Hello everyone!!! This is my first post here. I have been reading posts for about a month now as a guest but now Im stuck.

I have a 1993 Blazer Tahoe LT with a 4.3L CPI engine in it. I inherited it with two blown head gaskets. Initially I tried replacing the head gaskets, but then it spun a rod, so I decided to rebuild the whole engine. Block bored 30 over, decked, and cleaned out. reground crank, reground cam, new lifters, new rings, new bearings. Line bored the rods.... etc... The only thing I didn't do was rebuild the heads, but they looked fine.

So, the trouble is it runs really rough. I can actually pull three different spark plug wires without the engine running any worse. Numbers 6, 4, and 1. Its not throwing any codes... I have replaced the o2 sensor, verified the operation of the CPI by pulling the injectors and cranking the engine. All injectors were firing perfectly. I set the timing as instructed, unplug the computer, set it to 0, then plug the computer back in. It seems to run well when under acceleration. I'm at a complete loss as to what to do. Checked the fuel pressure, its 57lbs. Takes almost an hour to leak down. No leaks inside the upper intake. I also replaced the module inside the distributor.

its killing me having this nice new engine and not being able to drive the car. can someone suggest a few things i could try?

thanks!!

 

It definitely sounds like an ignition system problem. By 'module inside the distributor', do you mean the pickup coil that is under the rotor or the electronic piece that is off to the side? A problem with the pickup coil could cause erratic timing.

Is it timed correctly?

 

A faulty pickup coil huh?? Are those repairable/replaceable? Or do I need to find a new distributor to test this theory? Is there a way I can test this part? I replaced the module off to the side.

I timed the engine as specified. When the computer is unplugged, it runs rough, but the timing mark stays solid on zero. When the computer is plugged in, it jumps around. I figured that this was just because it was trying to make up for whatever issue was causing the rough running, but maybe its the cause and not a result.

The pickup coil would cause it to be the same cylinders that misfire too right?

Thanks for all the help!

 

Yes the pick up coil can be tested autozone does it for free .

 

You have to remove the distributor drive gear inorder to replace the pickup coil.

Here is an exploded view of the HEI-EST distributor:

 

Wow! Thanks you guys! You're all awesome!!! You don't know how happy Ill be if this is the problem.... or maybe you do... Lol.

 

ok, so i replaced the pickup coil, and no change... :-(

anyone have any other ideas???

 

I have at this point replaced pretty much every ignition component there is I think.

I have replaced...

Spark plugs, wires, cap, rotor, pickup coil, ignition module (other device in the distributor), coil, and also the ECM I just replaced. The car continues to run rough and at idle drops three cylinders.

The engine was just rebuilt and shows compression in all cylinders. The CPI Spider has been verified operational visually. I took the EGR off and checked it to be clean and moves freely.

I am at a loss. Anyone have any ideas that might help??? Please????

 

Well, just for everyone's info, the problem seems to be an issue with a few intake valves on the heads... i did a leak down test and found the issue finally...

Thanks for all the help.