I've had lots of trouble figuring this one out, figured I would see if you guys have any ideas.

A few months ago the car started running rough when it was cold intermittently. It would idle ok, but run terribly under any throttle unless it was wide open. Once the car warmed up, the problem went away. Now it is like this every time I start the car.

While chasing that problem, I have since set a code 33 and 34. I also set a code 14 but I think that was a seperate issue.

Just recently, the car has started pinging under heavy load. Ive had problems with ping before so the knock sensor is only a year old. Unless the sensor has failed, I dont think it is a timing problem.

I have been told a lean condition could cause ping, so I'm hoping the codes, stumbling and ping are all caused by the same thing. Does anyone have an idea of what could cause all of these?

Thanks for any help!

 

No idea what year Vette, but have you looked at:
-manifold vac.
-fuel pressure
-base timing
-MAF relays (if it has 2 of them)
-TPS opertion
-spark plugs & wires

 

Sorry about that! Its an 85, so I dont think it has the 2 relays.
I refreshed the ignition system a year ago - new plugs, wires, cap and rotor, and I set the timing.

Also, I've tried disconnecting the MAF to see what happens and the car doesnt behave any different.

 

You fix the codes from the front of the engine backwards, so you'll have to determine whether the MAF or the relay buried inside your dash is the problem.

 

Well its been a few months and I'm just as confused as when I started. Ive tested everything I can think of, and just finished replacing all the intake gaskets as well as the fuel pump since fuel pressure seemed slightly low. The only idea I have left is to replace the maf, but Ive tested all the inputs and outputs of the maf and they all seem perfect. Its getting 12v in, which I think means the mafs controller isnt the problem, and the output of the maf seems to be in range. The car still stumbles terribly when cold and pings under any load.

 

Welcome top the world of an 85..one off year , i had the 33 code for awhile now, i bought a new maf, same, replaced the pigtail same all i didnt do was the timing, now im fighting the vacum

 

Someone stated checking base timing, and that’s a good start. Your ECM and (I think) the timing control module can also affect timing issues. Pinging under load is often from excess advance. This can also be seen if excessive heat is present. Also, if you have the 4+3, excess timing can result in erratic or premature downshifting out of overdrive as the computer uses timing values as part of its decision making to downshift.
my experience with a MAF issue turned out to be a bad harness repair. This was on an ‘86. There was a very old and used up crimp connector, on the wire to the relay, about 8 inches from the MAF. It had failed, losing the connection. I put on a new connector and all was fine. I found it by checking continuity at the opposite ends of the wires. Without continuity, current flow is lost, so that’s how I first look at wiring.

I hope this helps either you or anyone reading this. Best of luck with the repairs.

 

Thanks for the help!

I got the timing set last month after weeks of confusion because the balancer slipped. Unfortunately, it didn't help the problem. What confuses me was the ping would occur immediately after startup- not temp related.

I replaced the knock sensor last night just to be sure it wasnt the culprit and was leaning towards a faulty esc unit when a fuel pressure guage sprung a leak and caught my engine on fire....

Now that the 85 efi has been put out of its misery, I can install something that will give me less headaches!

 

I have recreated pinging in my 85. I use base timing and 85 octane=pinging under load, but can drive normally no problem.
I like to increase my timing to 10btdc, and I can drive normally with 89 octane and need 91 to really go.Or it pings.
When I use 91 octane with my 10btdc I seem to get the best results and mileage..
Did you replace your balancer? It is one of the easier things on a 85.
I have replaced the EGR Valve and sensor(1985 only from ecklers) and cleaned the channels and my car is running better than ever.
So I believe timing is very important.

 

I do know the timing was set correctly. At one point I had the timing so retarded the car would barely run and it would still ping under heavy load, so it definitely wasnt because the timing was too advanced.

 

Well then the Timing Control Module as Bob stated actually controls the spark, it is mounted next to the blower. I would clean the connectors and clean the connectors to the egr solenoid , and visually make sure the vacuum line and egr temp sensor are hooked up and connectors clean. Using contact cleaner . Gonna be hard to see the EGR.

 

Yeah, Im pretty sure it was the esc module or the wiring to it causing the problem. But I guess I'll never know now. The egr valve and sensor went with the rest of the wiring on the top of the engine...

 

I would get that wiring back for the Timing control module. Mabey that harness is avail used.

 

If the timing was set correctly, there should be no pinging.
When we set the timing, typically, we use a timing light on the balancer. One possibility is the balancer outer ring has actually rotated to a point where you have no idea where your timing is. A way to check this is to take an old spark plug, hollow it out and run a bolt thru it to create a piston stop. Once in the #1 plug hole, rotate the engine one way until the piston GENTLY contacts the stop.
Mark your balancer.
Rotate the crank in the opposite direction and make another mark. Halfway between the marks is your true “0”.
this will tell you if the balancer has slipped.
No one likes the EGR system. It’s part of the emission system that historically robs power. But one thing the EGR do3s is it actually cools the combustion process. This is done to satisfy the EPA on the amount of heat that exits the tailpipe. The EGR is somewhat known for causing deposits in the combustion chamber and the backs of intake valves, as well. Garbage gas can also lead to these deposits, too. Wherever they come from, these deposits can build up to the point of unevenly increased compression and along with the heat they retain, ping happens. I thought of this when you mentioned that premium gas helped. High octane fuel burns more slowly,I’ve been told, and burns cooler to do this. This allows for the combustion event to last longer and have a,longer period of expansion on the power stroke.
I may be WAAAY wrong, but I hope this helps.
Best of luck.