4.3L Motor Swap , rough Idle after heats up

I just have installed a Long Block, which means I had to put all my metal onto the new engine and install it.

I installed a new water pump and hoses, Rotor Button, Dist Cap and Module. New Plugs and wires are 1 month old. New thermostat I think 190F.

All Vacuum lines have been replaced and checked for leaks. Had to install a new Fuel Injector on the Right Side of the TBI. It was not spraying like it should.

When engine is cold it runs and idles GREAT.... Once engine gets around 200 to 210F it will have a rough idle. Timing is set at 4 degrees like service manual states. Idles rough but will run on down the road with no problem, just when you come to a stop you think its going to shut off.

I need some idea on this.

did you do all the wireing correctly?? are there any grounds that are lose, corroded or you just didnt hook up, did you possibly hook up plug wires incorrectly? did you only replace the right injector or the left one(s) too?? maby the left was bad and not showing it... all the parts you listed, are they new or used? it possibly could be a pcv valve...

How did you set the timing? You should have disconnected the electronic timing advance wire and set it to zero if I am not mistaken. Good luck.

How did you set the timing? You should have disconnected the electronic timing advance wire and set it to zero if I am not mistaken. Good luck.


Correct, if you set the timing at 0 when there connected your timing is officially retarted.l

Why did he set it to 4 deg then? Bad timing would definitely cause his problems.

Maybe he couldn't find out where to unplug the electronic timing advance.

Lets hear from the thread starter. If he tells us the year we can tell him where that wire is. I doubt he doesn't know though, he did do a motor swap, but I guess anything is possible.

I set the timing by a timing light.. The wire I unpluged was in the floor board and the wire is behind the carpet area. I did the motor swap and I think that this is a little harder than setting the timing.

I unplugged the wire, started the engine, I pointed the timing light at the timing mark and lined it with 4 degrees like the SERVICE MANUAL states for this engine. Move the dist. until you have the timing set. Shut off engine and connect wire and restart engine. OH I forgot I did tighten the bolt down that keeps the Dist. from moving.

Nothing in the service manual states that you set the timing at ZERO and it fixed or learned.

I replaced the right injector, the left was down about a month ago so I did not replace it again. Also you can take a timing light and point it at a injector to see the spray pattern or drip......

There is one ground wire on the back side of the block, HOOKED UP. There is the Ground wire from the battery that is hooked up to a stud on the BLOCK, is this correct????? I Put labels on all wires and hoses and made notes on there location.

When I first started the engine I had the timing off 180 degrees and had to set this over. I had a nice back-fire and one of my Dads friend said I could have blow a intake gasket. Is there a good way to check this?????

Also the engine is running good until it heats up. Around 200 or 205F it starts the rough idle. I did not replace the EGR valve?

Thanks For all the help you are giving me. This is my 9th engine I have put in a car and no problems like this. I own a 68 and a 70 Mustang restored, I DID THE motor work and no problems, SO I am not as dumb as some of the emails I have gotten from some of these members on this site. I was just asking for help, not insults

I set the timing to 4 degrees because the GM service manual states on this 1992 4.3L Z code the timing should be at 4.

Can someone tell me how I should have set the timing.?????

Also could a intake gasket cause this once the engine hits the correct temp???

What is the best way to check for a blown intake gasket?

To check for a blown intake gasket, spray carb cleaner all around the gasket. If the idle changes, that means carb cleaner is getting in. That would be where it's blown.

I re-read your post, and noticed you didn't say you put a new coil on. After the truck heats up, turn it off and restart. If it still idles rough, or won't start I'd bet the coil is at fault. Sometimes they heat up and short out. You could also get a spark tester and see how many kV you have. I'd bet it's not enough. The HEI coil on my 86 silverado will jump a 35 kV gap... check your repair manual for the exact specifications of yours.

Don't take the insults you have recieved from some people seriously. Even a pro has things that go wrong every once in a while. Some people would throw a set of plug wires at every drivability problem they get, and then blame the car when that doesn't solve it.

I set the timing to 4 degrees because the GM service manual states on this 1992 4.3L Z code the timing should be at 4.

Can someone tell me how I should have set the timing.?????

Also could a intake gasket cause this once the engine hits the correct temp???

What is the best way to check for a blown intake gasket?


You set the timing to ZERO when the timing wire is unconnected.

Zero, not FOUR, ZERO.

Just being clear for you.

Your timing is too advanced.