97 Chevy S10 with WEAK SPARK on 1 Clyinder only

I have a 1997 S10 with a 2.2 4banger, that i completely rebuilt myself. New main bearings, cam bearings, piston rings, reseated valves, all new gaskets, new coils, plugs and wire, control module, fuel injectors, new air/fuel filters, new fuel pump regulator.. Did a compression test (12 cranks) 149-152 psi through out all cylinders. even switch the ECMout with a different one..

My problem is that Cylinder 4, when i pull the plug off to check the spark, it barely makes it out the boot. and when i disconnect it, theirs no drop in the performance of the engine. 1-3 has a strong spark, and when i pull those off the engine starts to hesitate more.

I switch the ECM with a junkyard one(it fired the car right up but had the same issues) because it threw a ECM replacement code with the ODB scanner

Codes: P0200, P0405

i have no blinking CEL

ive tried tracing the 5v 12V coming from the ECM, when i uplug the EGR connector the 5v and 12v are there, but as soon as i connect it to the EGR it goes away.

Sounds like a shorted egr. Ecm sees a short and shuts off to protect itself. P0405 is low voltage eger signal usually les than a volt. Check wiring to egr. Most likely a internal short in egr. Check all the following Scans codes and documents the freeze frame data in order to verify the problem.

Clears the engine codes and road tests the vehicle to verify whether the code comes back.

Visually checks the wiring and connections to the EGR control solenoid along with the EGR temperature sensor.

Disconnects and checks the EGR valve vacuum control solenoid for a short or open circuit in the solenoid.

Checks solenoid connection for corrosion in connection.

As for the p0200 thats injector related or ecm
Failed or failing injector
Open or shorted injector
Injector wiring harness has an open or short
Poor electrical connection
Faulty ECM

As for weak spark on cylinder 4 i would say bad coil or bad ground for icm/ over heating icm.

Seems like you have alot of electrical related issues. Before going to stir crazy go back over your wiring harnes and engine grounds. Could be as simple as insufficient ground of the block.

Sounds like a shorted egr. Ecm sees a short and shuts off to protect itself. P0405 is low voltage eger signal usually les than a volt. Check wiring to egr. Most likely a internal short in egr. Check all the following Scans codes and documents the freeze frame data in order to verify the problem.

Clears the engine codes and road tests the vehicle to verify whether the code comes back.

Visually checks the wiring and connections to the EGR control solenoid along with the EGR temperature sensor.

Disconnects and checks the EGR valve vacuum control solenoid for a short or open circuit in the solenoid.

Checks solenoid connection for corrosion in connection.

As for the p0200 thats injector related or ecm
Failed or failing injector
Open or shorted injector
Injector wiring harness has an open or short
Poor electrical connection
Faulty ECM

As for weak spark on cylinder 4 i would say bad coil or bad ground for icm/ over heating icm.

Seems like you have alot of electrical related issues. Before going to stir crazy go back over your wiring harnes and engine grounds. Could be as simple as insufficient ground of the block.

P0200 - ended up being a short in the injector harness (fixed) P0405 - was a EGR that shorted out (replaced) I also replaced the MAP just incase.. but shes back up and running strong, cylinder 4 spark is strong again. and nomore CEL. Wanna thank you for your help. and i hope this here will help someone with this same problem in the future

I have a '94 2.2 with that problem, at least similar: the spark was strong but erratic. turned out to be voltage variations from a loose big wire connection at the alternator, the other cyls just weren't affected as much. might be worth a look. made my gauges, headlights and dash lights waver especially going uphill.