Hello all,
I serviced the transmission on my 85 C4 and put new rotors and pads on the car. When I went to start it to warm the trans mission the engine ran poorly and seems to be missing at least one cylinder. After checking all the plugs, wires etc. Still ran like crap. I have fuel, air , and spark. I am thinking injectors. I have a new rotor and distributor/coil still to install. If that does not fix it I am not sure what to do next. Any advice would be great. Thanks
Mark

 

Find out which cylinder is missing. That would be MY first step.

You can unplug one injector at a time. The one that makes no diff, is your offending cylinder.
You can start it cold, then shoot the exhaust tubes with a temp gun. The "cold" one is the your offending cylinder.
You can lube the tip of a test light, connect the clip to ground, the back probe the spark plug boots to ground out a cylinder (and not get shocked). The one that makes no diff, is your offending cylinder.

^There^ are three easy ways to isolate and confirm the problem that you think you have.

 

Thanks for the quick response. Tomorrow I plan to swap the rotor and distributor. I dont think that is the issue but they need replacing anyway. Then I will try each injector. My guess is that after finding the culprit I will rapace all of them. This all came on suddenly. I think I should test the harness to each as well. Not sure how to do that. I am.learnimg as I go. This is my first vette. My first Chevy as well. Thanks again

 

Hi
First identify which cylinders are missing, i find starting from cold run 10 seconds or so then turn off.
Feel each exhaust to find which are cold ( long tube headers are perfect for this), then check if its a fouled spark plug or injector.
The injector connectors are fragile, pulling them off with the wire harness can can break the terminal strip inside.
The injectors are batch fired, all one side then all the other so you can swap the connector from the injector beside for trouble shooting.

Even one injector not firing will make the engine shake like crazy,

Common problems are spark plugs fouling, injector connectors damaged from people removing them by tugging at the wires.
The distributor cap has a carbon connector with spring from under the coil to rotor button, they can fail and arcing will destroy it.

Make sure you check each ignition lead with a multimeter, or use a jumper cable to ground the spark plug (once plugs are removed from engine) then get someone to crank the engine and make sure you can see a spark to eliminate the spark plugs.

Good luck the ignition system is pretty bulletproof.

Don't forget to check the fuel pressure, the fuel pumps don't last long.

Good luck

 

Thanks on that advice. Already have a new fuel pump and filter. It was the first thing I replaced. The cold pipe is a great idea. I am guessing that an injector or the wire going to it is faulty. I am new at electrical stuff. I have a circuit tester but I am not always sure what to set it on. I consider this work going to school. I am very motivated to get better

 

Does it run any smoother when the engine is warm?

 

Someone suggested that in post #2.

Three different ways of isolating a missing cylinder were offer, in post 2.

 

It starts easier when warm but the engine is not running on all 8 cylinders. This is clear based on the exhaust as well, kinda smokey. The fact that the car was running great and all of the sudden is not to me suggests some type of part failure. I will let you all know what happens today. Thanks for the help.

 

how did you “check” the plugs and wires?

 

I sprayed each cyl to find my injector was not plugged in completely.I noticed that instant fuel milage did not return to zero when stopped
and was vey low when driving during that time.. After finding the cyl(7) it is great. Also under the rotor make sure your little plugs are in good , or it can cause misfire and put strain on your plug wires(ask me how I melted 3 of them)

 

Thanks, I visually checked the wires to ensure they were fully seated. I put in new plugs about 2 weeks ago. I plan to replace the rotor and cap tomorrow. The wires to each injector look ok. Nothing appears to be broken. I have never pulled injectors before but it looks simple to me.

 

You can't always determine if a plug wire is bad by looking at it. You need to either ohm it or replace it.

 

Understood about the wires, I installed them when I put in the new plugs, they maybe have 100 miles on them. I also looked for arcing onto any surface of the exhaust or damage from heat. Nothing is burned. Indeed it could still be a wire. I really appreciate all of the support.

 

Ladies and Gentlemen,
thanks again for the support. After removing the distributor cap I found plastic parts that plug the side opening for wiring and that insulate inside exploded. Small brittle fragments were all over the place. I removed them all but ran out of time due to family dinner tonight. All other parts seem to be serviceable. I will get it all put back together later with a new rotor, cap, and coil. Looks like I will have to either rebuild or replace the distributor. Any thoughts would be great. Merry Christmas all and thanks again for the support.

 

Ok,
here is where I am at. I have spark, ohm tested the wires, all are good, replaced distributor cap, rotor and coil. What I found was the #8 cylinder was not firing. Pulled the plug and it was wet with fuel. Checked for spark, and had that. Ohm tested all of the injectors and got 18 or 19 for each. My next step is to replace the injectors. Probably clogged. Any suggestions would be great. The boot to the injector wire for the #1 cylinder tore,🤨🤔. Wire is intact I think




. Looking forward to everyone's wisdom.

 

You can clean and or buy one single injector and make sure to fix that connector, that was my problem but my cylinder was dry.
Good Luck

 

Thanks, I think when I get it all open I will replace them all. Kinda pricey but I want to go once and done if possible. I will keep you posted

 

My suggestion would be to confirm that you actually have a bad injector. You said the spark plug for the dead cylinder was wet with gas....how does that jive with a bad injector?

I would remove the fuel rail w/injectors intact, place them in bottles or over rags, then crank and see which ones are actually dispensing fuel. On your TPI, 4 injectors on one side should fire, then the other side, back and forth twice per revolution of the crank. It should be super obvious which are firing, and which are "piddling", or not doing anything.

I did this test on an L98 a while back, and 5 of the 8 injectors were plugged. That car wouldn't start....but my plugs weren't wet with gas, either.


.

 

Run a quick compression test on #8 to make sure you have enough compression to fire the mixture. You have spark, fuel but no ignition.