I'll try and describe this as best and accurately as possible. I've just noticed this over the last couple of days. Kind of came on all of a sudden. When I am pressing the gas, I've noticed that the engine surges a little bit while in boost. Almost like you would be slightly letting up and down on the gas while accelerating. I notice it more often at lower RPM's while in a higher gear. I've read a couple places that have said a possible boost leak. I haven't checked my lines yet, but will tomorrow as soon as I get some more daylight. Any thoughts or has something similar to this happened to any of you?
I can only assume that I should hope its the post MAF....I haven't even looked at the price of a coil pack, but can only assume it ain't cheap.
coil packs can be found cheap used, just make sure they are good. do you have any check engine lights? if you have a misfire in cylinder 1 for example, move that coil pack to cylinder 2 and drive again and see if the check engine light follows it. this will narrow down which coil pack is back and if that is indeed the problem. its actually a pretty common issue with both WRX/STi's. otherwise, pull your intercooler off (assuming you're still topmounted) and check all around the intake elbow (could actually be the intercooler lines too). but this is the only real way to be sure.
No check engine lights. I figured if it was something like a pack, the light would come on. Since it has not, I kind if figured it could be te FPR
The light will not come on unless it starts to misfire. A coil pack can still be going bad without the light coming on. Bad FPRs are not a common problem on Subarus. Techlord and Jake are on the right track.
Post MAF leak, IC leaks, check coils. Do you have a boost gauge? This actually sounds like boost/fuel cut. Is the boost going up then down and repeat? If so you could have mechanical boost creep or the the WGDC is all out of whack (I had that problem once). The boost would go from 20 to 15 to 20 to 15 exactly in the situations you described.....lower rpm high gear (more load). I see you swapped the EJ255 for a EJ257 so your compression has dropped on your car therefore if you are not custom tuned your maps are tweaked.
It's just a 257 block, but still the lower compression pistons. I do have a boost gauge. Not a fancy one, but seems to be pretty accurate. It's usually 7-10 and back to 7, but not a flickering type of fast. It's more like letting up and down on the gas kind of rate, but the whole time, I will be at WOT.
Did you reuse the EJ255 pistons or used EJ257 pistons? EJ257 lower compression than EJ255 iirc. Like 8.4 vs 8.2. My old issue did not flicker fast. It would build boost and fall build boost and fall just like you were getting on and off the gas. It was a very smooth build/fall and the culprit was a bad wastegate duty cycle in the tune itself.
remove vac line to WG and drive normal and then get some boost and see WGDC Q: Did you adjust the WG arm (if adjustable) ? Did you do anything to the BCS ? Did you change the PID or WGDC or boost targets (maps) ?
It's all 257 block (pistons, rods, crank, block). Everything else is 255. The way you are describing it is almost to a tee. I've got someone who is going to look at it tomorrow. He came recommended by B Reel, so I'm sure it'll be taken care of.
Do what goixiz said to do.....may boost lower in total but the boost should hold steady. If so then that is exactly what it is.
Ok, so I did what he said and it does build evenly now, but according to the gauge, it won't release until I let off the gas. It was reading as high as 17-18 and would release pressure until I let off the gas.
who tuned it ? target boost ? I would lengthen the WG arm 2 turns for now till you retune Your PID values may be too high
I was told by the person that I bought the engine from that just by adding only a 257 block, that I would not need to re-tune it. As I said, the only thing about my car that is 257 is the block (block, pistons, rods, crank). Everything else is 255. But then again, I was given a lot of bad advice when I was building this engine.
17-18 psi on WG pressure? Something isn't right here. Are you sure you pulled the wg line off cause on a stock turbo I think that wg is only 7-8 psi or so.
And yes you changed the block/pistons to a lower compression one. Your stock tune is not optimal. Even in stock form your stock tune was not optimal.
Nope. Changed the effective CR of the engine and left the tune on the EJ255 settings. jautry who is looking at your car that b reel recommended? Mike Sargent perhaps?
We still haven't met up to log the car... 9/10 the EBCS goes bad in these things. I have a handful of spares from customer's cars but IDK if I was bright enough to mark/ditch the bad ones... lol Steve
Well, I was finally able to meet up with him so he could log it, but of course with my bad luck, I hit the biggest fucking raccoon on the planet, tear my CV boot, and fuck up my wheel bearing. Soooooo, with that said, I still can't get data logged, and I now get to put on a new CB axle and wheel bearing.