (assuming you're sure about your ignition) it could be the injector or possibly a bad valve lifter, or a cylinder that is not holding compression (you may want to do a compression and/or leak down test as well).

 

Well, i replaced the plugs,cap,rotor,wires, and coil. It didn't make a difference. So i was looking at the injectors and i could feel all of them working really good except the back two on the drivers side. They where a bit faint. If the injectors are bad how much are stock replacement ones cost.

 

Not sure about price- probably around $40-$50. Check your local dealer.

 

Dealer? As in GM Dealer? More like $100+ from those sharks. Check Ebay for a full set of stock replacements. If you are going to replace 2 I would replace all of them, with a flow matched set.

 

Have you done the test I described? Try pulling the connector off of those two suspect injectors (one at a time) and see if the engine responds with a slightly decreased RPM. If there is no response, then that indicates that those injectors were not functioning properly.

 

Pro-Tour71

I havent done the test yet, i will be doing it today though.