Purple_Hatch

so a few months ago i had my eye on this 2000 em1 on craigs, he wanted $3500 but i talked him down a little less, and figure wow this is awesome... im about to get a relatively low mileage si for a good price. take it home. already knew about the exhaust leak coming from the header, the ripped intake boot that was roaring at high rpms omw home, had to Easy-Out one broken bolt for the header, and hope that whatever threads were left in the one next to it would hold with a stud in its place. but even after fixing those issues i still had a strange drop out in power between 3800-4300 rpms. weird thing is it only happens intermittently. if im beginning from a dead stop, no matter where my foot is in the gas, the car accelerates fine, but lets say for whatever gear im in, if im cruising anywhere between 3800-4300 rpm and i want to accelerate... there is a brief drop out in power, then not a second later its like new life breathed back into the motor and back to accelerating.

so i have ruled out the intake boot, the exhaust leak, the first week i bought the car i did... distributor (cap and rotor) cause it went out, main relay after, plugs, plug wires, timing belt, water pump, valve cover gasket, valve adjustment (to spec), i capped off the vacuum port for the pcv valve because the tube that connects to the bottom of the pcv valve into the breather box is all hardened and broken. so that leaves out the pcv valve, checked for anymore vacuum leaks and couldnt find squat. i used the oscilloscope at the shop i work at and tested for any drop outs in the tps, all good there, map is reading fine, O2 sensors seem to be switching fine (at idle). cats not plugged just replaced that about 2 months ago, its not my motor mounts, replaced them with hardrace motor mounts. changed out the seal and screen for the vtec solenoid (vtec works fine btw), did compression test, came out to 165-170 across the board, a bit low but its not bad yet, replaced the fuel pump, fuel filter, changed all of the injector seals, and spacers.

things i havent checked yet bought have considered is flattened cam lobe, which i thought about for a while, but if it were a flattened cam lobe then howcome the power comes back more than 1k rpm before vtec? why if it were a flattened cam lobe, would the power loss only be felt in a certain rpm range, and only intermittently. also have not checked the fuel pressure regulator, which i am hoping is all it is. but any input on what you might think is happening would be helpful taking into consideration all of the work and tests i have already performed on the vehicle. and for those that are thinking it, no the timing is not off, i checked it 3 times.

oh and one more thing i forgot, if i am down shifting from a high to low gear into said problematic rpm range, the same thing happens, power drops out for a brief second, then back to accelerating.

Former User

Post the CEL codes.

Purple_Hatch

no CEL or stored codes of any kind.

Former User

Bone stock Si?

Why aren't you fixing the PCV hose?

What plugs? Properly gapped?

What plug wires?

Purple_Hatch

yes bone stock, i guess i never thought the pcv hose would cause a problem like this. is that possible?

Former User

I'm not sure, but the ECU expects a certain amount of air from the PCV system in its calculation of the air:fuel ratio. It's a simple fix to rule it in or out.

Tests of the TPS and O2 sensor only yield useful information if you can reproduce the drop out.

Purple_Hatch

whoa for some reason my computer didnt show me that part of the message, im using oem replacement denso spark plugs at .052 inches, with ngk wires. i will replace the pcv and that broken hose tomorrow and see if that makes any difference. i always thought that the ecu adjust air fuel mixture based off of map sensor output voltage, TPS and O2 sensors. if the port was not capped off then i might understand the pcv valve being dissconnected is the issue because that would be a big *** vacuum leak. and the map sensor would notice the difference in manifold pressure with the port capped off, adjusting and compensating for the difference in manifold pressure? just a few thoughts.

Former User

I'm editing my posts while you're responding.

Which denso plugs? PK20PR-L13?

Tests of the TPS and O2 sensor only yield useful information if you can reproduce the drop out.

Purple_Hatch

Denso (4504) PK20TT Platinum TT Spark Plug
theyre the titanium tipped platinum plugs