Engine bucks with no boost, Help me diagnose the problem Options

[IllIllIll]

Hi all,

I finally got my 97 Celica convertible running with a 3SGTE from a ST215 Caldina.

Anyway it finally drives, but I have a problem. Long post but I tried to post all relevant details of my car & it's problems.

It drives in boost fine, but sometimes after driving a bit when everything is warmed up, I pull away form a stop or slow way down for whatever reason the engine starts bucking bad like it's firing on 3 cylinders or something. It seems to only do this when I slowly tip into the gas, & it goes away after the revs build & i get into boost. My tach isn't working yet, so I can't say for certain but it probably struggles until maybe 3 or 4 thousand rpm. If I gun it from a stop it goes without a hiccup most of the time. The engine runs fine even when flooring it in 5th gear going up a hill at 45, the boost comes on quickly. At first I thought I left the trans in the wrong gear when I pulled away from the stop sign, but that wasn't it. I've never had a slipping clutch, but I don't think that would cause the engine to buck, it would just go up in rpms without me going any faster if that was the case right?

I checked the spark plugs & they look fine, no odd smells or odd coloration. The oil isn't frothy & the coolant isn't oily. I have no visible smoke coming from the exhaust. I shorted the diagnostic pin & i don't have any codes. I checked my wiring again, nothing out of the ordinary.

I'm really stumped as to what is causing this issue. I am using all the stock Calidina sensors, ecu & turbo, so I would think it should all play together nicely & not give me any driveabilty issues like this if everything was working right. I have so much changed from stock with this swap, that I'm sure it's something I did or didn't do.

I am using the stock 5SFE 5 speed transmission, with a Fidanza aluminum flywheel, & a short throw shifter. I'm using the stock st215 injectors, fuel rail & fuel pressure regulator all fed by a new 355lpm warlboro fuel pump. I bought a new fuel filter, new belts & plugs & changed all the fluids. I did the wiring myself, but in hindsight I should have had Dr. tweak or someone do the harness for me as it was a PITA. I still haven't gotten the tach, A/C, or cruise control working yet. All of the wiring runs through the stock grommet so I extended the wires to reach the caldina ecu mounted in the stock location. I have the wires secured pretty well, but I wiggled everything around when the car was idling with out any problems. I even rechecked all the wiring for continuity since I got car running. I'm not using the fuel pump resistor as I couldn't figure out how to make it work, so the fuel pump is always running at full speed. Maybe that's the problem, idk. It's also an automatic ecu, but all the auto stuff is de-pinned & the wires removed from my harness.

I clocked the turbo outlet down, relocated the stock waste gate actuator, & extended the waste gate rod to set the car for 14 psi maximum boost. I'm using 2.5" aluminum ic pipes run to the FMIC & into the stock 3SGTE throttle body. I have the recirculating valve from the stock top mount setup dumping to atmosphere right now. I am using the stock turbo & the first half of the stock down pipe. I cut the stock catalytic convertor off right after the turbo & welded 3" exhaust tube on to what was left. From there I welded together a 3 inch exhaust with a high flow cat under the car near the transmission, a straight through resonator before the rear axle & then into a Dynomax Vt muffler with a single 3 inch inlet & pair of 2 or 2.5" inch outlets. This muffler has flap inside that opens up under high load to make it a straight through type muffler when your foot is in it. The flap is spring loaded at low exhaust flow to close and this really quiets the exhaust down. It's a convertible & I didn't want it crazy loud inside when driving. It's quiet as stock at idle & until I get my foot into it & give it some boost then it opens & sounds quiet nice, at least to my ears. I don't my exhaust is the problem, as I think I remember the engine bucking like that when I had the stock exhaust bolted up for the first test drive. It was last fall, so I don't remember, I welded the new exhaust together over the winter.

I might not have all the vacuum hoses routed like stock, as I'm not using one or two of the vacuum switching valves. I have an aluminum radiator & 2 of the biggest aftermarket electric fans I had room for. The engine sometimes gets up to 220 degrees F according to my real temp gauge, & the fans cool it back down to 180. I think I have a boost leak as I can hear a hiss when I'm in boost, but I haven't been able to locate it. So I know I have a few things to sort out, but none of that should cause the car to behave like this.

Please help.